Interlocking of primary and secondary metabolism in antibiotic-producing actinomycetes

Glycopeptides such as vancomycin are the drugs of last resort for the treatment of severe infections caused by antibiotic resistant gram-positive bacteria. As a model strain for analysing and manipulating glycopeptide biosynthesis we have chosen Amycolatopsis balhimycina which synthesizes the vancomycin-type glycopeptide balhimycin. The 66-kb gene cluster encoding the biosynthesis of balhimycin was identified and sequenced. The biosynthetic pathway was elucidated and functions were assigned to all genes of the cluster. Five out of seven amino acids of the heptapeptide backbone are – directly or indirectly – derived from the shikimate pathway: two molecules β-hydroxytyrosine (β-Ht) and hydroxyphenylglycine (Hpg) and one molecule dihydroxyphenylglycine (Dpg). In addition to the genes encoding the biosynthetic enzymes typical for secondary metabolism, the balhimycin gene cluster includes two genes (pdh, dahp) which encode key enzymes of the shikimate pathway. Since a second copy of each of these two genes is found in the genome outside of the balhimycin cluster, we assume that the “pathwayspecific” enzymes are responsible for an optimized provision of tyrosine, a precursor of the non-proteinogenic amino acids β-Ht, Hpg and Dpg. In the efficient excretion of balhimycin an ABC-transporter is involved whose inactivation led to an intracellular accumulation of balhimycin. Bbr, a StrR-type regulator, is involved in the transcriptional control of the biosynthetic genes. Furthermore a two component regulator system (VanRS) was identified which may encode an overriding control system responding to the presence of glycopeptide. In order to improve the yield of balhimycin, gene inactivation and overexpression studies were performed. The manipulation of the transcriptional regulation as well as targeted intervention in the primary metabolism should result in an increased balhimycin production.