The ability to hydrolyze chitin to utilize as a carbon source is an important characteristic of Streptomyces, which are considered to be major decomposers of chitin in soil. Chitinase genes have been cloned from Streptomyces species. Extensive analysis of these genes revealed an extraordinary high multiplicity of chitinase genes in Streptomyces. In S. coelicolor A3(2), seven distinct genes belonging to family 18 and 19 chitinases were dispersed on the chromosomal DNA. Such high-multiplicity of chitinase genes was observed in the wide range of species of Streptomyces. Genes for family 19 chitinases, which had been considered to be present only in higher plants, were found to be widely spread in Streptomyces. Proteolytic-cleavage of primary gene products also contribute to the high-multiplicity of chitinases produced by Streptomyces. Many of Streptomyces chitinases, especially those of family 18, have multiple domain structure consisting of substrate- binding domain, fibronectin type III-like domain, and catalytic domain. Chitinase synthesis in Streptomyces is induced by chitin and repressed by the presence of readily utilizable carbon sources such as glucose. The regulation of chitinase synthesis is carried out at the level of transcription. Present in the promoter region of almost all the chitinase genes of Streptomyces is a pair of 12-bp-direct repeat sequences, which was shown to be involved in the regulation of chitinase genes transcription. In glucose repression of chitinase production, glkA, a gene for glucose kinase, is involved in S. lividans, but apparently not in S. coelicolor A3(2).

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Chemistry (isolation, structures and structure-activity relationships) and mode of actions (aerial mycelium-inducing activity and antimicrobial activity) of pamamycins are discussed with emphasis on their unique structures.

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The taxonomy of a soil isolate, strain MK27-91F2 which produced a new antifungal antibiotics formamicin, was studied. We propose that the strain should belong to a new species of the genus Saccharothrix with the new name Saccharothrix tangerinus sp. nov., the type strain being MK27-91F2 (= JCM 10302 = IFO 16184 = FERM P-16053). This new species was characterized by a type III cell wall, galactose and rhamnose as whole-cell sugars, type PII phospholipids, MK-9(H₄) menaquinone, fatty acid components of i-16:0, i-14:0, i-15:0, 16:0, 16:1, 17:1 and i-16:1, but lacking mycolic acids, a G+C content in DNA of 74 mol %, and a base sequence of 16S ribosomal RNA gene.

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In the production culture of milbemycin α₁₁ and α₁₄ by Streptomyces hygroscopicus subsp. aureolacrimosus SANK 60393 (strain MA3-6126), two types of morphological mutants appeared in the late production phase, in which the milbemycin production rate had diminished. One strain was a bald type, which formed no spores and aerial mycelia, and the other was a black pigment-producing type. Taxonomic study indicated that, in addition to morphological differences, these two mutants possessed several physiological properties, such as acid production and carbon source utilization, distinctive from the original strain. The appearance of the morphological mutants during cultivation was stimulated by not only the mechanical shear stress caused by the addition of glass beads to a flask or by using a buffled flask but also by the addition of supernatant obtained from a 12-day flask-cultured broth. The morphological mutants were defective in their ability to produce and to convert milbemycins. These results suggested that the appearance of morphological mutants led to the decrease in production in the later phases of milbemycin production.

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Seventeen species of 11 rare actinomycete genera were treated with lysozyme and achromopeptidase to produce protoplasts. Fourteen of them could be protoplasted. Abundant protoplasts were obtained from Actinokineospora globicatena, Actinosynnema mirum and Amycolatopsis azurea, while relatively small amount of protoplasts were obtained from two Actinomadura species and Couchioplanes caeruleus subsp. azureus. Nine of 14 protoplasted species could regenerate on R1M and R2YE media with the range of regeneration frequency. The protoplasts of Amycolatopsis azurea regenerated on R1M and R2YE at the highest frequency (80%). Actinomadura atramentaria, A. echinospora, Catellatospora ferruginea and two Couchioplanes species could not regenerate on any tested media. A. azurea could be transformed with a Streptomyces vector, pIJ702, at the frequency of 1.6 x 10⁶ transformants per μg DNA. The other Streptomyces plasmid pRES18 was also able to be maintained in this strain.

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Basic and applied studies on multiple aminoglycoside antibiotic (AG) resistance in actionmycetes were carried out. AG producers exhibited individual AG resistance profiles representing substrate specificities of AG-modifying enzymes and/or AG-resistance specificities of ribosomes as self-resistance factors. In some strains, however, additional factors were found to be involved. They included AG acetyltransferases such as the activated cryptic AAC(3) in streptomycin-producing Streptomyces griseus SS-1198PR and an AAC(2’) in kasugamycin-producing S. kasugaensis MB273. In the former we demonstrated the gene activation due to one base substitution of T for C at the -10 promoter region and the modification at the novel site (3”-NH₂) of arbekacin (ABK) and amikacin (AMK). The latter was characterized by its novel capability of acetylating ABK and astromicin (ASTM) at 2’-NH₂. An AAC(6’) regarded as an nonself-resistance factor in an ABK resistant actinomycete strain #8 was characterized by its capability of acetylating semisynthetic AGs (ABK, AMK, isepamicin and netilmicin) and ASTM at 6’-NH₂.
As an application study of multiple AG resistance factors, these AACs were used for predictive investigations of the possible emergence of AAC-dependent resistance to ABK known to be refractory to the AACs of clinical origin. Consequently, we discovered the unexpected antibiotic activity of ABK acetylation products by AAC(3), AAC(2’) and AAC(6’) indicating little possibility of the emergence of AAC-dependent ABK resistance.

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