Susceptibility of protein synthesis to streptomycin in streptomycin-producing Streptomyces griseus

Structural biological study of self-resistance determinants in antibiotic-producing actinomycetes

As antibiotics act to inhibit the growth of bacteria, the drugs are useful for treating bacterial infectious diseases. However, microorganisms that produce antibiotics must be protected from the lethal effect of their own antibiotic product. In this review, the fruit of our group's current research on self-protection mechanisms of Streptomyces producing antibiotics that inhibit DNA, protein and bacterial cell wall syntheses will be described.

Blepharismin produced by a protozoan Blepharisma functions as an antibiotic effective against methicillin-resistant Staphylococcus aureus

A ciliated protozoan, Blepharisma japonicum, produces a photosensitive red pigment, blepharismin (BLR). This study showed that the pigment inhibits the growth of Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA) resistant to arbekacin (ABK), which is the most effective aminoglycoside antibiotic against MRSA and used world wide. Although the minimum inhibitory concentration (MIC) of BLR to the ABK-resistant MRSA strain was 6.25 micrograms/ml in dark, it was decreased to 1.25 micrograms/ml by irradiation with white light of 65 W/m2 for 30 min, suggesting that the antibacterial activity of BLR is photoactivated. Our findings suggested that the antibacterial activity of BLR in dark is due to inhibition of protein synthesis. In addition, we found that BLR is bactericidal and enhances synergistically the antibacterial activity of ABK.

Molecular cloning and expression in Streptomyces lividans of a streptomycin 6-phosphotransferase gene from a streptomycin-producing microorganism

The gene encoding streptomycin 6-kinase involved in the self-resistance of the streptomycin-producing Streptomyces griseus HUT 6037 was cloned in the plasmid vector pIJ703. The resulting plasmid, pSP6, contained 2.5 kb inserts of S. griseus DNA. When streptomycin-susceptible S. lividans 1326 was retransformed with pSP6, all transformants produced streptomycin 6-kinase. Addition of streptomycin to the culture medium of S. lividans carrying pSP6 plasmid brought about a remarkable increase in streptomycin 6-kinase activity in the cell extracts. It is suggested from the results that the production of streptomycin 6-kinase in streptomycin producer was induced by streptomycin accumulated during cultivation.

[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.