Sulphur transformation
Sulphur transformation includes two microbial processes that convert sulphur into different forms: Dissimilatory sulphate reduction and Sulphur oxidation.
Dissimilatory sulphate reduction occurs under low oxygen conditions. During this processes, bacteria and archaea (often referred to as sulphate-reducing micro-organisms) convert sulphate (SO4) into hydrogen sulphide (H2S), which has the characteristic smell of rotten eggs. This reaction allows bacteria and archaea to breath using sulphate rather than oxygen.
Sulphur oxidation can occur both under aerobic and anaerobic conditions. In this process, bacteria and archaea transform elemental sulphur (S0) or sulphide (S2-) to sulphate (SO4). Some micro-organisms capable of sulphur oxidation are autotrophs, meaning that they can fix CO2 directly from the atmosphere.
Sulphur transformation is considered in the Nutrient cycling model because it is an essential nutrient for plants and soil life. Note that the conversion of organic sulphur to sulphate is part of the process of mineralisation.
Dissimilatory sulphate reduction and sulphur oxidation can be estimated through incubation methods or measuring the abundance of specific microbial functional genes[1],[2],[3].
[1] Tourna M, Maclean P, Condron L, O’Callaghan M, Wakelin SA. 2014. Links between sulphur oxidation and sulphur-oxidising bacteria abundance and diversity in soil microcosms based on soxB functional gene analysis. FEMS Microbiology Ecology 88: 538–549.
[2] Moestedt J, Nilsson Påledal S, Schnürer A. 2013. The effect of substrate and operational parameters on the abundance of sulphate-reducing bacteria in industrial anaerobic biogas digesters. Bioresource Technology 132: 327–332.
[3] Wind T, Conrad R. 1997. Localization of sulfate reduction in planted and unplanted rice field soil. Biogeochemistry 37: 253–278.