Factors Controlling Anaerobic Ammonium Oxidation with Nitrite in Marine Sediments

Factors controlling the anaerobic oxidation of ammonium with nitrate and nitrite were explored in a marine sediment from the Skagerrak in the Baltic-North Sea transition. In anoxic incubations with the addition of nitrite, approximately 65% of the nitrogen gas formation was due to anaerobic ammonium oxidation with nitrite, with the remainder being produced by denitrification. Anaerobic ammonium oxidation with nitrite exhibited a biological temperature response, with a rate optimum at 15°C and a maximum temperature of 37°C. The biological nature of the process and a 1:1 stoichiometry for the reaction between nitrite and ammonium indicated that the transformations might be attributed to the anammox process. Attempts to find other anaerobic ammonium-oxidizing processes in this sediment failed. The apparent K_m of nitrite consumption was less than 3 μM, and the relative importance of ammonium oxidation with nitrite and denitrification for the production of nitrogen gas was independent of nitrite concentration. Thus, the quantitative importance of ammonium oxidation with nitrite in the jar incubations at elevated nitrite concentrations probably represents the in situ situation. With the addition of nitrate, the production of nitrite from nitrate was four times faster than its consumption and therefore did not limit the rate of ammonium oxidation. Accordingly, the rate of this process was the same whether nitrate or nitrite was added as electron acceptor. The addition of organic matter did not stimulate denitrification, possibly because it was outcompeted by manganese reduction or because transport limitation was removed due to homogenization of the sediment.     

beta-Alanine as an Ethylene Precursor. Investigations Towards Preparation, and Properties, of a Soluble Enzyme System From a Subcellular Particulate Fraction of Bean Cotyledons

A method is described for the preparation, from a subcellular particulate fraction of wax bean cotyledons, of a soluble enzyme system that is capable of converting β-alanine to ethylene. In the presence of ATP, CoA, thiamine pyrophosphate, MgSO₄, and pyridoxal phosphate, ethylene production is maximum at a 0.5 mm concentration of β-alanine. The system exhibits a pH optimum at 7.0 but when the pH is raised above 8, evolution of the volatile again increases and continues to do so up to pH 12. The enzyme system is stimulated by either NADPH or NADH; the concentration of NADPH necessary to obtain maximum activity is twice that of NADH. The requirement for a reducing agent is in agreement with the proposal that malonate semialdehyde, formed by an aminotransferase reaction from β-alanine, is reduced to β-hydroxypropionate. Both malonate semialdehyde and β-hydroxypropionate are better stimulators of production of the volatile in the soluble system than is β-alanine, and β-hydroxypropionate is a better stimulator than malonate semialdehyde. This system is also able to incorporate tritium from tritiated water into ethylene; this supports the proposal that ethylene is formed by the decarboxylation of acrylate, the latter being formed from β-hydroxypropionate.     

Nitrogen Redox Metabolism of a Heterotrophic, Nitrifying-Denitrifying Alcaligenes sp. from Soil

Metabolic characteristics of a heterotrophic, nitrifier-denitrifier Alcaligenes sp. isolated from soil were further characterized. Pyruvic oxime and hydroxylamine were oxidized to nitrite aerobically by nitrification-adapted cells with specific activities (V_max) of 0.066 and 0.003 μmol of N × min⁻¹ × mg of protein⁻¹, respectively, at 22°C. K_m values were 15 and 42 μM for pyruvic oxime and hydroxylamine, respectively. The greater pyruvic oxime oxidation activity relative to hydroxylamine oxidation activity indicates that pyruvic oxime was a specific substrate and was not oxidized appreciably via its hydrolysis product, hydroxylamine. When grown as a denitrifier on nitrate, the bacterium could not aerobically oxidize pyruvic oxime or hydroxylamine to nitrite. However, hydroxylamine was converted to nearly equimolar amounts of ammonium ion and nitrous oxide, and the nature of this reaction is discussed. Cells grown as heterotrophic nitrifiers on pyruvic oxime contained two enzymes of denitrification, nitrate reductase and nitric oxide reductase. The nitrate reductase was the dissimilatory type, as evidenced by its extreme sensitivity to inhibition by azide and by its ability to be reversibly inhibited by oxygen. Cells grown aerobically on organic carbon sources other than pyruvic oxime contained none of the denitrifying enzymes surveyed but were able to oxidize pyruvic oxime to nitrite and reduce hydroxylamine to ammonium ion.     

