Elinor Meynell

Sex pili and the classification of sex factors in the enterobacteriaceae.

The properties of sex pili determined by different plasmids of the Enterobacteriaceae suggest that there may be only two major classes of sex factor, typified by F and the factor of colicin factor lb.

A phage, phi chi, which attacks motile bacteria.

SUMMARY: A salmonella phage which attacks only flagellated bacteria (Sertic & Boulgakov, 1936 b) has been studied. Tests with naturally occurring strains, and with artificial serotypes to which foreign H antigens had been transduced, have shown that sensitivity depends on the H antigen: bacteria with antigens of the g-complex are resistant, and with antigens l…, e, h, or Arizona 13, are sensitive only to appropriate host-range mutants. Tests with non-motile and motile variants of the same strains showed that paralysed (non-motile H) as well as non-flagellated bacteria are resistant and thus that the flagella must be active as well as of correct antigenic type. Where resistance was due to absence of suitable flagella, it was associated with impaired adsorption of phage. Removal of the flagella from a sensitive strain led to diminished adsorption; a similar result was obtained when the bacteria were artificially paralysed in various different ways. No adsorption to detached flagella was detected, probably because they were inactive. Adsorption of the phage led to immobilization and agglutination of the bacteria, probably by a direct effect on the flagella. Electron micrographs showed phage particles attached to flagella, and infection could evidently follow adsorption to distal parts of a flagellum. The genome of the infecting particle may perhaps reach the bacterial body by being injected into an active flagellum at the point of initial attachment, and then travelling inside the flagellum.

The Relationship of F type Piliation and F phage Sensitivity to Drug Resistance Transfer in R+F- Escherichia coli K 12

SUMMARY: Resistance factors (R factors), of the kind which confer sensitivity to F specific phage as well as promoting conjugation in enterobacteria determine the production of a pilus similar to the specific pilus seen on F- bacteria. R factors, however, unlike F, also determine the production of a repressor of function: this means that in an established R+ culture, only a small proportion of the bacteria can conjugate, be infected with F phage, or produce the pilus. Under conditions where repression is lifted, the three characters, conjugation, F phage sensitivity and production of the pilus, are coordinately de-repressed.

The Roles of Serum and Carbon Dioxide in Capsule Formation by Bacillus anthracis.

SUMMARY: Capsule formation by virulent strains of Bacillus anthracis on nutrient agar is known to depend on incubation in air with added CO2 as well as the addition of serum or bicarbonate to the medium. The minimum effective concentration of CO2 varies with the pH of the medium in a way which shows that capsulation depends on a threshold concentration of bicarbonate in the medium. Serum is more effective than bicarbonate and appears to act by binding an agent which inhibits capsule formation since it is replaceable by activated charcoal. The inhibitor might be a fatty acid since certain acids prevented capsule formation. Capsules are formed on nutrient agar containing added bicarbonate only after the culture has become very dense which suggests that the organisms either inactivate the inhibitor or become resistant to its action as their growth rate falls on approaching the stationary phase.

Specific piliation directed by a fertility factor and a resistance factor of Escherichia coli.

SUMMARY: Production of pili directed either by the sex factor F or by the drug-resistance factor R 100 in Escherichia coli K12 is regulated by a gene which acts by producing a represser, and the mutant R100–1 no longer produces this repressor. The specific pilus determined by R100–1 resembled the F pilus morphologically, but differed in its affinity for F-specific RNA phages. Mutants of F and R100-I which had lost the ability to synthesize pili could each restore to the other the ability to produce pili on mixed infection of the same host.

Cyclic AMP and the production of sex pili by E. coli K-12 carrying derepressed sex factors

THE filamentous appendages, known as sex pili, determined by F-like and I-like sex factors in enterobacteria, have an essential function in conjugation1. But neither the exact nature of their function, nor their mode of formation is yet known. The number of sex pili ordinarily seen in cultures of Escherichia coli K-12 carrying derepressed F-like or I-like sex factors2 (where pilus production is not limited by specific repression) seldom exceeds an average of 1–2 per bacterium. With I-like pili, however, the numbers can be increased 50-fold or more by exposing the bacteria to either antiserum reacting with the pili3, or vigorous washing4.

Serological characteristics of pili determined by the plasmids R711b and F0lac.

The plasmids R711b (at present IncX) and F0lac (IncFV) both determine pili morphologically like those of F (IncFI), and confer sensitivity to the F-specific filamentous bacteriophages, but not to the F-specific isometric RNA phages. Detailed serological studies show that the two pilus types are unrelated, and that neither is related to any of the previously defined F pilus serotypes. Adsorption of the isometric RNA phage MS2 to R711b pili occurs in the presence but not in the absence of formalin, which presumably prevents elution of reversibly adsorbed virions. No adsorption occurs with F0lac pili. MS2 multiplication, as measured by titre increase tests in liquid medium, is found with neither plasmid. The two plasmids are not incompatible. These observations indicate that R744b and F0lac are different both from one another and from the plasmids belonging to the incompatibility groups IncFI--IV.

The Significance of Bacteriophage in Bacterial Classification

SUMMARY: A given race of phage grows in a relatively limited range of bacteria. A coli phage, for instance, will not lyse a staphylococcus or a corynebacterium. Within these limits, however, some phages have a much wider host-range than others: some attack only one or a few bacterial strains; some a whole species; and some can lyse members of several species which on other grounds are considered to be not too distantly related. For instance, some pasteurella phages also attack strains of Salmonella and Shigella (Lazarus & Gunnison, 1947). The phage-sensitivity of a strain as a basis for bacterial classification can be interpreted in two ways, just as there are two levels at which bacterial classification can itself be regarded. That is to say, either as just another phenotypic character which the two strains may have in common; or at the level of the genetic material, the nucleic acid, so that, if two bacterial strains interact with the same phage at the genetic level, each of the strains is manifesting some degree of genetic compatibility with the phage, and thus with each other.

Reverting and Non-Reverting Rough Variants of Bacillus anthracis

Non-capsulated variants of Bacillus anthracis have been said not to revert to the capsulated state. However, in the present work, capsulated revertants were isolated from about half the non-capsulated strains tested either by exposure to phage Wα, which attacks only non-capsulated organisms, or by passage in mice.

Characters of a Group of Bacillus Phages

SUMMARY: The general characters are given of a group of phages related to phage β, a temperate phage carried by Bacillus cereus strain W (McCloy, 1951, 1953, 1958). One phage, β, has been isolated only once but may be a mutant of phage β since it, and its clear plaque variant,