The last unidentified gene encoding an enzyme involved in ergosterol biosynthesis in Saccharomyces cerevisiae has been cloned. This gene, designated ERG27, encodes the 3-keto sterol reductase, which, in concert with the C-4 sterol methyloxidase (ERG25) and the C-3 sterol dehydrogenase (ERG26), catalyzes the sequential removal of the two methyl groups at the sterol C-4 position. We developed a strategy to isolate a mutant deficient in converting 3-keto to 3-hydroxy-sterols. An ergosterol auxotroph unable to synthesize sterol or grow without sterol supplementation was mutagenized. Colonies were then selected that were nystatin-resistant in the presence of 3-ketoergostadiene and cholesterol. A new ergosterol auxotroph unable to grow on 3-ketosterols without the addition of cholesterol was isolated. The gene (YLR100w) was identified by complementation. Segregants containing the YLR100w disruption failed to grow on various types of 3-keto sterol substrates. Surprisingly, when erg27 was grown on cholesterol-or ergosterol-supplemented media, the endogenous compounds that accumulated were noncyclic sterol intermediates (squalene, squalene epoxide, and squalene dioxide), and there was little or no accumulation of lanosterol or 3-ketosterols. Feeding experiments in which erg27 strains were supplemented with lanosterol (an upstream intermediate of the C-4 demethylation process) and cholesterol (an end-product sterol) demonstrated accumulation of four types of 3-keto sterols identified by GC͞MS and chromatographic properties: 4-methyl-zymosterone, zymosterone, 4-methylfecosterone, and ergosta-7,24 (28)-dien-3-one. In addition, a fifth intermediate was isolated and identified by 1 H NMR as a 4-methyl-24,25-epoxy-cholesta-7-en-3-one. Implications of these results are discussed.fungi ͉ sterol biosynthesis

Proper treatment of heavy metal ions present in wastewaters is a major concern. With extensive usage in various industries, Cr(VI) contamination has become threatening for the environment. Biosorption is a favorable technique for heavy metals removal. In the present study, dried cyanobacterial consortium of Dinophysis caudata and Dinophysis acuminata were used to assess its biosorption capability. The surface texture and morphology of the biosorbent were obtained through scanning electron microscopy. The presence of different chemical bonds, namely hydroxyl, C-H and C-N, was confirmed through FTIR study. Pseudo-second-order Mckay-Ho model was found to perform best to fit the kinetic data. Temkin adsorption isotherm model fit best to the equilibrium data. Response surface methodology (RSM) was employed to optimize Cr(VI) abatement. Effect of initial concentration (IC) of metal ion, temperature, pH variation and amount of adsorbent (AD) were studied during batch study. Maximum Cr(VI) abatement after 5 min contact time was 80.77% for an IC of Cr(VI) of 25 mg/L, at pH 11 and 45 °C with the AD of 2.5 g/L. The optimum removal conditions as shown by RSM study were IC of Cr(VI): 15 mg/L, AD: 1 g/L, pH: 11, and the removal was predicted as 81.72%. Artificial neural network-based model was further developed based on experimental points which indicated that the model can predict abatement of Cr(VI) for various operating conditions with reasonably high accuracy.

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