Alex Hyer, University of Utah
Geochemical reactions associated with the process known as serpentinization can generate copious quantities of organic carbon and chemical energy that support life, but these reactions also greatly increase the pH of serpentinization sites. High-pH environments hinder ATP production because the low proton concentrations at high pH can result in a reversed proton gradient across cell membranes. Organisms present at serpentinization sites are not well-characterized, and adaptations to their alkaliphilic lifestyle are unknown. Bacillus pseudofirmus OF4 was not isolated from serpentinization sites, but it is a well- studied alkaliphile that has several distinct adaptations for ATP production in high pH environments. Its sequence for ATP synthase, the molecular motor responsible for ATP generation in the cell, contains several distinctive mutations including an AXAXAXA motif that increases the C-ring stoichiometry, a P51XXE54XXP57 motif that creates a distinct kink in the outer helix of the C-subunit, and a V21 mutation granting rotamer freedom to E54. In this study, we search for similar mutations in metagenomic databases containing DNA sequences collected from serpentinization sites. Analysis of alignments from the programs BLAST and Exonerate indicate that V21 is present in several alignments, but P51 is found in only a single alignment from serpentinization sites. The AXAXAXA motif is non- existent in our databases, but the more common GXGXGXG motif is present with alanine replacements occurring periodically. In general, these results indicate that our DNA sequences from high-pH sites of serpentinization are more reminiscent of typical neutrophiles than of the alkaliphile B. pseudofirmus OF4. Therefore, serpentinization- adapted organisms may harbor other adaptations to high pH such as local pmf regulation. Future work will test for quantitative correlations between environmental pH measurements and the incidence of mutations in ATP synthase in order to identify novel adaptations to high pH in serpentinization-driven ecosystems.