Reduced lipid content as the basis for defective amino acid accumulation capacity in pantothenate- and biotin-deficient Lactobacillus plantarum

Lysozyme sensitivity of pantothenate-deficient Lactobacillus plantarum grown with exogenous fatty acids

A pantothenic acid deficiency in Lactobacillus plantarum reduces lipid synthesis, prevents normal uptake and retention of extracellular amino acids and markedly increases sensitivity of these cells to lysozyme induced lysis. Pantothenate-deficient cells provided with exogenous fatty acids synthesize additional lipids and express nearly normal solute transport activities. The present study has shown that such cells retain a heightened sensitivity to lysozyme induced lysis. These observations indicate that the lysozyme sensitivity of pantothenate-deficient cells is not produced as in indirect effect of membrane lipid depletion, but represents an independent consequence of pantothenate insufficiency.

Dicarboxylic acid transport in membrane vesicles from Bacillus subtilis

Membrane vesicles isolated from Bacillus subtilis W23 catalyze active transport of the C4 dicarboxylic acids L-malate, fumarate, and succinate under aerobic conditions in the presence of the electron donor reduced beta-nicotinamide adenine dinucleotide or the non-physiological electron donor system ascorbate-phenazine methosulfate. The dicarboxylic acids are accumulated in unmodified form. Inhibitors of the respiratory chain, sulfhydryl reagents, and uncoupling agents inhibit the accumulation of the dicarboxylic acids. The affinity constants for transport of L-malate, fumarate, and succinate are 13.5, 7.5, and 4.3 muM, respectively; these values are severalfold lower than those reported previously for whole cells. Active transport of these dicarboxylic acids occurs via one highly specific transport system as is indicated by the following observations. (i) Each dicarboxylic acid inhibits the transport of the other two dicarboxylic acids competitively. (ii) The affinity constants determined for the inhibitory action are very similar to those determined for the transport process. (iii) Each dicarboxylic acid exchanges rapidly with a previously accumulated dicarboxylic acid. (iv) Other metabolically and structurally related compounds do not inhibit transport of these dicarboxylic acids significantly, except for L-aspartate and L-glutamate. However, transport of these dicarboxylic amino acids is mediated by independent system because membrane vesicles from B. subtilis 60346, lacking functional dicarboxylic amino acid transport activity, accumulate the C4 dicarboxylic acids at even higher rates than vesicles from B. subtilis W 23. (v) A constant ratio exists between the initial rates of transport of L-malate, fumarate, and succinate in all membrane vesicle preparations isolated from cells grown on various media. This high-affinity dicarboxylic acid transport system seems to be present constitutively in B. subtilis W23.

Heterogeneous elevation of amino acid transport rates in pantothenate-and lipid-deficient Lactobacillus plantarum

The effect of a pantothenic acid deficiency in Lactobacillus plantarum on the initial rate of amino acid transport was investigated. Although the steady-state accumulation capacity for all amino acids was markedly reduced in pantothenate-deficient cells, initial rates of uptake either were not changed (asparagine, alanine, lysine) or were increased (glutamic acid, aspartic acid leucine). The findings suggest that a reduction in membrane lipid content heterogeneously affects the operation and/or synthesis of amino acid transport catalysts.

