“What is essential is invisible to the eye”

I take the liberty of borrowing this phrase written by Antoine de Saint-Exupèry in his wonderful work Le Petit Prince, translated into English as The little prince, to share a reflection (and well, also a claim, why not?) on a subject that directly concerns me and in which I have been working for almost three decades (at first on my own and now with Iker in our production company Science into Images).

And you may be wondering what it is that I (we) want to stand up for, of course.

Well then, here it goes, in bold and unfiltered, as we would say in the audiovisual field—in RAW.

The importance of microscopic life.

It’s quite possible that some of you, if you’ve decided to read this text, may think: “This guy is crazy.” And you probably wouldn’t be too far off.

But leaving aside my mental state, I’d like you to reflect, even if just for a few moments, on this claim.

What do I mean when I say “microscopic life”?

Let’s start as we should—at the beginning, with reflection and with some data to think about (take as much as you like).

The microscopic life I refer to is the life we cannot see with the naked eye. That life made up of countless living beings (because it couldn’t be otherwise) that our visual capacity does not allow us to perceive directly.

But let’s not fall into the mistake of thinking that because we don’t see them, they don’t exist. And no, here we can’t rely on the old saying “out of sight, out of mind.” In this case, even though our eyes cannot see, our heart, our lungs, our skin and, ultimately, everything that makes us “us,” can indeed feel. In fact, we could even say that, although our eyes don’t see, we don’t just feel them—we need them, and at times, we even suffer because of them.

Let me give you just two examples.

Have you ever seen diatoms or cyanobacteria? Most likely not, since one must use a microscope to do so. And yet, more than half of the oxygen in the atmosphere —yes, the very one we all breathe— is produced by them.

Have you ever seen a yeast cell? Probably not either, because it too is microscopic. But surely at some point you have eaten bread, or drunk wine or beer. Well, you should know that if you’ve done so, it was thanks to them.

So it seems that, although we don’t see them, we definitely feel them. And, above all, we feel their effects.

Well, now that we know, in broad strokes, what we’re talking about, let’s continue with the reflection.

And I’ll give you some figures to set the context.

In a single drop of seawater (one  milliliter), you can find up to 10 million viruses, 1 million bacteria, and more than 1,000 protozoa and microalgae. Sounds like a lot, right? Now think about how many drops of water are in the sea and imagine (no need to calculate) the number of microscopic living beings that inhabit it.

More data.

Bacteria are the most abundant organisms on the planet. It is estimated that in just one gram of fertile soil there can be up to 40 million bacteria, and when scientists attempt to calculate the total number of bacteria living on the planet, the figure is staggering. No less than a 5 followed by 30 zeros (5,000,000,000,000,000,000,000,000,000,000) —five quintillion! (and I won’t be the one to argue with the scientists’ calculations).

And now, a fact that may surprise many of you: the total number of bacteria living in our own bodies is 10 times higher than the number of our own cells.

You might say: “Okay, fine. But what do we care about the number of bacteria? Does it really affect us?”

Well, just so you get an idea (just an idea), without those bacteria living in our bodies we wouldn’t be able to take advantage of most foods —we would literally starve, even if we ate endlessly.

And something similar happens with the bacteria that live in the different environments of the planet. They are, for example, the ones that fix atmospheric nitrogen and make it available to plants. Without that nitrogen fixed by bacteria and used by plants, we —who eat both plants and the animals that feed on them— would not have nitrogen and therefore could not build our proteins or our nucleic acids. Yes, our DNA, our genes.

Let’s continue.

Scientists (thank goodness for scientists) have calculated that a bacterium like the well-known E. coli (its full name is Escherichia coli), which is one of the most abundant bacteria in our intestines but sometimes causes food poisoning, could cover the entire surface of the planet in just 30 hours if it could live in conditions suitable for its development. Sounds crazy, right? And a little scary too, if we’re honest.

Now let’s think: why doesn’t that happen? Why doesn’t E. coli, or any of the millions of bacteria that live on the planet, take it over and “wipe out” all the rest of us?

Because there are those who keep them in check, who control the growth of their populations.

And who are these “controllers of bacteria” to whom we owe our lives? Who are these “predators of bacteria”?

Well, no, they are not lions, nor tigers, nor blue whales, nor polar bears, nor golden eagles, nor… well, not us either. Not even our “antibiotics”, which protect us less and less (but that’s another story).

No, it is not those large animals, those big predators we love to watch in nature documentaries on TV, that protect us from bacteria, but others much, much smaller. So small that, just like bacteria, they are invisible to the naked eye. We can only see them with a microscope.

Our great defenders are ciliate and flagellate protozoa, amoebas, rotifers, chaetognaths, nematodes… a myriad of beings we almost never see and about which, unless we work in a lab, we know practically nothing. And no, I didn’t make up their names.

Strange, isn’t it? We know almost nothing about the living beings that are most important to our lives.

