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Microbiology Society logo - Volume 63, Issue 1, 1970

Volume 63, Issue 1

Volume 63, Issue 1, 1970

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  • Biochemistry

      • Inhibition by Isoniazid of Synthesis of Mycolic Acids in

        https://doi.org/10.1099/00221287-63-1-41

        SUMMARY

        Exposure of growing to 1 g. isoniazid/ml. inhibited the incorporation of C from [U-C] and [2-C]glycerol and [1-C]- glutamate into its walls by about 50 % over 12 h. because C incorporation into the mycolic acids of the walls was prevented. Isoniazid, 0·5 g. / ml. with or 0·1 g./ml. with H37 Ra, inhibited incorporation of C from [U-C] glycerol into total mycolic acids by about 90 % over 6 h., indicating that inhibition began within 1 h. of the addition of the drug. There was no effect on mycolic acid synthesis in an isoniazid- resistant strain of . The primary inhibitory action of isoniazid in sensitive mycobacteria is probably on mycolic acid synthesis, and this leads to formation of defective boundary layers of the bacteria.

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  • Development And Structure

      • Chemical Composition of Wild-type and Mutant Cell Walls. The Nature of Polysaccharide and Melanin Constituents

        https://doi.org/10.1099/00221287-63-1-75

        Summary: Chitin and a -linked glucan were the major chemical components of cell walls. Other monomeric residues identified in enzymic and acid hydrolyses of whole cell walls and cell-wall fractions included galactose, mannose, glucuronic acid and galactosamine. The -glucan contained (1 → 3) and (1 → 6) linkages and was two-thirds digested by an exo---1,3 glucanase prepared from a cell-wall lysing Streptomyces species. An -glucan was identified as a cell-wall component and it also contained (1 → 3) linkages. This latter polysaccharide was distinguishable from nigeran (an -1,3; -1,4 glucan present in other Aspergillus species) by infrared spectroscopy and by its low susceptibility to hydrolysis by an endo--1,3; 1,4 glucan glucanohydrolase. Both glucans were alkali-soluble, but the -glucan was completely solubilized only after acid extraction of the wall. The -acetylglucosamine to galactosamine ratio in the cell wall was 1·32 and the two hexosamines were shown to be constituents of distinct polymers. The remaining cell wall was accounted for by protein, lipids, readily extractable and bound, and, in the wild-type, melanin.

        The melanin was distributed throughout the cell wall but was associated particularly with the chitin fraction. The pigment has been partially characterized chemically and contains indolic residues; this result does not substantiate earlier views that indolic melanins are peculiar to the animal kingdom. Melanin appears to be a finite heteropolymer both in terms of its molecular size and its chemistry.

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    • Suppression of Methionyl Transfer RNA Synthetase Mutants of by Methionine Regulatory Mutations

      https://doi.org/10.1099/00221287-63-1-121

      SUMMARY

      Prototrophic ‘revertants’ of methionine-requiring methionyl-tRNA synthetase mutants () of were examined following an observation that some of them excreted methionine. A number were found to be phenotypically indistinguishable from a class () of methionine regulatory mutants. The mutations causing reversion, like mutations, were located between a serine () and a methionine () structural gene on the linkage map, and it was concluded that the ‘suppressors’ were mutations. The ability of independently isolated mutations to cause suppression of mutants was tested and was apparently related to their ability to cause methionine overproduction. A second kind of methionine regulatory mutation () also caused suppression, while a (homoserine--transsuccinylase) mutation leading to feedback insensitivity failed to do so. Spontaneous revertants due to secondary mutations were rare, and none due to secondary mutations was detected.

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  • Physiology And Growth

      • Effects of Nitrogenous Components of the Medium on the Carbohydrate and Nucleic Acid Content of BCG

        https://doi.org/10.1099/00221287-63-1-29

        Summary: The effects of varying the concentrations of the nitrogen sources in glycerol + asparagine, glycerol + asparagine + casein hydrolysate and glycerol + ammonium sulphate media on the composition and growth rate of grown in shaken culture for various periods were investigated. The bacteria were fractionated and the soluble, alkali-extractable, hot acid-soluble and residual fractions analysed for carbohydrate, RNA, DNA, free lipid, soluble amino compounds and soluble phosphates.

        The results indicate that several forms of growth restriction operated in these experiments: a progressive reduction in growth rate even in conditions when nutrients were not limiting, due to clumping of cells; a reduction in growth rate following any reduction in the amino acid content of the medium; a marked reduction in growth rate when the amino acid content of the medium fell below a critical level, or was replaced by ammonium ions. When the growth rate was reduced because of nutrient limitation, the carbohydrate content of the bacteria increased, but the pattern of accumulation varied with the experimental conditions. The RNA: protein ratio of the cells was little affected by growth rate.

    • Effects of Oxygen on Acetylene Reduction, Cytochrome Content and Respiratory Activity of

      https://doi.org/10.1099/00221287-63-1-63

      SUMMARY

      The respiratory activities and cytochrome contents of nitrogen-fixing continuous cultures of (8003) increased with the partial pressure of oxygen encountered during growth. Above 0·6 atm., wash-out of the culture occurred. Acetylene reduction by culture samples of low respiratory activity was far more easily inhibited by oxygenation than was that of samples of high respiratory activity, though their maximum acetylene- reducing activities at their optimal O values were similar. Inhibition by oxygen was reversible after mild oxygenation: 70 to 100 % of the original activity returned immediately when the degree of oxygenation was decreased. Irreversible inhibition occurred after vigorous oxygenation and was associated with a loss of activity in cell-free extracts, which was restored by adding the oxygen-sensitive protein component of Azotobacter nitrogenase. These observations support earlier proposals that augmented respiration can scavenge oxygen from the nitrogen-fixing site and that a conformational change in the state of nitrogenase can prevent damage to the enzyme by oxygen. Vigorous aeration, however, may overcome these protective mechanisms.

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    • Nitrogen Fixation by Sporulating Sulphate-reducing Bacteria Including Rumen Strains

      https://doi.org/10.1099/00221287-63-1-137

      The acetylene test for nitrogen fixation has been an important tool in reassessing the ability of various groups of micro-organisms to fix nitrogen (Parejko & Wilson, 1968; Millbank, 1969; Hill & Postgate, 1969). As a result of this reassessment, it has been found that several aerobic genera such as and yeasts probably do not fix N; on the other hand, nitrogen fixation has proved to be far more widespread among the sulphate-reducing bacteria of the genus than was earlier thought (Reiderer-Henderson & Wilson, 1970). This communication reports evidence for fixation by type strains of mesophilic, spore-forming, sulphate-reducing bacteria, genus (Campbell & Postgate, 1965), including strains originating from the rumens of hay-fed sheep. Some data with type strains of Desulfovibrio are included to supplement the findings of Reiderer-Henderson & Wilson (1970).

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