Abstract
Yarrowia lipolytica is an attractive host for sustainable bioprocesses due to its ability to utilize a variety of carbon substrates and convert them to a range of different product types (including lipids, organic acids and polyols) under specific conditions. Despite an increasing number of applications for this yeast, relatively few studies have focused on uptake and metabolism of carbon sources, and the metabolic basis for carbon flow to the different products. The focus of this work was quantification of the cellular performance of Y. lipolytica during growth on glycerol, glucose or a mixture of the two. Carbon substrate uptake rate, growth rate, oxygen utilisation (requirement and uptake rate) and polyol yields were estimated in batch cultivations at 1 litre scale. When glucose was used as the sole carbon and energy source, the growth rate was 0.24 h-1 and biomass and CO2 were the only products. Growth on glycerol proceeded at approximately 0.30 h-1, and the substrate uptake rate was 0.02 mol L-1 h-1 regardless of the starting glycerol concentration (10, 20 or 45 g L-1). Utilisation of glycerol was accompanied by higher oxygen uptake rates compared to glucose growth, indicating import of glycerol occurred initially via phosphorylation of glycerol into glycerol-3-phosphate. Based on these results it could be speculated that once oxygen limitation was reached, additional production of NADH created imbalance in the cofactor pools and the polyol formation observed could be a result of cofactor recycling to restore the balance in metabolism.
Highlights
With increasing focus on the development of sustainable technologies, the necessity for converting alternative, cheaper and waste carbon sources is emerging
The results obtained in this study demonstrate that the metabolism is dependent on the carbon source available, and use of glucose and glycerol infers entry into the metabolism at different points
Batch cultivations of Y. lipolytica have been performed in this study to quantify cellular performance during growth on different concentrations of glycerol and a combination of glucose and glycerol as carbon sources
Summary
With increasing focus on the development of sustainable technologies, the necessity for converting alternative, cheaper and waste carbon sources is emerging. The non-conventional yeast Yarrowia lipolytica has a high capability for growing on a range of carbon sources from glucose, fructose and xylose to glycerol and hydrophobic substrates (Coelho et al 2010, Fickers et al 2005; da Silva et al 2012) These substrates can be converted into value added products including citric acid (da Silva et al 2012, Papanikolaou et al 2002, Levinson et al 2007, Rymowicz et al 2010), sugar alcohols (Rymowicz et al 2009, Tomaszewska et al 2012) and single cell oils (Beopoulos et al 2009, Fontanille et al 2012), demonstrating the versatility of the organism to produce small organic compounds of industrial relevance. From a biotechnological point of view, it is interesting to understand these mechanisms and capabilities to further exploit them for industrial scale processes
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