- Volume 71, Issue 2, 1972

Several yeast water preparations and commercial yeast extracts varied in their toxicity to two strains of Rhizobium trifolii. Strains of R. japonicum and R. leguminosarum were also susceptible to yeast extract, while strains of R. meliloti were resistant.

An interaction between glycine and monovalent cations was the main cause of yeast extract toxicity. Divalent cations, notably Ca2+, added to inhibitory media prevented the toxicity and enhanced growth with increased concentrations of yeast extract.

Summary: Strains of Pseudomonas aeruginosa, P. putida, P. acidovorans and P. cepacia were tested for growth on minimal salt media containing aliphatic amides. All strains of P. aeruginosa, P. acidovorans, P. cepacia and some strains of P. putida biotype A grew on acetamide; some strains of P. putida and P. acidovorans also grew on butyramide. The inducible aliphatic amidases had both hydrolase and transferase activities and were similar in substrate specificities. All species hydrolysed propionamide more rapidly than acetamide while acetamide was the best substrate for the transferase reaction. The rate of butyramide hydrolysis was 2 to 3% of the rate of acetamide hydrolysis for all species including those strains able to grow on butyramide. The amidases of P. putida a87 and P. acidovorans 14 were inducible by butyramide. Cell-free extracts of P. aeruginosa strains induced with acetamide cross-reacted completely with antiserum prepared against purified P. aeruginosa amidase A. Partial cross-reactions occurred with P. putida and P. acidovorans amidases and a very weak cross-reaction with P. cepacia amidase.

Summary: Glycine homopeptides are concentrated by Escherichia coli and are completely hydrolysed by intracellular peptidases. Glycine peptides in which a peptide-bond nitrogen is methylated, i.e. glycylsarcosine and glycylglycylsarcosine, still use the peptide transport systems, but the substituted peptide bonds are not hydrolysed. Glycylsarcosine is thus nutritionally inactive, but it competes with other dipeptides for uptake. Only the N-terminal residue of glycylglycylsarcosine is utilized by a glycine auxotroph. The results reflect the different specificities of the peptide transport systems and the intracellular peptidases of E. coli.

Summary: The supernatant extracts from disrupted Escherichia coli had only low hydrolytic activity towards diglycine, divaline and prolylglycine, but latent peptidases were activated by Co2+ or Mn2+. The cations K+, Mg2+, Zn2+, Fe2+, Ni2+, Cu2+ Ca2+ and Cd2+ caused no increase in peptidase activity while Cd2+, Zn2+ and Cu2+ antagonized the effects of Co2+ and Mn2+. Measurements of optimum cation concentration, of pH optimum and of effects of various buffers led to the conclusion that the main peptidase activity towards these three peptides, and towards a broad spectrum of other dipeptides, resided in a single Co2+ activated enzyme. The activity of this peptidase was enhanced by phosphate and inhibited by veronal. Similar measurements with Mn2+ suggested the presence of several enzymes with lower activities and narrower substrate specificity than the Co2+ activated peptidase. Procedures were devised for the assay, under optimum conditions, of the main peptidase activities of a crude extract.

Summary: The activities of soluble, intracellular Co2+ and Mn 2+ activated dipeptidases of Escherichia coli varied with the growth conditions. With chemostat cultures, potassium-limitation and oxygen depletion produced high peptidase activities whereas activities were low in carbon-limited cultures; the activity of carbon-limited organisms approximated to that of exponential-phase batch-grown organisms. The effect of growth conditions on the specific activity of soluble tripeptidase, which did not require cations for activity, was different from that found for the dipeptidases; the highest activity was again found in potassium-limited organisms but lowest activity occurred with nitrogen and magnesium limitation. The activities of all these peptidases were independent of the pH of growth, within the range pH 7·0 to 5·5. These results are discussed in relation to the utilization of peptides by growing organisms and to measurements of the turnover of protein during growth.

Summary: Three host-controlled modification and restriction systems occurring among coagulase-negative staphylococci belonging to the Staphylococcus subgroup II are described. The phage patterns, observed by typing the staphylococci with a provisional typing set of eighteen phages, are mainly determined by these host specificity systems. A strain, which was not restrictive to the phages, did not become restrictive after lysogenization with any of the eighteen phages.

