Abstract
PurposeOleaginous yeasts can accumulate intracellular lipid bodies or triacylglycerides (TAGs) under nutrient limiting conditions. TAGs derived from those yeast strains are considered as an alternative to conventional plant-based oils for biodiesel production. In this study, we attempt to isolate and characterize yeast strains from selected traditional fermented foods of Manipur and Mizoram, India, and study their oleaginous attributes for biodiesel production.MethodFourteen potential oleaginous yeasts were isolated from fermented food samples of Manipur and Mizoram, India. The isolates were identified by 5.8S internal transcribed spacer (ITS) rRNA gene sequencing. Intracellular TAG accumulation by yeast cells were confirmed by Nile red fluorescence microscopy and spectrometry technique. The most promising isolates were evaluated for lipid accumulation having different initial carbon to nitrogen (C/N) ratios and also the full kinetic studies (depicting the glucose consumption, biomass, and lipid production) using optimum C/N ratio were estimated. Fatty acid methyl esters (FAME) profile of the transesterified lipids were analyzed by GC-MS.ResultsThe identified yeast isolates belonged to seven different genera viz. Rhodotorula, Pichia, Candida, Saturnispora, Wickerhamomyces, Zygoascus, and Saccharomyces. Under nitrogen-limiting conditions, maximum biomass concentration of 5.66 ± 0.03 g/L and 4.713 ± 0.03 g/L was produced by Wickerhamomyces anomalus FK09 and Pichia kudriavzevii FK02, respectively. The highest lipid concentration (g lipid/L fermentation broth) of 0.58 g/L was attained by Rhodotorula mucilaginosa R2, followed by Wickerhamomyces anomalus FK09 (0.51 g/L), and Zygoascus hellenicus FC10 (0.41 g/L). Rhodotorula mucilaginosa R2 exhibited the maximum lipid content (% lipid/g dry cell weight) of (21.63 ± 0.1%) after 96 h of growth. The C/N ratio of 40 and 20 was found to be optimum for R. mucilaginosa R2 and W. anomalus FK09 with a lipid content of 22.21 ± 0.4% and 12.83 ± 0.08% respectively.ConclusionNewly isolated yeast strains were obtained from traditional fermented food samples of Manipur and Mizoram, India. FAME analysis of the transesterified lipid extracts suggested the potential use of yeast-derived oil as an alternative to vegetable oil for biodiesel production.
Highlights
Plant-based oils are the primary source for the conventional production of biodiesel and act as a substitute to the depleting fossil fuel reserves (Sitepu et al 2014)
The highest lipid concentration (g lipid/L fermentation broth) of 0.58 g/L was attained by Rhodotorula mucilaginosa R2, followed by Wickerhamomyces anomalus FK09 (0.51 g/L), and Zygoascus hellenicus FC10 (0.41 g/L)
Identification of yeast strains isolated from selected fermented foods of Manipur and Mizoram Seventeen yeast isolates were established as pure culture from traditional fermented food and beverages of Manipur and Mizoram, India (Fig. 1 depicts the colony morphology of some of the representative yeast isolates growing on Yeast extract peptone dextrose (YEPD) agar medium)
Summary
Plant-based oils are the primary source for the conventional production of biodiesel and act as a substitute to the depleting fossil fuel reserves (Sitepu et al 2014). Yeasts are well-suited for commercial production of microbial lipids over other oleaginous microorganisms like algae and filamentous fungi because of its ability to reach high cell densities in a short time (Sitepu et al 2014), having similar composition of fatty acid as those of plant-based oils (Deeba et al 2016) and capability of producing a variety of metabolic co-products including high-value carotenoids, proteins and polysaccharide rich streams of deoiled biomass, and various organic acids (Bellou et al 2014; Kot and Kurcz 2016; Parsons et al 2020). High C/N ratio in the growth medium has been reported to induce lipogenesis (Ratledge 2002) During such stress conditions, oleaginous yeasts accumulate high amounts of triacylglycerol in the form of intracellular lipid bodies (LBs) (Poontawee et al 2018; Bardhan et al 2019a). Recent screening and molecular characterization studies have led to the identification of some novel oleaginous yeast strains which include Cystobasidium oligophagum JRC1 (Vyas and Chhabra 2017), Meyerozyma guilliermondii BI281A (Ramírez-Castrillón et al 2017), and Cystobasidium iriomotense (Tanimura et al 2018) as the potential feedstock for biodiesel production
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