Oleaginous Yeasts as Cell Factories for the Sustainable Production of Microbial Lipids by the Valorization of Agri-Food Wastes

The agri-food industry annually produces huge amounts of crops residues and wastes, the suitable management of these products is important to increase the sustainability of agro-industrial production by optimizing the entire value chain. This is also in line with the driving principles of the circular economy, according to which residues can become feedstocks for novel processes. Oleaginous yeasts represent a versatile tool to produce biobased chemicals and intermediates. They are flexible microbial factories able to grow on different side-stream carbon sources such as those deriving from agri-food wastes, and this characteristic makes them excellent candidates for integrated biorefinery processes through the production of microbial lipids, known as single cell oils (SCOs), for different applications. This review aims to present an extensive overview of research progress on the production and use of oleaginous yeasts and present discussions on the current bottlenecks and perspectives of their exploitation in different sectors, such as foods, biofuels and fine chemicals.

The Potential of Single-Cell Oils Derived From Filamentous Fungi as Alternative Feedstock Sources for Biodiesel Production

Microbial lipids, also known as single-cell oils (SCOs), are highly attractive feedstocks for biodiesel production due to their fast production rates, minimal labor requirements, independence from seasonal and climatic changes, and ease of scale-up for industrial processing. Among the SCO producers, the less explored filamentous fungi (molds) exhibit desirable features such as a repertoire of hydrolyzing enzymes and a unique pellet morphology that facilitates downstream harvesting. Although several oleaginous filamentous fungi have been identified and explored for SCO production, high production costs and technical difficulties still make the process less attractive compared to conventional lipid sources for biodiesel production. This review aims to highlight the ability of filamentous fungi to hydrolyze various organic wastes for SCO production and explore current strategies to enhance the efficiency and cost-effectiveness of the SCO production and recovery process. The review also highlights the mechanisms and components governing lipogenic pathways, which can inform the rational designs of processing conditions and metabolic engineering efforts for increasing the quality and accumulation of lipids in filamentous fungi. Furthermore, we describe other process integration strategies such as the co-production with hydrogen using advanced fermentation processes as a step toward a biorefinery process. These innovative approaches allow for integrating upstream and downstream processing units, thus resulting in an efficient and cost-effective method of simultaneous SCO production and utilization for biodiesel production.

Rapeseed Post-Frying Oil from Fish Fillets as a Carbon Source in Microbial Oil Synthesis

Microbial oils, also called single-cell oils, are lipids synthesized by microorganisms exceeding 20% of the dry weight of the cell. The aim of this work was to investigate the possibility of applying a rapeseed post-frying oil from fish fillets as a carbon source in growth medium for Yarrowia lipolytica oleaginous yeast species in order to synthesize a microbial oil. The key contribution of this work is that the solution provides a sustainable method for valorization of post-frying waste oil. Shaken batch cultures were provided and the influence of triacylglyceride hydrolysis on yeast growth was evaluated. In conclusion, post-frying rapeseed oil seems to be an easily utilizable carbon source by yeast. Regardless of the method of lipid substrate pretreatment, the yeast strain preferentially accumulated oleic acid (C18: 1) from 52.07% to 66.62% and linoleic acid (C18: 2) from 12.98% to 24.10%. To the best of our knowledge, this is the first report of using the oxygen nanobubbles as an unconventional method of aerating the culture medium containing lipid carbon sources. The use of water oxygenated with nano-sized bubbles to prepare culture media resulted in obtaining a higher yield of biomass compared to the biomass yield in distilled water-based medium.

Species identification of stranded seaweeds on eastern seashores of Thailand and utilization as a sole carbon source for single cell oils synthesized by oleaginous yeasts

Chantarasiri A. 2020. Species identification of stranded seaweeds on eastern seashores of Thailand and utilization as a sole carbon source for single-cell oils synthesized by oleaginous yeasts. Biodiversitas 21: 2353-2361. Many stranded seaweeds are left to decompose on the seashore. This study aimed to identify and utilize the stranded seaweeds collected from seashores in Rayong Province on the east coast of Thailand. Seaweeds were identified as Dictyota dichotoma strain A and Padina australis strain B based on their distinctive morphology and 18S rDNA sequence analyses. The most abundant seaweed, D. dichotoma strain A, was analyzed for chemical compositions following AOAC standard methods. This seaweed was considered a low-cost carbon source for the cultivation of three oleaginous yeasts without any other nutrient supplements. All oleaginous yeasts utilized the carbon source from Dictyota medium for growth and accumulation of single-cell oils (SCOs). The oleaginous yeast, Cryptococcus albidus strain TISTR 5103 accumulated SCOs at 51% (w/w). The resulting SCOs from oleaginous yeasts comprise many fatty acids with 10 to 22 carbon atoms. This study is the first to identify stranded seaweeds in Rayong Province using morphological and genetic techniques. Results showed the potential application of stranded seaweeds as a low-cost carbon source for SCO biosynthesis of oleaginous yeasts.