and a seven- or eight-amino-acid insertions in RpoC. Also, 21 conserved signature proteins are found only in members of cluster I. Another cluster has been proposed, consisting of C. jeikeium and C. urealyticum, which is supported by the presence of 19 distinct conserved signature proteins which are unique to these two species. Corynebateria have a high G+C content ranging from 46-74 mol%. Characteristics The principal features of the genus Corynebacterium were described by Collins and Cummins, for Coryn Taylor in 1986. They are gram-positive, catalase-positive, non-spore-forming, non-motile, rod-shaped bacteria that are straight or slightly curved. Metachromatic granules are usually present representing stored phosphate regions. Their size falls between 2 and 6 μm in length and 0.5 μm in diameter. The bacteria group together in a characteristic way, which has been described as the form of a "V", "palisades", or "Chinese characters". They may also appear elliptical. They are aerobic or facultatively anaerobic, chemoorganotrophs. They are pleomorphic through their lifecycles, they occur in various lengths, and they frequently have thickenings at either end, depending on the surrounding conditions. Some corynebacteria are lipophilic (such as CDC coryneform groups F-1 and G, C. accolens, C. afermentans subsp. lipophilum, C. bovis, C. jeikeium, C. macginleyi, C. uropygiale, and C. urealyticum), but most are not. The nonlipophilic bacteria may be classified as fermentative (such as C. amycolatum; C. argentoratense, members of the C. diphtheriae group, C. glucuronolyticum, C. glutamicum, C. matruchotii, C. minutissimum, C. striatum, and C. xerosis) or nonfermentative (such as C. afermentans subsp. afermentans, C. auris, C. pseudodiphtheriticum, and C. propinquum). Cell wall The cell wall is distinctive, with a predominance of mesodiaminopimelic acid in the murein wall and many repetitions of arabinogalactan, as well as corynemycolic acid (a mycolic acid with 22 to 26 carbon atoms), bound by disaccharide bonds called L-Rhap-(1 → 4)--D-GlcNAc-phosphate. These form a complex commonly seen in Corynebacterium species: the mycolyl-AG–peptidoglican (mAGP). Unlike most corynebacteria, Corynebacterium kroppenstedtii does not contain mycolic acids. Culture Corynebacteria grow slowly, even on enriched media. In nutritional requirements, all need biotin to grow. Some strains also need thiamine and PABA. Some of the Corynebacterium species with sequenced genomes have between 2.5 and 3.0 million base pairs. The bacteria grow in Loeffler's medium, blood agar, and trypticase soy agar (TSA). They form small, grayish colonies with a granular appearance, mostly translucent, but with opaque centers, convex, with continuous borders. The color tends to be