Isolation of Streptomyces tendae mutants with an altered nikkomycin spectrum.

Abstract

To isolate Streptomyces tendae mutants blocked in the biosynthesis of the nikkomycin nucleoside base 4-formyl-4-imidazoline-2-one, an assay was developed to detect the formation of nikkomycins containing this base during growth on solid medium. The assay is based on the reaction of the 4-formylimidazolonestructure of nikkomycinswith the aldehyde reagent barbituric acid leading to red-colored products. Among18,000 AT-methyl-JV'-nitro-TV-nitrosoguanidine treated clones tested in the barbituric acid assay, weisolated one mutant which was incapable of forming any nikkomycins containing the 4-formylimidazolone base (nikkomycins Cx, X and I) but instead produced nikkomycins containing uracil (nikkomycins C, Z and J). led to the isolation of Tu901/AECl and AEC2which produced exclusively nikkomycins Kz and Kx. According to their nikkomycin spectrum, these strains were blocked at the hydroxylation step occuring at the pyridyl residue during biosynthesis of the nikkomycin amino acid. 913Nikkomycins belong to the nucleoside peptide antibiotics and act as potent inhibitors of chitin synthetases from fungi and insects1~4). Streptomyces tendae Tu901 produces a spectrum of various nikkomycins with 4-formyl-4-imidazoline-2-one and uracil as variable bases5>6). The nucleoside moiety of biologically active nikkomycins produced by the wild type as major components is peptidically linked to the unusual amino acid 2-amino-4-hydroxy-4-(5-hydroxy-2-pyridyl)-3-methylbutyric acid (nikkomycin D, Fig. 1). Studies on the biosynthesis of nikkomycins revealed that the imidazolone base is derived from L-histidine7) and uracil from pyrimidine metabolism8). Furthermore, L-lysine was shown to be the precursor of the pyridyl residue and the attached hydroxymethylene carbon in nikkomycin D9). There is little knownabout enzymatic reactions and intermediate structures of nikkomycin biosynthesis. Therefore we decided to screen for mutants blocked in nikkomycin biosynthesis which could be employed as hosts for cloning experiments to isolate nikkomycin biosynthetic genes. We describe the isolation of strains of S. tendae with mutations affecting the biosynthesis of the imidazolone base and nikkomycin D.

Structural and Functional Characterization of NikO, an Enolpyruvyl Transferase Essential in Nikkomycin Biosynthesis

“…have been one of the richest sources for antibiotic drugs throughout the last 50 years, with every strain presenting its own, specific set of medically useful compounds. Among them, several structurally related peptide nucleosides, isolated from cell filtrates of Streptomyces tendae and Streptomyces ansochromogenes (1,2), have been found and termed nikkomycins. Structurally these compounds show similarities to UDP-N-acetylglucosamine, the substrate of chitin synthase, and thus are potent inhibitors of this enzyme (3,4).…”

Engineering of an industrial polyoxin producer for the rational production of hybrid peptidyl nucleoside antibiotics

“…The nucleoside skeleton and peptidyl moieties of polyoxins and nikkomycins are individually synthesized, and then joined by peptide bonds (Bormann et al, 1989;Chen et al, 2009).…”

Compounds active against cell walls of medically important fungi

“…In the case of the polyoxins, several derivatives with different amino acid or amino fatty acid compositions were prepared with the hope of improving uptake and biological activity (81,138,144,221,222). With the nikkomycins, the group led by H. Zahner used a different approach in that they first mutagenized the producing strain of Streptomyces tendae and then ran a directed fermentation providing pyrimidines, purines, imidazoles, or amino acids (24,25,66,67,69,101,114 Complicating the issue of differing susceptibilities is a recent report that suggests that, with S. cerevisiae, the gene products of CHSI and CHS2 show differential susceptibilities to the inhibitory effects of polyoxins and nikkomycins, with Chsl being more susceptible (34). As it has been confirmed that several different medically important fungi also have multiple forms of chitin synthetase (26), it is an obvious statement that a determination of the relative importance of each form to the growth of the cell must be made.…”