Microbial thiosulphate reaction arrays: the interactive roles of Fe(III), O2 and microbial strain on disproportionation and oxidation pathways

In this work, we experimentally evaluate pH and SO4(2-) dynamics associated with abiotic and microbial S2O3(2-) oxidation under varying [O2], [Fe(III)] and microbial strain/consortia (two pure strains, Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, their consortia, and two enrichments from an acidic environmental system, Moose Lake 2002 and Moose Lake 2003). Results of the batch experiments demonstrate highly active microbial processing of S2O3(2-) while abiotic controls under identical experimental conditions remain static with no pH decrease. When abiotic controls were manually titrated with acid to achieve similar pH decreases to those occurring in the microbial treatments, different S pathways were involved. In particular, disproportionation is a substantial component of initial microbial S2O3(2-) processing, and is accelerated by the presence of Fe(III), indicating that recycling of S through intermediate oxidation states is likely to be widespread in acidic mine environments where high [Fe(III)] is common. Furthermore, the microbially mediated S reaction pathways were dependent on both environmental conditions and microbial strain/consortia, indicating that microbial community structure also plays a key role. Collectively, these results highlight the importance of microbial activity, their poor representation by abiotic S models, the likelihood that Fe(III), rather than O2, is a key control on microbial S processing in acid environments and the need to identify the microbial community/strain involved.