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Resorcinol Hydroxylase of Azoarcus anaerobius: Molybdenum Dependence, Activity, and Heterologous Expression

The obligately anaerobic, denitrifying bacterium Azoarcus anaerobiusstrain LuFRes1 grows with resorcinol (1,3-dihydroxybenzene) as sole carbon and energy source. Resorcinol is oxidized to hydroxyhydroquinone (1,2,4-trihydroxybenzene) by resorcinol hydroxylase (RH), an inducible membrane-bound enzyme. Sequence comparison places resorcinol hydroxylase into the group of anaerobic molybdopterin oxidoreductases and dimethyl sulfoxide reductase-like enzymes. In the large subunit, a molybdopterin-binding domain was predicted, and the small subunit most likely contains two [4Fe-4S] centers. Growth of molybdate-starved cells was inhibited by tungstate, and in vitro resorcinol hydroxylase activity was inhibited by arsenite and selenite that are known to inhibit molybdenum-containing enzymes. The two genes encoding resorcinol hydroxylase could be expressed inEscherichia colibut the products remained in inclusion bodies.All attempts to purify RH fromA. anaerobiusor to produce soluble, active RH inE. colifailed. Nevertheless, RH was produced as a C-terminally Strep-tagged protein from plasmid pSKM1 inThauera aromaticaAR1 transconjugants carrying a transposon insertion in the coding gene for the large (Delta rhL) or the small subunit (Delta rhS) of RH from cosmid R+. RH in the membrane fraction of wild-type transconjugantT. aromaticaAR1/R(+)showed a specific activity of 80 mU mg(-1), and the specific activity of RH in the membranes of the complemented mutants was in the same range (80-95 mU mg(-1)). We conclude that RH ofA. anaerobiusis a membrane-bound molybdoenzyme consisting of two subunits which might require a further loosely bound subunit as membrane anchor.

P. I. Darley, J. Hellstern, B. Schink, and B. Philipp, Resorcinol Hydroxylase of Azoarcus anaerobius: Molybdenum Dependence, Activity, and Heterologous Expression, Current Microbiology. 2020, 77,  3385–3396.


MoO3 Nanowires Antibacterial


Polymer Blend Containing MoO3 Nanowires with Antibacterial Activity against Staphylococcus epidermidis ATCC 12228

Antibacterial activity of a polymer nanocomposite containing water-soluble poly(ethylene oxide) (PEO), water insoluble poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and MoO3 nanowires or MoO3 microparticles as antibacterial active substances is reported. The UV-vis absorption method was used for the illumination of dissolving of the MoO3 particles of different size and morphology in water. Dissolving of MoO3 nanowires (1 mg ml(-1)) decreases pH bellow 3.6 in only 3 min and below 3 in 15 min, while dissolving of the PEO/PVDF-HFP/MoO3 nanowires coating (5 mg ml(-1)) decreases pH bellow 3.6 in 90 min. These coatings completely destroy the Staphylococcus epidermidis ATCC 12228 bacterial strain within 3 h. The proposed applications are antibacterial protective coatings of contact surfaces.

U. G. Centa, P. Kocbek, 2A. Belcarz, S. D. Skapin, and M. Remskar,Polymer Blend Containing MoO3 Nanowires with Antibacterial Activity against Staphylococcus epidermidis ATCC 12228, Journal of Nanomaterials, 2020, |Article ID 9754024 | https://doi.org/10.1155/2020/9754024.