Effect of CO2 and phosphate deprivation on the control of nitrate, nitrite and ammonium metabolism in Chlorella

Chlorella vulgaris Beijerinck, strain 211/12, uses nitrate, nitrite and ammonium at pH 8.2 but not at pH 6.4 when kept under conditions of CO₂-deprivation, as observed in cell suspensions aerated with CO₂-free air during a 20–30. h period Most of the nitrate absorbed at pH 8.2, however, was not assimilated but was released into the external medium as nitrite and ammonium. Cells of Chlorella previously grown in phosphate-limited continuous cultures were unable to absorb nitrate, nitrite or ammonium under conditions of phosphate starvation at either pH 6.4 or 8.2 in cell suspensions flushed with air containing 5% CO₂, However, in cell suspensions flushed with CO₂-free air, the capacity of the alga to absorb and reduce nitrate and to excrete nitrite and ammonium at pH 8.2 was restored.
It is hypothesized that in Chlorella the metabolism of nitrate, nitrite and ammonium is influenced by the availability of other nutrients and controlled by the cell's carbon status at the level of ion entry into the cell. With respect to nitrate this carbon-dependent control is distinct and works independently of that triggered by the cell's nitrogen status.     

Kinetic Explanation for Accumulation of Nitrite, Nitric Oxide, and Nitrous Oxide During Bacterial Denitrification

The kinetics of denitrification and the causes of nitrite and nitrous oxide accumulation were examined in resting cell suspensions of three denitrifiers. An Alcaligenes species and a Pseudomonas fluorescens isolate characteristically accumulated nitrite when reducing nitrate; a Flavobacterium isolate did not. Nitrate did not inhibit nitrite reduction in cultures grown with tungstate to prevent formation of an active nitrate reductase; rather, accumulation of nitrite seemed to depend on the relative rates of nitrate and nitrite reduction. Each isolate rapidly reduced nitrous oxide even when nitrate or nitrite had been included in the incubation mixture. Nitrate also did not inhibit nitrous oxide reduction in Alcaligenes odorans, an organism incapable of nitrate reduction. Thus, added nitrate or nitrite does not always cause nitrous oxide accumulation, as has often been reported for denitrifying soils. All strains produced small amounts of nitric oxide during denitrification in a pattern suggesting that nitric oxide was also under kinetic control similar to that of nitrite and nitrous oxide. Apparent K_m values for nitrate and nitrite reduction were 15 μM or less for each isolate. The K_m value for nitrous oxide reduction by Flavobacterium sp. was 0.5 μM. Numerical solutions to a mathematical model of denitrification based on Michaelis-Menten kinetics showed that differences in reduction rates of the nitrogenous compounds were sufficient to account for the observed patterns of nitrite, nitric oxide, and nitrous oxide accumulation. Addition of oxygen inhibited gas production from ¹³NO₃⁻ by Alcaligenes sp. and P. fluorescens, but it did not reduce gas production by Flavobacterium sp. However, all three isolates produced higher ratios of nitrous oxide to dinitrogen as the oxygen tension increased. Inclusion of oxygen in the model as a nonspecific inhibitor of each step in denitrification resulted in decreased gas production but increased ratios of nitrous oxide to dinitrogen, as observed experimentally. The simplicity of this kinetic model of denitrification and its ability to unify disparate observations should make the model a useful guide in research on the physiology of denitrifier response to environmental effectors.     

Geranic Acid Formation, an Initial Reaction of Anaerobic Monoterpene Metabolism in Denitrifying Alcaligenes defragrans

Monoterpenes with an unsaturated hydrocarbon structure are mineralized anaerobically by the denitrifying β-proteobacterium Alcaligenes defragrans. Organic acids occurring in cells of A. defragrans and culture medium were characterized to identify potential products of the monoterpene activation reaction. Geranic acid (E,E-3,7-dimethyl-2,6-octadienoic acid) accumulated to 0.5 mM in cells grown on α-phellandrene under nitrate limitation. Cell suspensions of A. defragrans 65Phen synthesized geranic acid in the presence of β-myrcene, α-phellandrene, limonene, or α-pinene. Myrcene yielded the highest transformation rates. The alicyclic acid was consumed by cell suspensions during carbon limitation. Heat-labile substances present in cytosolic extracts catalyzed the formation of geranic acid from myrcene. These results indicated that a novel monoterpene degradation pathway must be present in A. defragrans.     

