Single cell visualization of sulfur cycling in intertidal microbial mats

Abstract:

Chemoautrophic microbial mats form in shallow intertidal pools adjacent to sulfidic hydrothermal vents in San Pedro, CA. Sulfide is primarily geologically derived. However, microscopy revealed deltaproteobacteria closely associated with Beggiatoa -like filaments, indicating an additional biogenic sulfide source, derived from sulfate reduction or sulfur disproportionation. At small scales the intercellular interaction of sulfide producing and sulfide consuming bacteria may play a important role in biogeochemical sulfur cycling. We explored the intracellular transfer of biologically derived sulfide in this system with triple and quadruple stable isotope labeling experiments: ¹³C, ¹⁵N, ³³S, and ³⁴S. Silicon wafers colonized by microbial mats in situ, were then incubated with ³⁴SO₄^2- or ³⁴SO₄^2- and ³³S₀ as well as ¹³C-acetate and ¹⁵NH₄⁺and analyzed by fluorescent in situ hybridization (FISH) coupled to nanometer-scale secondary ion mass spectrometry (NanoSIMS). We observed enrichment of ³⁴S and ³³S in both deltaproteobacteria and sulfide oxidizing gammaproteobacteria. Greater enrichment relative to killed controls occurred in deltaproteobacteria than the sulfide oxidizers during both sulfate reducing (Δ³⁴S_delta-killed = 240‰, Δ³⁴S_gamma-killed = 40‰) and sulfur disproportionating incubations (Δ³³S_delta-killed = 1730‰, Δ³³S_gamma-killed = 1050‰). These results provide a direct visualization of interspecies sulfur transfer and indicate that biogenic sulfide derived from either sulfate or intermediate oxidation state sulfur species plays a role in sulfur cycling in this system.