Penicillin Production by Lysine Auxotrophs of Penicillium chrysogenum

Abstract

Penicillium chrysogenum by feeding lysine at low concentrations to lysine auxotrophs in which the lysine pathways are blocked after a-aminoadipate has been investigated. Three such auxotrophs, strains H, 13a and 45, were isolated after ultraviolet light treatment and characterized. Only one of these mutants (strain H) could be induced to produce penicillin at a rate comparable to that of the parent strain; the others produced much smaller amounts. Chemostat continuous-flow culture of the parent strain and mutant strain H on increasing concentrations of lysine was undertaken. Microbiological assay of the lysine in the chemostat showed that it was completely utilized by both the parent strain and strain H, even when fed at several times the amount required for growth. In the parent strain, the qp,, slowly fell from a level of 2-94 u/mg dry biomass/h at zero lysine feed concentrations to 0.45 u/mg dry biomass/h with lysine amounts up to 400 mg/l in the feed medium. When the mutant strain was grown under similar conditions, penicillin production was stimulated as lysine feed concentrations increased until at 180 % excess over that required for growth, a qp,, of 2.64 u/mg dry biomass/h was reached, after which the qpen fell at a rate similar to that of the parent strain. At zero growth rate, a-aminoadipic acid stimulated penicillin production, more so when fed continuously to the cultures than when it was added in a single dose. Thus it was found that when lysine was growth-limiting for the auxotroph, and consequently present at minimal concentrations in the mould, penicillin synthesis was inhibited rather than stimulated.

Catabolism of lysine in Penicillium chrysogenum leads to formation of 2-aminoadipic acid, a precursor of penicillin biosynthesis

“…However, in Cephalosporium acremonium, lysine stimulated cephalosporin production, which argues against the hypothesis that high concentrations of lysine decrease the biosynthesis of 1-lactam antibiotics in this microorganism by limiting the availability of 2-aminoadipic acid (27). Attempts were made to block the lysine branch of the pathway to direct the pool of 2-aminoadipic acid toward penicillin (26,28). In P. chrysogenum H, a mutant strain which was defective in saccharopine dehydrogenase, lysine increased rather than decreased penicillin production (28).…”

“…2-Aminoadipic acid is a precursor of the tripeptide 8-(L-CX-aminoadipyl)-L-cysteinyl-D-valine, which is the first intermediate in the biosynthesis of 3-lactam antibiotics (6,24,25). 2-Aminoadipic acid may be the limiting precursor for penicillin biosynthesis in Penicillium chrysogenum (14,20,28,30). Addition of 2-aminoadipic acid (but not valine or cysteine)…”