High-throughput metabarcoding of SAR11 assemblages from the southwest Atlantic shelf and arid Patagonia: richness and associated rank abundance distributions.

The SAR11 clade is likely the most abundant microbial lineage on earth. Here, we provide detailed analyses of the group's richness and AD in poorly studied Southern microbiomes. This requires whole community composition analyses to be performed, which are also provided in conjunction with the SAR11-specific studies. In this way, the work describes unknown aspects of the diversity of an outstanding bacterial lineage and novel data on remote and relatively little-studied microbial communities. Background: Massively parallel sequencing of environmental DNA allows microbiological studies to be performed in greater detail than was possible with first-generation sequencing. For example, it facilitates the use of approaches hitherto largely applied to flora and fauna, such as rank abundance distribution (RAD) analyses. Methods: Here, we set out to advance the knowledge on Results: Microbial community composition analyses revealed that the studied SAR11 assemblages coexist with 27 bacterial phyla. SAR11 richness was in general very high, but ADs turned out to be highly uneven. The results were compatible with prior knowledge, and similar to that derived from point estimates of diversity. However, our comprehensive dissection allowed for more detailed quantitative comparisons to be made between the environments surveyed, and revealed differences regarding both richness and the underlying ADs. Conclusions: Despite SAR11 assemblages being extremely rich, their ADs are very uneven. Richness and AD