And yet, we sure know what the great cave bear or the saber-toothed tiger looked like. We even know what the mighty Tyrannosaurus rex or the small Velociraptor mongoliensis looked like, even though none of them live alongside us now—and some never did, since we never overlapped in time. (And for movie fans, the “velociraptors” in Jurassic Park didn’t actually represent dinosaurs from the genus Velociraptor, but rather larger ones from the genus Deinonychus).

And a quick note: no, humans never lived alongside dinosaurs. Dinosaurs disappeared around 65 million years ago, and we, members of the genus Homo (we belong to the species Homo sapiens, which means “wise man”), appeared less than 3 million years ago.

So far, then, we know that there are far more bacteria on our planet than any other living beings; that it’s not whales, lions, or other familiar animals used as environmental symbols that protect us from them; that it’s microscopic beings like ciliates and rotifers that keep bacterial populations under control; and that thanks to other microscopic beings like diatoms and cyanobacteria, we have the right amount of oxygen in the atmosphere. And we also know that we never coexisted with dinosaurs (just in case anyone had forgotten).

So why do most of us know practically nothing about microscopic beings—those that make up what we call “microscopic life”—when they are the very ones responsible for the development and persistence of life on our beloved planet Earth for some 4.5 billion years? Why does a high school student in our country know more about a tyrannosaurus than about a diatom? Does a dinosaur really have more impact on their daily life than a microalga? (By the way, I love dinosaurs, in case anyone thought otherwise).

I think we can agree that the answer to the first two questions is because we are not taught about them, they are not explained to us. And the answer to the third is clearly NO.

So now let’s return to the claim I mentioned at the start.

Where do we learn about the natural world of which we are a part? Where are we taught biology, geology, and all those sciences whose names end in -logy? Which institutions have the obligation (yes, the obligation) to provide us with the information and, above all, the training necessary to better understand our world?

I think it’s clear: both educational centers (schools, high schools, and universities) through educational programs, and museums, especially natural history museums through their collections, exhibitions, and educational resources.

Does this actually happen?

Has anyone ever been taught about rotifers in school? Has anyone ever seen a diatom or a chaetognath in a natural history museum?

I don’t think I’m too far off if I say no—or at most, perhaps a lucky few who had a natural science teacher willing to go beyond the standard curriculum and allow their students to gain deeper knowledge (and let it be clear, this is not meant as criticism of teachers but of the system and curricula).

And I’m also quite sure that only those who have visited the ARTIS-Micropia center in Amsterdam have seen a museum dedicated to that wonderful “microscopic life.”

It is true that other museums, such as CosmoCaixa in Barcelona, have in their permanent exhibitions some modules dedicated to it and, fortunately, also a unique and special space called the “Micrarium” dedicated to microscopy. Or that another museum, like the Museu de Ciències Naturals de Barcelona, includes in its permanent exhibition some models and interactives devoted to microbiology. The Senckenberg Naturmuseum in Frankfurt has also developed the immersive module entitled “Walk-in water drop” to show the hidden biodiversity inhabiting a water dorp in a very original way. Even the small but very active Museu de Ciències Naturals de Granollers has shown sensitivity to this subject and developed educational workshops on microscopic life and even participated in the production of educational audiovisuals to be shown in its planetarium.

I must admit that I have not visited all the natural history museums in the world and that surely there are others that also dedicate part of their space to microscopic life. But they are not the majority, and in most cases, microscopic life constitutes a tiny part of their content.

So, one must ask: why don’t natural history museums—institutions whose very mission is to make us aware of the natural characteristics of the world we live in—dedicate more space and resources to showcasing that microscopic life which makes up most of the living world on our planet and has profound implications for our own existence as human beings and members of the global ecosystem called the Biosphere?

And it is not because those practically invisible beings that make up microscopic life are unattractive. It is not because people have little interest nowadays. It is simply because, either through ignorance or supposed technical difficulties, there has been no real will to show them to us.

Reality is stubborn, and it clearly shows us that, in many cases (and this is one of them), we are wrong.

And now, allow me to use Science into Images as one of the many examples of this.

We are a very small audiovisual production company, specialized in disseminating scientific and natural history topics through documentaries, museum installations, publications, and—as is unavoidable in our time—on social media.

And our specialty, especially on social media, is —oh, what a coincidence! —microscopic life. The very same that, according to many museums, institutions, television channels, and publishers, is supposedly not at all attractive to the general public.

Well then, that “lack of interest” has resulted in us now having more than 190,000 followers on Instagram and more than 16,000 on Facebook. Does that mean that microscopic beings are not appealing to the public? Quite the opposite—for an audience, like that of the two mentioned platforms, which according to every study so far is little interested in science or natural history, and supposedly unwilling to “spend” more than 3 seconds on science-related content (much less on “microscopic critters,” of course).

Perhaps it is time for things to change.