Characterization and Antibacterial Activity Study of Hydrothermally Synthesized h-MoO3 Nanorods and alpha-MoO3 Nanoplates

A nanostructured material is a newly emerging field in healthcare environment application because it exhibits strong antibacterial activity by preventing bacterial growth as bacteria are gradually becoming antibiotic resistant. In this article, a potential candidate of antibacterial material, molybdenum trioxide (MoO3), having two phases: the hexagonal and orthorhombic nanocrystals, were successfully synthesized by facile hydrothermal method. Then, the structural, morphological, functional, and optical properties of both h-MoO3 nanorods and alpha-MoO3 nanoplates were characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis-NIR spectrophotometer, respectively. XRD patterns revealed hexagonal to orthorhombic phase transition after annealing at 450 degrees C for 2 h, supported by FTIR spectra. The micrograph analysis by FESEM also confirmed the 1D hexagonal nanorod structure collapsed and converted into two-dimensional (2D) plate-like orthorhombic structure after annealing. The crystallite size and optical bandgap increased from 35 to 135 nm and 2.83 to 2.87 eV, respectively, after phase transformation. The antibacterial activities of both samples were assessed against two Gram-positive bacteria viz. Bacillus subtilis and Staphylococcus aureus and two Gram-negative viz. Escherichia coli and Salmonella enteritidis by agar well diffusion method. The hexagonal nanorods exhibited more activity compared with nanoplates. It was found that the antibacterial activity of the nanoparticles decreased with increasing crystallite size.

S. K. Sen, S. Dutta, M. R. Khan, M. S. Manir, S. Dutta, A. Al Mortuza, S. Razia, and M. A. Hakim,Characterization and Antibacterial Activity Study of Hydrothermally Synthesized h-MoO3 Nanorods and alpha-MoO3 Nanoplates, Bionanoscience, 2019, 9, 873-882.


Near-Infrared Light-Triggered Therapy to Combat Bacterial Biofilm Infections by MoSe2/TiO2 Nanorod Arrays on Bone Implants

Light-triggered antibacterial therapy is a promising alternative to combat bone-implant-associated infections. Titanium dioxide (TiO2) is already widely used in biomedical engineering due to its excellent biocompatibility, corrosion resistance, and photocatalytic capability. However, the narrow absorption band in near-infrared (NIR) region restricts its practical application as photosensitizer for disinfection. Herein, molybdenum diselenide (MoSe2)/TiO2-Ti nanorod arrays (NRAs) with enhanced photothermal conversion and photocatalytic performance under 808 nm NIR light irradiation are prepared on titanium (Ti) by a two-step hydrothermal treatment. The combined actions of hyperthermia and reactive oxygen species give rise to excellent antibacterial activities on titanium requiring irradiation for only 10 min as demonstrated by the experiments conducted in vitro and in vivo. In addition, the introduction of arginine-glycine-aspartic acid can not only eliminate the weak toxicity of MoSe2, but also improve the cell adhesion, proliferation, and osteogenic differentiation of TiO2-Ti NRAs. This composite NRAs show great promise for in situ and nonsurgical treatment of biofilm infection on Ti implants.

G. N. Zhang, X. Y. Zhang, Y. Q. Yang, H. Y. Zhang, J. Shi, X. H. Yao, and X. Y. Zhang,Near-Infrared Light-Triggered Therapy to Combat Bacterial Biofilm Infections by MoSe2/TiO2 Nanorod Arrays on Bone Implants, Advanced Materials Interfaces, 2020, 7, 1901706. DOI: 10.1002/admi.201901706


Investigation on antibacterial and photocatalytic degradation of Rhodamine-B dye under visible light irradiation by titanium molybdate nanoparticles prepared via microwave method

Titanium molybdate (TM) nanoparticles were synthesized by two different methods using titanium tetrachloride and ammonium molybdate as starting precursor. The obtained nanoparticles were examined by various analytical techniques such as powder XRD, FESEM, HRTEM, UV-visible spectroscopy, PL spectroscopy and FTIR analysis. The tetrahedral phase and crystallite size were determined using powder XRD. The morphology of the samples was examined by FESEM and HRTEM techniques. Titanium molybdate prepared via precipitation method (TM1) shows irregular and unclear morphology whereas titanium molybdate prepared thru microwave method (TM2) exhibits pores and sphere like structure. The elemental composition (EDX) confirms the presence of elements in the order of O > Ti > Mo for TM1 and Mo > Ti > O for TM2 samples. The functional groups were determined using FTIR analysis it exhibits lower frequencies for TM2 than TM1. UV-vis spectra show the optical energy gap of 3.0 eV and 2.78 eV for TM1 and TM2 samples respectively. The antibacterial effect of titanium molybdate (TM2) sample prepared via microwave method was studied in Staphylococcus aurous, Escherichia coll. and Pseudomonuas aeruginosa. The obtained results states Staphylococcus aurous has noteworthy antibacterial activity than other two bacterial species. The photocatalytic activity of Rhodamine-B (RhB) under visible light irradiation expounded about 96% of dye was degraded after 150 min for titanium molybdate (TM2).

