Microbial Sulfur Metabolism and Ecology

Microbial sulfur metabolism encompasses a network of biochemical pathways by which microorganisms transform sulfur compounds across multiple redox states, linking the global cycles of sulfur, carbon, nitrogen and metals. These processes range from assimilatory sulfate reduction, in which sulfate is incorporated into cellular biomass, to dissimilatory sulfate and sulfite reduction, whereby microorganisms conserve energy by using sulfur oxyanions as terminal electron acceptors. Complementary oxidative pathways enable certain bacteria and archaea to convert reduced sulfur species back to sulfate, often via intracellular or extracellular sulfur intermediates. Such flexibility underpins the prevalence of sulfate‐reducing and sulfur‐oxidising microbes in diverse environments including marine and freshwater sediments, wetlands, deep subsurface ecosystems and hydrothermal systems. By mediating organic matter mineralisation, controlling greenhouse‐gas fluxes and facilitating metal corrosion or mineral formation, sulfur‐transforming microbes exert profound ecological and biogeochemical influence. Understanding their metabolic diversity and environmental interactions is essential for applications in bioremediation, bioenergy and climate‐change mitigation.

Research from Nature Portfolio

Recent studies have characterised a novel assimilatory sulfate reduction pathway in a marine methanogen, revealing that this archaeon employs a mosaic of assimilatory and dissimilatory enzymes—including an atypical PAPS reductase and a non‐canonical PAP phosphatase—to convert sulfate to sulfide for biosynthesis. Structural and biochemical analyses indicate that these enzymes were acquired through horizontal gene transfer and subsequently repurposed to support methanogenic growth on sulfate.

Investigations into an acidobacterial isolate have demonstrated remarkable metabolic versatility, showing that a single organism can alternately respire sulfate or oxygen while degrading complex polysaccharides under fluctuating oxic–anoxic regimes. Metatranscriptomic evidence highlights a facultative life style that blurs the traditional separation between strict anaerobic sulfate reducers and aerobic heterotrophs.

High‐resolution structural work on a coenzyme F420–dependent sulfite reductase has mapped the electron‐relay architecture connecting flavin and siroheme centres. This homotetrameric enzyme, found in marine methanogens, combines features of assimilatory and dissimilatory reductases and provides a model for early evolutionary assembly of sulphite detoxification systems.

Microbial Sulfur Metabolism and Ecology publication trend

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

Technical terms

Assimilatory sulfate reduction: Biosynthetic pathway converting sulfate to sulfide for incorporation into amino acids and cofactors.

Dissimilatory sulfite reductase (dsrAB): Enzyme complex that catalyses the six‐electron reduction of sulfite to sulfide during energy conservation.

PAPS: 3′‐phosphoadenosine 5′‐phosphosulfate, an activated sulfate donor in assimilatory pathways.

Siroheme: Iron–porphyrin cofactor that serves as the active centre of both assimilatory and dissimilatory sulfite reductases.

Coenzyme F420: Deazaflavin electron carrier found in methanogenic and certain sulfate‐reducing archaea, mediating low‐potential redox reactions.

Mixotrophy: Metabolic strategy combining autotrophic energy generation with heterotrophic substrate utilisation.

References

1. Assimilatory sulfate reduction in the marine methanogen Methanothermococcus thermolithotrophicus. Nature Microbiology (2023).
2. Oxygen respiration and polysaccharide degradation by a sulfate-reducing acidobacterium. Nature Communications (2023).
3. Microbe-driven elemental cycling enables microbial adaptation to deep-sea ferromanganese nodule sediment fields. Microbiome (2023).
4. Structures of the sulfite detoxifying F420-dependent enzyme from Methanococcales. Nature Chemical Biology (2023).
5. Global diversity and inferred ecophysiology of microorganisms with the potential for dissimilatory sulfate/sulfite reduction. FEMS Microbiology Reviews (2023).
6. Stepwise pathway for early evolutionary assembly of dissimilatory sulfite and sulfate reduction. The ISME Journal: Multidisciplinary Journal of Microbial Ecology (2023).