Anaerobic biodegradation of pyrene and benzo[a]pyrene by a new sulfate-reducing Desulforamulus aquiferis strain DSA.

The study of anaerobic high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) biodegradation under sulfate-reducing conditions by microorganisms, including microbial species responsible for biodegradation and relative metabolic processes, remains in its infancy. Here, we found that a new sulfate-reducer, designated as Desulforamulus aquiferis strain DSA, could biodegrade pyrene and benzo[a]pyrene (two kinds of HMW-PAHs) coupled with the reduction of sulfate to sulfide. Interestingly, strain DSA could simultaneously biodegrade pyrene and benzo[a]pyrene when they co-existed in culture. Additionally, the metabolic processes for anaerobic pyrene and benzo[a]pyrene biodegradation by strain DSA were newly proposed in this study based on the detection of intermediates, quantum chemical calculations and analyses of the genome and RTqPCR. The initial activation step for anaerobic pyrene and benzo[a]pyrene biodegradation by strain DSA was identified as the formation of pyrene-2-carboxylic acid and benzo[a]pyrene-11-carboxylic acid by carboxylation Thereafter, CoA ligase, ring reduction through hydrogenation, and ring cracking occurred, and short-chain fatty acids and carbon dioxide were identified as the final products. Additionally, DSA could also utilize benzene, naphthalene, anthracene, phenanthrene, and benz[a]anthracene as carbon sources. Our study can provide new guidance for the anaerobic HMW-PAHs biodegradation under sulfate-reducing conditions.