Perhaps concern about global climate change will awaken these institutions’ interest in showing us who it is that can help maintain balance; who can capture most of the carbon dioxide and bury it in the ocean depths so it does not act as a greenhouse gas in the atmosphere; who will continue producing the oxygen we need to breathe; who will protect different ecosystems from the threat of runaway bacterial growth; who are capable of regulating climate by releasing substances into the atmosphere that trigger the formation of clouds over the sea and rain over the land; who…

I could go on, but I will leave it here.

La entrada What is essential is invisible to the eye se publicó primero en Science into Images.

“There is nothing more useful than salt and the sun.”

This saying, attributed to the Roman writer and soldier Pliny the Elder almost 2,000 years ago, highlights the importance that humanity has given since ancient times to one of the main products extracted from seawater.

The salt

The salt Pliny was referring to is a mineral formed by the union of two chemical elements, chlorine and sodium, and is the only rock we can eat directly.

Most salt is dissolved in the water of seas and oceans, and to extract it, we have developed different techniques, most of them based on natural evaporation and crystallization processes, such as those carried out in coastal salt mines, where millions of tons are extracted each year.

Coastal salt mines are very special ecosystems. Their location makes them a haven for numerous bird species, many of which establish their breeding, feeding, or wintering colonies here.

The waters surrounding the salt flats, which are the same from which the salt will later be extracted, are home to a coastal marine ecosystem inhabited by representatives of a vast array of organisms. They are home to oxygen-producing cyanobacteria that form green mats that cover the shallow sediments.

A characteristic of these cyanobacteria is that their filaments are constantly moving, and nematodes, perhaps the most abundant animals on the planet, roam among them.

Some mollusk species also find these waters an ideal place for their newly hatched larvae to enjoy the tranquility they need to develop.

Polychaete worms are abundant and colonize both the surface of the sediment and the shells of other animals while filtering the water in search of organic particles or tiny planktonic microorganisms, something that urochordates such as sea squirts also constantly do.

Here, it is also possible to find tiny and delicate microscopic jellyfish and a large number of crustaceans, both in their adult and larval stages.

This entire marine ecosystem changes radically when water enters the salt flats. And the striking colors displayed by the lagoons where the salt crystallizes are simply a reflection of the unique biodiversity they harbor. A biodiversity made up of an enormous number of microscopic organisms adapted to living in conditions of extreme salinity and sunlight.

One of these organisms, perhaps one of the most characteristic, is the alga Dunaliella salina, known precisely as the “salt flats algae.”

Dunaliella salina is the eukaryotic organism with the highest salt tolerance, and it is this tolerance that allows it to inhabit these waters, whose salt content can reach extreme levels. But this causes stress, and when that happens, it produces a substance to protect itself.

This protective substance is beta-carotene, which is precisely what gives it its striking red color.

Dunaliella also produces large quantities of another substance, glycerol, which it uses to regulate the salt concentration inside the cell.

However, Dunaliella‘s membrane is not impermeable, and much of the glycerol escapes into the environment, which constitutes an excellent food source for the multitude of bacteria with which it coexists.

And this is where a special relationship between the microorganisms that live in salt flats and salt production emerges.

The abundance of Dunaliella and bacteria causes the water to heat up more quickly and reach temperatures much higher than ambient temperatures. Furthermore, each of the bacteria can act as a nucleus for the formation of salt crystals, accelerating the process.

But not all salt flats are found on the coast. Some are also located inland, in areas far from the sea.

Ilargi Martínez-Ballesteros, principal investigator of the MikroIker group at the University of the Basque Country/Euskal Herriko Unibersitatea (UPV/EHU), tells us about these salt flats and her recent discoveries.

“We are in Salinas de Añana.

This salt flat is perhaps different from those we can find in other places on the Iberian Peninsula, for example, since its unique characteristic is that the brine used for salt production comes out through the presence of a diapir in this valley, in the Añana Salt Valley.

Various studies have analyzed the depth at which this diapir may be located. It is not known specifically, but it appears to be more than 200 meters deep. The water that filters through has underground contact with the halite found deep underground and dissolves it before reaching the surface through various springs in the valley.

A curious fact about this valley, which we have also seen strongly influences the presence of halophilic microorganisms in the brine water at this salt mine, is that just a few meters away, there are different springs with different salinities.

For example, there are two springs, one called El Pico and the other El Pico Dulce, located just a few meters apart, and the microorganism taxa we found there are completely different. This is due to their adaptation and because the amount of salt in the brine in the different springs is very different.

At Pico Dulce, we are talking about saline water, which has around 20-30 grams of salt per liter, and at El Pico, it reaches 230-240 grams of salt per liter—it is completely salty.

That vast difference is what we’ve seen primarily determines the presence of one type of halophile or another in the brine.

Another characteristic we’ve been discovering by studying the presence of genetic material, DNA, in the water through its extraction and sequencing is that we’ve been able to identify bacterial and archaeal populations that have been previously described, but we’ve still missed out on many sequences, a lot of DNA, that we haven’t been able to identify.