A. Mobeen, C. M. Magdalane, S. K. J. Shahina, D. Lakshmi, R. Sundaram, G. Ramalingam, A. Raja, J. Madhavan, D. Letsholathebe, A. K. H. Bashir, M. Maaza, and K. Kaviyarasu,Investigation on antibacterial and photocatalytic degradation of Rhodamine-B dye under visible light irradiation by titanium molybdate nanoparticles prepared via microwave method, Surfaces and Interfaces, 2019, 17, 100381



An investigation of structural, magnetical, optical, antibacterial and humidity sensing of Zr(MoO4)2-ZrO2 nanocomposites

In this research work; we have prepared ZrO2 nanocomposites at different mole ratio by simple, eco-friendly, and low-cost co-precipitation method followed by solid state method. In this perspective, X-ray diffraction (XRD) shows monoclinic and hexagonal phases for zirconium oxide (ZrO2) and zirconium molybdate Zr(MoO4)2 with crystalline size of 36 nm and 16.18 nm respectively. The spherical structure with high porosity of composite was observed by field emission scanning electron microscopy (FESEM). The ferromagnetic behaviour of ZMZO46 composite was determined by vibrating sample magnetometer (VSM) at room temperature. UV-vis spectroscopy proved that the absorption edge Zr(MoO4)2-ZrO2 composites shifted to higher wavelength due to decrease in bandgap (2.40 eV-2.72 eV). Likewise, photoluminescence spectra (PL) elucidates the blue-green emission at 491 nm corresponds to surface defects. The humidity sensor was measured under dissimilar humidity atmosphere (RH5% to RH98%). It was originated that the sensitivity factor of samples increases with relative humidity. The ZMZO46 composite possess highest sensitivity of S-f = 3958. Additionally, response and recovery time was observed as 50 and 200 s respectively. The ZMZO46 composite displayed promising antibacterial activity against both Gram-positive and Gram-negative bacteria.

A. M. Amanulla, R. Sundaram, and K. Kaviyarasu,An investigation of structural, magnetical, optical, antibacterial and humidity sensing of Zr(MoO4)2-ZrO2 nanocomposites, Surfaces and Interfaces, 2019, 16, 132-140.


High antibacterial activity of chitosan - molybdenum   disulfide nanocomposite

Bacterial infections have evolved as a life-threatening problem afflicting people due to the abuse of antibiotics and emergence of drug-resistant bacteria. Thus developing novel antibacterial materials is an urgent need. Herein, chitosan-MoS2 (CS-MoS2) nanocomposite was synthesized through thiol ligand functionalization and chemical modification to achieve more efficient bactericidal activity. CS-MoS2 exhibited synergistic remarkable bactericidal capability against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E.coli), where bacterial viabilities were significantly reduced. After treatment with 10 mug/mL of CS-MoS2, 100% and 98.1% of S. aureus and E.coli cells were killed respectively. A mechanism study revealed that the positively charged CS-MoS2 could interact with cell membrane, then cause damage to the membrane and cellular constituents by generation of reactive oxygen species (ROS) and glutathione (GSH) oxidation, finally inhibit bacterial growth. The CS-MoS2 could be an attractive antibacterial agent with improved efficiency and provide more strategies for application of MoS2.

W. Cao, L. Yue, and Z. Wang,High antibacterial activity of chitosan - molybdenum   disulfide nanocomposite, Carbohydrate polymers, 2019, 215, 226-234.