Comparative Physiological Evidence that beta-Alanine Betaine and Choline-O-Sulfate Act as Compatible Osmolytes in Halophytic Limonium Species

The quaternary ammonium compounds accumulated in saline conditions by five salt-tolerant species of Limonium (Plumbaginaceae) were analyzed by fast atom bombardment mass spectrometry. Three species accumulated β-alanine betaine and choline-O-sulfate; the others accumulated glycine betaine and choline-O-sulfate. Three lines of evidence indicated that β-alanine betaine and choline-O-sulfate replace glycine betaine as osmo-regulatory solutes. First, tests with bacteria showed that β-alanine betaine and choline-O-sulfate have osmoprotective properties comparable to glycine betaine. Second, when β-alanine betaine and glycine betaine accumulators were salinized, the levels of their respective betaines, plus that of choline-O-sulfate, were closely correlated with leaf solute potential. Third, substitution of sulfate for chloride salinity caused an increase in the level of choline-O-sulfate and a matching decrease in glycine betaine level. Experiments with ¹⁴C-labeled precursors established that β-alanine betaine accumulators did not synthesize glycine betaine and vice versa. These experiments also showed that β-alanine betaine synthesis occurs in roots as well as leaves of β-alanine betaine accumulators and that choline-O-sulfate and glycine betaine share choline as a precursor. Unlike glycine betaine, β-alanine betaine synthesis cannot interfere with conjugation of sulfate to choline by competing for choline and does not require oxygen. These features of β-alanine betaine may be advantageous in sulfate-rich salt marsh environments.     

Purification of Two Nitrate Reductases from Xanthomonas maltophilia Grown in Aerobic Cultures

Xanthomonas maltophilia ATCC 17666 is an obligate aerobe that accumulates nitrite when grown on nitrate. Spectra of membranes from nitrate-grown cells exhibited b-type cytochrome peaks and A_615-630 indicative of d-type cytochrome but no absorption peaks corresponding to c-type cytochromes. The nitrate reductase (NR) activity was located in the membrane fraction. Triton X-100-extracted reduced methyl viologen-NRs were purified on DE-52, hydroxylapatite, and Sephacryl S-300 columns to specific activities of 52 to 67 μmol of nitrite formed per min per mg of protein. The cytochrome-containing NR_I separated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis into a 135-kDa α-subunit, a 64-kDa β-subunit, and a 23-kDa γ-subunit with relative band intensities indicative of a 1:1:1 α/β/γ subunit ratio and a M_r of 222,000. The electronic spectrum of dithionite-reduced purified NR displayed peaks at 425, 528, and 558 nm, indicative of the presence of a cytochrome b, an interpretation consistent with the pyridine hemochrome spectrum formed. The cytochrome b of the NR was reduced under anaerobic conditions by menadiol and oxidized by nitrate with the production of nitrite. This NR contained 0.96 Mo, 12.5 nonheme iron, and 1 heme per 222 kDa: molybdopterin was detected with the Neurospora crassa nit-1 assay. A smaller reduced methyl viologen-NR (169 kDa), present in various concentrations in the Triton X-100 preparations, lacked a cytochrome spectrum and did not oxidize menadiol. The characteristics of the NRs and the absence of c-type cytochromes provide insights into why X. maltophilia accumulates nitrite.     

Ammonium and Nitrite Inhibition of Methane Oxidation by Methylobacter albus BG8 and Methylosinus trichosporium OB3b at Low Methane Concentrations

Methane oxidation by pure cultures of the methanotrophs Methylobacter albus BG8 and Methylosinus trichosporium OB3b was inhibited by ammonium choride and sodium nitrite relative to that in cultures assayed in either nitrate-containing or nitrate-free medium. M. albus was generally more sensitive to ammonium and nitrite than M. trichosporium. Both species produced nitrite from ammonium; the concentrations of nitrite produced increased with increasing methane concentrations in the culture headspaces. Inhibition of methane oxidation by nitrite was inversely proportional to headspace methane concentrations, with only minimal effects observed at concentrations of>500 ppm in the presence of 250 μM nitrite. Inhibition increased with increasing ammonium at methane concentrations of 100 ppm. In the presence of 500 μM ammonium, inhibition increased initially with increasing methane concentrations from 1.7 to 100 ppm; the extent of inhibition decreased with methane concentrations of > 100 ppm. The results of this study provide new insights that explain some of the previously observed interactions among ammonium, nitrite, methane, and methane oxidation in soils and aquatic systems.     

