We observed growth and TAG synthesi

We observed growth and TAG synthesis when Y. lipolytica was
cultured with dextrose, pure glycerol, biodiesel-derived ‘‘waste’’
glycerol, and canola oil from multiple sources. Comparable biomass
production, total lipid accumulation, and FA composition
were seen with all substrates. Y. lipolytica behaved similarly with
pure glycerol and biodiesel-derived REG80, with slightly better
results for the ‘‘waste’’ glycerol.
Rich media (YP) was used to simulate a carbon- and nitrogensufficient
growth medium. Robust growth was seen in YP grown
cultures, but lipid production was reduced. We surmise that the
yeast extract and peptone contributed to the biomass production,
as the cell growth was the highest in rich medium cultures and
ammonium concentrations increased throughout the growth
phase. YP-control medium cultures had a significant increase in
pH within the first 24 h. This demonstrates that the peptone and
yeast extract are hydrolyzing and incorporating the peptides, while
releasing ammonium into the culture media.
Our results with minimal medium cultures were consistent
with the current paradigm that neutral lipid storage is stimulated
by nutrient-limitation. While other minimal media were examined,
a modified media used by Zhou et al. (2011), was used to
examine nitrogen-limited conditions (data not published). This
media contains dilute salts, nitrogen, and small amounts of yeast
extract (which act as a source of micronutrients) that could be used
in large-scale yeast cultivation. The growth and biomass accumulation
in this media was less than achieved by Y. lipolytica cultured
in rich media, but lipid accumulation was tripled. While ammonium
concentrations did not reach zero, the quantities remaining
in minimal media cultures ranged from 0.2 to 0.4 mg L1
. An alternative
to minimal media would be treated wastewater, which has been demonstrated previously for yeast SCO production (Chi et al.,
2011; Hall et al., 2010)