Large sulfur isotope fractionation during abiotic consumption of hydrogen sulfide after cessation of bacterial growth in batch culture experiments of sulfate reducing bacteria

•A sulfate reducing bacterium was cultivated long term to investigate microbial sulfur isotope fractionations.•Microbial sulfate reduction with varying fractionation factors prevailed during bacterial growth.•Sulfide concentration decreased after cessation of the bacterial growth.•The sulfide consuming reaction involved large sulfur isotope fractionations (<-10 ‰).•Abiotic organic matter sulfurization may be the sulfide consuming reaction.