2024-02-01 06:26:35
Because yes, there are predators and prey among bacteria! As in everything else in the living world, there are food chains in unicellular organisms. And this universe invisible to our eyes is extremely diverse.
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Bacterial predation difficult to study
We must imagine that by extrapolating the data we currently have, bacterial biodiversity could be 1,000 billion species, but it remains difficult to study. We know very little about these food networks – therefore who eats who – and until now we have focused on categorizing them somewhat arbitrarily.
Marie Vasse is a CNRS researcher in microbiology at the University of Montpellier: “Because among bacteria, it is difficult to isolate and work with bacteria that are described as predatory. We know relatively little about them and it is a technical challenge to work with them in the laboratory. So, there had relatively little knowledge, but until now, we attributed categories to these bacteria. There were the predatory bacteria and then those which were their prey. And so, if we make the analogy with animals, it was pretty much the same in the sense that we categorize the lion as a predator and the gazelle as prey. What we were trying to do was to set up experiments where we could try to understand how predatory bacteria became predators and behaved like predators. So concretely, how they looked for their prey, how they approached, how they killed them, how they recovered the nutrients afterwards. How the prey, on the other hand, tried to either flee or protect themselves physically, in groups or individually, from their predators.”
This researcher’s experimental approach is somewhat modeled on the animal world. The objective is to look at how bacteria can live together and organize themselves into a community. In this case the two species that interest us here are very common prey, Pseudomonas fluorescens and a predator: Myxococcus xanthus.
To study this predation, we must first “grow” bacteria separately then put them together, and we wait, as it were, for one to eat the other. And then, you have to reproduce, repeat, the experiments – at least 3 times generally in biology. And this is where it gets complicated… Marie Vasse therefore carried out the first two predation experiments, putting one and the other together and this gave identical results. And then, she leaves for another position and another researcher takes over the manipulation – this is quite common, but here, nothing happens as planned!
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A slight modification of the protocol… due to a traffic jam at the bench
The predatory bacteria has disappeared and the prey has grown well. So the two researchers try to understand if there were variations in their protocol. They redo the story – redo the manipulation together via remote video and they find a single discrepancy which seems trivial: the second researcher left the prey on the edge of the bench for 24 hours, at room temperature instead of 32°C usual… because there was simply no more room in the incubator.
“We laughed quite a bit when we said to ourselves, it’s very likely that it’s not that, but hey we’re still going to try to see if the temperature at which we grow our bacteria is correct before even putting it in presence of the predatory bacteria can explain our completely different results. We wrote a protocol to ask this question. We changed the research question and repeated the experiment. And at 32 degrees, Myxococcus xanthus is the predator : it kills and it feeds on Pseudomonas. And when Pseudomonas grows at 22 degrees, even before being put in the presence of Myxococcus at 32 degrees, since this interaction always takes place at 32 degrees, well the pseudomonas completely eliminates what was before its predator. It kills it completely, there are no detectable cells left for us of Myxococcus xanthus and it not only kills it, but it feeds on its nutrients and it can reproduce. The combination of killing and feeding on its victims is predation.” – Marie Vassefirst author of the study.
Imagine a gazelle, preyed on in the morning, who goes to hunt the lion in the evening. This is the very first time that such a complete reversal of the food chain due to a simple change in temperature has been demonstrated, and not just in the microbial world, but in the entire living world – and all because from a traffic jam to the bench! Serendipity, my love!
And there is even the beginnings of a biological explanation: at room temperature, Pseudomonas fluorescens secretes toxic molecules into its environment. The question that now arises is the nature of these substances – But more broadly, the results of this new study published in Plos One tend to challenge this compartmentalized vision of bacterial categories of prey or predators and even to change our view of what predation is in the microbial world.
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#Bacteria #change #sides #prey #predators