Nutrient effects on growth and armentomycin production in cultures of Streptomyces atmentosus

Abstract

A high-performance liquid chromatographic method for the analysis of armentomycin (L-2-amino-4,4-dichlorobutanoic acid) in culture broths was developed and calibrated using DL-2-amino-4,4-dichlorobutanoic acid synthesized in five steps from methyl acrylate, carbon tetrachloride, and sodium azide. Armentomycin was produced optimally (5–10 mM during 8 days' fermentation) by Streptomyces armentosus in media containing starch, lysine, chloride ions, and a low concentration of phosphate. Production was markedly affected by carbon and nitrogen sources: of those tested, starch supported both the highest biomass yield and the highest armentomycin titre; lysine was the best source of nitrogen for growth and for achieving the maximal armentomycin titre. Increasing the concentration of lysine from 40 to 120 mM nitrogen increased armentomycin production, and gave no evidence of nitrogen catabolite repression. Growth and armentomycin biosynthesis increased as the initial concentration of phosphate in media was increased up to 3 mM; further additions of phosphate tended to increase biomass and decrease the armentomycin titre, but the responses were marginal. Chloride ions were absolutely required for armentomycin synthesis, and at their optimal concentration, more than 80% of the chloride ions in the medium were incorporated into the antibiotic. Excess chloride in cultures reduced armentomycin biosynthesis. Neither bromide nor iodide was incorporated; bromide interfered with the biosynthesis of armentomycin, but iodide had no effect. Analysis of fermentation parameters showed that armentomycin biosynthesis paralleled growth and suggested that secondary metabolism was derepressed by a nitrogen-related limitation of the growth rate.Key words: 2-amino-4,4-dichlorobutanoic acid, antibiotic, armentomycin, halide ions, Streptomyces armentosus, secondary metabolism.