The activities of two pathways of nitrate reduction in Rhodopseudomonas capsulata

1. The disappearance of nitrate from suspensions of intact, washed cells of Rhodopseudomonas capsulata strain N22DNAR⁺ was measured with an ion selective electrode. In samples taken from phototrophic cultures grown to late exponential phase, nitrate disappearance was partially inhibited by light but was not affected by the presence of ammonium. Nitrate disappearance from samples from low density cultures in the early exponential phase of growth was first inhibited and later stimulated by light. In these cells ammonium ions inhibited the light-dependent but not the dark disappearance of nitrate. It is concluded that cells in the early exponential phase of growth possess both an ammonium-sensitive, assimilatory pathway for nitrate reduction (NRI) and an ammonium-insensitive pathway for nitrate reduction (NRII) which is linked to respiratory electron flow and energy conservation. In cells harvested in late exponential phase only the respiratory pathway for pitrate reduction is detectable.
2. Nitrate reduction, as judged by the oxidation of reduced methyl viologen by anaerobic cell suspensions, was measured at high rates in those strains of R. capsulata (AD2, BK5, N22DNAR⁺) which are believed to possess NRII activity but not in those strains (Kbl, R3, N22) which only manifest the ammonium-sensitive NRI pathway. On this basis we have used nitrate-dependent oxidation of reduced methyl viologen as a diagnostic test for the nitrate reductase of NRII in cells harvested from cultures of R. capsulata strain AD2. The activity was readily detectable in cells from cultures grown aerobically in the dark with ammonium nitrate as source of nitrogen. When the oxygen supply to the culture was withdrawn, the level of methyl viologen-dependent nitrate reductase increased considerably and nitrite accumulated in the culture medium. Upon reconnecting the oxygen supply, methyl viologen-dependent nitrate reductase activity decreased and the reduction of nitrate to nitrite in the culture was inhibited. It is concluded that the respiratory nitrate reductase activity is regulated by the availability of electron transport pathways that are linked to the generation of a proton electrochemical gradient.

     

Effects of Soil on Ammonia, Ethylene, Chloroethane, and 1,1,1-Trichloroethane Oxidation by Nitrosomonas europaea

Ammonia monooxygenase (AMO) from Nitrosomonas europaea catalyzes the oxidation of ammonia to hydroxylamine and has been shown to oxidize a variety of halogenated and nonhalogenated hydrocarbons. As part of a program focused upon extending these observations to natural systems, a study was conducted to examine the influence of soil upon the cooxidative abilities of N. europaea. Small quantities of Willamette silt loam (organic carbon content, 1.8%; cation-exchange capacity, 15 cmol/kg of soil) were suspended with N. europaea cells in a soil-slurry-type reaction mixture. The oxidations of ammonia and three different hydrocarbons (ethylene, chloroethane, and 1,1,1-trichloroethane) were compared to results for controls in which no soil was added. The soil significantly inhibited nitrite production from 10 mM ammonium by N. europaea. Inhibition resulted from a combination of ammonium adsorption onto soil colloids and the exchangeable acidity of the soil lowering the pH of the reaction mixture. These phenomena resulted in a substantial drop in the concentration of NH₄⁺ in solution (10 to 4.5 mM) and, depending upon the pH, in a reduction in the amount of available NH₃ to concentrations (8 to 80 μM) similar to the K_s value of AMO for NH₃ (~29 μM). At a fixed initial pH (7.8), the presence of soil also modified the rates of oxidation of ethylene and chloroethane and changed the concentrations at which their maximal rates of oxidation occurred. The modifying effects of soil on nitrite production and on the cooxidation of ethylene and chloroethane could be circumvented by raising the ammonium concentration in the reaction mixture from 10 to 50 mM. Soil had virtually no effect on the oxidation of 1,1,1-trichloroethane.     

Substrate induction of nitrate reductase in barley aleurone layers

Nitrate induces the formation of nitrate reductase activity in barley (Hordeum vulgare L. cv. Himalaya) aleurone layers. Previous work has demonstrated de novo synthesis of α-amylase by gibberellic acid in the same tissue. The increase in nitrate reductase activity is inhibited by cycloheximide and 6-methylpurine, but not by actinomycin D. Nitrate does not induce α-amylase synthesis, and it has no effect on the gibberellic acid-induced synthesis of α-amylase. Also, there is little or no direct effect of gibberellic acid (during the first 6 hr of induction) or of abscisic acid on the nitrate-induced formation of nitrate reductase. Gibberellic acid does interfere with nitrate reductase activity during long-term experiments (greater than 6 hr). However, the time course of this inhibition suggests that the inhibition may be a secondary one. Barley aleurone layers therefore provide a convenient tissue for the study of both substrate- and hormone-induced enzyme formation.     

