Rhodococcus

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Rhodococcus is a genus of aerobic, non-spore-forming, Gram-positive bacteria related to Mycobacterium and Corynebacterium. Most species are harmless and live in soil, water, and sometimes inside other organisms, but a few can cause disease. Some Rhodococcus have very large genomes; for example, Rhodococcus sp. RHA1 has about 9.7 million base pairs with a high GC content. The species also carry three large linear plasmids that add to their metabolic diversity.

They are valued for biotechnology and environmental uses. Rhodococcus bacteria can break down a wide range of chemicals, produce bioactive steroids, acrylamide, and acrylic acid, and help remove sulfur from fossil fuels. They are strong at bioconversion, turning cheap starting materials into useful products, and can detoxify pollutants such as toluene, naphthalene, herbicides, and PCBs. They oxidize aromatic rings to form diols and then cleave the rings in a stereospecific way, which can create chiral molecules useful in drug synthesis (for example intermediates for the HIV drug indinavir).

Rhodococcus is popular for bioremediation because it can work in both low- and normal-oxygen conditions, can fix nitrogen, and has a hydrophobic surface that helps it stick to hydrocarbons. It also has dioxygenase enzymes that break down stubborn pollutants like benzotrifluoride. Strain Q1, from soil and paper mill sludge, can degrade quinoline and related compounds. Some Rhodococcus can accumulate heavy metals, including radioactive cesium, aiding cleanup. They can also break down azo dyes, pesticides, and PCBs.

Two Rhodococcus species are pathogenic: R. fascians, which harms plants, and R. equi, which causes foal pneumonia and can infect immunocompromised humans. Each relies on a virulence plasmid to cause disease. Because Rhodococcus is common in the environment, it can sometimes contaminate DNA extraction kits and ultrapure water systems, potentially skewing metagenomic results.

In short, Rhodococcus includes many species with a wide range of environmental and biotechnological roles, from cleaning pollutants to producing useful chemicals, alongside a few plant and animal pathogens.