- Volume 94, Issue 1, 1976

Summary: The adenine nucleotide levels and derived energy charge value of a tyrothricin-producing strain of Bacillus brevis under aerobic conditions were in good agreement with published values for other bacteria. When growing cultures of B. brevis underwent a transition from aerobic to anaerobic conditions, cyclic variations in the level of adenine nucleotides were observed and the energy charge value oscillated between 0·87 and 0·70. The significance of these changes is considered in relation to antibiotic production as a possible regulatory mechanism in energy metabolism. It is concluded that tyrothricin is not directly involved in the observed changes in energy charge value.

Summary: Strains of Escherichia coli devoid of systems for the active transport of galactose (galP mgl) still grow on galactose but at rates that are a function of the galactose concentration of the medium: half-maximal growth rates require more than 2 mm-galactose to be present. Evidence is presented that galactose is taken up by such strains by facilitated diffusion on a carrier specified by the umg gene (or by a gene highly co-transducible with it) which is thus a part of, or closely associated with, an enzyme II for glucose of the phosphoenolpyruvate-phosphotransferase system. However, the entry of galactose does not require phosphotransferase activity, and the sugar taken up appears in the cells as free galactose.

Summary: Cell-free extracts prepared from spherical and rod-shaped cells of Arthrobacter crystallopoietes were assayed for enzymes during various periods of starvation. The level of NADH oxidase dropped to 20 and 30%, respectively, in spherical and rod-shaped cells during the first 1 to 2 days of starvation and then remained constant for 9 days. Catalase activity decreased continuously and reached a low level in 9 days. Enzymes involved in glucose metabolism and the tricarboxylic acid cycle were stable for the duration of the experiment (about 1 week). Succinic dehydrogenase, fumarase and aconitase were stable during 21 days of starvation, which is the longest time enzymes have been shown to be stable in any bacterium under conditions of total starvation.

Summary: Lipoteichoic acid (LTA) and deacylated lipoteichoic acid have been isolated from the bovine-rumen Gram-negative anaerobe Butyrivibrio fibrisolvens by phenol extraction. Lipoteichoic acid (21·8 µmol phosphorus/g cells) consisted of a conventional 1,3-phosphodiester-linked chain of glycerol phosphate units joined covalently to a glycolipid. It was not substituted with glycosyl or d-alanyl ester groups. Deacylated lipoteichoic acid (57·5 µmol phosphorus/g cells) was similar in constitution but lacked fatty acid esters. Lipoteichoic acid reacted serologically with antisera to the glycerol phosphate backbone of known lipoteichoic acids. The presence of similar teichoic acid polymers has also been demonstrated in some other strains of B. fibrisolvens and this is of significance in demonstrating that teichoic acids can occur in Gram-negative bacteria.

Summary: Twenty-one strains of actinomycetes were screened for the presence of chloramphenicol acetyltransferase, the enzyme responsible for chloramphenicol resistance in many species of bacteria. Only five strains, belonging to three species, yielded mycelial lysates which catalysed the formation of chloramphenicol acetates in the presence of acetyl-coenzyme A: Streptomyces coelicolor Müller, S. acrimycini, and S. griseus. A mutant of S. acrimycini selected for an increase in resistance to chloramphenicol had a higher specific activity for chloramphenicol acetyltransferase than that found in the parental strain; the enzyme was not inducible in the mutant, the parental strain, or any other strain tested. Chloramphenicol was not acetylated by lysates of a strain of S. venezuelae, the organism known to produce it.

Summary: Mutants of Sporobolomyces roseus resistant to benzimidazole fungicides varied in their responses to 2-(thiazol-4-yl)benzimidazole (thiabendazole, TBZ), methyl I-(butylcarbamoyl)-benzimidazol-2-yl carbamate (benomyl) and methyl benzimidazol-2-yl carbamate (carbendazim, MBC). Incorporation of [14C]MBC into trichloroacetic acid extracts of the sensitive strain S4 increased during a 2 h incubation period, whereas incorporation into the resistant mutant M55 was unchanged. [14C]MBC uptake by S4 cells was five times higher than that by M55. MBC was identified as the main radioactive compound inside the S4 cells and reached a level of 2·4 µg/100 mg dry wt.

The compound MBC enters the cells of Sp. roseus by a temperature-, energy-, pH- and concentration-dependent transport system which may be specific for compounds containing a benzimidazole nucleus. It is suggested that tolerance of m55 to MBC is due to decreased permeability of the cell to this compound

Summary: Two phage-bound polysaccharide hydrolases specific for Klebsiella aerogenes type 8 exopolysaccharides were isolated. Each enzyme was specific for the polysaccharide produced by the host strain. One enzyme hydrolysed a pyruvylated and acetylated polymer, while the other only acted on the substrate lacking these substituents. Both enzymes were endogalactosidases releasing tetrasaccharides from their substrates which were only hydrolysed to a limited extent.

Summary: Micronuclei of Paramecium aurelia at the prophase (crescent stage) of the first meiotic division during conjugation or autogamy were characterized by an elongated, somewhat curved shape. They contained small aggregates of a fibrillar material scattered uniformly throughout the nucleoplasm and a single layer of intranuclear microtubules located close under, and adhering to, the inner nuclear membrane. These microtubules ran parallel to each other and parallel to the long axis of the micronucleus. At one end of the crescent stage micronuclei, there were two electron-dense bodies, which may function as organizing centres for micro-tubular assembly. During subsequent meiotic divisions the single layer of intranuclear microtubules was absent but a microtubular meiotic spindle was present.

