Isolation of a putative sulfur comproportionating microorganism

Sulfur comproportionation is a heretofore undiscovered microbial catabolism that was predicted based on thermodynamic calculations. Here, we report the isolation of an Acidithiobacillus thiooxidans strain from extremely low pH snottite biofilms in the karst at Frasassi, Italy. The strain grew to cell densities of >107 cells mL-1 in autotrophic sulfur comproportionation medium. Whole genome sequencing of the isolate revealed the presence of numerous genes involved in sulfur transformations that could be linked in a sulfur comproportionation pathway. We describe an experimental framework, including measurements of sulfate, sulfide, and S0 concentrations, electron microscopy, and stable and radioisotope incubations coupled with NanoSIMS, scintillation counting and isotope ratio mass spectrometry, for future searches of sulfur comproportionators.