Various Escherichia coli strains differ in the composition of their major outer membrane proteins. However, all E. coli K12 strains tested possess the same major outer membrane proteins a, b, c and d, although quantitative differences were detected. The influence of growth conditions on the composition of the major outer membrane proteins of E. coli was analyzed. It was found that neither the growth phase at which the cells are harvested, nor the fatty acid composition of the phospholipids has a considerable influence on the composition of these proteins. However, the composition of the growth medium, and, to a less extent, the growth temperature, have a pronounced influence. Certain mutants, changed in the composition of their lipopolysaccharide, are deficient in protein b. Also mutants deficient in protein c and d respectively, are described. Proteins b and c of E. coli K12 were found to be associated with peptidoglycan. Protein bands, corresponding with flagellin and pilin respectively, were identified.
About half of pneumococci recovered from pediatric patients and one-third of isolates from adult patients yielded bacteriophages active against one or more of four noncapsulated indicator strains of pneumococcus. Strains of capsular types most frequently causing pediatric infections were associated with lysogeny. Classical restriction-modification phenomena have been demonstrated in vivo with some of the temperate phages, and correlation of restriction with the presence of one or the other of the two known pneumococcal restriction endonucleases has been established. The temperate phages differ serologically and in several other characteristics from virulent pneumococcal phages previously described. All pneumococcal phages so far studied can be classified into a minimum of three serological groups.
In the preceding paper, the isolation and some characteristics of a pneumococcus manifesting binary capsulation were described (1). This organism, which was shown to produce two capsular polysaccharides, was derived by transformation of a non-capsulated mutant of pneumococcus Type III with deoxyribonucleates (DNA) of pneumococcus Type I. A noteworthy property of the SI-III cell is the production by it of approximately normal amounts of Type III polysaccharide in contrast to the markedly diminished or absent production of this substance by the cell from which it was derived. Two hypotheses to account for the restitution of the synthesis of Type III polysaccharide by the cell manifesting binary capsulation are readily apparent. Either that part of the genome controlling synthesis of Type III polysaccharide has been restoled to normal in the process of cellular transformation to the binary capsular state or the increased production of Type III polysaccharide results from the simultaneous presence within the cell of the mutated Type III capsular genome and the normal Type I capsular genome. Distinction between these two hypotheses may be made by a study of genetic properties of DNA from the SLIII cell. In experiments in which DNA from cells with a binary capsule was applied to noncapsulated organisms derived from a strain of pneumococcus Type II, cells of the mutant S-m phenotype, SI cells and, rarely, SI-III cells were recovered. No organisms of the SIII phenotype have ever been observed in an experiment of this kind.
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