And yes, for now, we’ve discovered a new species that has been characterized here, in Salinas de Añana, in the brine of the main spring, the Santa Engracia Spring.

Perhaps microorganisms are living there that we don’t yet know about, and perhaps we’ll be able to isolate and observe them in the laboratory.

On the other hand, the study of halophiles is also interesting because it has been discovered that, thanks to the adaptations they have developed throughout their evolution to survive in these extreme salinity conditions, they produce different metabolites, products that may be of interest for biotechnological uses.

The new bacterium discovered in the Añana Salt Flats has been named Altererythrobacter muriae, and among its characteristics is its ability to live in water with a concentration of up to 200 grams of salt per liter, a characteristic that places it among the group of microorganisms considered halotolerant.

What does this bacteria feed on in the brine?

Altererythrobacter muriae does not carry out photosynthesis, does not have chlorophyll, and feeds on the organic matter present in the waters in which it lives, which is why it is considered a heteroorganotrophic organism.

Scientists have proven that Altererythrobacter muriae produces pigments called carotenoids.

What function do these pigments perform?

The main function of this pigment is to act as an antioxidant, preventing the damage that excess oxygen could cause to the bacteria.

Many of the microorganisms that inhabit inland salt marshes are considered extremophiles, since they have adapted to living in extreme environmental conditions. In this case, extreme salinity and, often, sunlight. But not all are extremophiles. Others, such as Halomonas, a bacteria common in these environments, are not extremophilic but halotolerant, meaning they are able to withstand the salinity typical of these waters, although it is not exclusive to them.

But… why are these inland waters salty? How did the salt get to these areas?

The thick layers of salt left behind by the disappearance of ancient seas transformed into a rock called halite, which forms what we now know as salt domes or diapirs.

Water circulating through underground aquifers passes through the diapir and dissolves it before exiting the surface with a high concentration of salt. This high concentration, combined with the increase in temperature caused by sunlight, causes the salts to begin to crystallize.

In addition to sodium chloride or common salt, which is the main component of halite, the rock that forms the diapir, water also dissolves other compounds as it passes through. Some of the most common are salts of elements such as calcium and magnesium, usually in the form of carbonates and sulfates.

You can see the beauty of the Añana Salt crystals forming at this link: https://www.youtube.com/watch?v=8wiI2X-J-vM
https://www.youtube.com/watch?v=8wiI2X-J-vM

In addition to the salt flats associated with diapirs, a special type of saline ecosystem occurs in the interior of continents. These are lagoons located in arid terrain, in areas where rainfall is very irregular and generally scarce. These wetlands are known as “las saladas.”

Salt marshes are what scientists call endorheic lagoons. This means they are lagoons that form in depressions in the ground because this is where rainwater accumulates. This water dissolves the salts that make up the rocks of the ground surrounding the lagoon before accumulating in the basin, from which it only emerges through evaporation caused by the sun.

It is within these salt waters that the Artemia salina, one of the animals most resistant to high salt concentrations, finds its ideal habitat. This crustacean whose morphology appears to have changed almost nothing since the Triassic period, which means it is extraordinarily well adapted to these unique and extreme environmental conditions. During the periods when the basins remain covered by water, the adult brine shrimp feed on the dense populations of microalgae and reproduce rapidly, often without the intervention of males, through a strategy called parthenogenesis.

But how do they survive long periods of drought?

The secret to their survival is a strategy called cryptobiosis, a kind of “hidden life.” When the water completely disappears, the eggs produced by the brine shrimp are trapped by the salt and exposed to the air and sun, where they can remain for a long time. Sometimes for more than ten years.

These are resistant eggs, which remain inactive until rainwater refills the lagoon. At that point, these eggs rehydrate, “awaken,” and hatch, releasing the new larvae that had remained dormant inside them in embryo form. In this way, these new generations reestablish brine shrimp populations in a seemingly endless cycle.

A natural cycle that has been in operation for more than 200 million years and is regulated by water and the concentration of one of the key elements in these ecosystems: salt.

You can watch the episode “The Salt of Life” (25 minutes. Original version in Spanish. Subtitled in English and Portuguese) from our series “Planet Microbe” at this link

https://caixaforumplus.org/v/la-sal-de-la-vida

La entrada The salt of Life se publicó primero en Science into Images.

“No hay nada más útil que la sal y el sol”

Esa sentencia, atribuida al escritor y militar romano Plinio el Viejo hace casi 2000 años, pone de manifiesto la importancia que la humanidad ha dado desde tiempos remotos a uno de los principales productos extraídos del agua del mar.

La sal.

La sal a la que se refería Plinio es un mineral que se forma por la unión de dos elementos químicos, el cloro y el sodio, y es la única roca que nos podemos comer directamente.

La mayor parte de la sal se encuentra disuelta en el agua de los mares y océanos, y para extraerla hemos desarrollado diferentes técnicas, la mayoría de ellas basadas en los procesos naturales de evaporación y cristalización como los que se llevan a cabo en las explotaciones salineras costeras donde, cada año, se extraen millones de toneladas.

