Antimicrobial activity of lactic acid bacteria isolated from goat's milk and artisanal cheeses: characteristics of a bacteriocin produced by Lactobacillus curvatus IFPL 105

A total of 203 lactic acid bacteria isolated from raw goat's milk and artisanal cheese were tested for antibacterial activity. Only two strains of Lactococcus lactis, one strain of Enterococcus faecalis and one strain of Lactobacillus curvatus were shown to produce a bacteriocin-like substance. Lactobacillus curvatus IFPL105 produced a heat-stable bacteriocin, which was hydrolysed by alpha-chymotrypsin, proteinase K and pancreatin and exhibited a broad spectrum of inhibitory activity. The bactericidal activity of the bacteriocin was more potent when sensitive strains were in the logarithmic growth phase, inducing cell lysis, as observed by decreases in optical density and release of intracellular marker enzymes. Curing experiments resulted in variants that lacked both bacteriocin activity and immunity to the bacteriocin. Plasmid profile analysis of the parental strain and the bacteriocin-negative variants indicated that a plasmid of about 46 kbp may be involved in bacteriocin production and immunity to this antibacterial compound.

Effect of methionine sulfoximine on nitrogen metabolism and externally supplied ammonium assimilation in kidney bean

L-Methionine sulfoximine (MSO) at concentration 1.25 mM in vivo causes the inhibition of glutamine synthetase (GS) in both roots and leaves of young seedlings of kidney bean following the accumulation of high levels of ammonia and decrease in amounts of free amino acids that is more pronounced in leaves. The inhibition of GS by MSO in leaves in the case of externally supplied 5 mM (15NH4)2SO4 assimilation leads to ammonia accumulation and the decrease in the amounts of glutamine and glutamic acid and the intensity of the incorporation of 15N into them. In roots the inhibition of GS is not followed by the decrease of 15N content into glutamate. It is concluded that the pathway of ammonia primary assimilation in leaves is via GS and glutamate synthase (GOGAT), while in roots glutamate dehydrogenase also plays an important role in this process.

Degradation of pyrimidine ribonucleosides by Pseudomonas aeruginosa

Pyrimidine ribonucleoside degradation in the human pathogen Pseudomonas aeruginosa ATCC 15692 was investigated. Either uracil, cytosine, 5-methylcytosine, thymine, uridine or cytidine supported P. aeruginosa growth as a nitrogen source when glucose served as the carbon source. Using thin-layer chromatographic analysis, the enzymes nucleoside hydrolase and cytosine deaminase were shown to be active in ATCC 15692. Compared to (NH4)2SO4-grown cells, nucleoside hydrolase activity in ATCC 15692 approximately doubled after growth on 5-methylcytosine as a nitrogen source while its cytosine deaminase activity increased several-fold after growth on the pyrimidine bases and ribonucleosides examined as nitrogen sources. Regulation at the level of protein synthesis by 5-methylcytosine was indicated for nucleoside hydrolase and cytosine deaminase in P. aeruginosa.

The CCAAT box-binding factor stimulates ammonium assimilation in Saccharomyces cerevisiae, defining a new cross-pathway regulation between nitrogen and carbon metabolisms

In Saccharomyces cerevisiae, carbon and nitrogen metabolisms are connected via the incorporation of ammonia into glutamate; this reaction is catalyzed by the NADP-dependent glutamate dehydrogenase (NADP-GDH) encoded by the GDH1 gene. In this report, we show that the GDH1 gene requires the CCAAT box-binding activator (HAP complex) for optimal expression. This conclusion is based on several lines of evidence: (1) overexpression of GDH1 can correct the growth defect of hap2 and hap3 mutants on ammonium sulfate as a nitrogen source, (ii) Northern (RNA) blot analysis shows that the steady-state level of GDH1 mRNA is strongly lowered in a hap2 mutant, (iii) expression of a GDH1-lacZ fusion is drastically reduced in hap mutants, (iv) NADP-GDH activity is several times lower in the hap mutants compared with that in the isogenic wild-type strain, and finally, (v) site-directed mutagenesis of two consensual HAP binding sites in the GDH1 promoter strongly reduces expression of GDH1 and makes it HAP independent. Expression of GDH1 is also regulated by the carbon source, i.e., expression is higher on lactate than on ethanol, glycerol, or galactose, with the lowest expression being found on glucose. Finally, we show that a hap2 mutation does not affect expression of other genes involved in nitrogen metabolism (GDH2, GLN1, and GLN3 encoding, respectively, the NAD-GDH, glutamine synthetase, and a general activator of several nitrogen catabolic genes). The HAP complex is known to regulate expression of several genes involved in carbon metabolism; its role in the control of GDH1 gene expression, therefore, provides evidence for a cross-pathway regulation between carbon and nitrogen metabolisms.

