Altering nutrient uptake and metabolite flow
Recombinant DNA has also been used for increasing growth rate, decreasing nutrient demand and higher attainable cell densities in several microbes for a variety of applications. These include the following examples : (i) A glutamate dehydrogenase gene, when transferred from E. coli to Methylophilus methylotrophus, increased its efficiency of carbon conversion from 4% to 7% and eliminated the requirement for A TP (M. methylotrophus has been developed as an animal feed material). (ii) Transfer of pyruvate decarboxylase and alcohol dehydrogenase genes from Zymomonas mobilis to E. coli led to a shift from acetate production (which inhibits growth) to ethanol production (ethanol is 'less inhibitory, and is an important industrial chemical).

(iv) Transfer of yeast ornithine decarboxylase gene to Nicotiana rustica, doubled the nicotine content in roots; similarly the transfer of hyoscyamine 6  β-hydroxylase from Hyoscyamus niger to Atropa belladonna increased the scopolamine content three to ten times. In both cases, the recombinant strains had rearrangement or shift of metabolite flux towards higher yield of desired product. (v) Quantity of an active protein can also be increased by genetic manipulation of protein processing pathways. Transfer of cyanobacterial rubisco genes to E. coli and its coexpression with over expression of E. coli genes for chaperone proteins GroES and GroEL, led to ten fold increase in the assembly of rubisco. Similar assembly of rubisco of higher plants in altered E. coli may be possible in future.