Streptomyces Strain 5-94, Obtained from the Subtropical Region in Okinawa, has Inhibitory Activity against Colletotrichum orbiculare

Abstract

We previously reported on the construction of a microbial library isolated from soils in Okinawa (Okinawa Microbial Library, OML, http://omlus.jimdo.com/), including the Yaeyama Archipelago, and validated its phylogenetic diversity. In the present study, we report that strain 5-94, obtained from soil samples collected from Ikei Island, Okinawa Prefecture, Japan, produced inhibitory compounds against Colletotrichum orbiculare, the causal agent of anthracnose disease. Mycelial growth of C. orbiculare was inhibited by strain 5-94 in a dual culture assay. Additionally, the use of culture filtrates of this strain significantly suppressed the spore germination in C. orbicular. The sequence analysis of the 16S rDNA region indicated that strain 5-94 was similar to the Streptomyces species. Anthracnose disease caused by C. orbiculare was suppressed by the strain 5-94 culture filtrate in cucumber leaves pretreated for 3 and 7 d. Furthermore, growth inhibition zones of C. orbicular in the culture filtrate of this strain were detected by a thin layer chromatography. These results, therefore, suggested that inhibitory compounds from the culture filtrate of Streptomyces strain 5-94 might be a promising source for the development of new chemical fungicides to prevent anthracnose disease caused by C. orbiculare.