Controls on Bacterial Cell Envelope Sulfhydryl Site Concentrations: The Effect of Glucose Concentration During Growth

Bacterial sulfhydryl sites can form strong complexes with chalcophilic metals such as Hg and Cd, thereby affecting the fate, transport, and bioavailability of these metals in both natural and engineered systems. In this study, five bacterial species were cultured in M9 minimal media containing a range of glucose concentrations as carbon source and in a high-nutrient TSB medium enriched with 50 g/L of glucose, and the sulfhydryl site concentrations of the obtained biomass samples were determined through selective sulfhydryl site-blocking, potentiometric titrations, and surface complexation modeling. The experimental results show that the glucose concentration in the M9 minimal media strongly affects the concentration of sulfhydryl sites that are present on the bacteria, with higher glucose concentrations yielding higher bacterial sulfhydryl site concentrations for each species studied. In contrast, although adding 50 g/L of glucose to the TSB medium significantly increases the sulfhydryl site concentrations for the three Bacillus species studied, the elevated glucose concentration does not significantly affect sulfhydryl site concentrations for S. oneidensis and P. putida samples when grown in the TSB medium. Our results suggest that bacterial sulfhydryl site concentrations in natural systems are likely affected by the composition of the bacterial community and by the available nutrients, and that these factors must be considered in order to determine and model the effects of bacterial cells on metal cycling and metal bioavailability in the environment.