Properties and Characteristics of a Bacteriocin from Serratia marcescens

A strain of Serratia marcescens was found to produce a bacteriocin that inhibits the growth of certain Escherichia coli strains. This inhibition was bacteriocidal rather than bacteriostatic and was not caused by a bacteriophage. Whereas the bacteriocin was inactive on the 7 Serratia strains tested, it killed 11 of the 20 E. coli strains tested for sensitivity. A relationship of the bacteriocin to a possible colicin cannot as yet be excluded, although E. coli mutants resistant to 1 or 2 of 15 different colicins remained sensitive to the bacteriocin. The bacteriocidal effect by the bacteriocin could be interrupted in a substantial fraction of the treated cell population by the addition of trypsin. The synthesis of the bacteriocin was inducible by ultraviolet light or by starvation for thymidine. Both procedures led to a similar increase in maximum bacteriocin titer relative to noninduced cultures.     

Kinetics of Induction of the Lactose Operon on an Episome in Salmonella typhimurium

A kinetic study of induction of the enzymes of the lactose operon was carried out under conditions known to affect the kinetics of derepression of the enzymes of the histidine operon. The results show that the lactose system is similar to the histidine system in its responsiveness to conditions thought to affect the formylating capacity of the cell. This was demonstrated in the following ways: (i) trimethoprim, which is known to reduce the formylating capacity of the cell, gives rise to a relatively long interval between the times of induction of beta-galactosidase and transacetylase; (ii) under conditions in which the histidine operon is derepressed, chloramphenicol causes a prolongation of the interval between the times of induction of the two enzymes, and this prolongation is reversed by adenine, methionine, and serine, compounds known to enrich the one-carbon pool of the cell; and (iii) 4-amino-5-imidazolcarboxamide ribonucleoside, a compound which may act as a drain for formyl groups, reverses the effect of the latter compounds. The finding that the interval between the times of induction of the two enzymes is shortened under conditions expected to maintain a relatively high intracellular fo rmylating capacity suggests that under certain conditions translation of the polycistronic messenger ribonucleic acid of the lactose operon may be initiated at more than one site or may proceed more rapidly from the operator end.     

Cold-sensitive Mutations in Salmonella typhimurium Which Affect Ribosome Synthesis

A number of mutations (45) expressed as cold-sensitive conditional lethal pheno-types were screened by transduction for their linkage to the streptomycin-resistance locus; 7 showed such linkage. Of these, two were studied in greater detail. The sedimentation profiles of ribosomes from cultures grown at low temperature differed from wild type and from one another. Both mutants lost ribonucleic acid control at low temperature. It is suggested that a high proportion of mutants expressing a cold-sensitive phenotype harbor mutations in genes affecting ribosome synthesis or regulation.     

Toxin Production in Clostridium botulinum as Demonstrated by Electron Microscopy

Spheroplasts of Clostridium botulinum 62A were prepared with the use of lysozyme. These spheroplasts were then exposed to ferritin-labeled type A antitoxin. Ultrathin sections of these specimens revealed the ferritin-labeled antibody symmetrically arranged around the outer spore coats but not within the spore cortex. The ferritin-labeled antibody was also observed in the bacterial cytoplasm. Here it was arranged in aggregates and strands, although it was not associated with any identifiable cell structure. Controls included sections of C. botulinum spheroplasts treated with a 1.5% solution of ferritin as well as spheroplasts of C. roseum and Bacillus subtilis treated with conjugated type A antitoxin or a 1.5% solution of ferritin. No intracellular or extracellular ferritin was demonstrable in these specimens.     

Effect of Sublethal Heat on the Metabolic Activity of Staphylococcus aureus

Cells of Staphylococcus aureus MF-31 which have been heat-injured at 52 C have an altered metabolic activity. Analyses of whole-cell preparations by means of the Thunberg technique and Warburg manometry showed decreased dehydrogenase activity and oxygen uptake on a variety of substrates. In cell-free extracts prepared from injured cells, it was demonstrated that the specific activity of fructose diphosphate aldolase, lactate dehydrogenase, and butanediol dehydrogenase was less than that of extracts prepared from normal unheated cells. Recovery of the heat-injured cells in a suitable medium supported a return of the dehydrogenase activity and oxygen uptake, but the activity of the enzymes in cell-free extracts prepared from such partially recovered cells did not fully return to the level of normal (unheated) preparations. Addition of chloramphenicol or actinomycin D to the recovery medium, singly or in combination, retarded the return of the normal metabolic activity. Radiorespirometric experiments indicated that the percentage participation of the Embden-Meyerhoff Parnas and hexose monophosphate pathways remained the same for normal and heat-injured cells. The sublethal heat treatment decreased the catabolic capabilities of S. aureus and the production of selected end products associated with the metabolism of glucose.     

Identification and genetic control of starch-degrading enzymes in maize endosperm

Three starch-degrading enzymes from liquid endosperm of maize have been separated by means of horizontal acrylamide gel electrophoresis. The three enzymes are tentatively identified as -amylase (zone 1), -amylase (zone 2), and -glucan phosphorylase (zone 3). Electrophoretic variants of these enzymes were found among ten inbred strains examined. Results of genetic crosses with respect to zone 2 amylase show that it is controlled by a pair of alleles (Amy-2 ^A and Amy-2 ^B) acting without dominance. It further appears that Amy-2 and Ct (catalase) are linked with 5% recombination frequency.This work was supported by the U.S. Atomic Energy Commission, under contract No. AT(11-1)-1338.     

Linkage analyses using biochemical variants in mice. II. Levulinate dehydratase and autosomal glucose 6-phosphate dehydrogenase

The level of hepatic -aminolevulinate dehydratase varies among inbred strains of mice and is regulated by codominant alleles at the Lv locus. Twenty-two inbred strains have been classified with respect to this locus. Lv is 5±2 recombination units from brown, b, in linkage group VIII. The locus for autosomal glucose 6-phosphate dehydrogenase (Gpd-1) has also been assigned to linkage group VIII and is 32±5 units from brown. The order of the loci is Lv-b-Gpd-1. Incidental note is made of linkage between the malic dehydrogenase (Mdh-1) and dilute (d) loci, linkage group II, with 10±3 % recombination between the two.Supported by the Roche Institute of Molecular Biology, Nutley, New Jersey, and by Public Health Service Research Grant CA-05873 from the National Cancer Institute.     

Postembryonic brain development in the monarch butterfly,Danaus plexippus plexippus L.

Development Genes and Evolution -