Mycinamicin is a 16-membered macrolide antibiotic produced by a “rare” actinomycete, Micromonospora griseorubida. Conditions for protoplasting of the mycelium of mycinamicin-producing M. griseorubida and regeneration of the protoplasts were established. A Micromonospora-E. coli shuttle cosmid vector, which was constructed from a cryptic plasmid of M. griseorubida and E. coli cosmid pJB8, was useful for manipulation of a long DNA sequence. The host vector system established in this way allowed to identify a gene (mycG) encoding a P-450-like protein probably responsible for both steps of hydroxylation and epoxidization of the lactone ring of mycinamicin. The mycG gene was located near myrB encoding a 23S rRNA methyltransferase as a self-resistance determinant and mycF encoding mycinamicin III O-methyltransferase. These studies will help to improve the mycinamicin productivity and to modify mycinamicin by genetic approaches.
Among some 50 actinomycete strains with Streptomyces-like morphology isolated from oil - polluted Kuwaiti desert soil, four arbitrary selected strains were characterized for n-alkane utilization. They were practically oligocarbophilic and grew on an inorganic medium without any supplemented organic matter. The growth was enhanced when n-hexadecane, n-octadecane or crude oil was added at the concentration of 1% (w/v). Gas-liquid chromatographic analysis revealed that the biomass of these strains could utilize n-hexadecane and n-octadecane, typical oil constituents. The analysis of the constituent fatty acids of total lipids from the biomass showed that the incubation with n-alkanes resulted in an increase of the fatty acids with chain lengths equivalent to those of the alkane substrates. It was concluded that these oligocarbophilic strains are capable of n-alkane utilization, and hence can be of value in bioremediation technology.
Although the name Streptomyces kasugaensis has already been used for a kasugamycin producer strain MB273-C4 that is approved as a Streptomyces host in the Japanese guideline for recombinant DNA experiments, the name has not been authorized taxonomically. We examined two kasugamycin producers, strains M338-M1 and MB273-C4, for their taxonomic properties including not only morphology and physiology, but also structures of some cell components and DNA. The results indicated that the two strains should belong together to a new species of the genus Streptomyces. We officially propose the name Streptomyces kasugaensis, the type strain being strain M338-M1 (= ATCC 15714). This new species was characterized by spiral spore chains, smooth spore surfaces, gray aerial mass, yellow to brownish soluble pigments, LL-diaminopimelic acid in cell walls, type PII phospholipids, a lack of mycolic acids, MK-9(H6,H8,H4) menaquinones, fatty acid components of ai-15:0,16:0, ai-17:0 and i-16:0, and a G+C content of 70.4 to 70.9 mol%.
The afsR gene encoding a regulatory protein and the afsK gene encoding a protein serine/threonine kinase constitute a protein phosphorylation system controlling secondary metabolism in Streptomyces coelicolor A3(2). The region between these two genes conferred the production of A-factor and the pigmented antibiotics actinorhodin and undecylprodigiosin on Streptomyces lividans, when it was carried on a high copy number plasmid. The nucleotide sequence between afsR and afsK revealed the presence of two small open reading frames named ORF-B of 176 amino acids and ORF-C of 63 amino acids. These ORFs showed no homology with proteins registered in the databases. ORF-B with the same orientation as AfsK contained three tandem repeats of Gly-Ser-Gly-Gly-Ser/Gly. ORF-C with the same orientation as AfsR contained three repeats of Thr-(X)2-Asp-Asn-His-Met-Pro-(X)2-Pro-Ala (X represents a nonconserved amino acid). Subcloning experiments showed that overexpression of ORF-C conferred pigment and A-factor production on S. lividans. The gene encoding ORF-C was therefore named afsS. It is thus apparent that afsS encoding a protein of 63 amino acids is involved in the regulation of secondary metabolism in S. coelicolor A3(2).
I have studied actinomycetes and their antibiotics over thirty-eight years except eight years for which I had been engaged in the research on the quality control for sterilization of microorganisms. My colleagues and I were successful to discover twelve new species of actinomycetes and fourteen new group antibiotics. In this review, I would like to describe rufomycins, enduracidins, validamycins, maridomycins, T-2636 antibiotics and ansamitocins in terms of their discovery, producers and/or industrial development. Rufomycins (cyclic peptides) with a specific activity to mycobacteria was discovered from Streptomyces atratus, a new species, in our screening program targeting anti-tuberculosis antibiotics. Enduracidins (Enramycins; cyclic peptides with a fatty acid side chain) were screened as antibiotics with low toxicity and strong bactericidal spectrum including multiple drug -resistant streptococci. As to aminocyclitol antibiotics, validamycins, new assay methods (reversed layer method and dendroid-test method) were established in order to develop an industrial fermentation for their agricultural use. As to T-2636 antibiotics with macrolacton ring, the esterase catalyzing the transformation of T-2636 C to T-2636 A was identified in the producing organism, S. rochei subsp. volubillis and then the industrial enzymatic transformation was established. Maridomycins, new macrolide antibiotics, were discovered as a complex of about twenty components from S. hygroscopicus No. B-5050. Selective and improved production of maridomycin III was established by strain improvement by mutation on the basis of the regulation of amino acid metabolism involved in maridomycin biosynthesis. Ansamitocins, new antitumor antibiotics, were discovered form a new species of Actinosynnema and turned out to be similar in structure to maytansine with a strong mitosis-arrest activity from tropical plants.