The Niche at the Edge of Life or the Microbial Ecology (Including Microfungi) of Cuatro Ciénegas: Mutualisms with Locals, Antagonisms Against Foreigners

In this chapter we will explore whether the niche concept is useful to understand microbes, since we believe that this key concept in ecology is particularly useful in the investigation of microbial biodiversity. On the one hand, with microbes we can conduct experiments to analyze in detail all the aspects of the Grinnellian niche, in a way that cannot be done in other organisms. On the other hand, even if complicated, we can develop different experiments and observations to start analyzing the Eltonian aspects of the niche. Here we develop our ideas on how to study the niche components in microbial systems and describe our advances in analyzing these components in a particular group of organisms in the Cuatro Cienegas Basin (CCB). In this oasis, the distinctive oligotrophic conditions of several freshwater systems in CCB promote unique microbial interactions in order to cope with nutrient stress, where antagonist and synergic effects influence bacterial diversity structure, modifying the nature and intensity of biotic interactions. For example, Bacillus has few antagonistic interactions among strains of a given sampling site but strong antagonisms when competing against strains from different sites. Interestingly, antagonistic strains belonged to two genetically close species, and their targets belonged to taxonomically separate groups. Even more so, the same Bacillus strains showed great diversity in the dependence of the different strains on other community members. While antagonistic strains were in general prototrophs, a large proportion of sensitive and resistant strains exhibited auxotrophy suggesting that they need their community in order to survive. At CCB we believe that the cohesion of the community through these positive interactions is paramount to explain survival in such a harsh environment. As a result, the multidimensional space where the theater of life plays in CCB is very rich and full of actors, which shifts constantly, as virus and other process “chop the head” of the dominant species and former “underdogs” of the rare biosphere take their roles. Finally, since this play of “life at the edge” has been continued in the same site for a very long time with coevolving communities, here the “conversations and negotiations” between microscopic actors seem to be the reason why this stage has persisted for such a long time.