Rhodococcus

Rhodococcus is a genus of aerobic, non-motile, Gram-positive bacteria in the family Nocardiaceae, within the Actinobacteria. They are characterized by high G+C content and cell walls rich in mycolic acids, which yields partial acid-fastness and a resemblance to other actinomycetes. Morphologically they are often filamentous and may form branching, rod- or coccoid-shaped cells; many species produce pigmented colonies, notably orange to red.

Ecology and metabolism: Rhodococcus species are widespread in soil, water, and plant-associated environments. They metabolize a broad range of organic compounds, including hydrocarbons and chlorinated solvents, via versatile catabolic pathways. This versatility underpins their use in bioremediation and industrial biocatalysis.

Pathogenic potential: Several species are opportunistic pathogens. Rhodococcus equi is the best known, causing pneumonia in foals and infections in immunocompromised humans and animals. Virulence in R. equi is largely plasmid-encoded, with VapA as a key determinant. Infections require antimicrobial therapy guided by susceptibility testing; outcomes depend on host status.

Laboratory features: On standard media Rhodococcus grows slowly as non-motile rods or coccobacilli with sometimes palisading or branching forms. They are typically catalase-positive and partially acid-fast. Pigmented colonies are common in some species, and identification often relies on molecular methods.

Taxonomy and diversity: The genus includes species such as R. erythropolis, R. rhodochrous, R. ruber, and R. equi. Genome sizes are generally in the 4–6 megabase range with high GC content around 60–70%. They are cultured under aerobic conditions.