Abstract
BackgroundAmong the third-generation biodiesel feed stock, oleaginous marine yeasts are the least studied microorganisms for such purpose.ResultsWild strains yeasts were isolated from various Tunisian marine sources including fish waste (Candida tenuis CtTun15, Debaryomyces hansenii DhTun2015, Trichosporon asahii TaTun15 and Yarrowia lipolytica YlTun15) and seawater (Rhodotorula mucilaginosa RmTun15). Following incubation with ethyl methanesulfonate (EMS: 75 mM) for various periods of time (T15, T30, T45, T60 min), the cell viability of these strains responded differentially according to yeast species. For instance, mutated CtTun15 did not survive after 30 min of EMS treatment; higher resistances were observed in DhTun2015 (45 min), in YlTun15, RmTun15 and in TaTun15 (60 min) but with significant decreased cell viabilities (survival rate: 6.02, 3.16, 11.22, 11.58, 7.70%, respectively). For all surviving mutated strains, the optima of biomass and lipid yields were detected after 96 h in YPD culture; but derived from strains submitted to different period of EMS incubation. In most mutated strains, the maximum biomass (BP) and lipid (LP) productivities coincided and were observed after 30 min of EMS incubation. Only CtTun15 showed different optima of BP and LP (after 30 min and 15 min, respectively). The fatty acids (FA) compositions considered essential in the prediction of biodiesel criteria; were highly affected by EMS mutagenesis. Essentially, 30- and 45-min EMS incubation induced the highest levels of PUFA and MUFA in YlTun15, RmTun15 and TaTun15 with non-significant differences in the different times. However, CtTun15 and DhTun2015 mutant strains responded differently, with the highest levels of MUFA observed following 15 and 45 min; and that of PUFA after 30 and 45 min, respectively.ConclusionThe methyl-esterification of FA from the three mutated yeast strains (30 min—YlTun15, RmTun15 and TaTun15) yielded biodiesel with physical proprieties consistent with the International Standard System. However, investigations are needed for up-scaling biodiesel production.
Highlights
Among the third-generation biodiesel feed stock, oleaginous marine yeasts are the least studied microorganisms for such purpose
The concentration and the volume of the mutant agent have significant effects on both colonies numbers counted and growth (p < 10−4) after 48 and 120 h, respectively, with the number of colonies inversely correlated with the concentration of ethyl methanesulfonate (EMS)
Comparing the results of biodiesel predicted to the different strains of this study, we found a similarity with the genus mentioned in some indices such as the cetane number, the iodine value, the kinematic value and cold filter plugging point which was close to the standard parameter of biodiesel (ASTM D6751, EN14214, Indian Biodiesel IS15607 and the commercial biodiesel)
Summary
Among the third-generation biodiesel feed stock, oleaginous marine yeasts are the least studied microorganisms for such purpose. Intensive investigations are currently oriented toward the exploration of renewable energy sources as substitutes to fossil fuels [1, 2]. Among such sources, oleaginous microorganisms that can accumulate more than 20% lipids dry weight represent promising substitutes [3]. To enhance lipid and FA content in yeast, several techniques were developed including the classical random metagenesis. For such a purpose, ethyl methanesulfonate (EMS) is amongst the most common alkylating agents used in yeast as mutation-inducing agents. EMS-random mutagenesis has been used to develop mutant strains of microalgae devoid of EPA [22]
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