Abstract
Detailed characterization of posttranslational modifications (PTMs) of proteins in microbial
communities remains a significant challenge. Here we directly identify and quantify a broad
range of PTMs (hydroxylation, methylation, citrullination, acetylation, phosphorylation,
methylthiolation, S-nitrosylation and nitration) in a natural microbial community from an
acid mine drainage site. Approximately 29% of the identified proteins of the dominant
Leptospirillum group II bacteria are modified, and 43% of modified proteins carry multiple
PTM types. Most PTM events, except S-nitrosylations, have low fractional occupancy.
Notably, PTM events are detected on Cas proteins involved in antiviral defense, an aspect of
Cas biochemistry not considered previously. Further, Cas PTM profiles from Leptospirillum
group II differ in early versus mature biofilms. PTM patterns are divergent on orthologues of
two closely related, but ecologically differentiated, Leptospirillum group II bacteria. Our results
highlight the prevalence and dynamics of PTMs of proteins, with potential significance for
ecological adaptation and microbial evolution.
