Fed-Batch Bioproduction of Spectinomycin
23
pressure head of 20 psig through a linear trim Badger control valve. The valve
actuator required air to open and its maximum flow rate at 20 psig was
12 1 min - ~
The maximum air flow rate attained during exponential phase was different
for the various glucose feed concentrations used. A maximum air flow rate of
11.5 1 min- ~ was required when the glucose feed concentration was 175 g l-~.
This is similar to the maximum air flow rate of 11 1 min- 1 for the glucose feed
concentration of 125 g 1-1. These two glucose feed concentrations are equidistant from the optimum value of 150 g 1 - ~. In fact, even the nature of the air flow
rate profiles are similar. Notice that the final and intermediate values of
spectinomycin concentrations are also in the same range. Clearly, the route for
the biosynthesis of spectinomycin followed by the microorganism is the same in
these two cases. Consequently, the energy requirements and hence the oxygen
demand are comparable. In the case of glucose feed concentrations of 100 g 1 - ~
and 200 g 1- ~ the maximum air flow rates are 8 1 min - 1 and 10.5 1 min - 1,
respectively. Here also the energy requirements and hence the oxygen demand
are comparable.
The lowest value for the maximum air flow rate of 5 1 min - ~ was obtained
for the glucose feed concentration of 400 g l- ~ followed by 5.5 lmin-1 for the
glucose feed concentration of 150 g l -~. The glucose feed concentration of
150 g 1 - 1 corresponds to the highest final spectinomycin concentration of 690
units. Also, the time-weighted average glucose uptake rate of 4.45 g h -~ is
intermediate, while its time-weighted average residual glucose concentration of
1.67gl -~ is the highest. These values indicate that the oxygen and carbon
utilization during both the growth phase and the production phase is more
balanced. Hence, the high spectinomycin yield is also energetically favored.
However, the lowest spectinomycin yield was obtained for the 400 g 1 - 1 feed
concentration. In this case, the other variables such as intermediate spectinomycin saturation and the residual glucose concentration also do not follow the
trends observed in the other feed concentration data. A more detailed study is
necessary before this phenomenon can be explained.
5 Two Metabolite Hypothesis
There are two routes for the synthesis of spectinomycin starting from glucose6-phosphate as shown in Fig. 1. Along the first route 1,3-myo-inosadiamine and
actinospectose combine to give desmethyl spectinomycin which on methylation
gives spectinomycin. Whereas the second route involves the methylation of
1,3-myo-inosadiamine first to actinamine. Actinamine then combines with actinospectose to produce spectinomycin. Depending on the amount of glucose
and oxygen present, production via one of these routes predominates. At low
glucose feed concentrations the carbon resource is not sufficient to sustain high
23
pressure head of 20 psig through a linear trim Badger control valve. The valve
actuator required air to open and its maximum flow rate at 20 psig was
12 1 min - ~
The maximum air flow rate attained during exponential phase was different
for the various glucose feed concentrations used. A maximum air flow rate of
11.5 1 min- ~ was required when the glucose feed concentration was 175 g l-~.
This is similar to the maximum air flow rate of 11 1 min- 1 for the glucose feed
concentration of 125 g 1-1. These two glucose feed concentrations are equidistant from the optimum value of 150 g 1 - ~. In fact, even the nature of the air flow
rate profiles are similar. Notice that the final and intermediate values of
spectinomycin concentrations are also in the same range. Clearly, the route for
the biosynthesis of spectinomycin followed by the microorganism is the same in
these two cases. Consequently, the energy requirements and hence the oxygen
demand are comparable. In the case of glucose feed concentrations of 100 g 1 - ~
and 200 g 1- ~ the maximum air flow rates are 8 1 min - 1 and 10.5 1 min - 1,
respectively. Here also the energy requirements and hence the oxygen demand
are comparable.
The lowest value for the maximum air flow rate of 5 1 min - ~ was obtained
for the glucose feed concentration of 400 g l- ~ followed by 5.5 lmin-1 for the
glucose feed concentration of 150 g l -~. The glucose feed concentration of
150 g 1 - 1 corresponds to the highest final spectinomycin concentration of 690
units. Also, the time-weighted average glucose uptake rate of 4.45 g h -~ is
intermediate, while its time-weighted average residual glucose concentration of
1.67gl -~ is the highest. These values indicate that the oxygen and carbon
utilization during both the growth phase and the production phase is more
balanced. Hence, the high spectinomycin yield is also energetically favored.
However, the lowest spectinomycin yield was obtained for the 400 g 1 - 1 feed
concentration. In this case, the other variables such as intermediate spectinomycin saturation and the residual glucose concentration also do not follow the
trends observed in the other feed concentration data. A more detailed study is
necessary before this phenomenon can be explained.
5 Two Metabolite Hypothesis
There are two routes for the synthesis of spectinomycin starting from glucose6-phosphate as shown in Fig. 1. Along the first route 1,3-myo-inosadiamine and
actinospectose combine to give desmethyl spectinomycin which on methylation
gives spectinomycin. Whereas the second route involves the methylation of
1,3-myo-inosadiamine first to actinamine. Actinamine then combines with actinospectose to produce spectinomycin. Depending on the amount of glucose
and oxygen present, production via one of these routes predominates. At low
glucose feed concentrations the carbon resource is not sufficient to sustain high