Hexavalent molybdenum reduction to Mo-blue by <Emphasis Type="Italic">Acinetobacter calcoaceticus</Emphasis>

A local molybdenum-reducing bacterium was isolated and tentatively identified as Acinetobacter calcoaceticus strain Dr.Y12 based on carbon utilization profiles using Biolog GN plates and 16S rDNA comparative analysis. Molybdate reduction was optimized under conditions of low dissolved oxygen (37 °C and pH 6.5). Of the electron donors tested, glucose, fructose, maltose and sucrose supported molybdate reduction after 1 d of incubation, glucose and fructose supporting the highest Mo-blue production. Optimum Mo-blue production was reached at 20 mmol/L molybdate and 5 mmol/L phosphate; increasing the phosphate concentrations inhibited the production. An increase in an overall absorption profiles, especially at peak maximum at 865 nm and the shoulder at 700 nm, was observed in direct correlation with the increased in Mo-blue amounts. Metal ions, such as chromium, cadmium, copper, mercury and lead (2 mmol/L final concentration) caused ≈88, 53, 80, 100, and 20 % inhibition, respectively. Respiratory inhibitors, such as antimycin A, rotenone, sodium azide and cyanide showed in this bacterium no inhibition of the Mo-blue production, suggesting that the electron transport system is not a site of molybdate reduction.     

Molybdate reduction by Pseudomonas sp. strain DRY2

Aims: To isolate and characterize a potent molybdenum‐reducing bacterium. Methods and Results: A minimal salt medium supplemented with 10 mmol l^?1 molybdate, glucose (1·0%, w/v) as a carbon source and ammonium sulfate (0·3%, w/v) as a nitrogen source was used in the screening process. A molybdenum‐reducing bacterium was isolated and tentatively identified as Pseudomonas sp. strain DRY2 based on carbon utilization profiles using Biolog GN plates and partial 16S rDNA molecular phylogeny. Strain DRY2 produced 2·4, 3·2 and 6·2 times more molybdenum blue compared to Serratia marcescens strain DRY6, Enterobacter cloacae strain 48 and Eschericia coli K12, respectively. Molybdate reduction was optimum at 5 mmol l^?1 phosphate. The optimum molybdate concentration that supported molybdate reduction at 5 mmol l^?1 phosphate was between 15 and 25 mmol l^?1. Molybdate reduction was optimum at 40°C and at pH 6·0. Phosphate concentrations higher than 5 mmol l^?1 strongly inhibited molybdate reduction. Inhibitors of electron transport system such as antimycin A, rotenone, sodium azide and cyanide did not inhibit the molybdenum‐reducing enzyme activity. Chromium, copper, mercury and lead inhibited the molybdenum‐reducing activity. Conclusions: A novel molybdenum‐reducing bacterium with high molybdenum reduction capacity has been isolated. Significance and Impact of the Study: Molybdenum is an emerging global pollutant that is very toxic to ruminants. The characteristics of this bacterium suggest that it would be useful in the bioremediation of molybdenum pollutant.     

Isolation and characterization of a chromium-resistant bacterium Serratia sp. Cr-10 from a chromate-contaminated site

A novel bacterium, Cr-10, was isolated from a chromium-contaminated site and capable of removing toxic chromium species from solution by reducing hexavalent chromium to an insoluble precipitate. Sequence analysis of 16S rRNA gene of strain Cr-10 showed that it was most closely related to Serratia rubidaea JCM 1240^T (97.68%). Physiological and chemotaxonomic data also supported that strain Cr-10 was identified as Serratia sp., a genus which was never specially reported chromate-resistant before. Serratia sp., Cr-10 was tolerant to a concentration of 1,500 mg Cr(VI) L⁻¹, which was the highest level reported until now. The optimum pH and temperature for reduction of Cr(VI) by Serratia sp. Cr-10 were found to be 7.0 and 37 °C, respectively. The Cr(VI) reduction was significantly influenced by additional carbon sources, and among them fructose and lactose offered maximum reduction, with a rate of 0.28 and 0.25 mg Cr(VI) L⁻¹ h⁻¹, respectively. The cell-free extracts and filtrate of the culture were able to reduce Cr(VI) while concentration of total chromium remained stable in the process, indicating that the enzyme-catalyzed mechanism was applied in Cr(VI) reduction by the isolate. Additionally, it was found that there was hardly any chromium on the cell surface of the strain, further supporting that reduction, rather than bioadsorption, plays a major role in the Cr(VI) removal.     