Pullulan production by Aureobasidium pullulans grown on ethanol stillage as a nitrogen source

Pullulan production by Aureobasidium pullulans strain RP-1 using thin stillage from fuel ethanol production as a nitrogen source was studied in a medium using corn syrup as a carbon source. The use of 1% thin stillage as a nitrogen source instead of ammonium sulphate elevated polysaccharide production by strain RP-1 cells when grown on a concentration of up to 7.5% corn syrup, independent of yeast extract supplementation. Dry weights of cells grown in medium containing ammonium sulphate as the nitrogen source were higher than the stillage-grown cells after 7 days of growth. The viscosity of the polysaccharide on day 7 was higher for cells grown on thin stillage rather than ammonium sulphate as a nitrogen source. The pullulan content of the polysaccharide elaborated by ammonium sulphate-grown cells on day 7 was higher than the pullulan content of polysaccharide produced by stillage-grown cells regardless of whether yeast extract was added to the culture medium.

Absolute requirement of ammonium sulfate for reconstitution of active 70S ribosomes from the extreme halophilic archaeon Haloferax mediterranei

Active 70S ribosomes from the halophilic archaeon Haloferax mediterranei have been reconstituted from their isolated rRNAs and proteins. The reconstitution procedure consists of a two-step incubation; first with 1 M ammonium sulfate and 100 mM magnesium acetate for 1 h at 42 degrees C, followed by a 90-min incubation at 50 degrees C after increasing the ammonium sulfate to 2 M final concentration. The total reconstitution of halophilic 70S ribosomes is a process with its own identity, which does not correspond to the conditions required for the reconstitution of the isolated subunits. Ammonium sulfate is the only salt capable of promoting the assembly of active ribosomes. The increase of ammonium sulfate salts in the second incubation step is obligatory for the isolation of functional particles.

Structures of charge-transfer complexes of flavoenzyme D-amino acid oxidase: a study by resonance Raman spectroscopy and extended Hückel molecular orbital method

The structure of the ligand in a charge-transfer complex of oxidized D-amino acid oxidase (DAO) formed upon aerobic addition of chloropyruvate and ammonium sulfate was determined by resonance Raman spectroscopy. The ligand in the complex is in the enamine form, 2-amino-3-chloracrylate, not in the imine form, 2-imino-3-chloropropionate. This conclusion is consistent with our hypothesis that the ligands in the charge-transfer complexes of oxidized DAO and reduced DAO are generally in the enamine and imine forms, respectively. The calculation of HOMO and LUMO of some enamine and imine forms by the extended Hückel molecular orbital method indicated that the enamine form is a better electron donor than the imine form and the imine form is a better electron acceptor than the enamine form. These results, as well as the information about the structure of enzyme-bound ligand, support the following ideas. (i) In the charge-transfer complex of reduced DAO, the reduced flavin is an electron donor. (ii) In the charge-transfer complex of reduced DAO, the reduced flavin is an electron donor and the ligand is an electron acceptor. Resonance Raman studies on the charge-transfer complexes of oxidized DAO and those of reduced DAO, and calculated results of HOMO and LUMO for some enamine and imine forms, corroborated the structure of the stacking form between the flavin ring and the ligand in the active site of DAO.

