Anaerobic phenanthrene biodegradation by a newly isolated sulfate-reducer, strain PheS1, and exploration of the biotransformation pathway.

Phenanthrene is a widespread and harmful polycyclic aromatic hydrocarbon that is difficult to anaerobically biodegrade. Current challenges in anaerobic phenanthrene bioremediation are a lack of degrading cultures and limited knowledge of biotransformation pathways. Under sulfate-reducing conditions, pure-cultures and biotransformation processes for anaerobic phenanthrene biodegradation are poorly understood. In this study, strain PheS1, which is phylogenetically closely related to Desulfotomaculum, was found to be a sulfate-reducing phenanthrene-degrading bacterium. Anaerobic phenanthrene biodegradation using PheS1 was proposed based on metabolite and genome analyses, and the initial step was identified as carboxylation based on the detection of 2-phenanthroic acid, [13C]-2-phenanthroic acid, and [D9]-2- phenanthroic acid when phenanthrene+HCO3-, phenanthrene+H13CO3-, and [D10]-phenanthrene+HCO3- were used as the substrate, respectively. PheS1 genome ubiD gene encoding of carboxylase putatively involved in the biodegradation was performed. Next, benzene ring reduction and cleavage that produced benzene compounds and cyclohexane derivative were reported to occur in the downstream biotransformation processes. Additionally, benzene, naphthalene, benz[a]anthracene, and anthracene can be utilised by PheS1, whereas pyrene and benz[a]pyrene cannot. We discovered a new phenanthrene-degrading sulfate-reducer and provided the anaerobic phenanthrene biotransformation pathway under sulfate-reducing conditions, which can act as a reference for practical applications in bioremediation and for studying the molecular mechanisms of phenanthrene in anaerobic zones.