3.4. Effect of higher concentration of ionic surfactants on
extracellular GSH accumulators
Extracellular accumulation of GSH was improved by
the addition of low concentrations of SDS and CTAB
prior to fermentation (Fig. 3). However, the total GSH
concentration was not enhanced due to the decreased
biomass and intracellular GSH content, which indicated
that it was not a good approach to add surfactant to the
medium prior to fermentation, even if the concentration
was very low.
The effect of the addition of growth-inhibitory concentrations
of SDS and CTAB after the exponential
growth phase on GSH production was examined, as
illustrated in Fig. 4. It was clear that the extracellular
accumulation of GSH increased dramatically on addition
of growth-inhibitory concentration of ionic surfactants.
Compared with the control, extracellular
accumulation of GSH was improved by more than
35% by SDS and more than 60% by CTAB. In addition,
the later the surfactants were added, the higher the
extracellular GSH concentration reached. Correspondingly,
the intracellular GSH content decreased sharply
to a very low level, which was less than 0.2 and 0.1% by
the addition of SDS and CTAB, respectively. Finally, it
was found that, although the extracellular GSH accumulation
improved significantly, the total GSH concentrations
in all cases of surfactants added, remained
lower than that of the control. Between 12 and 28% of
total GSH decreased by the addition of several concentrations
of SDS, and 16/36% by CTAB.