Y. lipolytica cells were grown in modified glycerol medium. Several
minimal media were examined before experimentation, and
the minimal medium reported by Zhou et al. (2011) was chosen
because it had the least components and resulted in the highest
lipid accumulation in our experimental conditions (data not
shown). The total biomass accumulated and supernatant pHs were
lower than rich media (as expected), as the total nitrogen availablewas significantly reduced (Fig. 1e). The total lipid accumulation
was approximately 31% dcw after 48 h, which was nearly triple
that of rich media (Tables 1 and 2). Glycerol was consumed at a
lower rate (55 mM per day) in the minimal medium compared
with YP with glycerol (rich medium) grown cells (88 mM per
day) (Fig. 2d). The ammonium concentration profiles of the two
cultures were very different. Ammonium was consumed and concentrations
decreased within 24 h in the minimal medium cultures.
In YP with Glycerol cultures, however, ammonium was
generated and concentrations increased as the substrate glycerol
became limiting, and the yeast extract and peptone component
of the medium were consumed.
Our biomass production and lipid accumulation data are consistent
with those reported by other researchers. In batch cultures
with similar minimal media supplemented by 27.5 g L1 glycerol,
Rywinska and Rymowicz (2010) observed 4.68 g L1 biomass production
with lipid accumulation of 22.3% with the Y. lipolytica
Wratislavia AWG7 and Wratislavia 1.31 mutants. In continuous cultures of Y. lipolytica strains ACA-DC 50109 and LGAM S(7)1, with
50 g L1 glycerol (pure and biodiesel-derived ‘waste’ glycerol), lipid
accumulation was 43–44% dcw (Papanikolaou and Aggelis, 2002,
2009). The total biomass accumulated was higher (8.1 g L1
), but
five times of the quantity of ammonium sulfate was added
(Papanikolaou and Aggelis, 2009).