The Origin of Bacterial Species

GENETIC HOMOLOGY BETWEEN ESCHERICHIA COLI K-12 AND SALMONELLA

“…Despite the obvious inhomologies, there is also ample evidence from this investigation and others (Zinder, 1960a;Smith and Stocker, 1962) that the general features of the Salmonella chromosome are the same as E. coli K-12. Thus, the early linkage data of Baron et al (1959a, b;1960) and Zinder (1960a), and the present recombinational analysis and interrupted mating data over a large part of the chromosome, point out an essentially identical gene order for the two organisms.…”

“…It should be interesting to examine the interrelationships observed from similar interspecific crosses. As has been pointed out previously (Luria and Burrous, 1957;Ravin, 1960), genetic examination of intermediate enteric organisms with Escherichia, Salmonella, and Shigella should yield important information as to the evolutionary phenomenon which have been and are occurring among the Enterobacteriaceae.…”

“…In both these instances, genetic homology has proved to be incomplete. It has been hypothesized (Ravin, 1960) that in the course of evolution the processes of mutation and perhaps recombination occurred in isolated, genotypically identical bacteria, which led to increasing divergence in the structure of their DNA. These differences of structure would be reflected in ineffective pairing during subsequent recombination.…”

Conditions for the Existence of Bacteriophage

“…Reproductive isolation and speciation in phages.-The idea that the consequences of reproductive isolation are the same among bacteria as among higher organisms has recently been discussed in detail (Ravin, 1960). The same considerations apply to phage.…”

Some Remarks on the Theoretical Aspects of Bacterial Taxonomy

“…Further, a meaning given to "species" in one biological discipline may not be used at all in another. For example, the bacteriologist does not usually refer to interbreeding or exchange of genetical material when describing the meaning of species as other biologists sometimes do, though recently an attempt has been made to introduce species in this sense in bacteriology as well (37). Yet again, some bacteriologists have considered a species to be a discrete segment of a phyletic line evolving independently of other segments (5, 28).…”