The kanamycin biosynthetic gene cluster from Streptomyces kanamyceticus.

Kanamycin is an aminoglycoside antibiotic produced by Streptomyces kanamyceticus1). Although it possesses broad range antibacterial activity, bacteria resistant to this antibiotic readily appear, and therefore its clinical use has been restricted to tuberculosis. Resistant bacteria inactivate kanamycin by modifying its specific aminoor hydroxygroup using acetyltransferase, phosphotransferase and nucleotidyltransferase2). Investigations concerning bacterial resistance mechanisms led to the development of semisynthetic kanamycin derivatives such as dibekacin3), amikacin4) and arbekacin5). These derivatives show good activities against kanamycin-resistant bacteria and, except arbekacin, have been used as chemotherapeutic agents against resistant bacteria of clinical importance. Arbekacin has been used as an effective anti-MRSA (methicillinresistant Staphylococcus aureus) orphan drug in Japan since 1990. Combinatorial biosynthesis, which has mainly dealt with investigations concerning polyketide synthases and nonribosomal peptide synthetases, is an attractive and potential technology for the production of modified or novel antibiotics6). The identification of biosynthetic gene clusters for other type secondary metabolites can offer additional possibilities for combinatorial biosynthesis. In the case of aminoglycosides, biosynthetic gene clusters have been isolated and characterized for streptomycin7), fortimicin A8), butirosin9), tobramycin10) and gentamicin (only sequence data available; AY524043). Concerning kanamycin, however, molecular biological studies have been restricted to its resistance genes11-15) and little is known about kanamycin biosynthetic genes. In this report we describe the isolation of the kanamycin biosynthetic gene cluster from S. kanamyceticus. Streptomyces kanamyceticus 21-18, a strain from our collection which is highly developed for kanamycin