Yeast as a production platform in biorefineries: conversion of agricultural residues into value-added products

ArticleIn contrast to a petroleum - based economy, which relies on the unlimited presence of fossi l fuels, a biobased economy utilizes a broad spectrum of natural crops and biomass as raw substrates for the production of valuable materials. Biorefineries represent a promising approach for the co - production of bioenergy (biofuels, biogas) and value - adde d products (biochemicals, biomaterials, food). Within Europe, wheat straw represents the major crop residue and has been extensively considered as a promising feedstock in the biorefining process. Firstly, wheat straw is hydrolysed to obtain a sugar soluti on that is further converted into the desired product in a biocatalytic manner. Microbial fermentation is the core component of biorefineries and yeast, as for instance Candida guilliermondii , is an effective production platform for both, biofuels and bioc hemicals. One limiting aspect in using yeast in the biorefinery approach is the presence of inhibitors in lignocellulosic hydrolysates, such as acetic acid or furfural, influencing cellular growth and diverse metabolic processes. In order to overcome this problem, several genetic engineering approaches are used to increase yeast resistance towards these inhibitors and to enhance the overall production. In this paper, we summarized: 1) the pretreatment technologies for wheat straw bioconversion; 2) the Candi da guilliermondii genetic engineering technologies and their biotechnological potential. In conclusion, biorefineries are a crucial factor in the transition towards a biobased and circular economy, and the implementation of yeast into this system offers a great opportunity to develop innovative strategies for a sustainable production in an environmentally friendly and economically feasible manner

Wheat straw and lipids: UV-mutagenized Yarrowia lipolytica for the conversion of wheat straw hydrolysate into lipids

ArticleDue to the rising energy demand of our modern society and the finite amounts of petroleum-based fuels, renewable forms of energy have become extremely important. Bio-based fuels like bioethanol and biodiesel represent an already applied and accepted alternative. Biodiesel is currently mainly produced from plant oils. A new and promising alternative, which avoids the use of food crops, is the cultivation of the oleaginous yeast Yarrowia lipolytica, which possesses the capacity to accumulate up to 40% of its biomass in form of lipids. Moreover, this non-conventional yeast is able to metabolize a broad range of carbon-sources, presenting a sustainable alternative to reutilize a wide spectrum of waste substrates. This makes it an auspicious candidate for the generation of non-edible oils for biodiesel production. In this work, we aimed to generate a Y. lipolytica mutant strain with enhanced lipid production when grown on wheat straw hydrolysate as sole carbon source. Therefore, UV mutagenesis was applied and mutants with a high-lipid content were selected by their ability to grow in the presence of the fatty acid inhibitor cerulenin. Further, growth of the mutants on wheat straw hydrolysate was evaluated. The fatty acid composition was analysed by GC-FID and the calculated total lipid content revealed an up to 33% increase compared to the wild type strain. Fermentation optimisation and the combination of various waste substrates as carbon sources are expected to further increase the total lipid yield by the Y. lipolytica mutant strain and serve as initial point for its industrial scale evaluation