Researchers noticed an "extraordinary" amount of genetic diversity in a tiny aquatic microbe.
Prochlorococcus is the "smallest and most abundant" marine microbe, a Massachusetts Institute of Technology news release reported. Researchers believe about billion billion billion of these single-celled photosynthetic bacteria live in the ocean.
The organisms are extremely important because they form the very bottom of the food chain.
The researchers performed a cell-by-cell genomic analysis on microbes found in less than a teaspoon's worth of water; they found hundreds of genetic subpopulations in this small sample.
The sample contained "core gene alleles" linked to different flexible genes; the researchers called this the "genomic backbone." Each cell in the sample was found to carry at least one set of reflective genes. The researchers found the organism's diversity varied by season.
The team believes the subpopulations diverged millions of years ago while the "backbone" has an even older origin.
"The sheer enormity of diversity that must be in the octillion Prochlorococcus cells living in the seas is daunting to consider," Sallie Chisholm, the Lee and Geraldine Martin Professor of Environmental Studies in CEE and in MIT's Department of Biology said in the news release. "It creates a robust and stable population in the face of environmental instability."
The scientists also believe ocean turbulence has the ability to affect the diversity of Prochlorococcus by spreading them more quickly through the ocean.
"The interesting question is, 'Why does such a diverse set of subpopulations exist?'" former CEE postdoc Nadav Kashtan said in the news release. "The huge population size of Prochlorococcus suggests that this remarkable diversity and the way it is organized is not random, but is a masterpiece product of natural selection."
The researchers believe a similar phenomenon would be observed in many other organisms.
"This is perhaps the most sophisticated and thorough study yet to be published on the fine-scale genetic diversification of an environmental microbial species, and it correctly, I think, predicts that amazingly diverse populations may be maintained over astonishingly long times," Ford Doolittle, a member of the biochemistry and molecular biology faculty at Dalhousie University who was not involved in the research, said in the news release. "If microbiologists persist in believing in 'species,' they will likely have to drastically revise upward their estimates of how many such things there are. What we will probably be arguing about for a long time is what processes or forces other than selection might be responsible for such stable diversity, and, unless we find such processes, how something so seemingly well mixed as the ocean can offer up so many different tiny selective regimes."
