The kac gene coding for KSM acetyltransferase cloned from kasugamycin (KSM)-producing Streptomyces kasugaensis MB273-C4 (Hirasawa et al., 1993 ; JP. A-05-23187) was investigated for its correlation with KSM-productivity. Genomic Southern hybridization analysis indicated that kac existed in the genome of all the KSM-producing Streptomyces strains tested, i.e., S. kasugaensis MB273-C4 and M338-M1, and S. celluloflavus JCM4126 as well as Streptomyces sp. MF861-C4 that has characteristics taxonomically and phylogenically remote from those of the formers. We also found in experiments using Streptomyces sp. MF861-C4 that kac gene was readily deleted during storage as a lyophile with skim milk at 10°C or as a frozen 20% sucrose suspension at −20°C of its aerial mycelia, accompanying the loss of KSM productivity.

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The use of synthetic antibacterial compounds as selective supplements in agar media for the isolation and enumeration of soil actinomycetes is described. A preliminary survey revealed that the combined application of trimethoprim (TP) and nalidixic acid (NA) had no deleterious effect on most test actinomycetes (35 genera and 159 species), while the growth of most test non-filamentous soil bacteria (10 genera and 20 species) was inhibited or discouraged. A mixture of TP (20 mg/l) and NA (10 mg/l) was incorporated into humic acid-vitamin (HV) agar and four other isolation media. The efficiency of isolating and enumerating actinomycetes cultivated under these conditions was evaluated using 13 different natural soil samples. The TP-NA combination substantially reduced the occurrence of competing non-filamentous bacteria on the isolation plates without adversely affecting actinomycete growth, thus greatly facilitating the recognition, enumeration and pure isolation of actinomycete colonies. A detailed taxonomic examination showed that the antimicrobial combination allowed the recovery of varieties of actinomycete genera. At least 11 different genera were isolated from a garden soil sample on HV plates containing TP and NA. The most frequently isolated Streptomyces strains were further categorized into various species-groups. The results suggest that the TP-NA combination may prove to be a useful tool for autecological and enumeration studies of actinomycetes, and for the isolation of wide varieties of actinomycete strains.

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A total of 335 actinomycete strains were isolated from 9 soil samples collected at Mojave Desert, California. A large number of actinomycete colonies emerged on the agar plates when cultured at 37°C than 27°C. Among 50 strains taken randomly from the isolates nine strains were rare actinomycetes containing meso-diaminopimelic acid in the cell wall. They were considered to belong to genera Microbispora, Nocardia, Microtetraspora, Amycolatopsis, Actinomadura and Saccharothrix. The five strains could grow even at 50°C.

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