Do microorganisms have biogeography? Because up to now we all belive in an old microbiological tenet ‘Everything is everywhere, but, the environment selects’.
Bacterial biogeography, in my opinion, is like the look for extra-terrestrial life. Both are difficult and both are worth it even if we fail to find any. Regardless, I honestly believe that there is bacterial biogeography. We cannot and should not base conclusions solely on 16S rRNA gene sequence data. With increase cheaper NGS methods we are able to get a better picture, but it is still not complete. Without too much of conflict of interest I can point you to a paper from my PhD. In that we found streptomycetes with >99% similarity in 4 different sites on a beach, however these strains had huge variations in their protein coding genes. So that poses the question on what is everything? Does it mean that we conclude that something is everywhere since that 16S OTU is found in different locations without considering other genes? I guess not. And then there is quite a recent paper by Rout and Callaway where they show geographical isolation and natural selection.
In my case, when I compared the sequences of 16S rRNA, house-keeping and symbiotic genes of rhizobia, I discovered biogeographic pattern (doi: 10.1111/j.1365-294X.2011.05368.x). Now a days many articles are coming describing biogeography among microbes. @ Sanjay : on the bases of multi-locus sequencing not only 16S rRNA gene. what we are getting is just due to adaptation or the geography is really playing crucial role in the distribution of microorganisms?
Very right Richa, so, we can agree that the famous microbiological tenet ‘Everything is everywhere, but, the environment selects’ is going to be a part of history.
Differentiation should precede selection and speciation. When dealing with smaller spatial scales what we observe is probably not selection but just differentiation. Therefore, within the purview of your question, I would doubt that this could be adaptation. Especially the ecosystem that I studied (coastal sanddunes) are very much physico-chemically similar and thus the adaptive pressures are almost same. It is surely not uncommon to see similar taxa in dissimilar ecologies and dissimilar assemblages in similar niches. So what we can assume is that there are too many factors that shape a particular assemblage and thus we are in no position to disregard the Baas-Becking hypothesis yet. Thats my two penny worth there.