Courtesy of Tobias Kieser, John Innes Centre, UK.

If you took antibiotics this winter to shift a troublesome sore throat, it's likely that they were produced by a relative of Streptomyces coelicolor — a soil-dwelling bacterium with an unusual talent for breaking down complex substances. Now, a team of UK and Taiwanese researchers report in Nature the sequencing of the genome of S. coelicolor A3(2), providing a first glimpse of the wealth of genes that underlie this bacterium's complex lifestyle and environmental adaptability. Importantly, this team have discovered previously unreported metabolic enzymes that could be put to good use to engineer new and much-needed antimicrobials.

The first surprise to emerge from S. coelicolor's genome is the number of genes present on its linear chromosome — 7,825 — nearly double the number of genes found in the related bacterium, Mycobacterium tuberculosis. This large number of genes is predominantly due to the presence of large protein families, as well as many new ones, which appear to be mostly involved in the regulation, transport and degradation of extracellular nutrients. And the surprises don't stop there, as S. coelicolor also has an unprecedented number of regulatory genes — mostly required to respond to stress and environmental stimuli — and 20 chromosomal gene clusters that encode enzymes predicted to function in secondary metabolism.

Although genes are distributed evenly over the S. coelicolor chromosome, a biphasic structure emerges when they are categorized according to their predicted functions — essential genes (such as those involved in cell division, transcription and translation) cluster in a central core, whereas 'contingency' genes, those with non-essential functions, are located on the chromosome's arms. The reason for this structure became clear when the authors compared S. coelicolor's genome with that of two other actinomycetes, M. tuberculosis and Corynebacterium diphtheriae. The core of S. coelicolor's genome is highly conserved with the genomes of these two pathogens, indicating their evolution from a common ancestor. However, the arms of S. coelicolor are not conserved and appear to be remarkably tolerant to genome rearrangements and insertions — the authors found evidence that 14 regions have recently been introduced to the genome by lateral transfer, adding to the bacterium's repertoire of metabolic enzymes.

Given this bacterium's medical importance — its close relatives produce two-thirds of all naturally derived antibiotics and many other pharmaceuticals, including anti-tumour agents and immunosuppressants — its genome is a tremendously important resource. Once the biological secrets of the newly discovered metabolic enzymes have been broken down, they can be used to engineer metabolic pathways to produce new therapeutic compounds.