Some bacteria are known to thrive in extreme ecological niches, but researchers did not expect to find such diversity there.
Even if humans are able to adapt to very different environmental conditions, we are very small players compared to what we find in the microscopic fault. There’s a whole swath of biology devoted to the study of what are called extremophiles, bacteria that thrive in – you guessed it – extreme conditions.
They are found in some of the most inhospitable places in the world. One can for example quote the geysers, or the vicinity of the hydrothermal chimneys; in addition to emitting large quantities of highly toxic material for the vast majority of living beings, such as sulphur, they are also a source of extreme heat that only a handful of species can tolerate.
Most of these extremophiles are still relatively poorly known, since their habitats are by definition rather difficult to explore. A situation that earned them the nickname of “black matter” bacterialto use the expression used by researchers from several prestigious universities in a paper published yesterday.
To study thisblack matter”, they took numerous samples from 70 sites on the Big Island of Hawaii. In particular, they explored caves and volcanic tubes but also fumaroles and other structures that presented a intense geothermal activity.
An ideal playground for extremophile bacteria. And as the researchers expected, they got their hands on many living beings of this category. But when they did the genetic analysis of all these bacterial populations, they found some unexpected and very interesting trends.
Impressive diversity
For starters, while the researchers did expect to find a fairly large amount of extremophiles, they also expected their diversity to be rather low. They have, however, observed quite the opposite, with what they describe as “surprisingly high levels of bacterial diversity” – a real small extremophile ecosystem, quite far from the model that prevailed until then.
The older the structures studied, the greater this diversity. But the most interesting thing is that these already surprisingly numerous bacterial communities do not just exist on their own; the researchers explain that in the most inhospitable environments, they develop interactions of staggering complexity.
In other words, this suggests that these extremophile bacteria did not just colonize these particular ecological niches; despite the extreme conditions, they participated in the emergence of truly complex ecosystems, with relatively interdependent organisms.
The other very interesting element is that the researchers very rarely found the same bacteria on different sampling sites; only a handful of species occupied many of these niches. This suggests that these communities developed on their own, in relative independence. And that raises a whole host of additional questions.
Dense and highly structured ecological niches
“Do extreme environments help create more interactive microbial communities, with more interdependent microorganisms ?” suggests Rebecca Prescott, a biologist at NASA’s Johnson Space Center. “And if so, what properties of these extreme environments contribute to creating this interdependence?”
To offer a beginning of an answer to these questions, the researchers decided to focus more particularly on the few species that occupy several of these niches. In particular, they focused on a rather special group called Chloroflexi.
This group was very far from being the most important quantitatively speaking. On the other hand, it was present at all the sampling sites. According to the researchers, this suggests that it could play a fundamental role as a hub in these communities.
This work was relatively exploratory, and above all made it possible to document the diversity of these populations. But now that they have highlighted this particularity, they are already planning to conduct a new study. The objective: to study the “roles” of these micro-organisms in their respective communities. But this will require a series of much more extensive genetic sequencing.
Leads for geosciences, biology and the search for extraterrestrial life
“Microbes do not grow in isolation”, explains Prescott. “They live, grow, and interact with many other microorganisms in a veritable sea of chemical signals produced by these other microbes. This can alter the expression of their genes, and thus affect their roles in the community”, he specifies.
And if so many researchers are interested in it so closely, it is not simply for the pleasure of discovery. Many specialists believe that these still relatively poorly known bacteria could play a central role in certain very important geological phenomena, such as the transformation of basaltic volcanic rocks.
NASA also regularly conducts work on this issue. For the space agency, these extremophiles are a real treasure; they make it possible to formulate assumptions about evolutionary strategies that life forms could have possibly adopted in environments like Mars or Enceladus, for example. What facilitate the work of machines like Perseverance, which is currently looking for biosignatures on the Red Planet.
The text of the study is available here.
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