AUTHOR=Boase Katelyn , González Carolina , Vergara Eva , Neira Gonzalo , Holmes David , Watkin Elizabeth 

TITLE=Prediction and Inferred Evolution of Acid Tolerance Genes in the Biotechnologically Important Acidihalobacter Genus

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.848410

DOI=10.3389/fmicb.2022.848410

ISSN=1664-302X

ABSTRACT=<p><italic>Acidihalobacter</italic> is a genus of acidophilic, gram-negative bacteria known for its ability to oxidize pyrite minerals in the presence of elevated chloride ions, a capability rare in other iron-sulfur oxidizing acidophiles. Previous research involving <italic>Acidihalobacter</italic> spp. has focused on their applicability in saline biomining operations and their genetic arsenal that allows them to cope with chloride, metal and oxidative stress. However, an understanding of the molecular adaptations that enable <italic>Acidihalobacter</italic> spp. to thrive under both acid and chloride stress is needed to provide a more comprehensive understanding of how this genus can thrive in such extreme biomining conditions. Currently, four genomes of the <italic>Acidihalobacter</italic> genus have been sequenced: <italic>Acidihalobacter prosperus</italic> DSM 5130<sup>T</sup>, <italic>Acidihalobacter yilgarnensis</italic> DSM 105917<sup>T</sup>, <italic>Acidihalobacter aeolianus</italic> DSM 14174<sup>T</sup>, and <italic>Acidihalobacter ferrooxydans</italic> DSM 14175<sup>T</sup>. Phylogenetic analysis shows that the <italic>Acidihalobacter</italic> genus roots to the Chromatiales class consisting of mostly halophilic microorganisms. In this study, we aim to advance our knowledge of the genetic repertoire of the <italic>Acidihalobacter</italic> genus that has enabled it to cope with acidic stress. We provide evidence of gene gain events that are hypothesized to help the <italic>Acidihalobacter</italic> genus cope with acid stress. Potential acid tolerance mechanisms that were found in the <italic>Acidihalobacter</italic> genomes include multiple potassium transporters, chloride/proton antiporters, glutamate decarboxylase system, arginine decarboxylase system, urease system, <italic>slp</italic> genes, squalene synthesis, and hopanoid synthesis. Some of these genes are hypothesized to have entered the <italic>Acidihalobacter</italic> via vertical decent from an inferred non-acidophilic ancestor, however, horizontal gene transfer (HGT) from other acidophilic lineages is probably responsible for the introduction of many acid resistance genes.</p>