CONICET | Buscador de Institutos y Recursos Humanos

At the heart of microbial sulfate reduction (MSR) is a cascade of redox transformations coupling organiccarbon and/or hydrogen oxidation to the dissimilatory reduction of sulfate. The product sulfide is depleted in theheavier isotopes of sulfur, relative to the reactant sulfate, consistent with a normal kinetic isotope effect. The netmagnitude of fractionation during MSR can vary upwards of 70 part per thousand (permil), consistent with a multi-stepreaction chain. Variations in this range in fractionation has been shown to mainly depend on the cell-specific sulfatereduction rate (csSRR), the ambient sulfate concentration, or both. In recent work we have examined the influence ofelectron donor, electron acceptor, and co-limitation under controlled steady-state culture conditions in order betterinform models of MSR isotope fractionation, and the physiological and isotopic response to differential environmentalforcings (e.g. Leavitt et al. (2013) PNAS). However, the range in fractionation under identical conditions differs amongstrains (Bradley, Leavitt et al. 2016 Geobio.), and clearly mediated by strain-specific processes, such as the quantityand efficiency of individual proteins involved in key sulfate reduction reactions, electron transport, and growth.Moreover, recent models of the rate?fractionation response make specific predictions for the responses of thecellular metabolome and proteome. Here we compare the steady-state S-isotopic fractionation and proteome of ?fast?versus ?slow? grown D. vulgaris, using replicate chemostats under electron donor limitation. We observe clear andstatistically robust changes in a subset of central MSR and C-metabolism enzymes. Interestingly, however, mostcritical energy-transfer enzymes show no statistically significant change in abundance. We discuss these results inlight of recent theoretical advances and their relevance to modern and ancient geochemical records.