Las salinas costeras son unos ecosistemas muy especiales. Su localización los convierte en zonas de acogida de aves de numerosas especies, muchas de las cuales establecen aquí sus colonias de cría, de alimentación o de invernada.

Las aguas que rodean a las salinas, que son las mismas de las que luego se extraerá la sal, albergan un ecosistema marino costero en el que aparecen representantes de una enorme cantidad de grupos de organismos. En ellas habitan, cianobacterias productoras de oxígeno que forman tapetes verdes que recubren los sedimentos poco profundos.

Una característica de estas cianobacterias es que sus filamentos están en constante movimiento y entre ellos deambulan los nemátodos, quizás los animales más abundantes en el planeta.

Algunas especies de moluscos ven también en estas aguas un lugar idóneo para que sus recién nacidas larvas dispongan de la tranquilidad necesaria para desarrollarse.

Los gusanos poliquetos son muy abundantes y colonizan tanto la superficie del sedimento como las conchas de otros animales mientras filtran el agua en busca de partículas orgánicas o diminutos microorganismos planctónicos, algo que también hacen constantemente urocordados como las ascidias.

Aquí es posible también encontrar diminutas y delicadas medusas microscópicas y una gran cantidad de crustáceos, tanto en sus estados adultos como en forma de larvas.

Todo ese ecosistema marino cambia radicalmente cuando el agua penetra en las salinas. Y los llamativos colores que muestran las lagunas en las que cristaliza la sal no son más que el reflejo de la singular biodiversidad que albergan. Una biodiversidad formada por una enorme cantidad de organismos microscópicos adaptados a vivir en unas condiciones de salinidad e insolación extremas.

Uno de esos organismos, quizás uno de los más característicos, es el alga Dunaliella salina, conocida precisamente como “alga de las salinas”.

Dunaliella salina es el organismo eucariota con mayor tolerancia a la sal y es esa tolerancia la que le permite habitar en estas aguas, cuyo contenido en sal puede alcanzar niveles extremos. Pero eso le provoca estrés, y cuando eso sucede, produce una sustancia con la que protegerse.

Esa sustancia protectora es el beta-caroteno, que es, precisamente, la que le proporciona su llamativo color rojo.

Dunaliella, además, produce grandes cantidades de otra sustancia, el glicerol que le sirve para regular la concentración de sal en el interior de la célula.

Pero la membrana de Dunaliella no es impermeable, y buena parte del glicerol escapa al medio, lo que constituye una excelente fuente de alimento, para la multitud de bacterias con las que convive.

Y es ahí donde aparece una relación especial entre los microorganismos que viven en las salinas y la producción de sal.

La abundancia de Dunaliella y de bacterias hace que el agua se caliente a mayor velocidad y que alcance temperaturas muy superiores a las del ambiente. Además, cada una de las bacterias puede actuar como núcleo para la formación de los cristales de sal de manera que el proceso se acelera.

Pero no todas las salinas se encuentran en la costa. Algunas también se localizan en el interior de los continentes, en zonas muy alejadas del mar.

Ilargi Martínez-Ballesteros, investigadora principal del griupo MikroIker, de la Universidad del País Vasco/Euskal Herriko Unibersitatea (UPV/EHU) nos habla de estas salinas y de sus recientes descubrimientos en ellas.

“Estamos en Salinas de Añana.

Esta salina es diferente quizás a las que podemos encontrar en otros lugares en la península, por ejemplo, ya que su característica singular es que la salmuera que se utiliza para la producción de sal sale por la presencia de un diapiro que está en este valle, en el Valle Salado de Añana.

Diferentes estudios han estado analizando a qué profundidad puede estar situado este diapiro, y no se sabe concretamente, pero parece puede tener más de 200 metros de profundidad. El agua que se filtra tiene contacto subterráneo con esa halita que hay en las profundidades que subterráneamente y la va disolviendo antes de salir a la superficie por diferentes manantiales que hay en el valle.

Una curiosidad de este valle, que además hemos visto que marca mucho la presencia de qué tipo de microorganismos halófilos hay en el agua de la salmuera en esta salina, es que a pocos metros de distancia hay diferentes manantiales con diferente salinidad.

Por ejemplo, hay dos manantiales, uno se llama El Pico y otro El Pico Dulce, que están a escasos metros de distancia, y los taxones, de los microorganismos que hemos hallado allí, no tienen nada que ver unos con los otros. Y esto es por la adaptación que han tenido y porque la cantidad de sal que hay en los diferentes manantiales, en la salmuera, es muy distinta.

En el Pico Dulce estamos hablando de un agua salina, que tiene en torno a 20-30 gramos de sal por litro, y en El Pico se alcanzan los 230-240 gramos de sal por litro, es totalmente salado.

