Biochemical Genetics of Bacteria

The general topic of biochemical genetics of bacteria encompasses a wide variety and assortment of gene-enzyme interactions. In this review we focus on the biochemical genetics of metabolic pathways, particularly the biosynthesis and, in a few cases, the catabolism of nitrogenous metabolites. The systems considered are those in which the metabolic steps in the pathway are essentially complete and gene assignments for the reactions are known and well documented ( 1 , 2). These and other earlier developments that were involved in identifying the nature of the mutations, the modifications they created, and their consequences on biochemical activities are not considered in detail here. The necessary background information and details of the systems considered may be obtained from the comprehensive reviews cited in each case. Other general reviews have recently been published that cover special features of biochemical genetics of bacteria that are not dealt with in detail here. They include the biochemical genetics of carbohydrate metabolism (3), ribosomes (4), drug resistance (5), and suppression (6). In the past few years, a major impetus in extension of the already well-defined systems has been directed toward elucidation and evaluation of mechanisms of genetic control and regulation of gene expression. These developments and our own research interests have prompted us to focus this review on the present status of the genetic regulation of the metabolic pathways to be considered. We examine these in terms of organization and elements of genetic regulatory units, unusual and unique features that have been revealed, divergence from accepted models, and unification of concepts. Our considerations deal primarily with the enteric bacteria, Escherichia coli and Salmonella typhimurium, (hereafter referred to only as Sal­ monella) because both the biochemical and genetic information relevant to regula­ tion is more complete in these organisms than in others. The reader is also directed to a number of recent reviews on various aspects of genetic regulation (7-11).