Spontaneous mutations in bacteria: chance or necessity?

Abstract

Several investigators have recently reported that significant numbers of appropriately adapted mutants can be induced in bacterial and yeast strains by exposing stationary phase cells to specific environmental challenges. The resulting mutants are said to be both selection-induced and demonstrably non-random in origin; if this interpretation is correct, it is in direct conflict with the conventional neo-Darwinian view, which is that spontaneous mutants are truly random in origin and arise without the intervention of any overtly adaptive forces. We believe that there are alternative ways of accounting for the appearance of many (and probably all) of the additional mutants which proponents of the adaptive mutation theory claim are observed only after they applied the appropriate selective pressure. Having reviewed the available evidence, we consider that most (if not all) of the sorts of mutants which are said to have been induced following exposure of stationary-phase cells to intense selective pressure are equally likely to have been generated during the operation of certain well-known, conventional (and essentially random) cellular DNA repair processes. Evidence in support of our view can be found in the mainstream literature on the origins of spontaneous mutations. We also note that some of the molecular models which have recently been proposed to explain the production of selection-induced mutations preferentially (or even only) in genes of adaptive significance may turn out to be of considerable interest in their own right, even although the mutants whose origins they were intended to explain may turn out to have arisen in a manner which is totally independent of the conditions used for their selection.

Effect of Drug Concentration on Emergence of Macrolide Resistance in Mycobacterium avium

“…However, this is misleading since the most important step in the generation of the progenitors (i.e., acquisition of the uncommitted state) happens in the absence of CLR, and thus, CLR does not truly direct the evolution of the resistant variants. In addition, evidence presented by others has largely discounted the directed mutation hypothesis (5,9,16,21). Previous reports proposed that hypermutable variants or mutators aid bacterial evolution (17,20).…”

A general account of selection: Biology, immunology, and behavior

“…Other workers can and do use it in a variety of other senses. Our discussion, however, concerns Lamarckian inheritance as a biological phenomenon (for a sampling of the recent literature on Lamarckian forms of inheritance, see Andersson et al 1998;Benson 1997;Jablonka & Lamb 1995;Lenski & Mittler 1993;MacPhee & Ambrose 1996;Peck & Eyre-Walker 1998;Rosenberg et al 1995).…”