Generation of zero-valent sulfur from dissimilatory sulfate reduction in sulfate-reducing microorganisms

Significance

Dissimilatory sulfate reduction (DSR) is one of the oldest and most prominent microbial metabolic pathways on Earth. It is generally accompanied by zero-valent sulfur (ZVS) that is involved in several cryptic pathways in marine and terrestrial environments. In this study, we identified a to-date unknown DSR pathway or sulfate-to-ZVS conversion mediated by sulfate-reducing microorganisms. This finding provides further insights into the sulfur cycle, which may help reveal details about cryptic element cycling pathways and improve our understanding of the sulfur metabolism in early Archaean microorganisms.

Abstract

Dissimilatory sulfate reduction (DSR) mediated by sulfate-reducing microorganisms (SRMs) plays a pivotal role in global sulfur, carbon, oxygen, and iron cycles since at least 3.5 billion y ago. The canonical DSR pathway is believed to be sulfate reduction to sulfide. Herein, we report a DSR pathway in phylogenetically diverse SRMs through which zero-valent sulfur (ZVS) is directly generated. We identified that approximately 9% of sulfate reduction was directed toward ZVS with S ₈ as a predominant product, and the ratio of sulfate-to-ZVS could be changed with SRMs’ growth conditions, particularly the medium salinity. Further coculturing experiments and metadata analyses revealed that DSR-derived ZVS supported the growth of various ZVS-metabolizing microorganisms, highlighting this pathway as an essential component of the sulfur biogeochemical cycle.