As shown
in Fig. 4, the optimal C/N ratio was obtained at 60/1 using nitrogenlimiting
MR medium for maximal PHA production (4.03 g L−1
dry cell weight, PHB content 53.59 wt% and PHB concentration
2.27 g L−1). However, treatability studies to determine optimal C/P
rations showed that phosphorous limiting condition (i.e., C/P ratio
at 30/1) seemed not to be viable to maximize PHA production
(i.e., dry cell weight 1.71 g L−1, PHB content 8.26 wt% and PHB
concentration 0.41 g L−1; data not shown). These indicated that
nitrogen-limited MR medium in C/N ratio of 60/1 was optimal for
PHB production in second stage culture.