TAXONOMY: Bacteria -> Terrabacteria group -> Actinobacteria -> Actinobacteria -> Corynebacteriales -> Nocardiaceae -> Rhodococcus
Aerobic, Gram-stain-positive to Gram-stain-variable, nonmotile actinomycetes that are usually partially acid–alcohol-fast at some stage of the growth cycle. Rods to extensively branched substrate mycelium may be formed. In all strains the growth cycle begins with the coccus or short rod stage, with different organisms showing a succession of more or less complex morphological stages by which the completion of the cycle is achieved. Cocci may germinate into short rods, form filaments with side projections, show elementary branching, or, in the most differentiated forms, produce extensively branched hyphae. The next generation of cocci and short rods are formed by fragmentation of the rods, filaments, and hyphae. Some strains form sparse microscopically visible aerial hyphae, which may be branched, or aerial synnemata consisting of unbranched filaments that coalesce and project upwards. Colonies may be rough, smooth, or mucoid and pigmented buff, cream, orange, red, or yellow, although colorless variants occur. Chemo-organotrophic with an oxidative type of metabolism. Catalase-positive, arylsulfatase-negative, and sensitive to lysozyme. Most strains grow well on standard media between 15 and 40°C, and use a wide range of organic compounds as sole sources of carbon for energy and growth.
DNA G+C content (mol%): 63–73 (HPLC, Tm).
Type species: Rhodococcus rhodochrous
This genus contains microbial species that can reside in the human gastrointestinal tract. [PMC 4262072]