3. Results
3.1. Time-course of GSH fermentation
In order to investigate the GSH biosynthetic behavior
of S. cerevisiae WSH-J701, a time/course of cell growth
and total GSH concentration was monitored in a batch
culture (Fig. 1). GSH production was associated with
cell growth, the maximum total GSH concentration,
64.7 mg/l, was achieved after 32 h cultivation. Afterwards,
both the biomass concentration and total GSH
concentration decreased.
3.2. Effects of surfactants on the cell growth
The effect of adding different type of surfactants on
cell growth is shown in Fig. 2. Cell growth was almost
unaffected when the SDS concentration was lower than
0.05 g/l but was completely inhibited when the SDS
concentration reached 0.5 g/l. CTAB had a similar
impact on cell growth as SDS, little cell growth was
observed when CTAB concentration reached 0.025 g/l.
Growth inhibition caused by Brij30 was not as significant
is that by SDS and CTAB. Forty percent of full
growth was achieved when the Brij30 concentration
reached 0.5 g/l, and only slight further inhibition was
observed even if the Brij30 concentration was increased
by ten times to 5 g/l. For Tween80, cell growth was
almost unaffected until its concentration reached 4.0 g/l.
A critical inhibitory concentration for cell growth,
when cultivated in the medium containing ionic surfactant,
can be determined from Fig. 2. The critical
concentrations of SDS and CTAB were 0.5 and 0.025
g/l, respectively. The culture would be completely
inhibited or growth ceased if the concentration of ionic
surfactant, exceeded the critical concentration. However,
there was no inhibitory concentration for nonionic
surfactant, which means that the effect of different type
of surfactant on cell growth was quite different, therefore,
the effect on the permeability of cell might also be
different.