RELATION OF BIOCHEMICAL MUTATIONS TO ACTINOMYCIN SYNTHESIS IN STREPTOMYCES ANTIBIOTICUS

Random mutagenesis as a tool for industrial strain improvement for enhanced production of antibiotics: a review

Secondary metabolites are produced by microbes in minimal quantities in the natural environment out of necessity. However, in the pharmaceutical industry, their overproduction becomes essential. To achieve higher yields, genetic modifications are employed to create strains that surpass the productivity of the initially isolated strains. While rational screening and genetic engineering have emerged as valuable practices in recent years, the cost-effective technique of mutagenesis and selection, known as "random screening," remains a preferred method for efficient short-term strain development. This review aims to comprehensively explore all aspects of strain improvement, focusing on why random mutagenesis continues to be widely adopted.

Streptomyces sp. JS520 produces exceptionally high quantities of undecylprodigiosin with antibacterial, antioxidative, and UV-protective properties

A Gram-positive, red-pigment-producing bacterial strain, designated JS520 was isolated from the pristine sediment from the cave on mountain Miroc in Serbia. Strain was confirmed to belong to Streptomyces genus based on phenotypic and genetic analysis. Streptomyces sp. JS520 has the ability to produce exceptionally high amounts of deep red pigment into both solid and liquid media. Liquid chromatography and mass spectroscopy of the purified pigments revealed the major component to be undecylprodigiosin (93 %) with minor component being oxidatively cyclized derivative. The pigment production was affected by medium composition, temperature, pH, and the aeration rate. By medium optimization, yields of undecylprodigiosin of 138 mg l(-1) were achieved, what is the highest level of undecylprodigiosin production reported for the members of Gram-positive Streptomyces genus. Purified pigment had antimicrobial properties against bacterial Bacillus and Micrococcus species (50 μg ml(-1)) and against Candida albicans species (100-200 μg ml(-1) range). The ability to affect auto-oxidation of the linoleic acid was demonstrated for the purified undecylprodigiosin, suggesting antioxidative properties of this pigment. Multiple ecophysiological roles of the pigment were revealed by comparing cultures grown under pigment-producing and pigment-nonproducing conditions. Cells grown under undecylprodigiosin-producing conditions could tolerate presence of hydrogen peroxide exhibiting three times smaller zones of inhibition at 100 mM H(2)O(2). Undecylprodigiosin-producing cells were also less susceptible to tetracycline, kanamycin, chloramphenicol, and 8-hydroxyquinoline. While the growth of the cells not producing pigment was completely inhibited by 15 min of exposure to ultraviolet light (254 nm), cells producing undecylprodigiosin and cells supplied with purified pigment in vitro showed survival rates at 22 and 8 %, respectively.

Genetic Recombination in Crosses Between Streptomyces aureofaciens and Streptomyces rimosus

Polsinelli, M. (University of Pavia, Pavia, Italy), and Maria Beretta. Genetic recombination in crosses between Streptomyces aureofaciens and Streptomyces rimosus. J. Bacteriol. 91:63-68. 1966.-Biochemical mutants were obtained from Streptomyces rimosus and S. aureofaciens by ultraviolet irradiation. Crosses were performed between auxotrophic strains of S. rimosus and S. aureofaciens with positive results. Data are reported which indicate that the interaction observed in some crosses is due to gene recombination.

Strain improvement for production of pharmaceuticals and other microbial metabolites by fermentation

Microbes have been good to us. They have given us thousands of valuable products with novel structures and activities. In nature, they only produce tiny amounts of these secondary metabolic products as a matter of survival. Thus, these metabolites are not overproduced in nature, but they must be overproduced in the pharmaceutical industry. Genetic manipulations are used in industry to obtain strains that produce hundreds or thousands of times more than that produced by the originally isolated strain. These strain improvement programs traditionally employ mutagenesis followed by screening or selection; this is known as 'brute-force' technology. Today, they are supplemented by modern strategic technologies developed via advances in molecular biology, recombinant DNA technology, and genetics. The progress in strain improvement has increased fermentation productivity and decreased costs tremendously. These genetic programs also serve other goals such as the elimination of undesirable products or analogs, discovery of new antibiotics, and deciphering of biosynthetic pathways.

[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.

Bacitracin production by the high-yielding mutant Bacillus licheniformis strain AL: stimulatory effect of L-leucine

The high-yielding mutant Bacillus licheniformis AL produced only small amounts of bacitracin in the chemically defined M2 medium. L-leucine markedly stimulated bacitracin production and restored the mutant strain to its place as a superior producer as compared to Bacillus licheniformis ATCC 10716. Leucine also stimulated the growth rate of the mutant. The stimulatory effect of leucine on bacitracin production is discussed in relation to control mechanisms and overproduction of antibiotics.