Operational Taxonomic Unit (OTU)

Within the same species, there exists a genetic diversity (according to the sequences of nucleotides). An OTU is a grouping of individuals of the same species whose 16S rRNA sequences present a 97.5% similarity.
This international standardization allows researchers in the same discipline to compare their results, but it does not neccessarily have a biological significance and other similarity values have been suggested. Individuals in different OTUs cannot belong to the same bacterial species.
In the case of the study of the cyanobacteria present in lakes Beak 1 and Beak 2 in Antarctica, different OTUs, named by numbers have made it possible to group cyanobacteria according to their genetic similarities and thus to facilitate the study of the variation of species over the centuries.