Strategies: Models and Problems
This afternoon we shall continue to discuss methods of modifying DNA in microorganisms with the object of increasing their economic value to man. But before any engineering is begun, we might take note of microbial enzymatic reactions at present in operation. What general patterns have been established by the more subtle pressures of evolution? Time is not available for an adequate survey, and a few examples from one important area must suffice: these will be taken from the reactions employed by aerobic microorganisms to degrade aromatic compounds. As a unit of biochemical structure, the benzene nucleus takes second place only to glucosyl units, and there is more lignin to be found in nature than protein. However, man, rats and E. coli have very little ability to degrade aromatic compounds, although it may be noted that recent work has shown that some strains of E. coli exhibit greater expertise than was once believed. And since these species have received so much attention, many biochemists who turn their attention to soil isolates find that bacterial aromatic catabolism is complicated and confusing. It is, in fact, neither; because the never-ending degradation of the Earth’s aromatic natural products has been confined to eight or so separate and distinct metabolic channels leading into the Krebs cycle.