- Volume 101, Issue 1, 1977

Mycobacterium smegmatis formed an alkaline phosphomonoesterase (EC 3·1·3·1) and an alkaline phosphodiesterase (EC 3·1·4·1). The former was regulated by inorganic phosphate and was repressed in medium containing a high concentration of phosphate. The synthesis and the function of the alkaline phosphodiesterase were not controlled by inorganic phosphate.

During the adaptation of Pseudomonas aminovorans from growth on succinate to growth on trimethylamine, the following enzymes were synthesized in the lag phase before exponential growth on trimethylamine began: trimethylamine and dimethylamine mono-oxygenases, trimethylamine-N-oxide aldolase (demethylase), glutathione- and NAD-dependent formaldehyde dehydrogenase, dye-linked formaldehyde dehydrogenase, hydroxypyruvate reductase and N-methylglutamate dehydrogenase. Differential plots suggested that the rate of enzyme synthesis in the lag phase exceeded the rate of synthesis during exponential growth. The evidence suggests that the enzymes discussed are essential for growth on trimethylamine, while the NADPH-dependent N-methylalanine dehydrogenase is not involved.

Walls of the bacteroid form of Rhizobium leguminosarum, from plant nodules, and walls of free-living R. leguminosarum were isolated and compared by extraction with aqueous phenol and chemical analysis. Bacteroid walls had less lipopolysaccharide than walls isolated from bacteria cultured on four different media. This difference may be relevant to the relatively greater permeability of the outer membrane of bacteroids, and important in symbiotic interactions.

DNA contents of different species of broth-cultured Rhizobium bacteria and bacteroids from root nodules were determined by cytofluorometry. In almost all species bacteroids appeared to contain more DNA than the corresponding bacteria. A correlation was found between the DNA content and size of the bacteroid, the latter being influenced by the host plant.

The structure of the flagellar filaments of 50 Escherichia coli strains, each with a different H antigen, was examined. Although the flagella within each strain were structurally identical, there was variability in flagellar surface pattern between strains with different H antigens. Investigation of additional strains confirmed that flagella structure was the same in all strains having the same H antigen. In three pairs of strains with cross-reacting H antigens, the antigenic relatedness was associated with identical flagella structure.

Summary: The molecular weights of the flagellins of 13 strains of Escherichia coli, each with a different H antigen, were estimated using polyacrylamide gel electrophoresis. In each case only one major polypeptide was demonstrated, although some strains possessed apparently sheathed flagella. Considerable differences in the molecular weight of flagellin accompanied the previously described structural differences between flagella from strains with different H antigens. The relationship between flagellar diameter and the molecular weight of the corresponding flagellins was similar for both unsheathed and apparently sheathed flagella. Cross-polymerization occurred between seed consisting of fragments of unsheathed flagella and flagellin solution from apparently sheathed flagella and vice versa. Co-polymerization of flagellin from unsheathed flagella and flagellin from apparently sheathed flagella was also demonstrated. These polymerization experiments indicate that the assembly pattern of flagellin molecules is probably the same in all E. coli flagella. The above and other evidence suggests that there is no true sheath, but that the differences in flagellar surface structure between different E. coli flagella are the result of differences in the superficial parts of the flagellin molecules.

The presence in recipient strains of Escherichia coli k12 of the plasmid R46 greatly reduced the yield of recombinants from crosses with several Hfr strains and virtually abolished the formation of recombinants by P1 transduction without, however, significantly affecting the transfer of the F prime from a strain carrying Fgal. The R46 plasmid had paradoxical effects on mutability: it appeared to enhance the yield of mutants following irradiation with ultraviolet light but it reduced the number of mutants detectable in unirradiated cultures. The effects of this plasmid on ultraviolet light survival of the wild type and several mutants defective for recombination and repair have been measured and the results, in the main, confirm similar observations by Tweats et al. (1976) . Not only is the survival of the strain harbouring R46 greater than that of the parent strain in all the cases studied, but the survival of ultraviolet irradiated bacteriophage λ is also greater.

The survival of ultraviolet-irradiated Escherichia coli k12 uvr + rec was increased by post-irradiation incubation in phosphate buffer. During this incubation both dimer excision and DNA breakdown were inhibited. It is suggested that the bacteria coped with the remaining dimers in a manner which did not involve excision.

Two mutants of the R plasmid pMG2, selected on the basis of loss of enhanced ultraviolet light (u.v.)-induced mutability, no longer protected a wild type, a uvr rec + type mutant, or a polA type mutant of Pseudomonas aeruginosa against the lethal effects of u.v. For one of the R plasmid mutants tested, pPL2, a plasmid-determined DNA polymerase was no longer detected. The properties of these mutants support the hypothesis that a plasmid gene function responsible for enhanced u.v.-induced mutability also confers u.v.-protection on the host cells. Furthermore a plasmid-determined DNA polymerase plays a major role in producing these effects.

On the basis of the effects of sodium arsenite on plasmid u.v.-protection and enhanced u.v.-induced mutability in strain trpf1, it is proposed that a recA-dependent, arsenite-sensitive repair pathway is present in P. aeruginosa.

