"Taking vitals after death: quantitative isotopic & proteomic indicators of a sulfate reducers metabolic state"

Microbial sulfate reduction (MSR) is central to Earths carbon cycle, in that it acts as a net sink for the electrons originally freed from water during oxygenic photosynthesis. At the heart of MSR is a cascade of redox transformations which ultimately couple the oxidation of organic carbon to the reduction of sulfate coupled to the conservation of energy through the production of ATP and energy carrier molecules. During MSR the net product sulfide tends to be depleted in heavy S isotopes relative to primary reactant sulfate. The net fractionation during MSR can vary upwards of 70 permil, consistent with a 4-enzyme step reaction sequence. Variations in the range in fractionation has been shown to depend on the cell-specific sulfate reduction rate, ambient sulfate concentrations, possibly enzyme abundance – together these are interpreted as a change in the flux/force relationship imposed on the organisms by their environment, however, key inputs to these models remain under constrained.

In recent studies, we have examined the influence of electron-donor, electron-acceptor, co-limited cultures and strain-specific responses, each growing and metabolizing at steady-state in chemostats. Here we quantify the steady-state proteomes, extra- and intracellular S-compound concentrations and isotopic compositions, water and lipid H isotopic compositions, and key electron-carrier abundances (e.g. menaquinones, NAD(P)(H)) during ‘fast’ (12hr) versus ‘slow’ (72hr) growing Desulfovibrio vulgaris Hildenborough cultures, conducted in replicate steady-state chemostats. We observe statistically robust changes in some central metabolic enzymes, metabolites, and intracellular sulfate/sulfite/APS concentrations and intracellular sulfate-S isotopic compositions. Intriguingly, most enzymes directly associated with sulfate acquisition and the sulfate and sulfite reduction reactions show little to no statistically significant changes in abundance, whereas those associated with the carbon oxidation reactions change dramatically. I will discuss these results in light of recent experimental (Sim et al. 2017. GCA) and theoretical (Wenk et al. 2017. ISME) advances and their relevance to modern and ancient geochemical records.

About this Seminar

The Chemical Oceanography, Geology, Geochemistry, and Geobiology Seminar [COG³] is a student-run seminar series. Topics include chemical oceanography, geology, geochemistry, and geobiology. The seminars take place on Fridays from 10-11am in Building E25, Room 119, unless otherwise noted (term-time only).