This was probably due to the substrate
inhibition. Similar observations were made
by other scientists. Belfaos et al., (1995) and
Shaaban et al., (2012) reported that glucose
and ammonium ions were inhibitory at
certain levels, which affect the specific
growth rate and PHB production. Inhibition
by ammonium ions Heinzle and Lafferty,
(1980) and substrate inhibition by carbon
source Lee and Yoo, (1991) on PHB
production have been reported.