Genomes and Plasmids in Rhodococcus

Abstract

Members of the genus Rhodococcus are a very diverse group of bacteria that are found in many different niches. They are commonly found in the wider environment, but are also associated with pathogenesis in plants and mammals, including humans. They possess the ability to degrade a large number of organic compounds including some of the most difficult compounds with regard to recalcitrance and toxicity. This ability appears to be based upon the acquisition of a wide and diverse range of catabolic genes by cells that can withstand stressful conditions. Recent completion of genome sequences and analysis has revealed that they have very large genomes (up to 9.7 Mbp) and many possess genes that encode multiple catabolic enzymes and pathways. In addition to smaller circular plasmids, they also harbour many large linear plasmids that contribute to their substrate diversity, and these appear to be vehicles for the “mass storage” of numerous catabolic genes. The presence of multiple catabolic pathways and gene homologues seems to be the basis of their catabolic versatility. However, many of the genes associated with the pathways are dispersed around the genome, and it is becoming clear that their co-regulation of gene expression is a feature of how the rhodococci adapt to utilise many substrates.