Induction of beta-galactosidase in Lactobacillus plantarum

beta-galactosidase (beta-galactoside galactohydrolase, EC 3.2.1.23) is inducible in Lactobacillus plantarum by d-galactose or thiomethyl galactoside, and to a much lesser extent by lactose, isopropyl thiomethyl galactoside, and d-fucose. Isopropyl thiomethyl galactoside is a competitive inhibitor of the enzyme with a K(i) of 4.2 mM. The K(m) of the crude enzyme for o-nitrophenyl beta-d-galactoside is 0.87 mM. Induction also requires a source of energy and amino acids. Chloramphenicol and actinomycin D inhibited induction. d-Glucose, d-fructose and to a lesser extent maltose and d-mannitol inhibited enzyme synthesis. Methyl-alpha-d-glucopyranoside was not inhibitory. Glucose exerts its effect through its ability to exclude galactose or lactose entry into the cell. The uptake of lactose and the metabolism of galactose by preinduced cells is severely inhibited by glucose. But neither galactose nor lactose severely affected the uptake of glucose by preinduced cells. Thus, glucose acts through catabolite inhibition, i.e., transport of inducer rather than repression through transcription or related mechanisms. This is supported by the inability of cyclic nucleotides to relieve the inhibition produced by glucose or to stimulate induction. Furthermore, intracellularly produced glucose did not inhibit enzyme synthesis. Acetate and mevalonate, the precursors of membrane lipids, stimulate induction independently of their effect on growth. Homobiotin partially abolished the acetate effect but did not inhibit induction or growth.

Control of pantothenate accumulation in Agrobacterium tumefaciens

Two pantothenate-requiring mutants of Agrobacterium tumefaciens have been isolated. One of them (strain WMP-1) is unusual in that growth levels equivalent to the parent strain are achieved only when the medium is additionally supplemented with aspartate or another compound related to the tricarboxylic acid cycle. Extracts of cells grown on limiting aspartate were found to contain four times more (14)C-pantothenate than those grown at optimal aspartate concentrations. This difference was found in both the perchloric acid-soluble and -insoluble fractions, presumably the coenzyme A pool and acyl carrier protein, respectively. These findings are discussed in terms of membrane integrity and the control of fatty acid biosynthesis.

Interrelated effects of cold shock and osmotic pressure on the permeability of the Escherichia coli membrane to permease accumulated substrates

Permease studies are generally carried out by incubating cells in growth medium with labeled substrate, collecting the cells on microporous membrane filters, and washing them free from extracellular radioactivity with ice-cold medium. Studies of thiomethylgalactoside, valine, and galactose accumulation indicate that in several strains of Escherichia coli the bacterial membrane is exquisitely sensitive to isosmotic cold shock. Substrate pools formed at 25 C may suffer almost total loss if the cells are rapidly chilled to approximately 0 C during sampling. In glycerol-grown cells, this rapid efflux of substrate is prevented or minimized if the cells are subjected at the moment of cold shock to a simultaneous hyperosmotic transition. Because of this protective effect, the apparent size of a permease accumulated substrate pool is extremely sensitive to the osmotic composition of the incubation medium and may appear to be increased as much as 10-fold when the osmolarity is reduced from approximately 0.3 to 0.1 osmolar. These differences vanish when sampling and washing are carried out with medium at room temperature. It is suggested that isosmotic cold shock causes crystallization of the liquid-like lipids within the membrane. The hydrophilic channels created in this process would facilitate the rapid efflux of permease accumulated substrates. The imposition of a simultaneous hyperosmotic transition by dehydrating the cell periphery would cause increased lipid interaction, thus preserving the integrity of the cells membrane.

Utilization of -aminobutyric acid as the sole carbon and nitrogen source by Escherichia coli K-12 mutants

Wild-type strains of Escherichia coli K-12 cannot grow in media with gamma-aminobutyrate (GABA) as the sole source of carbon or nitrogen. Mutants were isolated which could utilize GABA as the sole source of nitrogen. These mutants were found to have six- to ninefold higher activities of gamma-aminobutyrate-alpha-ketoglutarate transaminase (EC 2.6.1.19) and succinate semialdehyde dehydrogenase (EC 1.2.1.16) than those of the wild-type parent strains. Secondary mutants derived from these GABA-nitrogen-utilizing strains were able to grow on GABA as the sole source of carbon and nitrogen. They also grew faster on a variety of other carbon and nitrogen sources, and their growth was more strongly inhibited by different metabolic inhibitors than was that of the parent strains. The nature of the two mutations and the possible genes involved are discussed. A scheme of the pathway for GABA breakdown in E. coli K-12 is presented.