Nitrite reduction in Veillonella alcalescens.

Nitrite reduction was examined in Veillonella alcalescens C-1, and obligate anaerobe with an ATP-yielding nitrate-reducing system. Hydrogen donors for nitrite reduction included hydrosulfite, hydrogen gas, and pyruvate, but not pyridine nucleotides, in the presnece or absence of flavins. Pyruvate-linked nitrite reduction was not inhibited by 4,4,4-trifluoro-1-(2-thienyl) 1,3-butanedione, dicoumarol, or 2-heptyl-4-hydroxy-quinoline-N-oxide. The noninvolvement of membrane-bound factors was supported by the fact that 100% of pyruvate-linked activity remained in the soluble fraction after fractionation of crude extracts by ultracentrifugation. Using DEAE-cellulose column chromatography, however, the participation of ferredoxin in nitrite reduction was demonstrated. The product of nitrite reduction appeared to be ammonia, as determined from H2-to-NO2- ratios. Nitrite reductase was induced by nitrate or nitrite and was repressed by increased levels of reduced nitrogenous compounds.     

Multiple Impairment of Glycolysis in Veillonella alcalescens

The property of glucose nonfermentation, characteristic of the genus Veillonella, was investigated in V. alcalescens C1, a strain of sheep rumen origin. Cell-free extracts as well as intact cells were incapable of glucose fermentation, thereby eliminating the possibility of nonpermeation. Assimilation of (14)C-glucose was not detectable. Of the 10 glycolytic enzymes, hexokinase, phosphoglyceromutase, and pyruvate kinase were not detectable. The other glycolytic enzymes were present.     

Nitrate Reduction and the Growth of Veillonella alcalescens

Veillonella alcalescens, a strict anaerobe, was found to possess a nitrate reductase system which has characteristics of both assimilatory and respiratory nitrate reduction. The nitrate reductase has been identified tentatively as a particulate enzyme which utilizes a variety of electron donors for the reduction of nitrate. By use of ¹⁵N-labeled nitrate, it was shown that under appropriate conditions nitrate nitrogen is incorporated into cell material. V. alcalescens grown on pyruvate and nitrate has a greater growth rate than cells grown on pyruvate alone. Growth can occur in a medium with hydrogen and nitrate as the sole energy source. Ammonium chloride decreases the rate of nitrate reduction but does not completely inhibit reduction or incorporation. The results suggest that nitrate assimilation and respiration are not as distinct as in some other organisms.     

Putrescine and cadaverine are constituents of peptidoglycan in Veillonella alcalescens and Veillonella parvula.

Veillonella alcalescens ATCC 17745, a strictly anaerobic, gram-negative small coccus, requires putrescine or cadaverine for growth (M. B. Ritchey, and E. A. Delwiche, J. Bacteriol. 124:1213-1219, 1975). Both putrescine and cadaverine were demonstrated to be incorporated exclusively into the peptidoglycan layer of V. alcalescens ATCC 17745. V. parvula GAI 0574 also proved to contain putrescine as a component of peptidoglycan. The primary chemical structure of the peptidoglycan common to the two Veillonella species is N-acetylglucosamine-N-acetylmuramic acid-L-alanine-D-glutamic acid gamma-meso-diaminopimelic acid-D-alanine. Putrescine or cadaverine links covalently to the alpha-carboxyl group of the D-glutamic acid residue of the peptidoglycan is necessary for normal cell growth. In V. alcalescens ATCC 17745, above 40% saturation at cadaverine linked to the alpha-carboxyl group of the D-glutamic acid residue of the peptidoglycan is necessary for normal growth.     

Cell wall composition and incorporation of radio-labelled compounds by Veillonella alcalescens.

The cell wall of Veillonella alcalescens was shown to have a typically Gram-negative appearance and composition. The wall contains 24% lipid, 0.8% phosphorus, and 6.8% hexosamine. It is estimated to contain about 5% murein, unlike the 24% reported by other for Veillonella parvula. The amounts of 19 amino acids, including diaminopimelic acid, were determined. Though Veillonella sp. cannot metabolize sugars for energy, V. alcalescens incorporates ribose and fructose by separate, specific mechanisms and uses most of the incorporated sugar in nucleic acid synthesis. Large excesses of either sugar in the medium do not repress gluconeogenesis from the pyruvate level. We have been unable to detect phosphoglyceromutase (EC 2.7.5.3) by several assay methods but have no indication of a gluconeogenic pathway other than reverse glycolysis.     

Growth yield increase and ATP formation linked to succinate decarboxylation in Veillonella parvula

Veillonella parvula strain 259 (=DSM 2007) was able to grow on a mineral salts medium supplemented with (per litre) 1 g yeast extract, 1 g Tween-80, and 3 mg putrescine. 2 HCl, with 6 mM thioglycolate as reductant and lactate as growth substrate. Succinate did not serve as a growth substrate, but when added in conjunction with lactate, it was decarboxylated to propionate and resulted in a measurable increase in growth yield, corresponding to the formation of 2.4 g cell dry mass per mol succinate. A growth yield increase linked to succinate metabolism occurred only while lactate was also being metabolised. Experiments with cell suspensions showed that succinate decarboxylating activity was constitutive. Addition of succinate produced clear increases in cellular ATP levels in ATP-depleted washed cells.     

