Microbial cysteine degradation is a source of hydrogen sulfide in oxic freshwater lakes

Abstract The sulfur-containing amino acid cysteine is abundant in the environment including in freshwater lakes. Biological cysteine degradation can result in hydrogen sulfide (H 2 S), a toxic and ecologically relevant compound that is a central player in biogeochemical cycling in aquatic environments. Here, we investigated the ecological significance of cysteine in oxic freshwater lake environments, using isolated cultures, controlled growth experiments, and multi-omics. We screened bacterial isolates enriched from natural lake water for their ability to produce H 2 S when provided cysteine. In total, we identified 29 isolates that produced H 2 S and belonged to the phyla Bacteroidetes, Proteobacteria, and Actinobacteria . To understand the genomic and genetic basis for cysteine degradation and H 2 S production, we further characterized 3 freshwater isolates using whole-genome sequencing (using a combination of short-read and long-read sequencing), and quantitatively tracked cysteine and H 2 S levels over their growth ranges: Stenotrophomonas maltophilia (Gammaproteobacteria), Stenotrophomonas bentonitica (Gammaproteobacteria) and Chryseobacterium piscium (Bacteroidetes). We observed a decrease in cysteine and increase in H 2 S, and identified genes involved in cysteine degradation in all 3 genomes. Finally, to assess the presence of these organisms and genes in the environment, we surveyed a five-year time series of metagenomic data from the same isolation source (freshwater Lake Mendota, WI, USA) and identified their presence throughout the time series. Overall, our study shows that sulfur-containing amino acids can drive microbial H 2 S production in oxic environments. Future considerations of sulfur cycling and biogeochemistry in oxic environments should account for H 2 S accumulation from degradation of organosulfur compounds. Importance Hydrogen sulfide (H 2 S), a naturally occurring gas with biological origins, can be toxic to living organisms. In aquatic environments, H 2 S production typically originates from anoxic (lacking oxygen) environments such as sediments, or the bottom layers of thermally stratified lakes. However, the degradation of sulfur-containing amino acids such as cysteine, which all cells and life forms rely on, can be a source of ammonia and H 2 S in the environment. Unlike other approaches for biological H 2 S production such as dissimilatory sulfate reduction, cysteine degradation can occur in the presence of oxygen. Yet, little is known about how cysteine degradation influences sulfur availability and cycling in freshwater lakes. In our study, we identified diverse bacteria from a freshwater lake that can produce H 2 S in the presence of O 2 . Our study highlights the ecological importance of oxic H 2 S production in natural ecosystems and necessitates a change in our outlook of sulfur biogeochemistry.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.