Carbon and hydrogen isotope fractionation in lipid biosynthesis by Sporosarcina sp. DSK25

Pressure dependent fractionation (PDF) of carbon and hydrogen isotopes in lipid biosynthesis by gram-negative piezophilic bacteria has been reported thus far, however, such PDF for gram-positive piezophilic bacteria remains to be characterised. Here, we report for the first time simultaneous quantification of stable carbon and hydrogen isotopic fractionations in lipid biosynthesis by the deep sea gram-positive piezotolerant bacterium Sporosarcina sp. DSK25. DSK25 was grown on glucose at pressures of 0.1, 10, 20, 30, 40 and 50 MPa, and δD and δ¹³C of bacterial intact polar membrane lipids (IPLs) were determined. Carbon isotope fractionation between IPLs and glucose showed a positive correlation with bacterial growth pressure, whereas hydrogen isotope fractionation between IPLs and growth water exhibited an inverse correlation with growth pressure, suggesting that fractionation of both carbon and hydrogen isotopes is pressure dependent. We further examined the effects of pressure on the isotope enrichment factors of carbon and hydrogen isotopes and propose that the dual isotope derived lambda index, calculated based on bacterial growth pressure, can serve as a diagnostic tool for delineating microbially-driven biogeochemical processes in the deep ocean and deep biosphere.