Across-lineage prediction of within-KO sequence diversity by temperature and pH differs among subcellular compartments in hydrothermal spring communities

A general understanding of how extreme temperature and pH might universally shape the evolution of protein variants is lacking. Importantly, while pH is differentially regulated in microbial compartments, temperature is not. We hypothesise that these variables may partly explain the within-genome variability in protein rates of single-celled organisms, since genes encode proteins allocated to different compartments. To test this hypothesis, we examine the number of unique sequence contributors assigned to a KEGG across species as a coarse proxy for accumulated evolutionary divergence. Under a naive null expectation, orthologs of equal abundance should be represented by a similar number of variants. We examine sequence diversity in 17 metagenomes from El Tatio geothermal field (Chile), spanning temperatures of 45-62 {degrees}C, and pH values of 7.2-9.3. At equal abundance, warmer temperature is weakly associated to more ortholog variants, while alkaline pH is associated to fewer (in the ranges examined). The inclusion of these variables in the model robustly improved the prediction of the community-level within-KO unique sequence contributors from metagenomic abundance. KO variant diversity in the periplasm was only significantly affected by pH increases, providing partial support to the compartment hypothesis.