Impaired penicillin production in lysine regulatory mutants of Penicillium chrysogenum

Involvement of nitrogen-containing compounds in beta-lactam biosynthesis and its control

Biosynthesis of beta-lactam antibiotics by fungi and actinomycetes is markedly affected by compounds containing nitrogen. The different processes employed by the spectrum of microbes capable of making these valuable compounds are affected differently by particular compounds. Ammonium ions, except at very low concentrations, exert negative effects via nitrogen metabolite repression, sometimes involving the nitrogen regulatory gene nre. Certain amino acids are precursors or inducers, whereas others are involved in repression and, in certain cases, as inhibitors of biosynthetic enzymes and of enzymes supplying precursors. The most important amino acids from the viewpoint of regulation are lysine, methionine, glutamate and valine. Surprisingly, diamines such as diaminopropane, putrescine and cadaverine induce cephamycin production by actinomycetes. In addition to penicillins and cephalosporins made by fungi and cephamycins made by actinomycetes, other beta-lactams are made by actinomycetes and unicellular bacteria. These include clavams (e.g., clavulanic acid), carbapenems (e.g., thienamycin), nocardicins and monobactams. Here also, amino acids are precursors and inhibitors, but only little is known about regulation. In the case of the simplest carbapenem made by unicellular bacteria, i.e., 1-carba-2-em-3-carboxylic acid, quorum sensors containing homoserine lactone are inducers.

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

Penicillium chrysogenum L2, a lysine auxotroph blocked in the early steps of the lysine pathway before 2-aminoadipic acid, was able to synthesize penicillin when supplemented with lysine. The amount of penicillin produced increased as the level of lysine in the media was increased. The same results were observed in resting-cell systems. Catabolism of [U-14C]lysine by resting cells and batch cultures of P. chrysogenum L2 resulted in the formation of labeled saccharopine and 2-aminoadipic acid. Formation of [14C]saccharopine was also observed in vitro when cell extracts of P. chrysogenum L2 and Wis 54-1255 were used. Saccharopine dehydrogenase and saccharopine reductase activities were found in cell extracts of P. chrysogenum, which indicates that lysine catabolism may proceed by reversal of the two last steps of the lysine biosynthetic pathway. In addition, a high lysine:2-ketoglutarate-6-aminotransferase activity, which converts lysine into piperideine-6-carboxylic acid, was found in cell extracts of P. chrysogenum. These results suggest that lysine is catabolized to 2-aminoadipic acid in P. chrysogenum by two different pathways. The relative contribution of lysine catabolism in providing 2-aminoadipic acid for penicillin production is discussed.

Enhancement of bacitracin biosynthesis by branched-chain amino acids in a regulatory mutant of Bacillus licheniformis

DL-4-Azaleucine-resistant mutant of Bacillus licheniformis azlr-1 isolated after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis, was a better bacitracin producer than the parent strain. In the minimal medium, the antibiotic biosynthesis was 4 times higher in the mutant than in the parent strain and less dependent on L-leucine addition. In the complex fermentation medium, the yield was 18-20% higher in the mutant strain. Transaminase B activity measured in the crude extract revealed that the branched-chain amino acid biosynthetic enzymes were 5-10 times derepressed supplying bacitracin synthetase with enhanced quantity of isoleucine and leucine, the building units of bacitracin molecule.

[Possibilities for direct manipulation of gene expression of microbial secondary metabolism]

The present review deals with some theoretical and applied aspects of directed manipulations of control mechanisms governing the expression of microbial secondary metabolism. In attempting to make broad generalizations, the production of secondary metabolites is discussed in terms of the cellular differentiation of relevant organisms. On the basis of the actual information about the regulation of microbial idiolite synthesis, some potential ways for the quantitative and the qualitative improvement of secondary metabolite production are discussed. A number of examples demonstrate the effectiveness of rational strategies of strain development, e. g., the removal of non-specific repressions of secondary metabolism by environmental factors, the excessive production of precursors due to altered control of intermediary metabolism, the increased resistance of producer organism against the autotoxicity of some idiolites, the deletion of alternative pathways of the primary and secondary metabolism, manipulations concerning the product spectrum, the deletion of feedback mechanisms, and elimination of degradating pathways in the secondary metabolism etc. The scope and limitations of rational strategies of strain improvement by genetic and physiologic manipulations are subjected to final discussion.

Effects of lysine analogs on Penicillium chrysogenum

Compounds structurally related to lysine were tested against Penicillium chrysogenum Wis. 54-1255 for inhibition of growth, sporulation, and penicillin formation. This strain is relatively resistant to lysine analogs. The compounds that were the more active inhibitors of growth and whose activities were reversed by L-lysine were diaminohexynoic acid, N-epsilon-methyllysine, N-alpha-methyllysine, and diaminopimelic acid. These four compounds also inhibited sporulation, which was more sensitive to inhibition than growth was. Analogs strongly inhibiting benzyl-penicillin formation by resting mycelia were diaminohexynoic acid and N-epsilon-methyllysine. The action of the most active analog (diaminohexynoic acid) on penicillin synthesis was reversed by DL-alpha-aminoadipic acid.