Esa gran diferencia es lo que hemos visto que marca principalmente la presencia de uno u otro tipo de halófilos en la salmuera.

Otra de las características que hemos ido descubriendo al estudiar la presencia de material genético, de ADN, en el agua mediante su extracción y secuenciación, es que hemos podido identificar poblaciones bacterianas y de arqueas que han sido descritas previamente, pero se nos han quedado muchas secuencias, mucho ADN sin poder identificar.

Y sí que, por el momento, hemos encontrado que hay una especie nueva que se ha caracterizado aquí, en Salinas de Añana, en la salmuera del principal manantial, que es el Manantial de Santa Engracia.

Quizás estén viviendo microorganismos que todavía no conozcamos y quizás lleguemos a conseguir aislarlos y observarlos en el laboratorio.

Por otro lado, el estudio de los halófilos también es interesante porque se ha descubierto que, gracias a las adaptaciones que han ido desarrollando a lo largo de su evolución para poder sobrevivir en esas condiciones extremas de salinidad, producen diferentes metabolitos, productos, que pueden ser interesantes sus utilidades biotecnológicas.”

La nueva bacteria descubierta en las Salinas de Añana ha sido bautizada con el nombre de Altererythrobacter muriae, y entre sus características destaca su capacidad para vivir en un agua con una concentración de hasta 200 gramos de sal por litro, característica que la incluye en el grupo de los microorganismos considerados halotolerantes.

¿De qué se alimenta esta bacteria en la salmuera?

Altererythrobacter muriae, no lleva a cabo la fotosíntesis, no tiene clorofila, se alimenta de la materia orgánica que hay en las aguas en las que habita, por lo que se considera un organismo heteroorganotrófico.

Los científicos han podido comprobar que Altererythrobacter muriae produce unos pigmentos llamados carotenoides.

¿Qué función desempeñan estos pigmentos?

La principal función de este pigmento es el de actuar como un antioxidante, evitando los daños que el exceso de oxígeno pudiera causar a la bacteria.

Muchos de los microorganismos que habitan en las salinas de interior están considerados extremófilos, puesto que se han adaptado a vivir en condiciones ambientales extremas. En este caso en unas condiciones extremas de salinidad y, a menudo, también de insolación. Pero no todos son extremófilos. Otros, como Halomonas, una bacteria frecuente en estos entornos, no es extremófila sino halotolerante, es decir, que es capaz de soportar la salinidad propia de estas aguas aunque no es exclusiva de ellas.

Pero… ¿Por qué son saladas estas aguas de interior?  ¿Cómo ha llegado la sal hasta estas zonas?

Las gruesas capas de sal que quedaron al desaparecer mares antiguos se transformaron en una roca llamada halita, que es la que da cuerpo a lo que ahora conocemos con el nombre de domos o diapiros salinos.

El agua que circula por los acuíferos subterráneos atraviesa el diapiro y lo va disolviendo antes de salir al exterior con una elevada concentración de sal. Esa elevada concentración, unida al incremento de temperatura provocado por la insolación, hace que las sales comiencen a cristalizar.

Además del cloruro sódico o sal común, que es el principal componente de la halita, la roca que forma el diápiro, el agua también disuelve otros compuestos a su paso. Unos de los más frecuentes son sales de elementos como el calcio y el magnesio, generalmente en forma de carbonatos y sulfatos.

En este enlace podéis ver la belleza de los cristales de la Sal de Añana en formación: https://www.youtube.com/watch?v=8wiI2X-J-vM

Además de las salinas asociadas a los diápiros, en el interior de los continentes aparece un tipo especial de ecosistemas salinos. Se trata de lagunas que se localizan en terrenos áridos, en zonas en las que las precipitaciones son muy irregulares y generalmente escasas. A estos humedales se les conoce como “las saladas”.

Las saladas son lo que los científicos llaman lagunas endorreicas. Eso quiere decir que son lagunas que se forman en depresiones del terreno debido a que es allí donde se concentra el agua de lluvia. Un agua que disuelve las sales que conforman las rocas del terreno que rodea la laguna antes de acumularse en la cubeta, de la que únicamente sale por la evaporación provocada por el sol.

Es en el interior de esas aguas saladas donde encuentra su hábitat idóneo la Artemia salina, uno de los animales más resistentes a las altas concentraciones de sal. Se trata de un crustáceo cuya morfología parece no haber cambiado casi nada desde el período Triásico, y eso quiere decir que está extraordinariamente bien adaptado a esas singulares y extremas condiciones ambientales. Durante los períodos en los que las cubetas permanecen cubiertas por el agua, las artemias adultas se alimentan de las densas poblaciones de microalgas y se reproducen a gran velocidad, muchas veces sin intervención de los machos, mediante una estrategia que recibe el nombre de partenogénesis.

Pero ¿cómo sobreviven a las largas temporadas de sequía?

