As a replacement to existing fossil fuels, biofuels, have proven their worth; however, their widespread use is limited due to inconsistent yields, higher costs and poor productivity. An oleaginous yeast, Rhodosporidium toruloides has been reported to accumulate substantial amounts of lipids (that can be converted to biofuels) and therefore, it was selected for study and optimization. Apart from lipids, R. toruloides is also reported to produce carotene that can be used as a therapeutic agent. In this study, the culture medium was statistically modeled and optimized for concomitant production of lipids and carotenoids and for improving and maximizing the productivity of lipids as well as carotenes. The two metabolites were expressed differentially in the growth cycle of the organism. Culture medium components were simultaneously varied at five different levels using statistical modeling employing response surface methodology (RSM). Osmotic stress was introduced in order to simulate saline conditions and optimize the carotenoid as well as lipid production process, to be used in conditions with high salt contents. We observed a 10% (w/v) increase in carotenoid production in initial experiments under osmotic stress due to high salt concentration, while the increase in lipid synthesis was not pronounced. In this study, we demonstrate 36.2% (w/v) lipid production and 27.2% (w/v) carotenoid production, under osmotic stress with high salt concentrations, for the first time.

BackgroundVegetable ‘mandi’ (road-side vegetable market) waste was converted to a suitable fermentation medium for cultivation of oleaginous yeast Rhodosporidium toruloides by steaming under pressure. This cultivation medium derived from waste was found to be a comparatively better source of nutrients than standard culture media because it provided more than one type of usable carbon source(s) to yeast.ResultsHPLC results showed that the extract contained glucose, xylose and glycerol along with other carbon sources, allowing triauxic growth pattern with preferably usage of glucose, xylose and glycerol resulting in enhanced growth, lipid and carotenoid production. Presence of saturated and unsaturated fatty acid methyl esters (FAMEs) (C14-20) in the lipid profile showed that the lipid may be transesterified for biodiesel production.ConclusionUpscaling these experiments to fermenter scale for the production of lipids and biodiesel and other industrially useful products would lead to waste management along with the production of value added commodities. The technique is thus environment friendly and gives good return upon investment.Electronic supplementary materialThe online version of this article (10.1186/s12934-018-1026-4) contains supplementary material, which is available to authorized users.

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Surface culture citric acid fermentation was carried out by Aspergillus niger T55, a strain isolated from its natural source, using cane molasses, either untreated or treated by various methods. Citric acid biosynthesis is seriously impaired by both organic and inorganic inhibitors. A combined treatment of molasses with tricalcium phosphate, hydrochloric acid, and Sephadex fractionation minimizes the level of inorganic and organic inhibitors in molasses and increases the production of citric acid (65% weight yield based on total reducing sugar).The optimum level of individual metal ions for citric acid production depends on the concentration of other metals in the medium.

This study investigated the potential of oleaginous yeast Rhodosporidium toruloides strain (ATCC20409) for the sustainable production of microbial lipids as biodiesel feedstock and other economically important fatty acids in comparison to algal or plant-based biodiesel. The strain exhibited high lipid content (76% of dry cell weight biomass) through consolidated bioprocessing which was transesterified to produce biodiesel. Physico-chemical properties of the biodiesel produced showed that they were in accordance with ASTM standards, although few parameters such as acid value, calorific value and free fatty acid value differed to some extent, as also reported in plant-based/microalgal biodiesel. Fatty acid methyl esters analysis of biodiesel showed 50.18% unsaturated fatty acid and 49.81% saturated fatty acid. Total content of (monounsaturated fatty acid) MUFA was higher than (polyunsaturated fatty acid) PUFA, being 44.36% and 2.69%, respectively. Considering the yield and cost, lipid extracted from R. toruloides may become a promising alternative feed in biodiesel production.