amino acid sequences indicators of evolution

The evolution of SAR11 is an active area of research ( Giovannoni, 2017) that is critically important to understanding the determinants of its remarkable ability to maintain abundant populations in the global ocean. Successful cultivation efforts and single amplified genomes from the environment have led to studies revealing their critical role in marine carbon cycling ( Rappé et al., 2002 Giovannoni et al., 2005 Stingl et al., 2007 Oh et al., 2011 Tsementzi et al., 2016 White et al., 2019), and environmental sequencing surveys have offered detailed insights into the ecology of this ancient branch of life in aquatic environments across the globe ( Zinger et al., 2011 Brown et al., 2012). The SAR11 order Pelagibacterales ( Thrash et al., 2011 Ferla et al., 2013) is one of the most ubiquitous free-living lineages of heterotrophic bacteria in the world’s oceans ( Giovannoni et al., 1990 Morris et al., 2002 Carlson et al., 2009 Eiler et al., 2009 Schattenhofer et al., 2009 Treusch et al., 2009).

These findings suggest that environmentally-mediated selection plays a critical role in the journey of cosmopolitan surface ocean microbial populations, and the idea ‘everything is everywhere but the environment selects’ has credence even at the finest resolutions. SAAVs partitioned metagenomes into two main groups matching large-scale oceanic current temperatures, and six finer proteotypes that connect distant oceanic regions. Integrating amino acid and protein biochemistry with metagenomics revealed that systematic purifying selection against deleterious variants governs non-synonymous variation among very closely related populations of SAR11. Here, we employed single-amino acid variants (SAAVs) to investigate ecological and evolutionary forces that maintain the genomic heterogeneity within ubiquitous SAR11 populations we accessed through metagenomic read recruitment using a single isolate genome. Their extensive diversity challenges emerging operational boundaries defined for microbial 'species' and complicates efforts of population genetics to study their evolution. Members of the SAR11 order Pelagibacterales dominate the surface oceans.

Amino acid sequences indicators of evolution