The toxicity of substituted phenols in the nitrification inhibition test and luminescent bacteria test

The nitrification inhibition test and the luminescent bacteria test were used to determine the inhibiting effect of different phenolic compounds. The chlorinated phenols demonstrated an increased toxicity in the nitrification inhibition test, which was much more sensitive to these compounds than other bacterial toxicity tests. In practice, the nitrification inhibition test was very useful for estimating the toxicity of chemical compounds to nitrifying bacteria, but the test is not recommended for the assessment of general bacterial toxicity. In comparison to other bacterial toxicity tests, the luminescent bacteria test also proved to be very sensitive. Due to its character, which measures a certain physiological parameter, this test system could be used as a screening tool for possible inhibitory effects to bacteria, although positive results should be confirmed by other bacterial toxicity tests.

Identification and characterization of two nitrogen-regulated genes of the cyanobacterium Synechococcus sp. strain PCC7942 required for maximum efficiency of nitrogen assimilation

Two nitrogen-regulated genes were found in the genomic DNA region upstream of the nirA operon involved in uptake and utilization of nitrate in Synechococcus sp. strain PCC7942. The two genes (nirB and ntcB) are transcribed divergently from nirA and encode proteins of 349 and 309 amino acid residues, respectively. The levels of nirB and ntcB transcripts were low in cells growing on ammonium and increased upon transfer of ammonium-grown cells to nitrate-containing medium. The deduced NirB protein sequence has no similarities to other known proteins, whereas the deduced NtcB protein sequence is homologous to bacterial transcriptional activators of the LysR family. Defined mutants constructed by interrupting nirB or ntcB with a drug resistance marker grew as fast as the wild-type strain on ammonium but grew slower than the wild-type strain on nitrate or nitrite. The nirB mutant had higher activities of nitrate reductase, glutamine synthetase, and glutamate synthase than the wild-type strain, but its nitrite reductase activity was 40% of the wild-type levels. The mutant excreted nitrite into the medium during growth on nitrate, showing that nitrite reductase limits nitrate assimilation. These findings suggested that nirB is required for expression of maximum nitrite reductase activity. When grown on ammonium, the nirB mutant grew normally but cultures of the ntcB mutant still showed a yellowish-green color typical of nitrogen-limited cells. NtcB seems to regulate utilization of fixed nitrogen by controlling the expression of a certain gene(s) involved in nitrogen metabolism.

Acid phosphatase synthesis in Aspergillus flavus

Proteins with phosphatase activity were produced during the growth of Aspergillus flavus in a phosphate-supplemented liquid synthetic medium. The best carbon and nitrogen sources for the synthesis of phosphatase were glucose and ammonium sulfate, respectively. The proteins were separated by molecular exclusion and ion exclusion chromatography (IEC) into three components one of which showed phosphatase activity. The molar mass of the enzyme was approximately 62 kDa. The purified enzyme exhibited an optimum activity at pH 4.0 and at 45 degrees C. The activity of the enzyme was stimulated by Ca2+ and Mg2+ but inhibited by fluoride, iodoacetic acid, ethylenediaminetetraacetic acid and 2,4-dinitrophenol, and exhibited an apparent KM of approximately 420 mumol/L.

Growth and metabolism of Saccharomyces cerevisiae in chemostat cultures under carbon-, nitrogen-, or carbon- and nitrogen-limiting conditions

Aerobic chemostat cultures of Saccharomyces cerevisiae were performed under carbon-, nitrogen-, and dual carbon- and nitrogen-limiting conditions. The glucose concentration was kept constant, whereas the ammonium concentration was varied among different experiments and different dilution rates. It was found that both glucose and ammonium were consumed at the maximal possible rate, i.e., the feed rate, over a range of medium C/N ratios and dilution rates. To a small extent, this was due to a changing biomass composition, but much more important was the ability of uncoupling between anabolic biomass formation and catabolic energy substrate consumption. When ammonium started to limit the amount of biomass formed and hence the anabolic flow of glucose, this was totally or at least partly compensated for by an increased catabolic glucose consumption. The primary response when glucose was present in excess of the minimum requirements for biomass production was an increased rate of respiration. The calculated specific oxygen consumption rate, at D = 0.07 h-1, was more than doubled when an additional nitrogen limitation was imposed on the cells compared with that during single glucose limitation. However, the maximum respiratory capacity decreased with decreasing nitrogen concentration. The saturation level of the specific oxygen consumption rate decreased from 5.5 to 6.0 mmol/g/h under single glucose limitation to about 4.0 mmol/g/h at the lowest nitrogen concentration tested. The combined result of this was that the critical dilution rate, i.e., onset of fermentation, was as low as 0.10 h-1 during growth in a medium with a low nitrogen concentration compared with 0.20 h-1 obtained under single glucose limitation.