Mechanistic Analysis of Ammonium Inhibition of Atmospheric Methane Consumption in Forest Soils

Methane consumption by forest soil was studied in situ and in vitro with respect to responses to nitrogen additions at atmospheric and elevated methane concentrations. Methane concentrations in intact soil decreased continuously from atmospheric levels at the surface to 0.5 ppm at a depth of 14 cm. The consumption rate of atmospheric methane in soils, however, was highest in the 4- to 8-cm depth interval (2.9 nmol per g of dry soil per day), with much lower activities below and above this zone. In contrast, extractable ammonium and nitrate concentrations were highest in the surface layer (0 to 2 cm; 22 and 1.6 μmol per g of dry soil, respectively), as was potential ammonium-oxidizing activity (19 nmol per g of dry soil per day). The difference in zonation between ammonium oxidation and methane consumption suggested that ammonia-oxidizing bacteria did not contribute significantly to atmospheric methane consumption. Exogenous ammonium inhibited methane consumption in situ and in vitro, but the pattern of inhibition did not conform to expectations based on simple competition between ammonia and methane for methane monooxygenase. The extent of ammonium inhibition increased with increasing methane concentration. Inhibition by a single ammonium addition remained constant over a period of 39 days. In addition, nitrite, the end product of methanotrophic ammonia oxidation, was a more effective inhibitor of methane consumption than ammonium. Factors that stimulated ammonium oxidation in soil, e.g., elevated methane concentrations and the availability of cosubstrates such as formate, methanol, or β-hydroxybutyrate, enhanced ammonium inhibition of methane oxidation, probably as a result of enhanced nitrite production.     

Populations of Pratylenchus penetrans Relative to Decomposing Nitrogenous Soil Amendments

Populations of Pratylenchus penetrans decreased in soil following addition of 70 and 700 ppm N in the form of nitrate, nitrite, organic nitrogen, or ammonium compounds. Nitrate was less effective than other nitrogen carriers. Population reduction is principally attributed to ammonification during decomposition. This hypothesis is supported by chromatographic analyses of soil atmospheres, survival of nematodes in pure CO₂ and N₂, inverse relationship of CO₂, content in amended soils to nematode populations, and direct relationship of NH₃-N content of amended soils to nematode populations.     

Fate of Nitrate Acquired by the Tubeworm Riftia pachyptila

The hydrothermal vent tubeworm Riftia pachyptila lacks a mouth and gut and lives in association with intracellular, sulfide-oxidizing chemoautotrophic bacteria. Growth of this tubeworm requires an exogenous source of nitrogen for biosynthesis, and, as determined in previous studies, environmental ammonia and free amino acids appear to be unlikely sources of nitrogen. Nitrate, however, is present in situ (K. Johnson, J. Childress, R. Hessler, C. Sakamoto-Arnold, and C. Beehler, Deep-Sea Res. 35:1723–1744, 1988), is taken up by the host, and can be chemically reduced by the symbionts (U. Hentschel and H. Felbeck, Nature 366:338–340, 1993). Here we report that at an in situ concentration of 40 μM, nitrate is acquired by R. pachyptila at a rate of 3.54 μmol g⁻¹ h⁻¹, while elimination of nitrite and elimination of ammonia occur at much lower rates (0.017 and 0.21 μmol g⁻¹ h⁻¹, respectively). We also observed reduction of nitrite (and accordingly nitrate) to ammonia in the trophosome tissue. When R. pachyptila tubeworms are exposed to constant in situ conditions for 60 h, there is a difference between the amount of nitrogen acquired via nitrate uptake and the amount of nitrogen lost via nitrite and ammonia elimination, which indicates that there is a nitrogen “sink.” Our results demonstrate that storage of nitrate does not account for the observed stoichiometric differences in the amounts of nitrogen. Nitrate uptake was not correlated with sulfide or inorganic carbon flux, suggesting that nitrate is probably not an important oxidant in metabolism of the symbionts. Accordingly, we describe a nitrogen flux model for this association, in which the product of symbiont nitrate reduction, ammonia, is the primary source of nitrogen for the host and the symbionts and fulfills the association's nitrogen needs via incorporation of ammonia into amino acids.     

