Biosynthesis of Monomers for Plastics from Renewable Oils

Lipid production by oleaginous yeasts

Microbial lipid production has been studied extensively for years; however, lipid metabolic engineering in many of the extraordinarily high lipid-accumulating yeasts was impeded by inadequate understanding of the metabolic pathways including regulatory mechanisms defining their oleaginicity and the limited genetic tools available. The aim of this review is to highlight the prominent oleaginous yeast genera, emphasizing their oleaginous characteristics, in conjunction with diverse other features such as cheap carbon source utilization, withstanding the effect of inhibitory compounds, commercially favorable fatty acid composition-all supporting their future development as economically viable lipid feedstock. The unique aspects of metabolism attributing to their oleaginicity are accentuated in the pretext of outlining the various strategies successfully implemented to improve the production of lipid and lipid-derived metabolites. A large number of in silico data generated on the lipid accumulation in certain oleaginous yeasts have been carefully curated, as suggestive evidences in line with the exceptional oleaginicity of these organisms. The different genetic elements developed in these yeasts to execute such strategies have been scrupulously inspected, underlining the major types of newly-found and synthetically constructed promoters, transcription terminators, and selection markers. Additionally, there is a plethora of advanced genetic toolboxes and techniques described, which have been successfully used in oleaginous yeasts in the recent years, promoting homologous recombination, genome editing, DNA assembly, and transformation at remarkable efficiencies. They can accelerate and effectively guide the rational designing of system-wide metabolic engineering approaches pinpointing the key targets for developing industrially suitable yeast strains.

Recent advances in lipid metabolic engineering of oleaginous yeasts

With the increasing demand to develop a renewable and sustainable biolipid feedstock, several species of non-conventional oleaginous yeasts are being explored. Apart from the platform oleaginous yeast Yarrowia lipolytica, the understanding of metabolic pathway and, therefore, exploiting the engineering prospects of most of the oleaginous species are still in infancy. However, in the past few years, enormous efforts have been invested in Rhodotorula, Rhodosporidium, Lipomyces, Trichosporon, and Candida genera of yeasts among others, with the rapid advancement of engineering strategies, significant improvement in genetic tools and techniques, generation of extensive bioinformatics and omics data. In this review, we have collated these recent progresses to make a detailed and insightful summary of the major developments in metabolic engineering of the prominent oleaginous yeast species. Such a comprehensive overview would be a useful resource for future strain improvement and metabolic engineering studies for enhanced production of lipid and lipid-derived chemicals in oleaginous yeasts.

Production of long-chain hydroxy fatty acids by Starmerella bombicola

To decrease our dependency for the diminishing source of fossils resources, bio-based alternatives are being explored for the synthesis of commodity and high-value molecules. One example in this ecological initiative is the microbial production of the biosurfactant sophorolipids by the yeast Starmerella bombicola. Sophorolipids are surface-active molecules mainly used as household and laundry detergents. Because S. bombicola is able to produce high titers of sophorolipids, the yeast is also used to increase the portfolio of lipophilic compounds through strain engineering. Here, the one-step microbial production of hydroxy fatty acids by S. bombicola was accomplished by the selective blockage of three catabolic pathways through metabolic engineering. Successful production of 17.39 g/l (ω-1) linked hydroxy fatty acids was obtained by the successive blockage of the sophorolipid biosynthesis, the β-oxidation and the ω-oxidation pathways. Minor contamination of dicarboxylic acids and fatty aldehydes were successfully removed using flash chromatography. This way, S. bombicola was further expanded into a flexible production platform of economical relevant compounds in the chemical, food and cosmetic industries.