Pilot-plant cultivation of Streptomyces griseus producing homologues of nonactin by precursor-directed biosynthesis and their identification by LC/MS-ESI.

Precursor-directed biogenetic approach was used to produce a range of nonactin homologues in a 50 l fermentor cultivation of strain Streptomyces griseus 34/249 obtained by UV mutagenesis. The production medium contained sodium propionate, isobutyrate and isovalerate as individual precursors, and 10 g l(-1) Diaion HP20 styrene-divinylbenzene resin that maintains suitable precursor concentration by reversibly adsorbing and releasing it. The produced nonactin homologues were separated on two C18 reversed-phase liquid chromatography columns in series and analyzed by MS with ESI source in the positive ion mode. Formation of doubly charged ions was suppressed by an excess of Na(+) ions throughout the process. The production of the homologues increased up to day 5 and then it leveled off. Cultivations with individual precursors yielded a total of 18 nonactin homologues whose spectrum depended on the precursor used. The total production of the homologues was lowered but their spectrum was shifted to higher-molecular-weight compounds.