Influence of different levels of ammonium concentrations on cell growth, RNA and protein production by Candida albicans

Candida albicans starved cells were incubated in minimal synthetic liquid media containing different concentrations of ammonium sulphate (0.00, 0.02, 0.05, 0.10, 0.03, 0.50 g/L). Culture growth was monitored by measuring daily the optical density and by evaluating RNA and protein cellular content after 48 and 96 hours from the inoculum. The environmental availability of ammonium ion influenced the biomass production, that was maximum when its concentration was 0.10 and 0.30 g/L. In addition, an effect on cell duplication time was observed, this was particularly evident when the (NH4)2SO4 concentration was 0.10 g/L. The protein content increased in relation to the increase of ammonium ion availability, with a peak in correspondence to 0.30 g/L and a drop when the greatest concentrations were employed. RNA production was inversely proportional in respect to protein production. The optimal range of ammonium sulphate concentration for C. albicans growth was 0.10-0.30 g/L; over these concentrations there was an inhibitory effect. The rate of the protein and RNA syntheses seems to indicate the growth phase and the nitrogen nutritional conditions of the cultures, respectively.

Involvement of the 20S proteasome in the degradation of ornithine decarboxylase

Eukaryotic cells have been shown to contain two high-molecular-mass proteases of 700 kDa and 1400 kDa (20S and 26S proteases, respectively). It has been suggested that the 20S protease, also known as proteasome, may constitute the catalytic core of the 26S protease. While the role of the free 20S protease in intracellular protein degradation is unclear, the 26S protease is implicated in the degradation of ubiquinated proteins. We have recently demonstrated, that ornithine decarboxylase (ODC), one of the most labile proteins in mammalian cells, is degraded via an ATP-dependent but ubiquitin-independent proteolytic pathway. Here we extend these observations by demonstrating that in reticulocyte lysate ODC degradation is inhibited by antibodies raised against the C9 subunit of rat proteasome. Partial fractionation of the lysate demonstrated preferential degradation of ODC in the fraction of the lysate proteins that are precipitated by 38% ammonium sulfate. Since it was demonstrated that the 26S protease precipitates at this concentration of ammonium sulfate while the 20S proteasome remains soluble, our results suggest that the 26S protease is the one degrading ODC.

Purification and some properties of peroxidase isozymes from pineapple stem

The enzyme peroxidase is widely distributed among the higher plants. Isozymes of peroxidase are known to occur in a variety of tissues in a large number of plant species. In this study, peroxidase isozymes were purified from the extract of pineapple stem through successive steps of ammonium sulfate fractionation, CM-Sepharose CL-6B chromatographies and DEAE-Sepharose CL-6B chromatographies. By these steps, twelve isozymes of peroxidase were obtained. Some properties of the isozymes were studied and compared.

Preparation of 13C and 15N labeled bellenamine and its degradation products

A streptomyces metabolite, bellenamine, has been converted into D-beta-lysinamide and cyclized bellenamine in an acidic solution at 75 degrees C. The structure of the new cyclized compound was assigned as (R)-6-(3-aminopropyl)-1,3-diazacyclohexan-4-one by spectral analyses. [1-13C, Amide, 1'-15N2]bellenamine, which has been isolated from the culture by feeding both L-[1-13C]lysine and [15NH4]2SO4 to a synthetic medium, was degraded under acidic condition to obtain the stable isotope labeled D-beta-lysine, D-beta-lysinamide and cyclized bellenamine. These labeled compounds were analyzed by 13C and 15N NMR spectra, and will be used for the biosynthetic study on bellenamine.

