[M-IS09] Biogeochemistry

[MIS09-10] Deciphering the relationship between sulfur isotope effect and microbial cell specific sulfur reduction rate using subcellular level analysis

*Dong Kyun Woo¹, Bokyung Kim¹, Min Sub Sim¹ (1.School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Republic of Korea)

Keywords:Multiple sulfur isotope effect, Microbial sulfate reduction

Microbial sulfate reduction and its resulting sulfur isotope effect are a crucial part of understanding the sulfur cycle and interpreting past geological events. Throughout its long history of research, sulfur isotope effect by sulfate reducing microorganisms has been often explained by its inverse correlation with cell specific sulfur reduction rate. While majority of the previous data fit well into this relationship, several studies indicate that cell specific reduction rate alone cannot explain all the sulfur isotope effects during microbial sulfate reduction. One example of such case is sulfate respiration under diazotrophic conditions, where nitrogen fixing sulfate reducers fractionate sulfur isotopes more than those in the presence of fixed nitrogen despite the fact that diazotrophic growth display a higher specific sulfate reduction rate (Sim et al., 2012). In order to provide a theoretical base for the empirical relationship between the sulfur isotope fractionation and the specific respiration rate, here we monitored subcellular parameters together with the fractionation of quadruple sulfur isotopes. The sulfate reducing bacterium DMSS1 (Desulfovibrio sp.) was cultivated under ammonium-replete or diazotrophic conditions, and gene expression levels of the two major reductases in the sulfate reduction pathway, adenylyl-sulfate reductase (Apr) and dissimilatory sulfite reductase (Dsr), and intracellular ATP/AMP ratio were determined for vegetative cells. Since the former controls primarily the turnover rate of sulfur metabolites, and the latter dictates the reversibility of sulfate activation prior to its reduction, although preliminary, this is the first direct assessment of the biochemical mechanism underlying the covariance between specific respiration rate and sulfur isotope effect. We will also integrate our new findings into the multiple sulfur isotope model for dissimilatory sulfate reduction (Wing & Halevy, 2014), further examining the practicality of a conventional inverse relationship for the interpretation of biogeochemical sulfur isotope signatures.

Sim, M. S., Ono, S., & Bosak, T. (2012). Effects of iron and nitrogen limitation on sulfur isotope fractionation during microbial sulfate reduction. Applied and environmental microbiology, 78(23), 8368-8376.
Wing, B. A., & Halevy, I. (2014). Intracellular metabolite levels shape sulfur isotope fractionation during microbial sulfate respiration. Proceedings of the National Academy of Sciences, 111(51), 18116-18125.