Biostimulation induces syntrophic interactions that impact C,S and N cycling in a sediment microbial community

Stimulation of subsurface microorganisms to induce reductive immobilization of metals isa promising approach for bioremediation, yet the overall microbial community response istypically poorly understood. Here we used proteogenomics to test the hypothesis thatexcess input of acetate activates complex community functioning and syntrophicinteractions among autotrophs and heterotrophs. A flow-through sediment column wasincubated in a groundwater well of an acetate-amended aquifer and recovered duringmicrobial sulfate reduction. De novo reconstruction of community sequencesyielded near-complete genomes of Desulfobacter (Deltaproteobacteria),Sulfurovum- and Sulfurimonas-like Epsilonproteobacteria andBacteroidetes. Partial genomes were obtained for Clostridiales(Firmicutes) and Desulfuromonadales-like Deltaproteobacteria.The majority of proteins identified by mass spectrometry corresponded toDesulfobacter-like species, and demonstrate the role of this organism insulfate reduction (Dsr and APS), nitrogen fixation and acetate oxidation to CO₂during amendment. Results indicate less abundant Desulfuromonadales, and possiblyBacteroidetes, also actively contributed to CO₂ production via thetricarboxylic acid (TCA) cycle. Proteomic data indicate that sulfide was partiallyre-oxidized by Epsilonproteobacteria through nitrate-dependent sulfide oxidation(using Nap, Nir, Nos, SQR and Sox), with CO₂ fixed using the reverse TCA cycle.We infer that high acetate concentrations, aimed at stimulating anaerobic heterotrophy,led to the co-enrichment of, and carbon fixation in Epsilonproteobacteria.Results give an insight into ecosystem behavior following addition of simple organiccarbon to the subsurface, and demonstrate a range of biological processes and communityinteractions were stimulated.