Sulfur isotopic and proteomic profiles of sulfate reducers grown under differential steady-states.

VENCESLAU, SOFIA; BOIDI, FLAVIA; WALDBAUER, JACOB; BRADLEY, ALEXANDER; LEAVITT, WILLIAM; SMITH, DEREK

San Francisco

Encuentro; American Geophysical Union Fall Meeting 2016; 2016

American Geophysical Union

Microbial sulfate reducers (MSR) drive the Earth?s biogeochemical sulfur cycle. At the heart ofthis energy metabolism is a cascade of redox transformations coupling organic carbon and/orhydrogen oxidation to the dissimilatory reduction of sulfate to sulfide. The product sulfide isdepleted in the heavier isotopes of sulfur, relative to the reactant sulfate, consistent with a normalkinetic isotope effect. However, the magnitude of the net fractionation during MSR can rangeover a range of 70 permil, consistent with a multi-step set of reactions. This range in MSRfractionation has been shown to mainly depend on: i) the cell-specific sulfate reduction rate(csSRR), and ii) the ambient sulfate concentration. However, the fractionation under identicalconditions differs among strains (Bradley et al. 2016. Geobio), and so must also be mediated bystrain-specific processes, such as the nature and quantity of individual proteins involved insulfate reduction, electron transport, and growth. In recent work we have examined the influenceof electron donor, electron acceptor, and co-limitation under controlled steady-state cultureconditions in order better inform models of MSR isotope fractionation, and the physiological andisotopic response to differential environmental forcings (e.g. Leavitt et al. (2013) PNAS).Recent models of the fractionation response to MSR rate (c.f. Bradley 2016; Wing &Halevy, 2016) make specific predictions for the responses of the cellular metabolome andproteome. Here we compare the steadystateS-isotopic fractionation and proteomeof ?fast? versus ?slow? grown D. vulgaris,using replicate chemostats under electrondonor limitation. We observe clear andstatistically robust changes in some keycentral MSR and C-metabolism enzymes,though a host of the critical energy-transferenzymes show no statistically discernablechange. We discuss these results in light ofrecent theoretical advances and theirrelevance to modern and ancientgeochemical records.