Nitrogen regulation of avermectins biosynthesis in Streptomyces avermitilis in a chemically defined medium

Abstract

The biosynthesis of avermectins was significantly affected by the nitrogen source used. The maximum yield of AVMs') was achieved in a chemically defined medium with ammonium sulfate as the sole nitrogen source. Higher concentrations of ammonia inhibited the production of AVMs without the inhibition of the growth. AVMs of the group B were prevailing in the complex until I5 mM ammonium sulfate. At higher concentrations, AVMs of the group A predominated. Of various amino acids tested, lysine and asparagine were found to be the best for the biosynthesis of AVMs. The concentration of most amino acids higher than 0.2% inhibited the production, while the mycelium was still growing. The biosynthesis of AVMs was completely suppressed by 15.2 m~ isoleucine, however, this inhibition was reversed by adding alanine at the beginning of cultivation.A considerable attention has recently been devoted to the regulation of biosynthesis of so called secondary metabolites by nitrogen containing substrates. In previous studies, e.g. of the biosynthesis of chlortetracycline, it has already been shown that some amino acids are metabolized to precursors (malonylCoA) forming a nitrogen free. nonaketide skeleton PODOJIL et al. 1973, BEHAL et al. 1979. The regulation of antibiotic biosynthesis by nitrogen compounds was reviewed by AHARONOWITZ (1980). These regulations were studied in producers of p-lactam antibiotics, e.g. Streptomyces clavuligerus (AHARONOWITZ and DEMAIN 1979, B R A~A et al. 1985 In the present work we studied the effect of nitrogen source on the biosynthesis of avermectins. These compounds have neither antibacterial nor antifungal activity, but they are excellent anthelmintics and insecticides. They are pentacyclic lactones with a disaccharide cr-L-oleandrose, which do not contain nitrogen in their molecule, although it is formally possible to derive their starting unit from isoleucine or valine (Fig. 1). Streptomyces avermitilis produces a complex of 8 avermectins consisting of 4 major (Al,, A,=, B1,, B,,) and 4 minor (Albl A,,, B,,, B2d components. As far as their efficiency is concerned Bla is the most interestmg compound.The production of avermectins was studied in a chemically defined medium where amino acids or ammonium sulfate were the only nitrogen source.') AVM = Avermectin

The effects of temperature, pH and growth rate on secondary metabolism in Streptomyces thermoviolaceus grown in a chemostat

“…Many workers have noted a variety of repressors of secondary metabolism which may be responsible for this. These include the nature of the carbon source (Hu et al, 1984;Payne & Wang, 1989), and levels of ammonia which tends to repress many antibiotic biosynthetic pathways (Vu-trong & Gray, 1987;Dekleva et al, 1985;Tanaka et al, 1985) or the synthesis of some of antibiotic pathway enzymes (Zhang et al, 1989;Cimburkova et al, 1988;Shapiro & Vining, 1983). The levels of growth substrates in the growth medium did not appear to exert any direct catabolite repression or inhibition of granaticin synthesis when S .…”

Pivalic acid acts as a starter unit in a fatty acid and antibiotic biosynthetic pathway in Alicyclobacillus, Rhodococcus and Streptomyces

“…The strain of S. avermitilis was cultivated under previously described conditions (Cimburkova et al ., 1988), see also . Sodium salt of deuterium‐labelled pivalic acid (its synthesis is described below) was added at the beginning of cultivation, the biomass was centrifuged and extracted with a mixture of solvents.…”

“…The mutant strain S. avermitilis C‐18 was obtained by genetic improvement (Cimburkova et al ., 1988) of ATCC 1267. The inoculum was cultivated for 1 day in a complex medium containing (g l −1 ): glucose 5; soybean meal 15; and yeast extract 5; fermentation flasks were inoculated with 2% of the inoculum (1 day old) and cultivated for 10 days.…”

“…deuterium-labelled pivalic acid, and identified the corresponding avermectin, having on carbon 25 not only isopropyl or 2-methylbutyryl but also t-butyl side-chain. The strain of S. avermitilis was cultivated under previously described conditions (Cimburkova et al, 1988), see also Experimental procedures. Sodium salt of deuteriumlabelled pivalic acid (its synthesis is described below) was added at the beginning of cultivation, the biomass was centrifuged and extracted with a mixture of solvents.…”

N-Acetyl-isoleucine in Streptomyces avermitilis

“…Streptomyces a~'ermitilis C-18 derived from strain ATCC 31 267 [5] was cultivated for 2 days in a chemically defined medium (%): glucose, 3; (NH4)2 SO4, 0.2; CaCO 3, 0.5; NaCI, 11.2; K2HPO 4, 0.05: FeSO~" 7H:O, 0.005; ZuSO 4" 7H,O, 0.005: MnSO4 ' 7H_,O, 0.~i1)5; MgSO4 • 7H_,O, 0.01 [5]. A subsequent fermentation was performed by inoculation of the chemically defined medium ( + 0.2% isoleucine) with 4% inoculum and cultivated for 10 days.…”