Thesis (Ph.D.)--Chulalongkorn University, 2013

Seventy nine isolates of actinomycetes were isolated from twenty nine soil samples collected from Krung Ching Waterfall National Park, Angthong Islands National Park and Similan Islands National Park by using starch casein nitrate agar and potato starch-glycerol agar. All isolated actinomycetes were taxonomically identified on the basis of their phenotypes and genotypes using 16S rRNA gene sequence analysis. Seventy four isolates were classified as twenty four species of Streptomyces. Among them, five strains were proposed as four new species, including strains KC-031 and KC-038 as Streptomyces siamensis, strain KC-106 as S. similanensis, strain KC-035 as S. krungchingensis, and KC-112 as S. andamanensis. In addition, strain KC-061 was proposed as a new Nonomuraea thailandensis. Moreover, three strains KC-001, KC-005 and KC-143 were identified as two species of Kitasatospora and strain KC-132 was identified as Amycolatopsis. Forty five isolates cultivated in production media no. 51 and 53 showed antimicrobial activity against Kocuria rhizophila ATCC 9341, Bacillus subtilis ATCC 6633, Escherichia coli NIHJ KB213, Xanthomonas campestris pv. oryzae KB88, Candida albicans KF1 and Mucor racemosus IFO 4581T. Twenty four Streptomyces strains were selected to cultivate in production medium no. 54 and their crude EtOAc extracts of the culture broths were analyzed for chemical profiles by HPLC. The crude extracts of S. tendae strain KC-097 and S. cavourensis strain KC-121 showed interesting chemical profiles and were selected for secondary metabolite study. The isolation of the extract from S. tendae strain KC-097 yielded N-acetyltryptamine, phenethylacetamide, germicidin B, germicidin C, germicidin A and isogermicidin A. The isolated compounds exhibited no test biological activities, except N-acetyltryptamine exhibited cytotoxicity against cancer cell NCI-H187 (IC50 46.87 µg/ml). Meanwhile, the extract of S. cavourensis strain KC-121 provided bafilomycin D and 21-(O-methyl)-bafilomycin A1 from fraction KC121F2F3 which exhibited antimalarial activity against Plasmodium falciparum K1 (IC50 0.21 µg/ml), cytotoxicity against Vero cells (IC50 0.37 µg/ml) and cytotoxicity against cancer cells (KB; IC50 18.39 µg/ml, MFC-7; IC50 4.18 µg/ml and NCI-H187; IC50 0.23 µg/ml).