Clethramycin, a new inhibitor of pollen tube growth with antifungal activity from Streptomyces hygroscopicus TP-A0623 I.: Screening, taxonomy, fermentation, isolation and biological properties

The cytoskeletal proteins, actin and myosin, play a central role in pollen tube growth. The pollen tube growth is inhibited by cytochalasin, which interferes with actin polymerization. In the screening of pollen tube growth inhibitors, clethramycin was found from the fermentation broth of an actinomycete strain TP-A0623. The producing strain was isolated from a root of Clethra barbinervis collected in Toyama, Japan and identified as Streptomyces hygroscopicus based on the. taxonomic study. Clethramycin showed in vitro antifungal activity against yeast such as Candida albicans and C. glabrata with the MIC of 0.5 similar to 8 mug/ml, but weak activity against Gram-positive and negative bacteria (MIC greater than or equal to64 mug/ml). Cytotoxicity of clethramycin was moderate and the IC50 was 57 mug/ml against HeLa cells and 120 mug/ml against WI-38 cells.