Nitrate Utilization by the Diatom Skeletonema costatum: II. Regulation of Nitrate Uptake

Nitrate utilization has been characterized in nitrogen-deficient cells of the marine diatom Skeletonema costatum. In order to separate nitrate uptake from nitrate reduction, nitrate reductase activity was suppressed with tungstate. Neither nitrite nor the presence of amino acids in the external medium or darkness affects nitrate uptake kinetics. Ammonium strongly inhibits carrier-mediated nitrate uptake, without affecting diffusion transfer. A model is proposed for the uptake and assimilation of nitrate in S. costatum and their regulation by ammonium ions.     

Seed Dormancy in Red Rice : III. Response to Nitrite, Nitrate, and Ammonium Ions

Sodium nitrite at 10 millimolar breaks dormancy of dehulled red rice (Oryza sativa). While germination is light independent, low pH conditions (pH 3) are required for maximum response. Water and buffer controls at pH 3 remain dormant. The response to nitrite occurs at 25 and 30°C but is reduced at 20°C, although nondormant seeds germinate readily at this temperature. The contact time for response to nitrite is less than 2 h at the start of imbibition. Seeds imbibed first in water show reduced germination when subsequently transferred to nitrite. Dehulled seeds show little or no response to nitrate and ammonium ions.

Intact seeds remain dormant in the presence of nitrite or nitrate unless partially dry-afterripened. The pH dependence of nitrite sensitivity is reduced in intact, afterripening seeds. In highly dormant seeds, vacuum infiltration experiments suggest that the hull restricts uptake of nitrite.

     

An Archaeal Glutamate Decarboxylase Homolog Functions as an Aspartate Decarboxylase and Is Involved in β-Alanine and Coenzyme A Biosynthesis

β-Alanine is a precursor for coenzyme A (CoA) biosynthesis and is a substrate for the bacterial/eukaryotic pantothenate synthetase and archaeal phosphopantothenate synthetase. β-Alanine is synthesized through various enzymes/pathways in bacteria and eukaryotes, including the direct decarboxylation of Asp by aspartate 1-decarboxylase (ADC), the degradation of pyrimidine, or the oxidation of polyamines. However, in most archaea, homologs of these enzymes are not present; thus, the mechanisms of β-alanine biosynthesis remain unclear. Here, we performed a biochemical and genetic study on a glutamate decarboxylase (GAD) homolog encoded by TK1814 from the hyperthermophilic archaeon Thermococcus kodakarensis. GADs are distributed in all three domains of life, generally catalyzing the decarboxylation of Glu to γ-aminobutyrate (GABA). The recombinant TK1814 protein displayed not only GAD activity but also ADC activity using pyridoxal 5′-phosphate as a cofactor. Kinetic studies revealed that the TK1814 protein prefers Asp as its substrate rather than Glu, with nearly a 20-fold difference in catalytic efficiency. Gene disruption of TK1814 resulted in a strain that could not grow in standard medium. Addition of β-alanine, 4′-phosphopantothenate, or CoA complemented the growth defect, whereas GABA could not. Our results provide genetic evidence that TK1814 functions as an ADC in T. kodakarensis, providing the β-alanine necessary for CoA biosynthesis. The results also suggest that the GAD activity of TK1814 is not necessary for growth, at least under the conditions applied in this study. TK1814 homologs are distributed in a wide range of archaea and may be responsible for β-alanine biosynthesis in these organisms.     

Production of an Amylase-Sensitive Bacteriocin by an Atypical Leuconostoc paramesenteroides Strain

An atypical Leuconostoc paramesenteroides strain isolated from retail lamb produced a bacteriocin, leuconocin S, that was inactivated by α-amylase, trypsin, α-chymotrypsin, protease, and proteinase K but not by lipase or heat treatment at 60°C for 30 min. Supernatants from culture broths produced two glycoprotein bands on sodium dodecyl sulfate-polyacrylamide gels; these had molecular weights of 2,000 and 10,000 and activity against Lactobacillus sake ATCC 15521. The crude bacteriocin preparation was bacteriostatic and dissipated proton motive force. Bacteriocin activity was produced over a wide pH range (5.2 to 7.9) on buffered agar medium, with an optimum pH of pH 6.15. The optimum pH for production in broth was 6.5 to 7.0.