Microbial Insights to Organic Sulfur Degradation in Freshwater Sediments
Abstract
The sulfur cycle is a complex biogeochemical cycle that involves both inorganic and organic species. However, the role of organic sulfur to the sulfur cycle is underappreciated. Recent studies have suggested organic sulfur likely fuels sulfate reduction, potentially through a cryptic sulfur cycle, and these processes were likely important in Earth's geologic past. Using Lake Superior sediments, which are low in sulfate, we conducted sediment incubations to measure the biotransformation capability of organic sulfur compounds. Additionally, we searched metagenomic sequence libraries for the presence of and expression profiles of key sulfur cycling genes. In sediment metagenomes, pathways and genes for sulfur reduction, oxidation and organic sulfur degradation were found. Sediments from different depths were individually incubated with enrichments of taurine, methionine, cysteine, and sodium dodecyl sulfate (SDS) to identify usage patterns. Preferential degradation was seen across all depths in incubations with enrichments of SDS and taurine over other enrichments of methionine and cysteine. In addition to preferential degradation of organic sulfurs, incubation data indicates there is a spatial structure to where the compounds degrade, shown by varying ratios of sulfide to sulfate production across sediment depth. This can especially be seen in incubations containing cysteine, where despite producing lower values of sulfate than other incubations, there is a clear spatial structure of biotransformation with microbes outputting higher values of sulfate at deeper depths than the samples at the surface of the sediment. Analysis of metabolic pathways present in the metagenomes show the prevalence of taurine degradation. Additionally, taurine degradation could potentially link with the sulfoacetaldehyde degradation pathway, which is present in 92% of microbial genomes sampled. Sulfoacetaldehyde degradation generates sulfite that could then be oxidized to sulfate, supporting our biotransformation of taurine into sulfate in sediment incubations. By combining biotransformation results and metagenomics, a robust frame work for sulfur cycling in sediments informs how pathways may have operated in the past.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B11L2248H
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0460 Marine systems;
- BIOGEOSCIENCES;
- 0463 Microbe/mineral interactions;
- BIOGEOSCIENCES;
- 0488 Sulfur cycling;
- BIOGEOSCIENCES