The lipid supernatant in cytosolic extracts from yeast cells

The oxygen consumption of the branched mitochondrial respiratory chain from D. hansenii was analysed in whole cells cultured in different carbon sources.  In agreement with the results obtained by Veiga A. et al. in 2002, we found CRR induced during the stationary growth phase. Ubiquinone feeds cyanide-resistant-AOX directly with electrons skipping proton-pumping activities of canonical complexes (Guerrero-Castillo et al., 2011) that had been suggested as an adaptation mechanism to the variable energy demands. Alternative-oxidoreductases expression in the stationary phase, a nondividing resting state, reduces ATP production independently of high oxygen consumption (low ATP/O ratio) (Veiga A., et al., 2003). In addition to the growth phase, changes in carbon source supplies modify AOX activity. Non-fermentative substrates like lactate or succinate may saturate cytochrome route, and an active CRR would provide an alternative route to electron flux. However, in glycerol-containing media, also a non-fermentative carbon source, AOX activity was poorly detected during the whole growth curve. Besides, biomass yield in glycerol-grown cells was higher than in other three carbon sources, except glucose, and could be related to biosynthetic pathways, and lipid storage carried out by oleaginous yeast species (Adler L. et al., 1985). Probably D. hansenii did not express AOX to keep the Oxidative Phosphorylation highly coupled to support ATP needs for glycerol-promoted lipid biosynthesis (Luévano-Martínez LA. et al., 2010) an idea supported by the observation of lipid supernatant in cytosolic extracts from yeast cells grown in YP Glycerol 0.6M NaCl, Fig 4. This result is of interest since crude glycerol, a byproduct of biodiesel production, could be used by D. hansenii as feedstock for reincorporating this derivate to the production chain or for generation of value-added chemicals (Sestric R. et al., 2014).