Amino acid transport in membrane vesicles of obligately anaerobic Veillonella alcalescens.

Membrane vesicles of Veillonella alcalescens, grown in the presence of L-lactate and KNO-3, actively transport amino acids under anaerobic conditions in the presence of several electron donors and the electron acceptor nitrate. The highest initial rates of uptake are obtained with L-lactate, followed by reduced nicotinamide adenine dinucleotide, glycerol-1-phosphate, formate, and L-malate.. The membrane vesicles contain the dehydrogenases for these electron donors, and these enzymes are coupled with nitrate reductase. In membrane vesicles from cells, grown in the presence of nitrate, the dehydrogenases are not coupled with fumarate reducatase, and anaerobic transport of amino acids does not occur with fumarate as electron acceptor. Under aerobic conditions none of the physiological electron donors can energize transport. However, a high rate of uptake is observed with the electron donor system ascorbate-phenazine metho-sulfate. This electron donor system also effectively energizes transport under anaerobicconditions in the presence of the electron acceptor nitrate.     

Phosphorylative fumarate reduction in Vibrio succinogenes: Stoichiometry of ATP synthesis

1. Cells of Vibrio succinogenes, treated with EDTA at pH 8, catalyze the phosphorylation of their endogenous ADP and AMP as a function of the electron transport from formate to fumarate. The P/fumarate ratio obtained from the initial velocity of the phosphorylation on initiation of the electron transport and from the activity of fumarate reduction in the steady state was 0.90. The phosphorylation was prevented by 10μmol/g protein carbonylcyanide-3-chlorophenylhydrazone.
2. The esterification of external phosphate in the presence of ADP, hexokinase and glucose is catalysed by a membrane preparation of V. succinogenes in the steady state of fumarate reduction by H₂. The phosphorylation was fully abolished by either 5μmol/g protein carbonylcyanide-4-trifluoromethoxyphenylhydrazone or 30μmol/g protein carbonylcyanide-3-chlorphenylhydrazone. Phosphorylation was blocked also by dicyclohexylcarbodiimide, an inhibitor of the Mg²⁺-dependent membrane bound ATP synthase, and by low concentrations of the inhibitors of electron transport 2-(n-nonyl)-4-hydroxyquinoline-N-oxide or 4-chloromercuriphenylsulfonate.
3. The P/fumarate ratios, measured with the membrane preparation, were found to increase with progressive inhibition of the electron transport from hydrogen to fumarate by means of 4-chloromercuriphenylsulfonate. The extrapolated ratio at vanishing electron transport activity was 0.47.
4. About 50% of the membrane preparation was found to consist of inverted vesicles with the hydrogenase and formate dehydrogenase oriented to the inside. The residual part is considered as being incapable of performing energy transduction. The extrapolated P/fumarate ratio valid for the inverted vesicles was 0.94.

     

Purification and characterization of a new sodium-transport decarboxylase. Methylmalonyl-CoA decarboxylase from Veillonella alcalescens

Upon resolution of the particulate cell fraction of Veillonella alcalescens by gel chromatography, membranes and ribosomes were clearly resolved. Methylmalonyl-CoA decarboxylase was bound to the membranes and not to ribosomes as reported earlier. Membrane vesicles containing methylmalonyl-CoA decarboxylase were prepared by disrupting V. alcalescens cells with a French pressure chamber. About 64% of the decarboxylase was oriented in these vesicles with the substrate binding site facing to the outside. The vesicles performed a rapid accumulation of Na+ ions in response to the decarboxylation of methylmalonyl-CoA. Decarboxylation and transport were highly uncoupled. The efficiency of the transport was considerably increased if methylmalonyl-CoA decarboxylation was retarded by using a low temperature or by slowly generating the substrate enzymically from propionyl-CoA. Under optimized conditions Na+ was concentrated inside the inverted vesicles eight-times higher than in the incubation medium. Methylmalonyl-CoA decarboxylase was solubilized from the membranes with Triton X-100 and purified about 20-fold by affinity chromatography on monomeric avidin-Sepharose columns. The decarboxylase was specifically activated by Na+ ions (apparent Km approximately equal to 0.6 mM). Whereas (S)-methylmalonyl-CoA was the superior substrate (apparent Km approximately equal to 7 microM), malonyl-CoA was also decarboxylated (apparent Km approximately equal to 35 microM). The decarboxylation of methylmalonyl-CoA yielded CO2 and not HCO-3 as the primary reaction product. Analysis of the purified enzyme by dodecylsulfate gel electrophoresis indicated the presence of four different polypeptides alpha, beta, gamma, delta with Mr 60 000, 33 000, 18 5000 and 14 000. The latter of these polypeptides was clearly visible only after silver staining but not after staining with Coomassie brilliant blue. A low molecular weight polypeptide with similar staining properties was also found in oxaloacetate decarboxylase. Methylmalonyl-CoA decarboxylase contained about 1 mol covalently bound biotin per 125 500 g protein which was localized exclusively in the gamma-subunit. This subunit therefore represents the biotin carboxyl carrier protein of methylmalonyl-CoA decarboxylase. A new very sensitive method for the detection of biotin-containing proteins is described.     

