Approach |
Features |
Example/Remarks |
Recombinant DNA Technology |
Genes from other organisms transferred into microorganisms |
New genes transferred; entirely new products, modified products, enhanced product yields, etc. |
| 1. Recombinant Proteins |
Proteins encoded by the transgenes are the products of interest |
Examples listed in Table 9.1 |
| 2. Metabolic engineering |
Metabolites catalyzed by the transgene encoded enzymes are the products of interest |
Existing metabolic pathways modified, extended, made more efficient or new pathways introduced |
| i. Product modification |
The new enzyme modifies the product of existing biosynthetic pathway |
Conversion of cephalosporin C into 7-aminocephalosporanic acid by D. amino acid oxidase (in A. chrysogenum) |
| ii. New substrate utilization |
Inaccessible substrate converted into accessible form |
Beer fermentation by yeast: cyclodextrins converted into glucose utilized by yeast |
| iii. Completely new metabolite |
All the genes of a new pathway transferred |
E. coli; transfer of two genes for polyhydroxybutyrate synthesis from Alcaligenes eutrophus |
| iv. Enhanced metabolite production |
Amplification of the gene encoding that enzyme whose activity is rate limiting |
Gene cefEF of C. acremonium catalysing conversion of penicillin N; increased cyclosporin yield |
| v. Enhanced growth |
Enhanced substrate utilization |
E. coli glutamate dehydrogenase gene into M. methylotrophus; carbon conversion increased from 4% to 7% |
