Yarrowia No Es Mio

Yarrowia lipolytica






Background


Yarrowia lipolytica is an oleaginous yeast strain routinely isolated from different food media or from natural environments like oil fields or lipid containing effluent plants. The yeast grows primarily in a haploid state and cells can differentiate into yeast pseudomycelium and true mycelial forms depending on growth conditions. Yarrowialipolytica, when cultivated on mixtures of free fatty acid substrates was found to remove C12:0, C14:0, (Delta9) C18:1, (Delta9,12)C18:2 and (Delta9,12,15)C18:3 at significantly higher rates than C16:0 and C18:0, regardless of fatty acid composition of the initial substrate (Papanikolaou and Aggelis 2003a). The maximum concentration of lipid accumulated inside the wild type yeast cell, as well as themaximum specific accumulation rate of cellular lipids, was favored in high stearic acid content media (Papanikolaou and Aggelis 2003b). Single-cell oil having a composition similar to cocoa-butter up to 3.4 g/L can be produced in wild type strains (Papanikolaou et al 2003). Studies on lipid accumulation during primary anabolic growth indicated that this was influenced by the medium pH and theincubation temperature, was independent of the nitrogen concentration in the culture medium, but was favoured at a high carbon substrate level and at a low aeration rate. At pH 6 and a temperature of 28-33 0C, 9-12 g/l of dry biomass was produced, whereas significant quantities of lipids were accumulated inside the yeast cells (0.44-0.54 g of lipid per gram of biomass) (Papanikolaou et al 2002). Analysisof Yarrowia showed that it had the
tendency to degrade its storage lipids, although significant amounts of substrate fat, rich in stearic acid, remained unconsumed in the culture medium (Papanikolaou et al 2002) hence even the wild type strain can accumulate lipid in significant amounts.





















Fat accumulation


The yeast stores its fat in fat particles,which appear to bud from the yeast endoplasmic reticulum. When grown with fatty substrates, oleic acid was the major fatty acid species esterified into lipid particles. When cells were grown on oleic acid, these lipid particles were shown to increase in size some 3-8-fold (Athenstaedt et al 2006). Analysis of proteins associated with such lipid particles has revealed an increasing number ofpolypeptides when cells were shifted from glucose- to oleic acid-containing medium, some twenty-one major proteins were identified under both growth conditions, and additional nine polypeptides were specific for growth on oleic acid (Athenstaedt et al 2006). Identification of these proteins by MS and comparison of the deduced ORFs to those from Saccharomyces cerevisiae revealed that most of these proteinsof Y. lipolytica are involved in lipid metabolism with many proposed to be involved in storage and mobilisation of these lipid particles (Athenstaedt et al 2006). The sequencing and analysis of the Yarrowia lipolytica genome has revealed much about the process of lipid storage and metabolism in Yarrowia (Casaregola et al 2003). This includes the interaction of hydrophobic substrates with the yeastcells, their uptake and transport, the primary alkane oxidation to the corresponding fatty alcohols and then by different enzymes to fatty acids, and the subsequent degradation via oxidation or storage into lipid bodies (Fickers et al 2005). Several enzymes involved in hydrophobic substrate utilisation belong to multigene families, such as lipases/esterases (LIP genes), cytochromes P450 (ALKgenes) and peroxisomal acyl-CoA oxidases (POX genes) (Fickers et al 2005). For the accumulation of lipid tryptone N1 and oleic acid have been shown to be the most suitable nitrogen and carbon sources for the production of the extracellular lipase by Y. lipolytica (Fickers et al 2003). The lip2 gene was previously reported to encode all extracellular lipase, however the demonstration that growth of a...