Acetate kinase from Veillonella alcalescens. Regulation of enzyme activity by succinate and substrates.

Acetate kinase of Veillonella alcalescens has been shown to be highly regulated enzyme exhibiting two levels of control: the requirement for succinate as a heterotropic allosteric effector, and cooperative binding at the substrate level. Succinate addition was necessary for enzymatic activity in both the direction of acyl phosphate synthesis and that of ATP synthesis. Control at the substrate level was apparent in the cooperative binding (Hill coefficients of 2) of acetyl phosphate, ATP, and ADP. Typical Michaelis kinetic data were observed for succinate (Ka = 20 mM for acetyl phosphate synthesis, 0.4 mM for ATP synthesis), acetate, and propionate. The primary effect of succinate was to increase the apparent Vmax of the enzymatic reaction for the variable substrates, ATP, ADP, and acetyl phosphate. The results are interpreted as evidence that, as a heterotropic effector of the acetate kinase reaction, succinate may regulate levels of propionyl-CoA (produced from propionyl phosphate by action of phosphotransacetylase), a compound required for the conversion of succinate to propionate. Acetase kinase has been shown to be a probable dimeric protein composed of two subunits of molecular weight 44,000 each.     

Effect of sulfide on nitrate reduction in mixed methanogenic cultures

The effect of sulfide on nitrate reduction and methanogenesis was investigated in two mixed, mesophilic (35 degrees C) methanogenic cultures: sulfide-free and sulfide-acclimated (67 mg S/L total sulfide). A mixture of dextrin/peptone served as the carbon/electron donor source for the two stock cultures, as well as in all assays reported here. The sulfide-free enriched culture was amended with both nitrate (75-350 mg N/L) and sulfide (10-100 mg S/L). Denitrification was the predominant pathway at all sulfide levels tested and methanogenesis did not recover in any of the sulfide- and nitrate-amended cultures, except in the 10 mg S/L culture. Accumulation of denitrification intermediates such as NO and N(2)O took place, which irreversibly inhibited the methanogens and resulted in the complete cessation of methane production. In contrast, conversion of nitrate to nitrite and then to ammonia via dissimilatory nitrate reduction to ammonia (DNRA) prevented the accumulation of denitrification intermediates and led to the recovery of methanogenesis in the nitrate-amended, sulfide-acclimated, mixed methanogenic culture. The effect of the COD/N value on nitrate reduction was assessed with the sulfide-acclimated, methanogenic culture at COD/N values of 10, 20, and 60. As the COD/N value increased, the fraction of nitrate reduced through DNRA also increased. The results of this study have significant implications relative to the combined anaerobic treatment of carbon-, nitrogen-, and/or sulfur-bearing wastes.     

Structural specificity of diamines covalently linked to peptidoglycan for cell growth of Veillonella alcalescens and Selenomonas ruminantium.

Putrescine and cadaverine are essential constituents of the peptidoglycan of Veillonella alcalescens, Veillonella parvula, and Selenomonas ruminantium and are necessary for the growth of these organisms (Y. Kamio and K. Nakamura, J. Bacteriol. 169:2881-2884, 1987, and Y. Kamio, H. P?s?, Y. Terawaki, and L. Paulin, J. Biol. Chem. 261:6585-6589, 1986). In this study, the structural specificity of the diamine requirement for normal cell growth of these bacteria was examined by using a series of diamines with a general structure of NH3+ X (CH2)n X NH3+. Diaminohexane (n = 6) which was incorporated into the peptidoglycan was as effective as putrescine (n = 4) and cadaverine (n = 5) for normal cell growth. However, diaminopropane (n = 3) and diaminoheptane (n = 7) were less effective for growth than diaminohexane, although they were incorporated into the peptidoglycan to the same extent.     

Aerobic nitrate and nitrite reduction in continuous cultures of Escherichia coli E4

Nitrate and nitrite was reduced by Escherichia coli E4 in a l-lactate (5 mM) limited culture in a chemostat operated at dissolved oxygen concentrations corresponding to 90–100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, and oxygen and nitrate concentrations. At a low growth rate (0.11 h^–1) nitrate and nitrite reductase activities of 200 nmol · mg^–1 protein · min^–1 and 250 nmol · mg^–1 protein · min^–1 were measured, respectively. At a high growth rate (0.55 h^–1) both enzyme activities were considerably lower (25 and 12 nmol mg^–1 · protein · min^–1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both nitrate and nitrite reductase activity were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with growth rate than the nitrate reductase. The chemostat biomass concentration of E. coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E. coli E4 was able to grow in continuous cultures on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is related to the activity of nitrate and nitrite reductase and hence, inversely proportional to growth rate.