Abstract & Overview
A collection of over 300 streptomycetes, comprising both natural isolates and type strains, were assessed for the distribution of fatty acids, antibiotic resistances, compounds in solvent extracts, and sequences that hybridized to antibiotic resistance gene probes. These data were clustered using numerical methods and groups of similar strains were delimited. The production of selected antibiotics by all strains was also determined and the data examined for any correlations with the defined clusters. Production of bioactive compounds was observed in twenty percent of the natural isolates studied; nigericin and geldanamycin production was common. Geldanamycin was only biosynthesized by strains which also produced nigericin and most strains which were thought to produce a novel antibiotic were also capable of nigericin production. When the sources and concentrations of nutrients in the cultures of antibiotic producers were altered, differentiation responses and the expression of antibiotic production were found to be strain specific. In addition to this, nigericin production could be repressed by oxygen limitation. In a production medium, fluctuations in fatty acid profiles occurred concomitantly with antibiotic biosynthesis, although this could not be correlated. However, fatty acid profiles did not allow the delimitation of groups of taxonomically related strains, which were cultured in a growth medium. Thin layer chromatography patterns obtained from the solvent extracts of streptomycete cultures showed much variation and were not suitable for use as systematic data. Antibiotic resistance patterns allowed the delimitation of bioactive strains from certain non-bioactive groups of strains; antibiotic producers showed multiple antibiotic resistance phenotypes, whereas a single selected resistance and a multiple sensitive phenotype was characteristic of non-bioactive strains. Most strains were resistant to penicillin and a large proportion were resistant to nigericin, but strains with resistance to aminoglycosides were rare. Preliminary evidence showed that DNA from strains with multiple resistance patterns hybridized more often to gene probes (these were internal fragments of aphD, aph, vph, bar, tsr Nbr) than did DNA from strains with multiple sensitive phenotypes. Similarités were observed between strains grouped by their hybridization patterns and those grouped by the chemical class of their product. This work also allowed the selection of phenotypically resistant strains with different resistance genes and possible resistance mechanisms.