Question

Suppose in an E.coli fermentation attempt,we use a continuous culture system with a feed of 25 g/(L*hr) glucose to produce a biofuel (C4H10O). We have determined that even though all the glucose is consumed, only 35% of the energy from glucose goes towards creating biomass. Assume the glucose is degraded aerobically through glycolysis and the TCA cycle. Also, assume each molecule of NADH gives 3 molecules of ATP, each molecule of FADH2 gives 2 molecules of ATP, the YX/ATP = 4.63 g biomass/mol ATP, and one molecule of GTP is equivalent to one molecule of ATP.

Calculate the amount of biomass produced from the culture .

Answer 1

We know that under the assumptions given in the question, 1 mol of Glucose produces 36 moles of ATPs through glycolysis and TCA cycle.

Now, given the feed rate of glucose = 25 g/L.h. We know mol wt of Glucose is 180g/mol.

Therefore, no. of mols of Glucose in feed of 25 g/L.h = 25/180 = 0.14 mols of Glucose/L.h.

So, mols of ATPs produced by 0.14 mols of Glucose through glycolysis and TCA cycle = 0.14*36 = 5 mols of ATP/L.h.

Since only 35% of energy from Glucose goes towards creating biomass, therefore, out of 5 mols of ATP that are created, only 35% of those will be used for biomass.

So, ATPs used for biomass = 0.35*5 = 1.75 mols of ATP/L.h.

Now, given yield of biomass with respect to ATP is Y_X/ATP = 4.63g/mol of ATP.

Therefore, biomass generated by 1.75 mols of ATP = 4.63*1.75 = 8.1 g of biomass.

Now we will write the answer in terms of rate of biomass produced i.e. 8.1 g/L.h

Thanks!