Bacteria – The Last Stronghold of Lamarckism?

French naturalist J.B. Lamarck is most commonly known for popularizing the theory that some traits acquired during the life of an organism can be inherited in his 1809 book. German biologist A. Weismann presented evidence in his 1891 book that acquired traits were not heritable in sexually reproducing animals. But so little was known about bacteria that they were considered to be the last stronghold of Lamarckism. The “fluctuation test” of S. Luria and M. Delbrück in 1943 seemed to confirm that Lamarckism in bacteria was indeed dead. This review, however, proposes that today bacteria may be viewed as the source from which much of our present knowledge of epigenetics, evolutionary developmental biology (evo-devo), and the induction or inheritance of acquired characters has grown. French naturalist J.B. Lamarck (1744-1829) is best known for popularizing the ancient theory of the inheritance of adaptive acquired characteristics. He believed that unusual changes in an organism’s environment or activity can induce adaptive anatomical, physiological, or behavioral changes during the life of the individual that can then be transmitted to succeeding generations. Acquired traits are phenotypes that develop during the lifetime of an individual in response to unusual environmental influences, rather than being determined by the genetic constitution of the individual. All acquired characters are not necessarily adaptive, but only adaptive traits are likely to persist over many generations in a population of organisms. Charles Darwin (1809-1882) did not know how phenotypic variations arose, and since Lamarckism was the only germane scientific theory of heredity then available, he subscribed to it. By cutting off the tails of mice for several generations and breeding only from them, A. Weismann (1833-1914) reported in his 1891 book that the tail lengths of all the descendants grew to normal length (Weismann 1891). Many people assumed from these experiments that if characteristics acquired during the lifetime of individuals by such extreme measures had no heritable consequences, then the more subtle effects of natural environmental factors would also be ineffective in changing their hereditary endowment. Lamarckism thus fell into general disrespect as far as plants and animals are concerned. But not so with bacteria. Even after the rediscovery of Mendelism in 1900, early bacteriologists thought that microbes had “soft heredity” that could be easily modified by changes in their environment. The “norm of reaction” is the phenotypic variability produced by a given genotype under the range of environmental conditions common to the natural habitat of the species under standard culture or experimental conditions. Pleiomorphism or “phenotypic plasticity” is a phenomenon in which a given genotype may develop