Gene Recombination in the Bacterium Escherichia coli.

The study of inheritance in bacteria has, for the most part, been confined to the investigation. of mutational changes in the course of clonal reproduction. With the exception of experiments on pneumococcus type transformations there have been few studies on the direct hereditary interaction of one bacterial type with another. The conception that bacteria have no sexual mode of reproduction is widely entertained. This paper will be devoted to the presentation of evidence for the occurrence in a bacterium of a process of gene recombination, from which the existence of a sexual stage may be inferred. On the basis of mutation studies many investigators have concluded that the hereditary properties of bacteria are based on the existence of genes (Luria and Delbruck, 1943; Roepke et al., 1944; Lwoff, 1941; Demerec and Fano, 1945; Gray and Tatum, 1944), although it is not clear whether these genes should be homologized with the Mendelian factors of higher organisms, or with the extranuclear factors which have been demonstrated in some microorganisms and higher plants (Sonneborn, 1943; Spiegelman et al., 1945; Rhoades, 1943). The genic basis of microbial inheritance does not depend on the demonstrability of a sexual phase in bacteria. However, more powerful genetic methods paralleling classical Mendelian analysis would be available if it were possible to follow the inheritance of characters in the products of a sexual fusion. The few examples of this approach thus far reported have provided no incontrovertible evidence for sexual reproduction in bacteria. The phenomenon of paragglutination in the colon-typhoid-dysentery group might be regarded as an instance of bacterial hybridization, and was so interpreted by Almquist (1924). As reported by numerous authors, paragglutination refers to the development of new types which react with antisera for each of two distinct strains when these are grown together in mixed culture (Kuhn and Ebeling, 1916; Salus, 1917; Wollman and Wollman, 1925). The significance of these observations has been attacked by several authors (Breinl, 1921; Arkwright, 1930; Kauffmann, 1941), chiefly on the grounds that the paragglutination represents a nonspecific cross reactivity characteristic of "rougher" phases of these organisms. Hansen (1929) failed to obtain paragglutination in her experiments. In the light of more detailed recent information on the antigenic structure of this group, this problem certainly deserves a critical reinvestigation.