BioWorld International Correspondent
LONDON - Researchers searching for novel antibiotics and other pharmacologically active compounds have shown that it is possible to produce and manipulate a cluster of genes from a species of bacteria that has a reputation for manufacturing clinically useful compounds. The strategy will allow bacterial geneticists to generate a whole library of compounds that can be systematically tested for antimicrobial activity.
David Widdick, postdoctoral research fellow at the John Innes Centre in Norwich, Norfolk, told BioWorld International: "This is the first time anyone has been able to manipulate a gene cluster of this type from the Streptomyces genus of bacteria, which have a reputation for producing pharmacologically interesting compounds, and not just antibiotics."
The Norwich group has patented the finding and licensed its commercial application to Novacta Biosystems Ltd., also of Norwich, a spin-out of the John Innes Centre.
A report of the research appears in the Proceedings of the National Academy of Sciences (published online March 17, 2003) titled "Cloning and engineering of the cinnamycin biosynthetic gene cluster from Streptomyces cinnamoneus cinnamoneus DSM40005."
The bacterium, Streptomyces cinnamoneus cinnamoneus DSM40005, produces a peptide antibiotic called cinnamycin. Because the compound contains chemical features called lanthionine bridges, it is classed as a lanthionine-containing antibiotic, or lantibiotic.
Of the lantibiotics, the most well-known member of the group is nisin, which is used in Europe and the U.S. to preserve dairy products and beer. Although nisin has been in use for at least 50 years as a food preservative, there have been no reports of resistance to it.
Lantibiotics have been classified into the subclasses Type A and Type B. The antimicrobial activity of Type A lantibiotics, which have been widely studied, is due to their ability to form pores in the cell membranes of other bacteria. Type B lantibiotics might inhibit enzymes involved in the biosynthesis of cell walls.
Widdick, together with colleagues at the Institute of Food Research, also in Norwich, and at the Johann Wolfgang Goethe University in Frankfurt, Germany, set out to look at the production of cinnamycin, a Type B lantibiotic, by Streptomyces, soil bacteria that are the source of many useful antibiotics. Their aim was to study the regulation of lantibiotic production at the genetic level.
Widdick said: "This is not particularly easy, because there are several genes involved. There are biosynthetic genes, genes involved in modification, genes involved in protecting the producer from the compound it produces and genes for regulating the production of the compound. But we were pleased to find that we could get the entire cluster of genes onto a single plasmid because people who have worked on the nisin cluster, for example, had found it difficult to get the whole cluster onto a single plasmid."
Having done this, Widdick and his colleagues found that it was relatively easy to manipulate the major structural gene on the plasmid so that it would produce different forms of lantibiotic than the original. By introducing changes into the DNA sequence of this gene, they were able to make the related lantibiotics, duramycin and duramycin B.
The structural genes for duramycin and duramycin B differ from that for cinnamycin by only one amino acid each. Writing in PNAS, Widdick and colleagues concluded, "These changes . . . show that there is some flexibility in the cinnamycin-production machinery that will tolerate at least some changes in unmodified amino acid residues."
Attempts to make a related lantibiotic that differs from cinnamycin by six amino acid residues failed, however, suggesting, "the cinnamycin biosynthetic machinery does not appear to be able to cope with all of these changes," as the authors wrote.
Widdick said the results illustrated the potential for producing many different variants of the original drug. He predicted that pharmacologists would be interested in testing the alternative compounds for different types of activity. Other lantibiotics have also been shown to have varying degrees of useful pharmaceutical properties, such as inhibition of angiotensin-converting enzyme, phospholipase A2 and prostaglandin, as well as inhibition of leucotriene biosynthesis.
Widdick said, "The reported activities are not strong enough to allow the compounds to be used clinically, but by looking at variants, it might be possible to find compounds that have the same desirable traits but are more active."
The team still has not achieved its aim of studying the regulation of the genes involved in making cinnamycin. Widdick said this work will be important because scientists wanting to manufacture novel compounds will need to know what the functions of the different genes in the gene cluster are.