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An attempt to classify fourteen strains of Clostridium sporogenes and thirty strains of Clostridium botulinum types A, B, C, D, E, and F by numerical taxonomy was made. All proteolytic strains of C. botulinum types A, B, and F and C. sporogenes were classified in the phenon I at a level of 86% S‐value. In the phenon I, these strains coexisted in a mixed‐up fashion, irrespective of conventional species or type of bacteria. A concentrated lysin solution, which was prepared from an induced lysate of a C. botulinum A190 culture, lysed vegetative cells of all proteolytic C. botulinum and C. sporogenes strains classified in the phenon I, but did not lyse the cells of the other Clostridia. However, cells of nonproteolytic C. botulinum F‐OSU and four out of five strains of Clostridium tetani were lysed by the concentrated lysin to a limited extent. The phenon II contained all nonproteolytic strains of C. botulinum B, C, D, E, and F, which were mutually linked with S values of more than 85%. Strains of Clostridium histolyticum used as a reference group formed the phenon III. Any strain grouped in one phenon was differentiated from strains grouped in the other phenons by low S‐values, that were less than 77%. A striking difference in the number of strains susceptible to mitomycin C was demonstrated between C. botulinum and C. sporogenes. In all thirty‐five cultures, except four substrains of C. botulinum B‐NIH, of proteolytic and nonproteolytic C. botulinum, bacterial lysis was consistently induced by the treatment of 1 μg per ml of mitomycin C, while only four out of thirty‐seven C. sporogenes strains were as sensitive to mitomycin C as C. botulinum. Toxigenic substrains of C. botulinum B‐NIH, NIH15 and NIH19, were sensitive to mitomycin C, but nontoxigenic strains, NIH5, and NIH‐NP, were not.

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A 7.6-kb fragment of Salmonella typhimurium LT2 containing the liv gene cluster, which specifies the high-affinity branched-chain amino acid transport system (LIV-I), has been isolated. The upstream region contains the livB and livC genes encoding the leucine-isoleucine-valine-threonine and leucine-specific binding proteins, respectively. In this study, the nucleotide sequence of the 4-kb downstream segment was determined and found to contain four reading frames, designated as livA, livE, livF, and livG, that encode putative membrane-associated proteins. The livA and livE genes encode hydrophobic proteins composed of 308 and 425 amino acid residues, respectively. The livF and livG genes encode hydrophilic proteins of 255 and 237 amino acids, respectively; both the proteins contain consensus amino acid sequences found in proteins with ATP-binding sites. These four genes linked together have a potential rho-independent transcriptional terminator adjacent to the 3'-end of livG. No promoter sequence was found in the immediate upstream region of the livAEFG cluster. The livA, livE, livF, and livG gene products were identified as proteins with apparent M(r)s of 25,500, 34,500, 28,000, and 26,000, respectively, by SDS-polyacryl-amide gel electrophoresis. The deduced amino acid sequences of these four proteins showed strong homology to those of the corresponding membrane-associated proteins required for the high-affinity branched-chain amino acid transport systems from both Escherichia coli and Pseudomonas aeruginosa.

SUMMARY:The mutation rate from histidine auxotrophy to prototrophy in Escherichia coli was measured during growth and in the stationary phase at different temperatures. During growth the rate of mutation/mutable unit/hr. had the same temperature coefficient as the rate of growth. Therefore the rate of mutation/ mutable unit/generation was the same at all temperatures. The temperature coefficient of the rate of mutation/unit/hr. during the stationary phase may be the same as that during growth, indicating that although mutation is slower in this phase it may involve the same process as during growth.In Serratia marcescens the percentage of colour mutants in colonies of different size but of the same age has been shown to be equal (Kaplan, 1947 Lee, 1953;Fox, 1955;Moser, 1958). The rate of mutation in both of these cases was further shown to have a Qlo of c. 2. Because Novick & Szilard used the chemostat which allowed the maintenance of identical growth rates at different temperatures, they were able to separate experimentally the effect of temperature on mutation from its effect on growth, a condition not met in previous studies on temperature and mutation. Unfortunately the chemostat device employed, which provides the desirable conditions of continuous logarithmic growth in a virtually constant environment, can be used simply for the measurement of few mutations, so far as is known; many mutants do not increase in the linear way predicted by theory, perhaps because of selection (Novick & Szilard, 1950;de Rothschild, 1954;Moser, 1958). Consequently, the generality of Novick & Szilard's conclusions on the properties of mutations in bacteria may be questioned.Stocker (1949) found that the rate of mutation of factors influencing flagellar antigens and the growth of Salmonella typhimurium itself were influenced in the same way by temperature and nutritional conditions. Witkin (1953), using a completely different technique and resistance to bacteriophage T, in Escherichia coli showed that the temperature coefficients of spontaneous mutation/unit time and of cell division were identical; the Qlo again was c. 2. Thus, the natural mutation rate/generation was constant over