Stenoxybacter acetivorans gen. nov., sp nov., an acetate-oxidizing obligate microaerophile among diverse O2-consuming bacteria from termite guts

In termite hindguts, fermentative production of acetate-a major carbon and energy source for the insect-depends on efficient removal of inwardly diffusing oxygen by microbes residing on and near the hindgut wall. However, little is known about the identity of these organisms or about the substrate(s) used to support their respiratory activity. A cultivation-based approach was used to isolate O-2-consuming organisms from hindguts of Reticulitermes flavipes. A consistently greater (albeit not statistically significant) number of colonies developed under hypoxia (2% [Vol/Vol] O-2) than under air, and the increase coincided with the appearance of morphologically distinct colonies of a novel, rod-shaped, obligately microaerophilic beta-proteobacterium that was <95% similar (based on the 16S rRNA gene sequence) to its closest known relative (Eikenella corrodens). Nearly identical organisms (and/or their 16S rRNA genes) were obtained from geographically separated and genetically distinct populations of Reticulitermes. PCR-based procedures implied that the novel isolates were autochthonous to the hindgut of R.flavipes and comprised ca. 2 to 7% of the hindgut prokaryote community. Representative strain TAM-DN1 utilized acetate and a limited range of other organic and amino acids as energy sources and possessed catalase and superoxide dismutase. On solid medium, the optimal O-2 concentration for growth was about 2%, and no growth occurred with O-2 concentrations above 4% or under anoxia. However, cells in liquid medium could grow with higher O-2 concentrations (up to 16%), but only after proportionately extended lag phases. The genetic and physiological distinctiveness of TAM-DN1 and related strains supports their recognition as a new genus and species, for which the name Stenoxybacter acetivorans gen. nov., sp. nov. is proposed.