Non-sulfate-based hydrogen sulfide production in engineered systems

Unwanted microbiological production of hydrogen sulfide (H2S) is a major challenge in engineered systems, such as sewage treatment plants, landfills, and aquaculture systems. While sulfur-rich amino acids and other substrates for non-sulfate-based H2S production are commonly present, the ability and potential of different microorganisms to perform sulfate-free H2S production has not yet been resolved. Here, we reveal the identity, activity, and genomic characteristics of bacteria that degrade cysteine to produce H2S in anaerobic enrichment bioreactors seeded with material from aquaculture systems. We compared them with canonical sulfate reducing bacteria and found that both sulfur sources led to microbial H2S production, yet with the process being more rapid with cysteine than with sulfate. 16S rRNA amplicon sequencing and metagenomic analysis showed four bacterial families, Dethiosulfatibacteraceae, Fusobacteriaceae, Vibrionaceae, and Desulfovibrionaceae to be centrally involved in non-sulfate H2S production. Metagenome/metatranscriptome assembled genomes uncovered the main cysteine-degradation pathway mediated by cysteine desulfidase cyuA and revealed that some bacteria potentially also use cysteine as a carbon source in sulfate-based H2S production. Our findings call for a revised view of microbial H2S production in engineered systems.