The influence of growth conditions on the synthesis of molybdenum cofactor in Proteus mirabilis

Cell-free extracts of Proteus mirabilis were able to reconstitute NADPH-dependent assimilatory nitrate reductase in crude extracts of the Neurospora crassa mutant strain nit-1, lacking molybdenum cofactor. Molybdenum cofactor was formed in the cytoplasm of the bacterium even in the presence of oxygen during growth though under these conditions no molybdo enzymes are formed. As a consequence no cofactor could be released by acid treatment from membranes of cells grown aerobically. The amount of cofactor released from membranes of cells grown anaerobically under various conditions was proportional to the amount of molybdo enzymes formed. During growth in the presence of tungstate a cofactor, which lacks molybdenum, was found in the cytoplasm. For detection of this so-called demolybdo cofactor the presence of molybdate during reconstitution was essential. Moreover, the cytoplasmic cofactor pool in cells grown in the presence of tungstate appeared to be two to three times higher than in cells grown under similar conditions without tungstate. After anaerobic growth in the presence of tungstate, the inactive demolybdo reductases were shown to contain partly no cofactor and partly a demolybdo cofactor. The P. mirabilis chlorate resistant mutant S 556 did not contain molybdenum cofactor. In two other chl-mutants the cofactor activity was the same as in the wild type.     

On the significance of electron transport systems for growth of Rhodospirillum rubrum

The inhibitory effects of 2-hydroxybiphenyl on various electron transport reactions of isolated membranes and growth in the presence of malate of either phototrophic or chemotrophic cells of Rhodospirillum rubrum were studied. 50% inhibition of both oxygen uptake of whole cells and growth under chemotrophic conditions (i.e. aerobiosis in the dark) was achieved in the presence of 0.09 mM 2-hydroxybiphenyl. With isolated membranes the same effect on NADH oxidase was obtained with 0.08 mM of inhibitor. Succinate dependent respiratory reactions were inhibited by 50% at a concentration of 0.36 mM. Growth under phototrophic conditions (i.e. anaerobiosis in the light) was inhibited by 50% in the presence of 0.17 mM (wild type strain) or 0.21 mM (blue-green mutant, strain VI) of 2-hydroxybiphenyl. Photophosphorylation and light dependent NAD⁺ reduction by succinate were inhibited by 50% at concentrations of 0.21 mM and 0.03 mM of inhibitor, respectively. After phototrophic growth of the organisms for about five doublings of cell mass in the presence of 0.18 mM of 2-hydroxybiphenyl coloured carotenoids could no longer be detected. Membrane fractions of such cultures exhibited normal activities of succinate cytochrome c reductase but activities of NADH cytochrome c reductase were decreased by 80%. In comparison with a blue green mutant, strain VI, of R. rubrum light induced absorbance changes at 865 nm as well as activities of photophosphorylation were unaffected. However, no activity of light dependent NAD⁺ reduction with succinate could be detected. The data indicate that cellular respiration as well as chemotrophic growth depend largely on NADH dependent respiration. Phototrophic growth, on the other hand, is limited by photophosphorylation while energy dependent reversed electron flow to NAD⁺, if at all, is of rathe minor importance.Abbreviation BChl bacteriochlorophyll     

Tungstate can substitute for molybdate in sustaining growth of Methanobacterium thermoautotrophicum

