Microbial Ecology of Sulfur Cycling in Anoxic Environments

In oxygen-depleted habitats such as marine oxygen minimum zones, stratified lakes and deep-sea sediments, sulphur transformations underpin key biogeochemical processes. Microbial communities mediate a spectrum of reactions from dissimilatory sulphate reduction—yielding hydrogen sulphide—to oxidation of reduced sulphur species back to sulphate. These processes are carried out by diverse functional groups, including strictly anaerobic sulphate reducers, chemolithoautotrophic sulphur oxidisers and phototrophic sulphur bacteria in illuminated anoxic zones. Interactions among bacteria, archaea and viruses modulate community structure and metabolic fluxes, while redox gradients and nutrient availability shape ecological niches. The resulting sulphur cycle has global significance, influencing carbon sequestration, nitrogen loss, trace-metal bioavailability and greenhouse-gas dynamics, and offers promising avenues for biotechnological applications such as bioremediation and bioenergy production.

Research from Nature Portfolio

Recent studies have revealed that viruses infecting phototrophic sulphur bacteria carry auxiliary metabolic genes for pigment synthesis, carbon fixation and reductive sulphur assimilation, suggesting a viral role in modulating host metabolism and the geochemical signatures of ancient euxinic environments. In parallel, high-resolution network analyses of 16S rRNA amplicons in a seasonally anoxic inlet identified discrete microbial subnetworks: one driven by aerobic heterotrophs at the oxycline and another by keystone anaerobic taxa that couple sulphur oxidation to denitrification and influence nitrous oxide dynamics. These findings underscore the importance of viral–host interactions and microbial network structure in controlling sulphur-driven elemental cycles under anoxia.

Microbial Ecology of Sulfur Cycling in Anoxic Environments publication trend

The graph below shows the total number of articles in microbial ecology of sulfur cycling in anoxic environments across all publications each year (not limited to Nature Index journals).

Technical terms

Sulfate-reducing bacteria (SRB): Anaerobic prokaryotes that conserve energy by reducing sulfate to hydrogen sulphide.

Sulfur-oxidizing bacteria (SOB): Chemolithoautotrophs that oxidise reduced sulphur species (e.g. sulphide, thiosulfate) to sulphate.

Euxinia: Aquatic conditions characterised by anoxia combined with elevated hydrogen sulphide concentrations.

Chemocline: A stratified interface in a water column separating oxygenated surface layers from underlying anoxic, sulphidic zones.

Auxiliary metabolic genes (AMGs): Viral genes that alter host metabolic pathways, enhancing viral replication and affecting biogeochemical cycles.

Wood–Ljungdahl (WL) pathway: Reductive acetyl-CoA pathway used by anaerobic autotrophs for carbon fixation under low-energy conditions.

References

1. Viruses of sulfur oxidizing phototrophs encode genes for pigment, carbon, and sulfur metabolisms. Communications Earth & Environment (2023).
2. Network analysis of 16S rRNA sequences suggests microbial keystone taxa contribute to marine N2O cycling. Communications Biology (2023).
3. The bacterial sulfur cycle in expanding dysoxic and euxinic marine waters. Environmental Microbiology (2020).
4. Phylogenetically and metabolically diverse autotrophs in the world’s deepest blue hole. ISME Communications (2023).
5. A diverse uncultivated microbial community is responsible for organic matter degradation in the Black Sea sulphidic zone. Environmental Microbiology (2020).