Biosynthesis of bellenamine by Streptomyces nashvillensis using stable isotope labeled compounds

The biosynthesis of bellenamine was studied by feeding 13C and 15N labeled precursors to the synthetic medium culture of Streptomyces nashvillensis MD743-GF4. The high degree of incorporation of D-[1-13C]beta-lysine indicated that it is a direct intermediate, while supplemented L-beta-lysine repressed the production of bellenamine. [2-13C]Glycine was well incorporated into the C-1' of the open-chain aldoaminal structure. All four nitrogens of bellenamine were derived from [15NH4]2SO4 present in the synthetic medium. In the addition of L-lysine and glycine, [15NH4]2SO4 was highly incorporated into CONH. The feeding experiments of 13C labeled acetates suggested that the D-beta-lysine moiety was derived from L-lysine by catalysis of a new 2,3-aminomutase, and L-lysine was biosynthesized from acetates via the TCA cycle and diaminopimelic acid pathway.

The effect of the UL42 protein on the DNA polymerase activity of the catalytic subunit of the DNA polymerase encoded by herpes simplex virus type 1

The effect that the UL42 protein of herpes simplex virus type 1 has on the DNA polymerase activity of the DNA polymerase catalytic subunit (Pol) of the same virus has been investigated. The observed effects are critically dependent on the salt used and its concentration, such that the UL42 protein may inhibit, have little or no effect on, or activate the Pol activity, depending on the condition used. The observed effects are due to the values for Km(app) for activated DNA and Vmaxapp for Pol and the Pol-UL42 protein complex differently varying with salt concentration.

Effect of nitrogen sources on oxidoreductive enzymes and ethanol production during D-xylose fermentation by Candida shehatae

The effect on D-xylose utilization and the corresponding xylitol and ethanol production by Candida shehatae (ATCC 22984) were examined with different nitrogen sources. These included organic (urea, asparagine, and peptone) and inorganic (ammonium chloride, ammonium nitrate, ammonium sulphate, and potassium nitrate) sources. Candida shehatae did not grow on potassium nitrate. Improved ethanol production (Y(p/s), yield coefficient (grams product/grams substrate), 0.34) was observed when organic nitrogen sources were used. Correspondingly, the xylitol production was also higher with organic sources. Ammonium sulphate showed the highest ethanol:xylitol ratio (11.0) among all the nitrogen sources tested. The ratio of NADH- to NADPH-linked D-xylose reductase (EC 1.1.1.21) appeared to be rate limiting during ethanologenesis of D-xylose. The levels of xylitol dehydrogenase (EC 1.1.1.9) were also elevated in the presence of organic nitrogen sources. These results may be useful in the optimization of alcohol production by C. shehatae during continuous fermentation of D-xylose.

Role of the disordered terminal regions of flagellin in filament formation and stability

Terminal regions of flagellin from Salmonella typhimurium, residues 1 to 65 and 451 to 494, have no ordered tertiary structure in solution, which makes them very susceptible to proteolytic degradation. Flagellin was subjected to mild controlled proteolytic treatment with highly specific proteases to remove terminal segments from the disordered regions. It is demonstrated here that various fragments can be readily prepared that differ from each other in 1 x 10(3) to 2 x 10(3) Mr segments in their NH2- or COOH-terminal regions. Terminally deleted fragments of flagellin were used to clarify the role of the disordered regions in the self-assembly of flagellin. The polymerization ability of the fragments was tested by inducing filament formation with ammonium sulfate. We found that fragments of flagellin containing large terminal deletions could form straight filaments, although the stability of these filaments required high salt concentrations. Even a fragment lacking the whole mobile COOH-terminal part of flagellin and 36 residues from the NH2-terminal region could form long filaments. The fragments could be also polymerized onto native flagellar seeds, suggesting that the subunit packing of the filaments of fragments is similar to that of the native ones. The fragments could also copolymerize with native flagellin, resulting in various helical forms. Filaments of fragments were found to be straight at both pH 4.0 and pH 12.5, indicating that they might have lost their polymorphic ability. Our results show that the major part of the disordered terminal regions of flagellin is not essential for polymerization, but it does play an important role in stabilization of the filaments and in influencing their polymorphic conformation.

The influence of carbon and nitrogen nutrition on fusarin C biosynthesis by Fusarium moniliforme

The influence of various carbon and nitrogen sources on fusarin C synthesis was examined in submerged cultures of Fusarium moniliforme NRRL 13616. Using a zinc-deficient, synthetic medium, highest levels of fusarin C were produced by cultures grown with urea or ammonium sulfate as the nitrogen source and fructose, sucrose, or glucose as the carbon source. In media supplemented with various concentrations of glucose and ammonium sulfate, glucose concentrations which provided excess carbohydrate significantly increased fusarin C synthesis, regardless of the ammonium sulfate concentration.