El secreto de su supervivencia es una estrategia que recibe el nombre de criptobiosis, algo así como “vida escondida”. Cuando el agua desaparece completamente, los huevos producidos por la artemia quedan atrapados por la sal y expuestos al aire y al sol, situación en la que pueden permanecer durante mucho tiempo. En ocasiones durante más de diez años.

Son huevos de resistencia, que permanecen inactivos hasta que el agua de lluvia vuelve a rellenar la laguna. Es entonces cuando esos huevos se rehidratan, “despiertan” y eclosionan dejando salir al exterior a las nuevas larvas que habían permanecido dormidas en su interior en forma de embrión. De esta manera, esas nuevas generaciones restablecen las poblaciones de artemia en un aparente ciclo sin fin.

Un ciclo natural que se ha mantenido en funcionamiento desde hace más de 200 millones de años y que está regulado por el agua y por la concentración de uno de los elementos clave en estos ecosistemas, la sal.

Puedes ver el episodio “La sal de la vida” (25 minutos. V.O. en Español. Subtitulado en Inglés y Portugués) de nuestra serie “Planeta microbio” en este enlace:

https://caixaforumplus.org/v/la-patrulla-ambiental

La entrada La sal de la vida se publicó primero en Science into Images.

IN SEARCH OF IMMORTALITY

The search for immortality has been one of the obsessions of human beings since they became aware of their own death.

Leaving aside any other approach, and looking at it from a purely biological point of view, we can consider any living being as a physical system. And, consequently, subject to the laws of the physical world.

One of the most important laws in this field are the laws or principles of thermodynamics.

The first, perhaps the best known, states that energy is neither created nor destroyed, it only transforms. And the second, expressed colloquially, says that any physical system has a tendency to spontaneously become disordered.

In principle, these laws are applicable to any closed system, that is, isolated from the environment.

However, living beings are not closed systems. We maintain a permanent exchange of matter and energy with our environment. And thanks to this exchange we can escape the thermodynamic yoke and maintain our “order”, at least for a certain time.

Maintaining this order is what we call homeostasis, and it is what allows us to stay alive in a constant state of dynamic equilibrium.

But what happens when we are unable to maintain this balance?

Well, we become disordered and, finally, we die.

Why do we become disordered? Why do we lose the ability to maintain homeostasis?

All living beings today store genetic information in the form of DNA.

Eukaryotic organisms, like us, have our DNA protected within the nucleus of our cells and organized into small packages. Each of these packages is what is called a chromosome.

Studies on the aging and death of our cells have shown that it is precisely in this way of organizing our DNA where the problem lies.

Chromosomes are made up of linear DNA molecules, and at the ends of each of them there is a portion of DNA called a telomere. This portion is what prevents the different chromosomes from linking together at the ends during cell division. But every time a cell divides, the telomeres of its chromosomes get shorter. Eventually, after a certain number of divisions, the telomeres are so short that the DNA in the chromosomes cannot be duplicated properly, the cell cannot divide, and it dies.

Final stage of binary division or bipartition of a ciliated protozoan.

This process of cell death is called apoptosis. And the number of times a cell can divide before dying is called the Hayflick limit, and it varies from organism to organism.

For most of our cells, this limit is around 60 divisions. However, we have cells that can overcome it.

These cells are germ cells -which give rise to ovules and sperm- and stem cells, which can divide indefinitely.

Does this mean that these cells are immortal?

Apparently so. Sometimes, other cells in our body are able to avoid the Hayflick limit and begin to divide uncontrollably. When this happens, we face a serious problem: cancer.

Human cancer cells in different mitosis phase.

As explained by Professor Pedro Luis Fernández, Head of the Pathological Anatomy Service at the Germans Trias i Pujol Hospital, “the term cancer is a Latin word meaning crab, and it is how ancient Greek and Roman physicians called lesions that were destructive to the body and that usually had the shape of this animal.

The origin of cancer is found within the body’s own cells. Some of these cells can undergo changes in their normal behavior and behave in an aggressive manner. These are what we call cancer cells.

In reality, cancer is not a disease but a series of diseases that have some characteristics in common. They can appear in any cell of the body and in any tissue, but they can eventually behave in such a way that they can end up killing the individual.

Large cancerous tumor in a patient’s lung.

The common characteristics of cancer cells are multiple, but three stand out:

The first is that they can evade programmed cell death, what we call apoptosis, and therefore they can live much longer than normal. The second is that they can multiply much more quickly and many times more than normal, exceeding what we call the Hayflick limit. In addition, if we put these cells in culture and provide them with the appropriate nutrients, we can say that they become immortalized.

And finally, a third characteristic would be that, as they are cells that arise from the organism itself, they are able to evade the systems that recognize them as foreign and, therefore, evade that death produced by the organism itself, among which the evasion of the immune surveillance system stands out.

We can compare this cancerous process, using the famous Ridley Scott film, to an alien. An alien that emerges, grows, feeds and can eventually kill the organism. But it is a selfish entity, a stupid and suicidal entity, because it will eventually kill its source of subsistence, since, unlike what happened with the entity in the film, it cannot pass from one individual to another.

