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Selected species of the order Peronosporales, which are unable to epoxidize squalene and thus synthesize sterols, are able to metabolize exogenous cycloartenol to lanosterol and in some organisms to fucosterol, ergosterol, and cholesterol. Lanosterol was less effectively utilized but some ergosterol and cholesterol were yielded. Fucosterol was very efficiently metabolized by most species to ergosterol, A7-ergostenol, A5-ergostenol, cholestanol, and cholesterol. Several unknown sterols were observed in most trials. These data suggest a vestigial sterol synthetic pathway derived from cycloartenol, followed by possible isomerization to lanosterol and then to other sterols.It has been established that species of Pythium and Phytophthora require exogenous sterols for sexual reproduction (1, 2). These organisms are unable to synthesize sterols because of a missing squalene epoxidase (3). Metabolism of exogenous sterols has been observed in Phytophthora cactorum by Langeake (4), who reported possible conversion of lanosterol to cholesterol. Nes and Patterson (5) reported that Phyt. cactorum was unable to transform cycloartenol or lanosterol to other sterols. Conversion ofA7 and A5'7 sterols to A5 sterols has been reported by Elliott and Knights (6) in Phyt. cactorum, which additionally synthesizes cholesteryl esters, cholesteryl glucosides, and acyl sterol glycosides (7,8). Other than the above, sterol conversions in Phytophthora or Pythium have, in general, not been demonstrated in detail.Lagenidium giganteum is another Oomycete, but of the Lagenidiales, that requires exogenous sterols to produce zoospores (9). Warner and Domnas (10) have shown that this organism converts cycloartenol, but not lanosterol, to cholesterol. Because Lagenidium species are able to metabolize cycloartenol, it was ofconsiderable interest to observe ifthis compound could be metabolized by selected species ofthe Peronosporales. This article reports our observations. Inoculation and growth were as described (10) (10) and the unsaponifiable lipid fraction was obtained. The sterols were separated on HPLC with a Waters instrument by using a 10-,um C18 column (4.6 x 250 mm). Fractions were eluted with methanol/H20 (96:4) at 2 ml/min flow with UV detection at 210 nm. MATERIALS AND METHODS MicroorganismsSterols were identified by gas/liquid chromatography on 3% SE-30 and 1% QF-1 with a Packard 417 FID chromatograph as described (10). Confirmation ofidentification was obtained with gas chromatography/electron impact mass spectroscopy (70 eV) with a Finnegan 4023 instrument. A 15-m flexible fused silica capillary coated with OV-101 was programmed from 160 to 2600C at 10°C/min with an initial hold of 3 min. RESULTSNo sterols were found in control organisms to the limit of detection (0.0001%). Uninoculated control cultures yielded a stoichiometric recovery of the administered sterols.Sterols Isolated After Administration ofCycloartenol. Table 1 illustrates the substances identified in the organisms examined. Clear evidence was obtained for the ...

This review is directed toward the study of the physiology and biochemistry of parasitic fungi on insects and stresses the usefulness and utility of these organisms from the standpoint of applied research and biotechnology. The review covers the principal contributions made by investigators toward elucidation of the infective mechanisms of the entomogenous fungi, and the various biochemical attributes of these organisms. The interplay of the various enzymes and associated biochemical substances which are involved in the infective process is discussed as well as the important studies of the peculiar physiology frequently associated with these microorganisms.

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