Harnessing the Effect of pH on Lipid Production in Batch Cultures of Yarrowia lipolytica SKY7.

The objective of this research was to investigate the kinetics of lipid production by Yarrowia lipolytica SKY7 in the crude glycerol-supplemented media with and without the control of pH. Lipid and citric acid production were improved with the pH control condition. There was no significant difference observed in the biomass concentration with or without the pH control. In the pH-controlled experiments, the biomass and lipid concentration reached 18 and 7.78 g/L, (45.5% w/w), respectively, with lipid yield (Yp/s) of 0.179 g/g at 60 h of fermentation. The lipid production was directly correlated with growth and the process was defined as growth associated. After 60 h of fermentation, the lipid degradation was noticed in the pH-controlled reactor whereas it occurred after 84 h in the pH-uncontrolled reactor. Apart from lipid, citric acid was produced as the major extracellular product in both fermentations but the much lower concentration in uncontrolled pH. Based on the experimental results, it is evident that controlling the pH will enhance the lipid production by 15% compared to pH-uncontrolled fermentation.

A substrate-based approach for the selection of oil-bearing heterotrophs from nitrogen-deficient soil for lipid production.

In this study, nine heterotrophic yeast isolates were tested for their ability to assimilate crude glycerol and consecutive conversion to triacylglycerides (TGAs). All the organisms were initially screened on crude glycerol-based selection media, and those producing lipid globules were further evaluated for lipid production. Sudan Black B staining of eight isolates showed lipid globules. These strains were further studied at different C/N ratio. The molecular identification revealed that the isolates belonged to the genera of Yarrowia and Candida. Among these isolates, SKY7 (Yarrowia lipolytica) produced up to 42.04 ± 0.11 % of lipid w/w) with a C/N ratio of 100 and fermentation time of 72 h. The other strains produced 5.82 ± 0.4 to 34.57 ± 0.44 % lipid (w/w). The GC-flame ionization detector (FID) lipid profile showed that the lipid produced by the strains had close resemblance with vegetable oil and could serve as a feedstock for biodiesel production. Biolog test of the isolates revealed a wide spectrum of carbon utilization.