Oxygen pressure, fatty acid composition and ergosterol level in Rhodotorula gracilis

The mitochondrial respiratory chain from Rhodotorula mucilaginosa, an extremophile yeast

Rhodotorula mucilaginosa survives extreme conditions through several mechanisms, among them its carotenoid production and its branched mitochondrial respiratory chain (RC). Here, the branched RC composition was analyzed by biochemical and complexome profiling approaches. Expression of the different RC components varied depending on the growth phase and the carbon source present in the medium. R. mucilaginosa RC is constituted by all four orthodox respiratory complexes (CI to CIV) plus several alternative oxidoreductases, in particular two type-II NADH dehydrogenases (NDH2) and one alternative oxidase (AOX). Unlike others, in this yeast the activities of the orthodox and alternative respiratory complexes decreased in the stationary phase. We propose that the branched RC adaptability is an important factor for survival in extreme environmental conditions; thus, contributing to the exceptional resilience of R. mucilaginosa.

Lipid Accumulation in an Oleaginous Yeast ( Candida 107) Growing on Glucose Under Various Conditions in a One- and Two-Stage Continuous Culture

Lipid accumulation and fatty acid composition in Candida 107 have been studied using a two-stage continuous culture system in which the first vessel was run under carbon-limited conditions and then the entire output was passed into a second vessel, where lipid accumulation was stimulated by adding only glucose. Maximum lipid accumulation (28% of yeast [dry weight]) occurred for a volume ratio of vessel 1 to vessel 2 of 3:5, with 30 g of glucose per liter being added to vessel 2 operated at 25°C with an aeration rate of between 0.1 and 1.0 volume of air/volume of medium per min. Although the maximum specific rate of lipid formation (0.05 g of lipid/g of yeast per h) was higher than in a nitrogen-limited, single-stage system, the efficiency of lipid formation was much less and never exceeded 14 g of lipid produced per 100 g of glucose consumed. The fatty acid composition was not significantly altered in either the two-stage or single-stage culture (nitrogen-limited) systems by changes in growth temperature (from 19 to 33°C) or aeration rates (0.05 to 1.0 volume of air/volume of medium per min); or, in the two-stage system, by changes in the residence time of the yeast in the second vessel (from 3.2 to 24.4 h), or, in the single-stage system, by changes in pH (from 3.5 to 7.5). Only when the concentration of glucose entering vessel 2 of the two-stage system was less than 30 g/liter did significant changes in the fatty acids occur. Thus, although a two-stage continuous culture system allows lipid accumulation to be separated from the growth phase, it offers no practical advantages over a single-stage system as a means of producing microbial oils and fats.