Biogeochemical Implications of N(2)O-Reducing Thermophilic Campylobacteria in Deep-Sea Vent Fields, and the Description of Nitratiruptor labii sp. nov.

Nitrous oxide (N(2)O) is a potent greenhouse gas and has significantly increased in the atmosphere. Deep-sea hydrothermal fields are representative environments dominated by mesophilic to thermophilic members of the class Campylobacteria that possess clade II nosZ encoding nitrous oxide reductase. Here, we report a strain HRV44(T) representing the first thermophilic campylobacterium capable of growth by H(2) oxidation coupled to N(2)O reduction. On the basis of physiological and genomic properties, it is proposed that strain HRV44(T) (=JCM 34002 = DSM 111345) represents a novel species of the genus Nitratiruptor, Nitratiruptor labii sp. nov. The comparison of the N(2)O consumption ability of strain HRV44(T) with those of additional Nitratiruptor and other campylobacterial strains revealed the highest level in strain HRV44(T) and suggests the N(2)O-respiring metabolism might be the common physiological trait for the genus Nitratiruptor. Our findings provide insights into contributions of thermophilic Campylobacteria to the N(2)O sink in deep-sea hydrothermal environments.