Sulfur is an important component of both environmental and human microbiomes. Karthik Anantharaman seeks to understand how microbial diversity is associated with sulfur cycling across multiple ecosystems. He’s not shy about picking favorites – according to Karthik, sulfite reductase is the most important enzyme in the sulfur cycle. Studying the diversity of sulfite reductase genes in the environment revealed multiple instances of lateral gene transfer (exchange of DNA between organisms), and the genes were sometimes found in organisms not previously known to contain sulfite reductase.
Anaerobic sulfite reductase shows a similar history of lateral gene transfer and discovery in new organisms. Organisms with this type of sulfite reductase are highly expressed in fracking shales, where they metobolize thiosulfate and sulfite. Even within the candidate phylum radiation, lateral gene transfer is the name of the game for another sulfite reductase gene, dsrD.
In the many environments, phages carry genes involved sulfur transformations. Why phages would have this is still a mystery, so Karthik is working to set up a host system to further study phage-encoded sulfur cycling genes.