The Family Actinomycetaceae: The Genera Actinomyces, Actinobaculum, Arcanobacterium, Varibaculum, and Mobiluncus
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The Family Actinomycetaceae: The Genera Actinomyces, Actinobaculum, Arcanobacterium, Varibaculum, and Mobiluncus KLAUS P. SCHAAL, ATTEYET F. YASSIN AND ERKO STACKEBRANDT
Introduction The family Actinomycetaceae was created by Buchanan in 1918 and was originally used to accommodate many diverse organisms such as members of the genera Actinobacillus, Leptotrichia, Actinomyces and Nocardia. After several revisions, membership of the family was restricted to bacterial species that appeared to be linked taxonomically by the following phenotypic characteristics: ability to produce Grampositive, branching and, later on, fragmenting filaments without aerial hyphae and spores; comparatively exacting nutritional requirements; facultatively anaerobic (capnophilic) to anaerobic growth; and fermentative carbohydrate metabolism (Slack, 1974; Slack and Gerencser, 1975). Taking into account these common characters, the family Actinomycetaceae was thought to include the genera Actinomyces, Arachnia, Bifidobacterium, Bacterionema and Rothia (Slack, 1974). However, the validity of this family concept was increasingly questioned after modern and more relevant taxonomic techniques such as chemotaxonomic, numerical phenetic, and molecular genetic procedures had been applied to the respective organisms. As currently defined, the family Actinomycetaceae (Buchanan 1918) with the type genus Actinomyces (Harz 1877) is a member of the suborder Actinomycineae (Stackebrandt et al., 1997), order Actinomycetales (Buchanan 1918; Skerman et al., 1980), emend. Stackebrandt et al., 1997. This order has been included in the class Actinobacteria by Stackebrandt et al. (1997). The type species is Actinomyces bovis (Harz, 1877). Besides the genus Actinomyces, the family includes the genera Arcanobacterium (Collins et al., 1982c) with the type species Arcanobacterium haemolyticum, Mobiluncus (Spiegel and Roberts, 1984a), type species Mobiluncus curtisii, Actinobaculum (Lawson et al., 1997), type species Actinobaculum suis, and Varibaculum (Hall et al., 2003e), type species Varibaculum cambriense.
The species that are currently considered valid members of the family and the sources of their isolation have been compiled in Table 1. Actinomyces species that were reclassified are listed in Table 2, and synonyms and basonyms of members of the Actinomycetaceae have been compiled in Table 3. Many new species were described after the chapter on the genera Actinomyces. Arcanobacterium and Rothia had been published in the second edition of The Prokaryotes (Schaal, 1992b), and the phylogeny of the order Actinomycetales has been studied extensively. In contrast, little progress has been made with respect to physiology and chemotaxonomy, and the ecological significance of many of the novel species is not fully understood. This is also exemplified by the almost complete lack of information on as yet uncultured actinomycetes i
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