Patterns of Sexual Recombination in Enteric Bacteria1 P

TRAIN K-12 of Escherichia coli has played a preeminent role in the study of bacterial sexuality. New knowledge of the mechanism of sexual differentiation and the development of more sensitive techniques and test strains have subsequently brought many more bacteria within the orbit of this breeding system. The immunogenetics of Salmonella poses many interesting problems ( LEDERBERG and IINO 1956; IINO 1958, 1961a,b; LEDERBERG 1961) that could be only partly analyzed by methods of phage-mediated transduction. This paper presents a survey of crossing behavior in Salmonella and some other enteric bacteria which was conducted as a basis for the further study of flagellar phase variation in Salmonella. Sexual recombination in E. coli is dependent on a fertility factor F which confers the property of maleness on cells carrying an F particle either in the cytoplasm or fixed to the chromosome (LEDERBERG, CAVALLI and LEDERBERG 1952; JACOB and WOLLMAN 1961). The impact of F is expressed in at least two ways: the modification of the cell surface allowing for the conjugation reaction of an F+ with Facceptor cells, and the impulse to the chromosome to migrate from the male partner via the conjugal bridge to synapse and crossover with the corresponding chromosome of the female partner. Even in the F+ cell where the F particle is characteristically extrachromosomal, it probably forms at least a temporary association with the chromosome in those cells actually involved in conjugation. In general, the point on the chromosome at which the F particle is located tends to be the last segment to be transferred during an orderly progressive process of conjugal exchange, perhaps on account of a fixation of the F factor that binds the chromosome to a position on the cell surface whose modification is involved in the formation of the conjugal bridge. The F particle sometimes acquires a translocated fragment of chromosome, a few recognizable markers now sharing the contagious transmission of the F element (JACOB and ADELBERG 1959; HIROTA 1959). These compound F elements, designated F’ (F prime) have the advantage that their transmission can be more readily followed through the diagnosis of the translocated markers. They