Or can it?

There is what specialists call hereditary cancer, but, in reality, it does not pass from one person to another at the time of reproduction, what it means is that the reproductive cells, the eggs or the sperm, can harbor genetic alterations that can be transmitted to the offspring without necessarily meaning that they will suffer from cancer. It may simply happen that, throughout an individual’s life, and due to external influences, such as carcinogens, other genetic alterations occur that end up developing a malignant disease, cancer, which usually occurs in adults.

The appearance of cancer causes an imbalance in the organisms that suffer from it, a loss of their homeostasis, of their ability to self-regulate and maintain their normal functioning. However, the apparent “immortality” of cancer cells gives us some clues to find possible ways to achieve the long-awaited immortality.”

Since its appearance on the planet, life has diversified enormously. Biological evolution, always in response to the evolution of the planet itself, has given rise to the appearance of numerous life forms. And each of them has developed a unique, singular way of maintaining its homeostasis.

Is it possible that any of them has managed to avoid disorder and, consequently, death?

The answer to that question will surely have to be sought in life forms much older and simpler than us.

Protozoa and microalgae, all eukaryotic organisms formed by a single cell, have inhabited the planet since long before animals appeared. So we could think that they have had much more time to look for a solution to the problem.

Group of ciliated protozoa of the genus Paramecium.

Have they found it? Have they managed to be immortal?

Organisms as seemingly simple as protozoa are capable of dividing more than 200 times, many more times than our normal cells. They also have their DNA organized into chromosomes like ours, and those chromosomes also have telomeres at their ends.

How do they prevent those telomeres from shortening?

The secret lies in an enzyme, a molecule that rebuilds telomeres after each division. That apparently “magic” molecule is called telomerase.

That same enzyme appears in our germ cells, our stem cells and, unfortunately, also in cancer cells.

However, it has been proven that protozoa such as paramecia also suffer senescence, that is, they also age and end up losing their reproductive capacity. Therefore, it seems that these organisms have not achieved immortality either.

Sequence of membrane destruction and subsequent death of two ciliated protozoans. Above: Paramecium bursaria. Below: Paramecium caudatum.

All the organisms we have talked about so far are made up (we too) of eukaryotic cells, cells with a nucleus and with DNA organized in the form of linear chromosomes. But what about bacteria and archaea?

Bacteria and archaea are prokaryotic organisms, they do not have a defined cell nucleus. And their genetic material, their DNA, is not packaged in linear chromosomes, but forms a single circular chromosome.

Being circular, the bacterial chromosome has no ends and, therefore, no telomeres, so it does not suffer shortening during the cycles of division and reproduction.

We might think, as has been thought for a long time, that, due to this characteristic, bacteria and archaea are immortal. However, recent studies carried out with one of the best-known bacteria, the famous Escherichia coli, have shown that this is not entirely true. Some of the cells resulting from the division of this bacteria, from its reproduction by bipartition, show a lower reproductive capacity than that of their sisters, that is, they age and, finally, their line of descent ends up disappearing.

It seems, then, that neither reproduction by bipartition, nor the possession of a circular chromosome, without telomeres, ensures immortality.

Is there any other strategy? Is there any other possibility of being immortal?

Some groups of bacteria, including those that make up the genera Bacillus and Clostridium, have the ability to form endospores as a resistance strategy when environmental conditions are not suitable.

We could consider these bacterial endospores as tiny “time capsules” inside which the bacteria remains in a “dormant” state. When environmental conditions become favorable again, the spore opens, germinates, and the bacteria inside it reappears.

Bacterial population with some sporulated cells.

The question then is how long can the bacteria remain inside the spore in this “dormant” state?

In 1995, California researchers published the “resurrection” of a bacteria, or rather, the germination of one of these bacterial spores, found inside the intestine of a bee preserved in amber for more than 25 million years. (Cano, R. J. and Borucki, M. K.: 1995, Revival and Identification of Bacterial Spores in 25–40 Million-Year-Old Dominican Amber, Science 268, 1060–1064.)

But there is more.

Five years later, in 2000, another American group of researchers published a study in which they claimed to have “resurrected” another bacteria. This time the spore was contained in a salt crystal extracted from more than 500 m deep in the Salado geological formation in New Mexico. It was 250 million years old. (Vreeland, R. H., W. D. Rosenzweig and D. W. Powers. 2000. Isolation of a 250 million-year-old halotolerant bacterium from a primary salt crystal. Nature. 407 (6806): 897-900.)

Is this immortality?

You can watch the episode “In search of immortality” (25 minutes. O.V. in Spanish. Subtitled in English and Portuguese) of our series “Planeta microbio” through this link:

https://caixaforumplus.org/v/en-busca-de-la-inmortalidad

La entrada IN SEARCH OF IMMORTALITY se publicó primero en Science into Images.