Azoarcus anaerobius sp. nov., a resorcinol-degrading, strictly anaerobic, denitrifying bacterium

Researchers isolated and characterized a novel strictly anaerobic bacterium, strain LuFRes1, capable of degrading resorcinol under anoxic conditions while using nitrate as an electron acceptor. The organism completely oxidizes resorcinol to CO2 and reduces nitrate quantitatively to dinitrogen gas, but cannot utilize oxygen even at low pressures. Biochemical tests showed the bacterium is catalase-negative but superoxide-dismutase-positive and accumulates poly-β-hydroxybutyrate. 16S rRNA gene sequence analysis revealed highest similarity (96.1-97.1%) to Azoarcus evansii and Azoarcus tolulyticus, though sufficiently divergent to warrant species designation. The strain cannot fix nitrogen through nitrogenase activity but assimilates nitrate as a nitrogen source. Based on phylogenetic analysis and physiological characteristics, the authors propose this isolate as a new species, Azoarcus anaerobius sp. nov., with the type strain designated LuFRes1T (DSM 12081T). The bacterium was originally isolated from anoxic sewage sludge and exhibits optimal growth at 28°C and pH 7.2.

Key findings

• Azoarcus anaerobius is a strictly anaerobic, resorcinol-degrading bacterium that uses nitrate as the sole electron acceptor, reducing it to N2 gas
• The strain exhibits 16S rRNA sequence similarity of 96.1-97.1% to A. evansii and A. tolulyticus, supporting its classification as a new species distinct from existing Azoarcus species
• Unlike most Azoarcus species, A. anaerobius lacks nitrogenase activity but can assimilate nitrate as a nitrogen source
• The bacterium completely oxidizes diverse substrates including aromatic compounds to CO2 and cannot tolerate oxygen as an alternative electron acceptor