Increased Availability of Selective Trace Elements Enhanced Anaerobic Benzoate Oxidation in Geotalea daltonii

Anaerobic biodegradation of aromatic contaminants is constrained by unfavorable thermodynamics in the absence of oxygen and high activation energy required for aromatic ring-cleavage. Thus, identifying factors that enhance anaerobic aromatic degradation by microorganisms such as the Geotalea daltonii strain FRC-32 is crucial. Trace elements (TEs) function as rate-limiting cofactors for anaerobic carbon catabolism enzymes. Cobalt, molybdenum, selenite, and tungsten amendments stimulated G. daltonii growth on benzoate and anaerobic benzoate oxidation. To elucidate mechanisms of cobalt amendments in G. daltonii, we characterized a putative cobalt-specific energy-coupling factor (ECF) transporter CbiMNQO. The cbiMNQO genes form an operon and were upregulated under cobalt limitation, indicating a role in cobalt homeostasis. In silico structural predictions of CbiMNQO, ligand binding predictions of CbiMN, and alignment to known cobalt transporters suggested that CbiMNQO facilitates cobalt transport in G. daltonii. Structural and ligand binding predictions of BamB and BamF, and transcript-level analyses indicated that bamB and bamF, encoding molybdenum- and selenite-tungsten-dependent benzoyl-CoA reductase-subunits, modulate TE-dependent anaerobic benzoate degradation. Regulation of bamB and bamF in response to TE amendments corresponded with enhanced anaerobic benzoate oxidation, indicating stimulated benzoate dearomatization. Collectively, our findings demonstrated that TE amendments enhance anaerobic aromatic metabolism in G. daltonii and may contribute to anaerobic bioremediation.