Indole-3-ethanol produced by Zygorrhynchus moelleri, an indole-3-acetic acid analogue with antifungal activity

Abstract

Indole-3-ethanol (IEt) was identified as a major secondary metabolite in cultures of Zygorrhynchus moelleri containing casein hydrolysate as the nitrogen source. Much smaller quantities of indole-3-acetic acid (IAA) were produced. In a medium containing an inorganic nitrogen source Z. moelleri metabolized tryptophan to IEt and IAA. The highest yield of IAA was produced at pH 4·5 while that of IEt was maximal in less acidic conditions. Tryptamine was also metabolished to IEt. When supplied with exogenous IEt Z. moelleri did not produce IAA, and IEt oxidase was not detected in either culture filtrate or fungal mycelium. IEt inhibited germination of zoospores of Phytophthora cinnamomi , oogonia of two Pythium spp. and conidia of Fusarium oxysporium f sp. lini with ED 50 values between 1·8 and 12·7 μg ml −1 . Mycelial growth of these fungi and Rhizoctonia solani and Sclerotinia sclerotiorum was also suppressed by IEt.