The first cultivation for mcl-PHA biosynthesis was carried out
using a 2 L setup with 1 L minimal medium containing the double
concentration for all ingredients as described in chapter 2.1. The
bioreactor was inoculated with the same volume of a dense culture
(cultivated for 24 h) of the production strain Ps. chlororaphis.
A concentration of 5 g/L saturated biodiesel as carbon source was
used, in accordance to the excellent growth at this concentration in
fluid cultures on shaking flask scale. The mean OD420 at the start of
the cultivation was 7.3. After an initial phase of 12 hours, sampling
was performed every 3 hours. The growth phase lasted for 27 hours
and achieved a mean OD420 of 148.5. Afterwards the process was
switched from growth to accumulation phase by a change of bases
for pH-value control. The sampling after 42 hours showed a reduction
of nitrogen and the PHA accumulation was continued until
49 hours, when a mean OD420 of 223.5 was reached (Fig. 1). At this
point, the optical density was already reduced, which is an indicator
of having exceeded the maximum mcl-PHA content possible
under given circumstances and the cells started the intracellular
degradation of the PHA. Therefore, the cultivation was ended by
pasteurization and followed by further downstream processing of
the cell suspension for polymer recovery.