Methanobacterium thermoautotrophicum (strain Marburg) was found to grow on media supplemented with tungstate rather than with molybdate. The Archaeon then synthesized a tungsten iron-sulfur isoenzyme of formylmethanofuran dehydrogenase. The isoenzyme was purified to apparent homogeneity and shown to be composed of four different subunits of apparent molecular masses 65 kDa, 53 kDa, 31 kDa, and 15 kDa and to contain per mol 0.4 mol tungsten, <0.05 mol molybdenum, 8 mol non-heme iron, 8 mol acid-labile sulfur and molybdopterin guanine dinucleotide. Its molecular and catalytic properties were significantly different from those of the molybdenum isoenzyme characterized previously. The two isoenzymes also differed in their metal specificity: the active molybdenum isoenzyme was only synthesized when molybdenum was available during growth whereas the active tungsten isoenzyme was also generated during growth of the cells on molybdate medium. Under the latter conditions the tungsten isoenzyme was synthesized containing molybdenum rather than tungsten.Abbreviations MFR methanofuran - CHO-MFR N-formylmethanofuran - MGD molybdopterin guanine dinucleotide - MAD molybdopterin adenine dinucleotide - MHD molybdopterin hypoxanthine dinucleotide - FPLC fast protein liquid chromatography - SDS/PAGE sodium dodecylsulfate/polyacrylamide gel electrophoresis - ICP-MS inductively coupled plasma mass spectrometry     

Lead-Enhanced Siderophore Production and Alteration in Cell Morphology in a Pb-Resistant <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> Strain 4EA

A lead-resistant bacterial strain 4EA from soil contaminated with car battery waste from Goa, India was isolated and identified as Pseudomonas aeruginosa. This lead-resistant bacterial isolate interestingly revealed lead-enhanced siderophore (pyochelin and pyoverdine) production up to 0.5 mM lead nitrate whereas cells exhibit a significant decline in siderophore production above 0.5 mM lead nitrate. The bacterial cells also revealed significant alteration in cell morphology as size reduction when exposed to 0.8 mM lead nitrate. Enhanced production of siderophore was evidently detected by chrome azurol S agar diffusion (CASAD) assay as increase in diameter of orange halo, and reduction in bacterial size along with significant biosorption of lead was recorded by scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDX). Pseudomonas aeruginosa strain 4EA also exhibits cross tolerance to other toxic metals viz. cadmium, mercury, and zinc besides resistance to multiple antibiotics such as ampicillin, erythromycin, amikacin, cephalexin, co-trimoxazole, mecillinam, lincomycin, ciphaloridine, oleondamycin, and nalidixic acid.     

Isolation and characterization of a Serratia marcescens with insecticidal activity from Polyphylla olivieri (Col.: Scarabaeidae)

Members of the genus Serratia are known for their abilities to infect insects. In this study, a red‐pigmented S. marcescens was isolated and characterized from the infected larvae of Polyphylla olivieri using bacterial cultivation, phylogenetic analysis as well as bioassays against larvae of the two insect pests, Plodia interpunctella and Ephestia kuehniella. Comparative 16S rRNA and groEL gene sequence BLAST analyses strongly suggested that the isolated strain should be placed in the genus Serratia, sharing high sequence similarities with several strain of S. marcescens associated with insects. Phylogenetic analysis placed the isolated bacterium with other S. marcescens bacteria in a clade with high bootstrapping values. To assess pathogenicity of the S. marcescens isolate, the bacterial cells were either injected into the haemolymph of the fifth‐instar larvae or added to the diets of insects. Survival curves of the control insects and those challenged with six different concentrations of S. marcescens showed that the S. marcescens isolate significantly reduced survival rates of the larvae. The LC₅₀s of the bacterium on P. interpunctella and E. kuehniella were 1992.26 and 1.09 × 10⁴ (CFU/μl) for injection bioassays at 6 h post‐injection, and 4.48 × 10⁴ and 1.96 × 10⁵ (CFU/10 μl) for feeding bioassays at 24 h post‐feeding, respectively. Injection of the bacterial culture supernatant into the larvae led to continuous bleeding from the site of injection, while injection of heat‐treated culture supernatant of the bacterium did not cause continuous bleeding. Together, our results showed the possibility of using this S. marcescens isolate in microbial control of the insect pests after addressing the safety concerns. Moreover, it might be considered as a source of useful bioactive molecules and genes with application in insect control and biotechnology via developing insect‐resistant plants.     