Summary: Five mutants of Salmonella typhimurium strain lt2 trpD1 (ColE1)+, initially detected because they released little or no colicin when tested on solid medium, proved to be sensitive to ultraviolet light (u.v.). Further testing indicated that one of the mutants was deficient in genetic recombination and was probably a recA-type mutant, while three of the others were deficient in DNA polymerase activity and appeared to be typical polA mutants. The fifth mutant was less sensitive than the others to methyl methanesulphonate, showed reduced proficiency in genetic recombination, and was of approximately normal u.v. mutability. This mutant may be a counterpart of the class known as uvrD in Escherichia coli. All five mutants degraded significantly more of their DNA following exposure to u.v. than did the wild-type strain. The recA-type mutant and the possible uvrD mutant also degraded significantly more of their DNA spontaneously than did the wild-type. Treatment with visible light and acridine orange (photodynamic treatment) caused no significant degradation of DNA in the wild-type strain, a highly significant increase in the extent of DNA degradation in a polA mutant, and a decrease in the extent of degradation in the recA-type mutant.

Summary: Germination and growth of six xerophilic fungi, Aspergillus flavus, Aspergillus ochraceus, Eurotium chevalieri, Chrysosporium fastidium, Wallemia sebi and Xeromyces bisporus were examined on media of a wide range of water activities (aw ). The influence of three solutes, NaCl, glycerol and a glucose/fructose mixture, was studied at pH 4·0 and pH 6·5 using a plate-slide technique. Germination times and growth rates were affected by solute type, but the influence of pH was less marked. Except for Wallemia sebi, the fungi grew most strongly on glucose/fructose and were partially or completely inhibited by NaCl. The results showed that a universal isolation medium for xerophilic fungi could be based on glycerol or glucose/fructose but not on NaCl as aw -limiting solute.

The capacity of culture filtrates of Mycobacterium smegmatis growing in iron-deficient medium to solubilize inorganic iron increases throughout the growth phase. When the source of iron, either ferric phosphate or ferritin, was contained within diffusion capsules, bacteria grew unimpeded indicating that freely-diffusible iron chelates were being produced which could support growth. The maximum production of the iron-binding compounds, termed exochelins, occurred with 0·03 μg iron ml−1 in the medium; with 1·0 μg iron ml−1 (giving iron-sufficient growth) the amount of exochelin produced was less than 0·1% of the maximum level. Using ion-exchange chromatography at least six exochelins were recovered from culture filtrates. The major compound, constituting about 60% of the total, was isolated, purified and partially characterized. It solubilized iron from inorganic and organic forms, stimulated growth of M. smegmatis in serum, was freely diffusible in both its ferri and desferri forms, and transferred the chelated iron to cells at a rate which was independent of its concentration.

A chemostat culture under a nitrogen atmosphere with a formate and inorganic salts medium fed at dilution rates up to 0·1 h−1 and inoculated from a sewage works anaerobic digester, proved to be an easy way of isolating a stable methanogenic bacterial culture. Formate-limited growth yielded a mixed culture containing predominantly methanogenic bacteria morphologically similar to Methanobacterium formicicum and Methanobacterium ruminantium.

When glucose was substituted for formate, a facultative anaerobe capable of metabolizing glucose was selected. This species far outnumbered any other on aerobically incubated nutrient agar and was identified as a species of Citrobacter. The main products of glucose fermentation by this citrobacter were acetate, formate, ethanol and lactate. When the spent medium from the citrobacter fermentation of glucose was fed to the methanogenic culture, formate and lactate appeared to be the substrates which limited methane production. When each of the citrobacter products (acetate, ethanol and lactate) was fed as the sole carbon source to a methanogenic culture selected by growth on formate, lactate by itself could maintain methane production, but acetate and ethanol by themselves were not substrates for methane production. Lactate is thus a major intermediate in the conversion of glucose to methane by the mixed culture.

Germ hyphae from zoospores of Achlya bisexualis are positively chemotropic to casein hydrolysate. The active concentration ranges of casein hydrolysate, some amino acid mixtures and single amino acids have been determined. Data on the uptake of amino acids in germlings are presented and discussed in relation to chemotropism.

The anionic requirement for the oxidation of ferrous ions by suspensions of Thiobacillus ferrooxidans was satisfied by selenate as well as sulphate. Selenate was toxic to the organism and suppressed growth in ferrous iron media, even in the presence of high concentrations of sulphate. After treatment with dilute hydrochloric acid at 0°C, T. ferrooxidans, which specifically required SO4 2− or SeO4 2− for iron oxidation, showed no activity in response to 12 other anions tested. However, after the introduction of SO4 2− or SeO4 2−, addition of anions such as TeO4 2−, WO4 2−, AsO4 3− or PO4 3− further enhanced the rate of iron oxidation. Under these conditions, Cl-, B4O7 2− and ClO3 - had no significant effect at low concentration, whereas Br-, NO3 - and MoO4 2− were inhibitory. These observations distinguish between a specific and a non-specific anionic requirement for the oxidation of ferrous ions by T. ferrooxidans. The specific requirement is satisfied only through the uptake of SO4 2− or SeO4 2− by the bacteria. The non-specific requirement is satisfied by any one of several anions, including SO4 2− and SeO4 2−, which are presumed to act as ligands for iron in solution.

In blue light Penicillium isariiforme assimilates less CO2 and excretes less citric acid into the medium than when grown in continuous darkness. This is due to a decreased supply of pyruvate which is carboxylated to form citric acid via oxaloacetate. Pyruvate carboxylase rather than phosphoenolpyruvate carboxylase or phosphoenolpyruvate carboxykinase is mainly responsible for CO2 assimilation in this fungus. Of the glycolytic intermediates assayed, steady-state concentrations of pyruvate were low and concentrations of glucose 6-phosphate, glucose 1-phosphate and fructose 6-phosphate were high in mycelium grown in the light compared with those in mycelium grown in the dark. Results of experiments with specifically-labelled glucose suggest that light stimulates the pentose phosphate pathway and inhibits the supply of pyruvate for citric acid synthesis via the Embden-MeyerhofParnas pathway.