Bio-Inspired Growth of Silver Nanoparticles on 2D Material's Scaffolds as Heterostructures with Their Enhanced Antibacterial Property

We developed a facile and green bio-inspired strategy to fabricate silver nano-particles growth in-situ on different scaffolds materials, building novel heterostructures for promoting their antibacterial activities and durability. Firstly, fluorinated graphene oxide (FGO) nanosheets, layered molybdenum disulfide (MoS2), and layered tungsten disulfide (WS2) were exfoliated by chemical liquid with intense sonication. And silicon dioxide (SiO2) nano-spheres were prepared via wet chemical method. Then, silver nanoparticles were grown onto those surfaces of layered nanosheets and nano-spheres, hybridizing three dimensional hetero-architectures. The obtained silver-hybridized nanoarchitechtures were further analyzed by TEM and EDS. Additionally, three bacteria were applied to evaluate their antibacterial property, illustrating distinctive antibacterial effects, expecting to explore more applications in water disinfection and food packing fields.

G. Gao, L. Wang, P. Yang, L. Huang, X. Xie, J. Wu, C. Qiu, and L. Cai,Bio-Inspired Growth of Silver Nanoparticles on 2D Material's Scaffolds as Heterostructures with Their Enhanced Antibacterial Property, J Nanosci Nanotechnol, 2018, 18, 3893-3900.


Antibacterial, magnetic, optical and humidity sensor studies of beta-CoMoO4 - Co3O4 nanocomposites and its synthesis and characterization

Cobalt Molybdate (beta-CoMoO4) and Cobalt Oxide (Co3O4) nanocomposite was prepared via co-precipitation and solid-state methods. Various techniques like powder XRD, FESEM, HRTEM, FTIR, VSM, UV-Vis and PL spectroscopy were used to investigate the structure and morphology of as prepared samples. Powder X-ray diffraction (XRD) reveals monoclinic and cubic structure for beta-CoMoO4 and Co3O4 respectively. The surface morphology was observed using field emission electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM), which shows the formation of nanocomposites at nanoscale range, the presence of elements were determined by energy dispersive x-ray spectroscopy (EDX). FTIR analysis confirms the formation and bonding nature of the samples. The anti-ferromagnetic behavior of CMCO64 composite was determined by vibrating sample magnetometer (VSM). The bandgap values were calculated by extrapolating the straight line on the energy axis (hnu), and the values of beta-CoMoO4, CO3O4 and beta-CoMoO4 - CO3O4 composites were determined to be 2.20, 2.09eV and 1.54-2.44eV respectively. The weak blue emission peak observed at 489nm is corresponds to crystal defects only observed in CMCO01 and CMCO64 composite, for CMCO10 the peak shifted to green region. Antibacterial studies illustrate good result for the CMCO64 composite against both Gram-negative and Gram-positive bacteria. The sensor studies were measured at different humidity environment (RH5% to RH98%). It was found that the increase in relative humidity leads to increase in the sensitivity factor of the samples. Among the samples CMCO64 composite possess highest sensitivity factor of (Sf=4851) with response time of 60s and recovery time of 230s respectively.

A. Mobeen Amanulla, S. K. Jasmine Shahina, R. Sundaram, C. Maria Magdalane, K. Kaviyarasu, D. Letsholathebe, S. B. Mohamed, J. Kennedy, and M. Maaza,Antibacterial, magnetic, optical and humidity sensor studies of beta-CoMoO4 - Co3O4 nanocomposites and its synthesis and characterization, Journal of photochemistry and photobiology. B, Biology, 2018, 183, 233-241.

Molybdenum in bacteria

Light-enhanced bioaccumulation of molybdenum by nitrogen-deprived recombinant anoxygenic photosynthetic bacterium Rhodopseudomonas palustris

As molybdenum (Mo) is an indispensable metal for plant nitrogen metabolisms, accumulation of dissolved Mo into bacterial cells may connect to the development of bacterial fertilizers that promote plant growth.