Characterisation of two quorum sensing systems in the endophytic Serratia plymuthica strain G3: differential control of motility and biofilm formation according to life-style

Background  

N-acylhomoserine lactone (AHL)-based quorum sensing (QS) systems have been described in many plant-associated Gram-negative bacteria to control certain beneficial phenotypic traits, such as production of biocontrol factors and plant growth promotion. However, the role of AHL-mediated signalling in the endophytic strains of plant-associated Serratia is still poorly understood. An endophytic Serratia sp. G3 with biocontrol potential and high levels of AHL signal production was isolated from the stems of wheat and the role of QS in this isolate was determined.     

A novel extracellular phospholipase C purified from a marine bacterium, <Emphasis Type="Italic">Pseudoalteromonas</Emphasis> sp. J937

Marine bacterial isolates were screened for phospholipase C (PLC) activity on PCY agar plates containing phosphatidylcholine (PC) as substrate. The strain that showed the highest activity on a PCY screening agar plate and a thin-layer chromatography was identified as a strain of Pseudoalteromonas and subsequently designated Pseudoalteromonas sp. J937. The extracellular PLC of the strain J937 was purified to a specific activity of 33 U mg⁻¹ protein by serial ion exchange and gel filtration column chromatography. It had a molecular mass of 32 kDa estimated by SDS–PAGE. The optimal pH and temperature of the enzyme were about pH 8 and 45°C, respectively. The PLC hydrolyzed phosphatidylethanolamine as well as PC but not other glycerophospholipids. Its activity was enhanced by 150% with Ca²⁺ (200 mM) and by 180% with Na⁺ (500 mM), suggesting that the purified PLC is a marine-type enzyme.     

Biodegradation of methyl parathion and <Emphasis Type="Italic">p</Emphasis>-nitrophenol: evidence for the presence of a <Emphasis Type="Italic">p</Emphasis>-nitrophenol 2-hydroxylase in a Gram-negative <Emphasis Type="Italic">Serratia</Emphasis> sp. strain DS001

A soil bacterium capable of utilizing methyl parathion as sole carbon and energy source was isolated by selective enrichment on minimal medium containing methyl parathion. The strain was identified as belonging to the genus Serratia based on a phylogram constructed using the complete sequence of the 16S rRNA. Serratia sp. strain DS001 utilized methyl parathion, p-nitrophenol, 4-nitrocatechol, and 1,2,4-benzenetriol as sole carbon and energy sources but could not grow using hydroquinone as a source of carbon. p-Nitrophenol and dimethylthiophosphoric acid were found to be the major degradation products of methyl parathion. Growth on p-nitrophenol led to release of stoichiometric amounts of nitrite and to the formation of 4-nitrocatechol and benzenetriol. When these catabolic intermediates of p-nitrophenol were added to resting cells of Serratia sp. strain DS001 oxygen consumption was detected whereas no oxygen consumption was apparent when hydroquinone was added to the resting cells suggesting that it is not part of the p-nitrophenol degradation pathway. Key enzymes involved in degradation of methyl parathion and in conversion of p-nitrophenol to 4-nitrocatechol, namely parathion hydrolase and p-nitrophenol hydroxylase component “A” were detected in the proteomes of the methyl parathion and p-nitrophenol grown cultures, respectively. These studies report for the first time the existence of a p-nitrophenol hydroxylase component “A”, typically found in Gram-positive bacteria, in a Gram-negative strain of the genus Serratia. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Modulation of tolerance to Cr(VI) and Cr(VI) reduction by sulfate ion in a <Emphasis Type="Italic">Candida</Emphasis> yeast strain isolated from tannery wastewater

