ACQUISITION OF NEW METABOLIC-ACTIVITIES BY MICROBIAL-POPULATIONS

This chapter illustrates some examples of selection methods in both laboratory organisms and in organisms of industrial interest. Microorganisms have three major means by which they can acquire new activities. The first involves regulatory mutations; classical cases are those in which the novel substrate for growth is already a substrate for an existing catabolic pathway but is not an inducer for expression of that pathway. The second way of acquiring new activities is by mutations that alter properties of structural gene products, such as enzymes and transport proteins. The third mechanism is by mutations that activate cryptic or silent operons. These three mechanisms of acquiring new activities are not by any means mutually exclusive. The key elements for success in isolating mutants with novel capabilities, especially those capabilities that require multiple mutations are (1) large populations, (2) intense selection, and (3) prolonged periods of selection that may last up to several weeks. © 1993