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CHAPTER 1.1.18 ehT

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The Genus Mycobacterium—Nonmedical SYBE HARTMANS, JAN A. M. DE BONT AND ERKO STACKEBRANDT

Introduction Because new Mycobacterium species are being described in rapid order and because awareness of the importance of these organisms in the clinical and nonclinical environment is increasing, the editors of The Prokaryotes think that a thorough coverage of the rapidly growing species should await extensive comparative studies and a deeper analysis of their biotechnological and ecological role. Several genomes of slowly growing mycobacteria have been or are in the process of being sequenced, e.g., several strains of Mycobacterium tuberculosis, Mycobacterium bovis, Mycobacterium leprae, and the two subspecies of M. avium. Only one genome of rapidly growing mycobacteria, i.e., Mycobacterium smegmatis MC2155 (see The Institute for Genomic research website), has been sequenced; this approach will certainly be applied to more members of these organisms. For the time being, the reader is referred to the recent descriptions of novel species (Table 2) to obtain information on specific properties and to the original chapter by Hartmans and De Bont (1991) in The Prokaryotes. The phylogenetic placement of nonmedical strains next to their medically relevant neighbors is shown in Figs. 1–4. Mycobacteria are aerobic, acid-fast actinomycetes that usually form slightly curved or straight nonmotile rods (0.2–0.6 × 1.0–10 µm). Branching and mycelium-like growth may take place with fragmentation into rods and coccoid elements. Many species form whitish or creamcolored colonies, but especially among the rapid growers, there are also many bright yellow or orange species containing carotenoid pigments (David, 1984). In some cases, the pigments are only formed in response to light (photochromogenic species), but most pigmented species also form these pigments in the dark (scotochromogenic species). Mycobacterium is the only genus listed in the Family Mycobacteriaceae in Bergey’s Manual of Systematic Bacteriology (Wayne and Kubica, 1986), but the genus is considered to be closely related to the other mycolic acid-containing gen-

era of cell wall chemotype IV: Caseobacter, Corynebacterium, Nocardia and Rhodococcus (Goodfellow and Cross, 1984). Chemical differentiation of mycobacteria from the other mycolic acid-containing genera is possible by analysis of the fatty acid esters formed upon pyrolysis of the mycolic acid esters, in combination with the identification of the major menaquinone present in the plasma membrane (Table 1). The Ziehl-Neelsen stain for acid fastness, however, remains the most obvious method to quickly identify mycobacteria (Barksdale and Kim, 1977). Mycobacteria are the causal agents of two important diseases, tuberculosis and leprosy, and there has thus been a significant clinical interest in the two responsible species. This started with the work of Koch (1882), who detected the tubercle bacillus in stained infected tissues. The generic name Mycobacterium was introduced by Lehmann and Neumann (189