The main aim of this study was to investigate the influence of the sulfate ion on the tolerance to Cr(VI) and the Cr(VI) reduction in a yeast strain isolated from tannery wastewater and identified as Candida sp. FGSFEP by the D1/D2 domain sequence of the 26S rRNA gene. The Candida sp. FGSFEP strain was grown in culture media with sulfate concentrations ranging from 0 to 23.92 mM, in absence and presence of Cr(VI) [1.7 and 3.3 mM]. In absence of Cr(VI), the yeast specific growth rate was practically the same in every sulfate concentration tested, which suggests that sulfate had no stimulating or inhibiting effect on the yeast cell growth. In contrast, at the two initial Cr(VI) concentrations assayed, the specific growth rate of Candida sp. FGSFEP rose when sulfate concentration increased. Likewise, the greater efficiencies and volumetric rates of Cr(VI) reduction exhibited by Candida sp. FGSFEP were obtained at high sulfate concentrations. Yeast was capable of reducing 100% of 1.7 mM Cr(VI) and 84% of 3.3 mM Cr(VI), with rates of 0.98 and 0.44 mg Cr(VI)/L h, with 10 and 23.92 mM sulfate concentrations, respectively. These results indicate that sulfate plays an important role in the tolerance to Cr(VI) and Cr(VI) reduction in Candida sp. FGSFEP. These findings may have significant implications in the biological treatment of Cr(VI)-laden wastewaters.     

Biosorption of tungstate by a Bacillus sp. isolated from Anzali lagoon

An attempt was made to isolate bacterial strains capable of biologically removing tungstate (WO₄²⁻). Thirty-eight water samples were collected from various areas of Anzali lagoon, Iran. Initial screening of a total of 100 bacterial isolates at pH 5, resulted in the selection of one isolate with maximum adsorption capacity of 65.4 mg tungstate/g dry weight. It was tentatively identified as Bacillus sp. according to morphological and biochemical properties and named strain MGG-83. Tungsten concentration was measured spectrophotometrically using the dithiol method. Higher adsorption capacity was observed in the acidic pH ranging from 1 to 3. At pH 2, the strain removed 274.4 mg tungstate/g dry weight within 5 min from the solution with 300 mg WO₄²⁻/l initial concentration and thereafter adsorption rate decreased remarkably. The applicability of the Freundlich isotherm for representation of the experimental data was investigated. Using 1 mM sodium azide and 10 mM 2,4−dinitrophenol, it was shown that only 20% reduction occurred in adsorption and steam sterilization of the bacterial cells resulted in 11% decrease in tungstate uptake. Temperature variations (20–40°C) had no significant effect on tungstate uptake. Pretreatment with the cations had no effect in uptake but pretreatment with anions decreased the tungstate uptake as indicated: sulfate > chromate > nitrate > molybdate > selenate > rhenate. Tungstate was removed from metal-laden biomass after desorption treatments by addition of different desorbing solutions with the results sodium acetate > EDTA > NaCl > KOH > H₂SO₄.     

Sulfate inhibition of molybdenum-dependent nitrogen fixation by planktonic cyanobacteria under seawater conditions: a non-reversible effect

