Relationship between sporulation and mutations impairing glutamine synthetase in Bacillus megaterium

New class of Bacillus subtilis glutamine-requiring mutants

By using genetic analysis, the mutations of eight glutamine-requiring mutants isolated from Bacillus subtilis 168 were all shown to be linked to the thyA marker. A three-factor transduction analysis performed with one of the gln mutations indicated that the gene order in this region of the B. subtilis chromosome was gltA-thyA-gln. On the basis of recombination index values, two closely linked groups were identified. The mutations belonging to one group were assigned to the structural gene for glutamine synthetase, and those belonging to the other group might impair a regulatory locus. The residual glutamine synthetase activities and the cross-reacting materials of the mutants from both recombination groups supported these conclusions.

Regulation of the activity of the Bacillus licheniformis A5 glutamine synthetase

The regulation of glutamine synthetase activity by positive and negative effectors of enzyme activity singularly and in combinations was studied by using a homogeneous enzyme preparation from Bacillus licheniformis A5. Phosphorylribosyl pyrophosphate at concentrations greater than 2mM stimulated glutamine synthetase activity by approximately 70%. The concentration of phosphorylribosyl pyrophosphate required for half-maximal stimulation of enzyme activity was 0.4 mM. Results obtained from studies of fractional inhibition of glutamine synthetase activity were consistent with the presence of one allosteric site for glutamine binding (apparent I0.5, 2.2mM) per active enzyme unit at a glutamate concentration of 50 mM. At a glutamate concentration of 30 mM or less, the data were consistent with the enzyme containing two binding sites for glutamine (one of which was an allosteric site with an apparent I0.5 of 0.4 mM). Bases on an analysis of the response of glutamine synthetase activity to positive and negative effectors in vitro and to the intracellular concentration of these effectors in vivo, the primary modulators of glutamine synthetase activity in B. licheniformis A5 appear to be glutamine and alanine (apparent I0.5, 5.2mM).

Properties of the Bacillus licheniformis A5 glutamine synthetase purified from cells grown in the presence of ammonia or nitrate

The glutamine synthetase from Bacillus licheniformis A5 was purified by using a combination of polyethylene glycol precipitation and chromatography on Bio-Gel A 1.5m. The resulting preparation was judged to be homogeneous by the criteria of polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, equilibrium analytical ultracentrifugation, and electron microscopic analysis. The enzyme is a dodecamer with a molecular weight of approximately 616,000, and its subunit molecular weight is 51,000. Under optimal assay conditions (pH 6.6, 37 degrees C) apparent Km values for glutamate, ammonia, and manganese.adenosine 5'-triphosphate (1:1 ratio) were 3.6, 0.4, and 0.9 mM, respectively. Glutamine synthetase activity was inhibited approximately 50% by the addition of 5 mM glutamine, alanine, glycine, serine, alpha-ketoglutarate, carbamyl phosphate, adenosine 5'-diphosphate, or inosine 5'-triphosphate to the standard glutamine synthetase assay system, whereas 5 mM adenosine 5'-monophosphate or pyrophosphate caused approximately 90% inhibition of enzyme activity. Phosphorylribosyl pyrophosphate at 5 mM enhanced activity approximately 60%. We were unable to detect any physical or kinetic differences in the properties of the enzyme when it was purified from cells grown in the presence of ammonia or nitrate as sole nitrogen source. The data indicate that B. licheniformis A5 contains one species of glutamine synthetase whose catalytic activity is not regulated by a covalent modification system.

Alteration of the Bacillus subtilis glutamine synthetase results in overproduction of the enzyme

A mutational leading to glutamine auxotrophy was located near a 5-fluorouracil resistance marker in the citB-thyA region of the Bacillus subtilis chromosome. This mutation resulted in a glutamine synthetase with altered kinetic and feedback properties. The specific activity of manganese-stimulated glutamine synthetase activity in crude extracts was 18-fold higher, and the magnesium-stimulated activity was about 30% that of the wild type. Quantitation of the enzyme by precipitation with antibody prepared against pure enzyme confirmed the presence of high enzyme levels in the mutant. This mutation is very closely linked (recombination index of 0.03) to another glutamine auxotroph containing enzyme with altered electrophoretic and heat sensitivity properties. Mutations in the structural gene for glutamine synthetase may result not only in altered catalytic and regulatory properties but also in altered production of the enzyme.

Role of glutamate in the sporogenesis of Bacillus cereus

Bacillus cereus T, sporulating in a chemically defined medium under optimum conditions, requires substrate quantities of glutamate during the first 4 h of sporogenesis. Seventy percent of the glutamate utilized was catabolized to CO2 during this period, with the remaining glutamate carbon assimilated into various spore constituents, principally protein and nucleic acid. The importance of glutamate as the primary source of reducing potential and energy for early stages of spore formation was investigated. Although the relative efficiency at which tricarboxylic acid cycle intermediates substituted for glutamate was suggestive of oxidation via the tricarboxylic acid cycle, only partial inhibition of glutamate oxidation by fluoroacetate was observed.

The program of protein synthesis during sporulation in Bacillus subtilis

The program of protein synthesis was examined during sporulation in Bacillus subtilis as an index of the control of gene expression. At various stages of growth and spore formation, cells of B. subtilis were pulse-labeled with (35)S-methionine. Protein was extracted from the radioactively labeled bacteria and then subjected to high resolution one-dimensional and two-dimensional slab gel electrophoresis. We report that sporulating cells restricted or "turned off" the synthesis of certain polypeptides characteristic of the vegetative phase of growth. In certain cases, this "turn off" was prevented in a mutant (SpoOa-5NA) blocked at the first stage of spore formation. Sporulating bacteria also elaborated new polypeptide species that could not be detected in vegetatively growing cells or in cells of the asporogenous mutant SpoOa-5NA in sporulation medium. The synthesis of these sporulation-specific proteins was "turned off" in a temporally defined sequence throughout the period of spore formation. Spore coat protein, for example, was first synthesized at 4 hr after the onset of sporulation, the time at which refractile prespores appeared. Certain sporulation-specific polypeptides including the coat protein were among the most actively produced polypeptides in sporulating cells.