Role of cryptic genes in microbial evolution

Cryptic genes are phenotypically silent DNA sequences, not normallyexpressed during the life cycle of an individual. They may, however, beactivated in a few individuals of a large population by mutation,recombination, insertion elements, or other genetic mechanisms. Aconsideration of the microbial literature concerning biochemical evolution,physiology, and taxonomy provides the basis for a hypothesis of microbialadaptation and evolution by mutational activation of cryptic genes.Evidence is presented, and a mathematical model is derived, indicating thatpowerful and biologically important mechanisms exist to prevent the loss ofcryptic genes. We propose that cryptic genes persist as a vital element ofthe genetic repertoire, ready for recall by mutational activation in futuregenerations. Cryptic genes provide a versatile endogenous genetic reservoirthat enhances the adaptive potential of a species by a mechanism that isindependent of genetic exchange.