The trace element molybdenum is a central component of several enzymes essential to bacterial nitrogen metabolism, including nitrogen fixation. Despite reasonably high dissolved concentrations (for a trace metal) of molybdenum in seawater, evidence suggests that its biological reactivity and availability are lower in seawater than in freshwater. We have previously argued that this difference is related to an inhibition in the uptake of molybdate (the thermodynamically stable form of molybdenum in oxic natural waters) by sulfate, a stereochemically similar ion. Low molybdenum availability may slow the growth rate of nitrogen-fixing cyanobacteria, and in combination with an ecological control such as grazing by zooplankton, keep fixation rates very low in even strongly nitrogen-limited coastal marine ecosystems. Here we present results from a seawater mesocosm experiment where the molybdenum concentration was increased 10-fold under highly nitrogen-limited conditions. The observed effects on nitrogen-fixing cyanobacterial abundance and nitrogen-fixation inputs were much smaller than expected. A follow-up experiment with sulfate and molybdenum additions to freshwater microcosms showed that sulfate (at seawater concentrations) greatly reduced nitrogen fixation by cyanobacteria and that additions of molybdenum to the levels present in the seawater mesocosm experiment only slightly reversed this effect. In light of these results, we re-evaluated our previous work on the uptake of radio-labeled molybdenum by lake plankton and by cultures of heterocystic cyanobacteria. Our new interpretation indicates that sulfate at saline estuarine levels (>8–10 mM) up to seawater (28 mM) concentrations does inhibit molybdenum assimilation. However, the maximum molybdenum uptake rate (V _max) was a function of the sulfate concentration, with lower V _max values at higher sulfate levels. This indicates that this inhibition is not fully reversed at some saturating level of molybdenum, as assumed in a simple competitive inhibition model. A multi-enzyme, mixed kinetics model with two or more uptake enzyme systems activated in response to the environmental sulfate and molybdate conditions may better explain the repressive effect of sulfate on Mo-mediated processes such as nitrogen fixation.     

Characterization of a mutant of Chlamydomonas reinhardtii deficient in the molybdenum cofactor

Molybdenum (Mo) is an essential micronutrient for almost all organisms. In eukaryotes, it forms a part of the molybdenum cofactor (Moco), which is required for numerous enzymes involved in carbon, nitrogen and sulfur metabolism. Mo is taken up by cells in the form of molybdate and recently molybdate transporters have been identified in Arabidopsis thaliana and Chlamydomonas reinhardtii. Here, we report the characterization of a novel mutant (DB6) of C. reinhardtii generated by random insertional mutagenesis that is unable to assimilate nitrate as a nitrogen source because it lacks functional nitrate reductase (NR). Besides lacking NR, DB6 also lacks xanthine dehydrogenase activity; a common requirement of both enzymes is Moco. DB6 displays a ‘molybdate‐repairable’ phenotype—growth on nitrate is partially restored by supplementing media with high levels of molybdate. This phenotype is typically associated with mutants defective in either molybdate transport or insertion of Mo into the pterin precursor of Moco. Mo content was found to be significantly lower in DB6 than in the wild‐type strain, AOXR1, which suggests that DB6 is defective in Mo uptake. Genetic complementation with a variety of candidate genes that include the known molybdate transporter MOT1 and DNA that spans the site of mutation was unable to recover the wild‐type phenotype. Taken together, our results indicate that DB6 is a novel molybdate transport‐deficient mutant.     

Molybdenum cofactor from the cytoplasmic membrane of Proteus mirabilis

Molybdenum cofactor was extracted from membranes of Proteus mirabilis by three methods: acidification, heat treatment and heat treatment in the presence of sodium-dodecylsulphate (SDS). Extracts prepared by the latter method contained the highest concentration of molybdenum cofactor. In these extracts molybdenum cofactor was present in a low molecular weight form. It could not penetrate an YM-2 membrane during ultrafiltration suggesting a molecular weight above 1000. During aerobic incubation of cofactor extracts from membranes at least four fluorescent species were formed as observed in a reversed-phase high performance liquid chromatography (HPLC) system. The species in the first peak was inhomogeneous while the species in the others seem to be homogenous. In water, all fluorescent products had an excitation maximum at 380 nm and an emission maximum at 455 nm. Their absorption spectra showed maxima at around 270 nm and 400 nm. Fluorescent compounds present in the first peak could penetrate an YM-2 membrane during ultrafiltration, whereas the compounds in the other peaks hardly did. Using xanthine oxidase from milk as source of molybdenum cofactor apparently identical cofactor species were found. Cytoplasmic nor membrane extracts of the chlorate resistant mutant chl S 556 of P. mirabilis could complement nitrate reductase of Neurospora crassa nit-1 in the presence of 20 mM molybdate. However, fluorescent species with identical properties as found for the wild-type were formed during aerobic incubation of extracts from membranes of this mutant.Non-common Abbreviations HPLC high performance liquid chromatography - I.D. internal diameter - SDS sodium dodecyl sulphate     

