Investigation of actinomycete diversity in the tropical rainforests of Singapore

Five thousand actinomycetes were isolated from soil samples collected from rainforests in Singapore and the generic identities of these isolates were determined by using a procedure that combined morphological, chemotaxonomic and 16S rDNA sequence-based phylogenetic analyses. Actinomycetes belonging to a total of 36 genera were identified. The most abundant isolates are me mbers of Streptomyces, Micromonospora, Actinoplanes, Actinomadura, Nonomuri a, Nocardia and Streptosporangium. By phylogenetic analysis of 16S rDNA seq uences of our isolates together with those of known actinomycete species, w e also evaluated the species diversity of several genera including Streptom yces, Micromonospora, Nonomuria, and Actinomadura, We found that: first, th e tropical isolates are present in most clades represented by known species ; and second, many tropical isolates form new clades distant from the known species, indicating the presence of unidentified taxa at both species and genus levels. Based on these results, we conclude that actinomycete diversi ty in the tropical rainforest is very great and should represent an excelle nt source for discovery of novel bioactive compounds.