Microaerophile among Diverse O 2 Consuming Bacteria from Termite Guts 2 3 Running Title: Microaerophilic Bacteria from Termites 8

9 In termite hindguts, fermentative production of acetate – a major carbon and energy 10 source for the insect – depends on efficient removal of inwardly diffusing oxygen by microbes 11 residing on and near the hindgut wall. However, little is known about the identity of these 12 organisms or the substrate(s) used to support their respiratory activity. A cultivation-based 13 approach was used to isolate O 2-consuming organisms from hindguts of Reticulitermes flavipes. 14 A consistently greater (albeit not statistically significant) number of colonies developed under 15 hypoxia (2% v/v O 2) than under air, an increase coincident with the appearance of 16 morphologically distinct colonies of a novel, rod-shaped, obligately microaerophilic β-17 proteobacterium that was <95% similar (based on 16S rRNA gene sequence) to its closest 18 known relative (Eikenella corrodens). Nearly identical organisms (and/or their 16S rRNA genes) 19 were obtained from geographically separated and genetically distinct populations of 20 Reticulitermes. PCR-based procedures implied that the novel isolates were autochthonous to the 21 hindgut of R. flavipes and comprised ca. 2-7% of the hindgut prokaryote community. 22 Representative strain TAM-DN1 utilized acetate and a limited range of other organic and amino 23 acids as energy sources and possessed catalase and superoxide dismutase. On solid medium, the 24 optimal O 2 concentration for growth was about 2%, with no growth above 4% or under anoxia. 25 However, cells in liquid medium could grow in higher (up to 16%) O 2 concentrations, but only 26 after proportionately extended lag phases. The genetic and physiological distinctiveness of 27 TAM-DN1 and related strains support their recognition as a new genus and species, for which 28 the name Stenoxybacter acetivorans gen. nov. sp. nov. is proposed. 29