Effect of talc-formulated entomopathogenic fungus Beauveria against leaffolder (Cnaphalocrosis medinalis) in rice

Thirteen Beauveria strains were isolated from the soil and infected insects. Among the various isolates, B₂ isolate (Arachalore) showed a higher percentage of mortality against C. medinalis (73.3%) under in vitro conditions. Conidial concentration of 1 × 10⁸ of the B2 strain registered maximum mortality of 76.7%. The least LT₅₀ value of 4.4 days was registered in B2 isolate with the spore concentration of 1 × 10⁸ and the LC₅₀ value was 3.4 × 10⁴. Beauveria strains altered the feeding behavior of C. medinalis, reduced the pupal weight, prolonged the pupation period, malformed the pupa and adult under in vitro. The efficacy of the talc-based bioformulation of Beauveria (B2) strain was tested as seed treatment + seedling dip + soil application + foliar spray against rice leaffolder under in vitro and greenhouse conditions. The percentage damage was significantly less (5.5) in B2 as compared to untreated healthy control (25.8). In addition, the same treatment increased the activities of defense-related enzymes, namely peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase, chitinase, and phenolics in rice.     

Release of molybdenum co-factor from nitrate reductase and xanthine oxidase by heat treatment

Heat treatment (90 sec at 70°) is shown to convert the bound molybdenum co-factor of tobacco cell-free extracts and bovine milk xanthine oxidase into a form capable of complementing the Neurospora crassa mutant nit-1.In the presence of 1 mM ascorbic acid, 25 mM molybdate and, for plant extracts, sulphydryl group protecting agents, the molybdenum co-factor can survive incubations up to 100° whilst maintaining its biological activity. Especially with plant extracts, the efficiency of heat treatment is considerably higher than that of the acidification procedure which is often utilized for releasing molybdenum co-factor.     

Control of biogenic H(2)S production with nitrite and molybdate

The effects of the metabolic inhibitors, sodium nitrite and ammonium molybdate, on production of H₂S by a pure culture of the sulfate-reducing bacterium (SRB) Desulfovibrio sp. strain Lac6 and a consortium of SRB, enriched from produced water of a Canadian oil field, were investigated. Addition of 0.1 mM nitrite or 0.024 mM molybdate at the start of growth prevented the production of H₂S by strain Lac6. With exponentially growing cultures, higher levels of inhibitors, 0.25 mM nitrite or 0.095 mM molybdate, were required to suppress the production of H₂S. Simultaneous addition of nitrite and molybdate had a synergistic effect: at time 0, 0.05 mM nitrite and 0.01 mM molybdate, whereas during the exponential phase, 0.1 mM nitrite and 0.047 mM molybdate were sufficient to stop H₂S production. With an exponentially growing consortium of SRB, enriched from produced water of the Coleville oil field, much higher levels of inhibitors, 4 mM nitrite or 0.47 mM molybdate, were needed to stop the production of H₂S. The addition of these inhibitors had no effect on the composition of the microbial community, as shown by reverse sample genome probing. The results indicate that the efficiency of inhibitors in containment of SRB depends on the composition and metabolic state of the microbial community. Journal of Industrial Microbiology & Biotechnology (2001) 26, 350–355. Received 02 August 2000/ Accepted in revised form 17 April 2001