Graduation date: 2006
Dissociation between catabolism and anabolism, generically termed
“metabolic uncoupling”, has been studied for aerobic cultures of Shewanella
oneidensis MR-1. Under conditions promoting metabolic uncoupling, the cell yield
diminishes while the substrate utilization rate remains largely unchanged. The
effects of excess substrate conditions and TCS addition on the metabolism of
pyruvate by S. oneidensis MR-1 were examined and modeled. In the first phase,
the observed cell yield (Yobs) was successfully modeled as a function of relative
substrate concentration (S0/X0), under excess substrate conditions. The degree of
uncoupling was determined by uncoupling coefficient (Eu). Cellular yield was
shown to decrease with increasing substrate concentrations. Preliminary
experiments illustrated the effectiveness of TCS in reducing the cell concentration.
In the later phase, an expression is proposed to model the effect of excess substrate
as well as TCS addition, simultaneously. This model was verified by using the
experimental data obtained by introduction of three different TCS doses to cells
grown under excess substrate conditions. The uncoupling coefficient was used to
distinguish between the uncoupling effects of TCS addition and excess substrate
conditions. In our experiments, it was observed that acetate accumulated as a
metabolic intermediate. Average protein content of the cells was also found to
increase with an increase in concentrations of either the substrate or the uncoupler.
These could be the possible pathways for consumption of substrate for non-growth
associated activities. Determining an optimum combination of substrate and
uncoupler concentrations could be very useful in controlling the biomass growth in
engineered microbial practices like wastewater treatment and bioremediation.