Both gamete pronuclei in each conjugant contained microtubules distributed evenly throughout the nucleoplasm and aligned in one direction. The migratory (male) pronucleus formed pseudopodia during its passage through the cytoplasmic bridge and was surrounded by extranuclear bundles of microtubules located in the cytoplasm close to the nuclear envelope. Stationary (female) pronuclei had no extranuclear microtubules.

During all stages of conjugation or autogamy the nuclear envelope remained intact.

Summary: A method has been developed for isolating nuclei from the filamentous fungus Aspergillus nidulans. In this procedure, the mycelia from 14 to 16 h spore-derived cultures of A. nidulans NR1, a stable diploid strain, were frozen with liquid nitrogen and homogenized in a Waring blender. After homogenization, the mycelia were warmed to 4 °C and the nuclei were purified from the homogenate by differential centrifugation followed by sedimentation through 2·1 m-sucrose. The final nuclear yield was 15 to 20%, based on DNA estimations. The purified nuclear pellet was free of whole cells. The morphology of the isolated nuclei resembled that of the in situ nuclei; they contained a nucleolus, chromatin, and had a surrounding double membrane. The purified nuclei were characterized by a DNA:RNA: protein ratio of 1:2.8:8·7.

Summary: The dipeptide antibiotic bacilysin is active against a wide range of bacteria and against Candida albicans. Its C-terminal amino acid, anticapsin, is a very poor antibacterial agent. The activities of both substances are strongly dependent on the nature of the culture medium. In a minimal medium the minimum inhibitory concentration for bacilysin with E. coli b is 10−3 µg ml−1. The action of bacilysin is antagonized by a variety of dipeptides and that of anticapsin by a number of amino acids. With several bacteria, bacilysin-resistant mutants are found in unusually large numbers. It is suggested that peptide and amino acid transport systems play a role in these phenomena. The antimicrobial action of bacilysin is also inhibited by glucosamine and N-acetylglucosamine. This antibiotic may therefore interfere with glucosamine synthesis and thus with the synthesis of microbial cell walls.

Summary: Bacilysin is hydrolysed to l-alanine and anticapsin by suspensions of a bacilysin-sensitive strain of Staphylococcus aureus but not by those of a resistant strain derived from it. In contrast, it is hydrolysed by extracts of both strains. Anticapsin is a powerful inhibitor of glucosamine synthetase in extracts of both the bacilysin-sensitive and -resistant strains of Staph. aureus. Bacilysin, by comparison, is a relatively poor inhibitor of glucosamine synthetase in crude extracts when its hydrolysis is inhibited by EDTA. A phenylalanine auxotroph of Staph. aureus readily uses l-alanyl-l-phenylalanine for growth, but a bacilysin-resistant mutant of this strain does not. It is suggested that the antibacterial activity of bacilysin depends on its transport into the organism, its hydrolysis to anticapsin and on inhibition by the latter of glucosamine synthetase, and that bacilysin-resistant mutants are defective in a transport system.

Summary: Rhodopseudomonas palustris was chosen as a model organism for studying bacterial differentiation. Synchronous populations selected by sucrose gradient centrifugation yielded more than 95% swarmer cells. The appearance and disappearance of cell morphological groupings and the doubling of cell numbers in cultures of such swarmer populations were very well defined. Cells were only motile for the first half of the division cycle, but motility was regained before division. Development gave rise to a distinct and characteristic pattern of extinction increase and particle volume distribution. The development of swarmers into mother cells and the dimorphic division of R. palustris are discussed as simple examples of differentiation.

Summary: A thermophilic bacillus growing on acetamide as both carbon and nitrogen sources produces an inducible amidase. This amidase hydrolysed the following amides in decreasing order of activity, in comparison with acetamide (1·00): pro-pionamide (0·97), fluoroacetamide (0·84), formamide (0·35) and glycinamide (0·12). Cyanoacetamide, dimethylacetamide, dimethylformamide and urea also induced the synthesis of the amidase, but were not substrates of the enzyme. Studies with protoplasts suggest that the amidase is located in the cytoplasm.

Glucose strongly inhibited amidase synthesis; and limiting nitrogen did not release this inhibition. Urea strongly inhibited amidase activity in a competitive manner; but the inhibition caused by iodoacetamide and cyanoacetamide was non-competitive. Both thioacetamide and thiourea were effective inhibitors of enzyme induction.

Bacteria grown on a succinate-minimal medium exhibited a lag in amidase synthesis, which could be eliminated by decreasing the concentration of succinate. Acetate- or pyruvate-grown cultures behaved similarly, while those grown on alanine or glutamate exhibited no lag in enzyme induction.

In the mutant strain e21, repression of amidase synthesis by glucose was much less evident and no lag for induction was apparent with any of the other carbon sources mentioned.

Summary: Motile cells of aerobically cultivated Rhodospirillum rubrum, containing no detectable bacteriochlorophyll, assembled at a spot of strong light projected through a dark-field condenser. Far-red light was not effective, indicating that bacteriochlorophyll and thus photosynthetic metabolism was not responsible for the phenomenon. Bacteria moving towards the centre of the light spot changed direction less frequently than those moving towards the margin. They also responded to temporal changes in the intensity of light, altering their swimming direction more frequently after a sudden decrease in light intensity than after an abrupt increase.