© 2017 American Society for Microbiology. Description of Didymococcus gen. nov. Didymococcus gen. nov. (Di.dy.mo.coc'cus. Gr. fem. n. didymos pair; N.L. masc. n. coccus (from Gr. masc. n. kokkos, grain, seed), coccus; N.L. masc. n. Didymococcus a coccus in pairs). Description of Didymococcus colitermitum sp. nov. Didymococcus colitermitum sp. nov. (co.li.ter'mi.tum. L. n. colon, colon, part of the large intestine; L. n. termes -itis, wood-eating worm, termite; N.L. gen. pl. n. colitermitum, of the gut of termites). Cells are coccoid (0.25 μm to 0.5 μm in diameter) and occur almost exclusively in pairs, with a Gram-negative cell wall morphology that includes an outer membrane. Cells are nonmotile, obligate aerobes and are microaerophilic. The shortest generation times occur in liquid medium under an atmosphere of 2 to 8% O2 (balance N2). On solid R2A medium, colonies are 2 to 4 mm in diameter, have an entire margin and a low convex, mucoid morphology, and are cream colored. Cells do not possess catalase or NADH/ NADPH peroxidase activity. Nitrogenase activity is inferred through growth on nitrogen-free medium. Growth occurs in liquid media between 15 and 35°C (optimum, 30°C); there is no growth at 37°C or 4°C. Growth occurs at a pH range of 5.5 to 7.5 (optimum, 7.0); there is no growth at a pH of ≤5 or ≥8. Substrates utilized as energy sources include starch, D-cellobiose, D-maltose, D-glucose, D-galactose, and one or more components present in yeast extract. Microcrystalline cellulose, methylcellulose, carboxy methylcellulose, xylan, D-fructose, D-mannose, D-trehalose, sucrose, D-ribose, D-xylose, L-arabinose, D-mannitol, D-sorbitol, D-raffinose, DL-lactate, sodium pyruvate, sodium fumarate, sodium acetate, allantoin, D-glucuronate, D-galacturonate, D-gluconic acid, xanthine, tannic acid, resourcinol, vanillic acid, sodium benzoate, and trimethylbenzoate are not utilized. The genome of type strain TAV2 is 5.2 Mb in size, contains 60.5 mol% G+C, and possesses one 16S rRNA gene copy. The type strain, isolated from guts of Reticulitermes flavipes (Kollar) collected in Dansville, MI, is TAV2 (ATCC BAA-2264; DSM 25453).