Diversity and antagonistic potential of Actinobacteria from the fungus-growing termite Odontotermes formosanus

43 Actinobacteria were isolated from the nest of Odontotermes formosanus. A phylogenetic analysis of 23 Actinobacteria isolates with different morphotypes showed that they did not form a monophyletic group. Antifungal bioassays exhibited that many strains inhibit both the termite cultivar Termitomyces and the competitor Xylaria. However, Actinobacteria inhibited the competitor Xylaria more severely than the termite cultural fungus Termitomyces. Furthermore, two Actinobacteria (Streptomyces sp. T33 and S. bellus T37) had a selective antifungal effect on Xylaria, with the inhibition zone of 25.5 and 8.9mm, respectively. An actinomycin D was isolated from the strain T33 and had potent antifungal activity against Xylaria with IC50 value of less than 3.1 mu g/mL. In addition, further bioassays showed that actinomycin D possessed potent antifungal activities against Magnaporthe grisea (IC50=0.9 mu g/mL), Fusarium oxysporum f. sp. cucumerinum (IC50=2.2 mu g/mL), Valsa mali (IC50=1.7 mu g/mL), Rhizoctonia solani (IC50=10.3 mu g/mL), Dothiorella gregaria (IC50=12.5 mu g/mL) and F. oxysporum f. sp. mornordicae (IC50=14.3 mu g/mL), which were comparable to those of referenced cycloheximide. The findings of the present study suggest that the termite-associated Actinobacteria have a potential to be used as microbial fungicide.