Esterification of 4-14C-Cholesterol by Phytophthora Cactorum

Abstract

Species of the plant pathogenic fungi Phytophthora and Pythium require cholesterol, sitosterols, or stigmasterol for sexual reproduction (1, 2, 3, 5). A species of Pythium incorporated all of the added cholesterol into protoplasmic and intracellular membranes, but little or no transformation of the sterol was found (6, 7). The use of saponification in the extraction procedure however, may have prevented detection of any cholesterol esters present (4). Hendrix (4) reported the production by Pythium periplocum Drechsler of at least two metabolites from cholesterol, one being an ester. This paper reports the investigation of esterified transformation products of cholesterol in Phytophthora cactorum (Leb. & Cohn) Schroet., ATCC 10,091. A defined glucose-L-asparagine medium with thiamine (6) was used and 5 mg (4 /c)/liter 4-14C-cholesterol was added in ether immediately after autoclaving, to 250-ml flasks containing 25 ml medium each. Cultures were incubated for 10 days in still culture in darkness at 20 C. Filtered mycelium was air dried and extracted in a soxhlet apparatus with ethyl acetate, yielding 84% recovery of activity. The medium contained less than 1% of the recovered activity. The extract of the mycelium was resolved on silica gel thin-layer chromatography plates (Eastman Kodak Type K301R) in 5% ethyl acetate in hexane. Twentytwo percent of the recovered activity appeared in a nonpolar fraction with Rf 0.88 and the remainder was identified as cholesterol on the