Screening of new oleaginous yeasts for single cell oil production, hydrolytic potential exploitation and agro-industrial by-products valorization

Abstract

Abstract Microbial lipid production using renewable raw material is considered an alternative for biodiesel production. In this study, several biotopes have been targeted for new oleaginous yeasts isolation. 205 yeast strains were screened to find efficient and more suitable oleaginous yeasts for agro-industrial wastes bioconversion. Using the qualitative fluorometric technique, 12 strains were pre-selected and the morphology of their lipid bodies was studied. The molecular identification showed that our isolates are closely related to six genera of oleaginous yeast. Cultivated on nitrogen limited medium, lipid content of all yeast strains exceeds 20% (w/w), confirming their oleaginous character. The highest lipid yield and content were achieved by Candida viswanathii Y-E4 (3.55 g/L) and Rhodotorula babjevae Y-SL7 (39.17%), respectively. All the lipid profiles analyzed are mainly formed by triacylglycerols of oleic acid. In addition to the lipogenic aptitude, the hydrolytic potential including cellualse and lipase activities was also studied. The highest CMCase (0.11 U/mL) and β-glucosidase (0.55 U/mL) activities were produced by the Trichosporon asahii Y-SL1 strain. However, the highest lipase activity (50 U/mL) was detected in the liquid culture of Yarrowia lipolytica Y-D1P. To minimize the SCO production cost, oleaginous yeasts were evaluated for their capacity to use agro-industrial by-products for lipids and enzymes production. Cultivated on wheat bran acid-hydrolysate, Rhodotorula mucilaginosa Y-MG1 exhibits the highest lipid yield (2.2 g/L). In parallel, a considerable lipid content 64% (w/w) and lipase activity (174.1 U/mL) were achieved by Yarrowia lipolytica Y-D1P and Trichosporon asahii Y-D1 respectively, when the soap stock of pomace olive oil refining was used as carbon source. This study opens up new perspectives in the use of industrial wastes for production of microbial lipids and high-added value products.