Infection of a restricting host with 3H-labelled phages was followed by a rapid breakdown of phage DNA, as demonstrated by the appearance of radioactive label in the cold-acid-soluble DNA fraction of extracted adsorption mixtures.

Extracellular protease of Aspergillus nidulans is repressible by ammonium. A mutant (xprDI) selected for derepression of protease in the presence of ammonium is also derepressed for nitrate reductase, xanthine dehydrogenase and glutamate uptake; it retains the ability to use ammonium as sole nitrogen source. The mutant is partially dominant in heterozygous diploids. The mutation does not confer methylamine resistance, nor are methylamine-resistant(meaA) strains derepressed for protease.

Summary: We have discovered different host specificities in the z 20 and cf2004-6 strains of a particular Escherichia coli O4 serotype. The host specificities are controlled by a chromosomal locus linked to threonine. They are differentiated on the basis of results from plating efficiencies of phage ⊘,04, conjugation, and generalized transduction. The host specificities of E. coli strains k12 and cf2004-6 seem to be similar and distinct from that of z20.

Summary: DNA synthesis in recA and recA exrA strains of Escherichia coli is strongly inhibited without delay by low doses of gamma-radiation. The synthesis that does occur in these strains appears to take place mainly on chromosomes that have not received a lethal hit. Low doses produce much less inhibition of DNA synthesis in exrA, recB, recA recB and wild-type strains. We conclude that the recA - gene product acts immediately, certainly before DNA replication, in the repair of lesions produced by gamma-irradiation. In recB bacteria the recA + gene product is not required for continued DNA synthesis, although the synthesis which occurs in recA recB strains may be abnormal since it is not reflected in increased survival. The exrA + gene product is not necessary for continued DNA replication, suggesting that its time of action in repair may be at a later stage.

Summary: Genetic recombination occurs with a rather high frequency (up to 10-3) in mixed cultures of auxotrophic and streptomycin-resistant mutant derivatives of Thermo-actinomyces vulgaris strain t9 growing on agar medium. It is shown that transformation by DNA is responsible for this recombination. Certain other newly isolated strains resemble t9 in being competent for transformation and are interfertile with each other and with t9. Some other strains are incompetent but can act as donors to the first set of strains. A fully synthetic minimal medium and conditions for efficient mutagenesis have been defined.

Summary: 2-Deoxy-d-glucose (deGlc), d-glucosamine (GA) and l-sorbose (Sor) inhibited extension of Coprinus lagopus hyphae; deGlc was about four times more inhibitory than GA, while the latter was about five times more inhibitory than Sor. The inhibitory effects were not uniformly additive. There were indications that the analogues competed with one another, suggesting they shared at least one point of action. Acetate and fructose were virtually ineffective in reversing the inhibitory effect. Glucose was 10 times more effective than mannose and about 100 times more effective than fructose or acetate in reversing inhibition. The fact that the analogues inhibited most on media which either lacked normal carbon source or which contained acetate was interpreted as indicating that growth-rate inhibitions which occurred on media containing hexose sugar did not result from any significant effect on sugar transport.

All three analogues caused gross morphological changes. The most characteristic aberration was a distinct swelling of the hyphal tip. This was most severe with GA which caused the tip cell to balloon into a spheroid some five to six times the diameter of the subtending hypha. The most extreme consequence of swelling occurred on media containing deGlc; after swelling to two to three times their normal diameters, tips frequently became vacuolated and often burst. Tip lysis was not observed on media containing either GA or Sor.

Summary: Cytochalasin A inhibited growth of Bacillus subtilis and Escherichia coli and increased motility of the latter. Both cytochalasins A and D have antifungal properties, inducing branching and, at higher concentrations, swelling of hyphal tips in Botrytis cinerea. Cytochalasin B showed neither antibacterial nor antifungal activity. The observed antimicrobial effects of cytochalasins A and D are discussed in relation to those of related antibiotics.