Sulfur isotope variability of oceanic DMSP generation and its contributions to marine biogenic sulfur emissions.

Oceanic dimethylsulfoniopropionate (DMSP) is the precursor to dimethylsulfide (DMS), which plays a role in climate regulation through transformation to methanesulfonic acid (MSA) and non-seasalt sulfate (NSS-SO(4)(2-)) aerosols. Here, we report measurements of the abundance and sulfur isotope compositions of DMSP from one phytoplankton species (Prorocentrum minimum) and five intertidal macroalgal species (Ulva lactuca, Ulva linza, Ulvaria obscura, Ulva prolifera, and Polysiphonia hendryi) in marine waters. We show that the sulfur isotope compositions (δ(34)S) of DMSP are depleted in (34)S relative to the source seawater sulfate by ∼1-3‰ and are correlated with the observed intracellular content of methionine, suggesting a link to metabolic pathways of methionine production.

Evidence of magnetic isotope effects during thermochemical sulfate reduction.

Thermochemical sulfate reduction experiments with simple amino acid and dilute concentrations of sulfate reveal significant degrees of mass-independent sulfur isotope fractionation. Enrichments of up to 13‰ for (33)S are attributed to a magnetic isotope effect (MIE) associated with the formation of thiol-disulfide, ion-radical pairs. Observed (36)S depletions in products are explained here by classical (mass-dependent) isotope effects and mixing processes.

Cloning and in situ expression studies of the Hydrogenobaculum arsenite oxidase genes.

Novel arsenite [As(III)] oxidase structural genes (aoxAB) were cloned from Hydrogenobaculum bacteria isolated from an acidic geothermal spring. Reverse transcriptase PCR demonstrated expression throughout the outflow channel, and the aoxB cDNA clones exhibited distribution patterns relative to the physicochemical gradients in the spring. Microelectrode analyses provided evidence of quantitative As(III) transformation within the microbial mat.

Relative importance of H2 and H2S as energy sources for primary production in geothermal springs.

Geothermal waters contain numerous potential electron donors capable of supporting chemolithotrophy-based primary production. Thermodynamic predictions of energy yields for specific electron donor and acceptor pairs in such systems are available, although direct assessments of these predictions are rare. This study assessed the relative importance of dissolved H(2) and H(2)S as energy sources for the support of chemolithotrophic metabolism in an acidic geothermal spring in Yellowstone National Park.