Regulation of biosynthesis of bacilysin by Bacillus subtilis

Production of the dipeptide antibiotic bacilysin by Bacillus subtilis 168 was growth associated and showed no evidence of repression by glucose or sucrose. Carbohydrates other than glucose and sucrose yielded lower specific titers of bacilysin. Bacilysin production in three such carbon sources (maltose, xylose, ribose) was delayed until growth slowed down. Ammonium salts were poor for bacilysin production when used as the sole nitrogen source. When added to the standard medium containing glutamate, they suppressed antibiotic production. Aspartate was slightly better than glutamate for antibiotic production as sole nitrogen source. No other nitrogen source tested, including inorganic, organic or complex, approached the activity of glutamate or aspartate. When added to glutamate, casamino acids, phenylalanine and alanine (a substrate of bacilysin synthetase) suppressed bacilysin production while stimulating growth. Phosphate provided for optimum growth and production at 7.5 mM and both processes were inhibited at higher concentrations. Ferric citrate stimulated growth and inhibited bacilysin production, the effects being due to both the iron and the citrate components. Elimination of ferric citrate stimulated production as did increasing the concentration of Mn to its optimum concentration of 6.6 x 10(-4) M.

Optimal concentration of ammonium ion in a minimal synthetic medium for the growth of Candida albicans

Candida albicans strain B 311-10 with and without starvation was cultivated in the minimal synthetic medium of Shepherd et al., modified without biotin, amino acids, low glucose concentration and with decreasing amounts of (NH4)2SO4, to determine the optimal growth requirement for this strain. All the experiments were carried out under sterile conditions at 25 degrees C in a thermostat with initial O.D.s (675 nm) of 0.500 and 0.100. Cell growth was generally monitored everyday for six days with a spectrophotometer by determining the absorbance of the cultures at 675 nm. All the experiments were repeated three times and a statistical analysis of the data with a probability of 99% and 1% of error was performed to confirm the validity of the results. Best growth was obtained with starved cells at an initial O.D. of 0.100 and with a 0.1 g/L concentration of (NH4)2SO4. At this concentration, the growth of C. albicans B 311-10 was best between the first and the fourth day with the maximum at the third day. With (NH4)2SO4 concentrations of 0.05 and 0.5 g/L, cell growth was the same.

[The role of thrombin on lung fibroblast growth and fibrosis in bleomycin-induced lung disorder]

In order to clarify the role of thrombin on the development of pulmonary fibrosis in diffuse interstitial lung diseases, we examined the relationship between fibroblast growth-stimulating activity (FGA) and thrombin activity in bronchoalveolar lavage fluid (BALF) from rats with bleomycin-induced interstitial lung disorders. Male Wistar strain rats (body weight about 200 g) were given a single intratracheal injection of 0.9 mg bleomycin, and bronchoalveolar lavage was performed on days 2, 6 and 15. The BALF was centrifuged at 250 X g for 10 min to remove cells, and then the supernatant was recentrifugation at 27,000 X g for 40 min to remove pulmonary surfactants. The supernatant (10 ml) was dialyzed overnight against distilled water, frozen at -70 degrees C, freeze-dried, and resuspended in 2 ml of Dulbecco's modified Eagle medium (concentrated 5-fold). The 5-fold concentrated BALF was added to rat lung fibroblast culture media, and assayed for cytotoxic activity and FGA. Thrombin activity in 250 X g supernatant was measured by using fluorescence assay with the synthetic peptide substrate, Boc-Val-Pro-Arg-4-methylcoumaryl-7-amide. Histological examination showed a prominent increase in fibroblast number in the pulmonary interstitium on day 6, and transformation of fibroblasts into mature forms, fibrocytes, on day 15. On day 2 after bleomycin administration, no FGA was seen but cytotoxic activity was detected in the BALF. On day 6, the cytotoxic activity was not found, whereas FGA showed a significantly higher level than the control value. On day 15, the FGA decreased to the control value.(ABSTRACT TRUNCATED AT 250 WORDS)