In order to enhance Mo bioaccumulation, nitrogen removal and light illumination were examined in anoxygenic photosynthetic bacteria (APB) because APB possess Mo nitrogenase whose synthesis is strictly regulated by ammonium ion concentration. In addition, an APB, Rhodopseudomonas palustris, transformed with a gene encoding Mo-responsive transcriptional regulator ModE was constructed.

Mo content was most markedly enhanced by the removal of ammonium ion from medium and light illumination while their effects on other metal contents were limited. Increases in contents of trace metals including Mo by the genetic modification were observed.

Thus, these results demonstrated an effective way to enrich Mo in the bacterial cells by the culture conditions and genetic modification.

Naito, T., Sachuronggui, Ueki, M., and Maeda, I., Light-enhanced bioaccumulation of molybdenum by nitrogen-deprived recombinant anoxygenic photosynthetic bacterium Rhodopseudomonas palustris, Bioscience, biotechnology, and biochemistry, 2016, 80, 407-13.

Azotobacter vinelandii

Molybdate and iron are metals that are required by the obligately aerobic organism;Azotobacter vinelandii to survive in the nutrient-limited conditions of its natural. soil environment. A high concentration of molybdate (1 mM) affects the formation of A. vinelandii siderophores such that the tricatecholate protochelin is formed to the exclusion of the other catecholate siderophores, azotochelin and aminochelin. Molybdate combines readily with catecholates and interferes with siderophore function. Stable molybdosiderophore complexes were formed but were readily destabilized by Fe3 + . Protochelin accumulates in the presence of molybdate because protochelin uptake and conversion into its component parts, azotochelin and aminochelin, are inhibited by interference with ferric reductase. Molybdate partially inhibited the activity of ferric reductase, an enzyme important in the deferration of ferric siderophores.

Molybdenum trioxide. Enhancement of the antimicrobial properties of orthorhombic molybdenum trioxide by thermal induced fracturing of the hydrates

The oxides of the transition metal molybdenum exhibit excellent antimicrobial properties. We present the preparation of molybdenum trioxide dihydrate (MoO3x2H2O) by an acidification method and demonstrate the thermal phase development and morphological evolution during and after calcination from 25 degrees C to 600 degrees C. The thermal dehydration of the material was found to proceed in two steps. Microbiological roll-on tests using Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were performed and exceptional antimicrobial activities were determined for anhydrous samples with orthorhombic lattice symmetry and a large specific surface area. The increase in the specific surface area is due to crack formation and to the loss of the hydrate water after calcination at 300 degrees C. The results support the proposed antimicrobial mechanism for transition metal oxides, which based on a local acidity increase as a consequence of the augmented specific surface area.

 Shafaei, S., Van Opdenbosch, D., Fey, T., Koch, M., Kraus, T., Guggenbichler, J. P., and Zollfrank, C.,Enhancement of the antimicrobial properties of orthorhombic molybdenum trioxide by thermal induced fracturing of the hydrates, Materials science & engineering. C, Materials for biological applications, 2016, 58, 1064-70.

Sulfate reducing bacteria including inhibition by Mo

The activity of sulfate-reducing bacteria (SRB) intensifies the problems associated to corrosion of metals and the solution entails significant economic costs. Although molybdate can be used to control the negative effects of these organisms, the mechanisms triggered in the cells exposed to Mo-excess are poorly understood. In this work, the effects of molybdate ions on the growth and morphology of the SRB Desulfovibrio alaskensis G20 (DaG20) were investigated. In addition, the cellular localization, ion uptake and regulation of protein expression were studied. We found that molybdate concentrations ranging between 50 and 150 A mu M produce a twofold increase in the doubling time with this effect being more significant at 200 A mu M molybdate (five times increase in the doubling time). It was also observed that 500 A mu M molybdate completely inhibits the cellular growth. On the context of protein regulation, we found that several enzymes involved in energy metabolism, cellular division and metal uptake processes were particularly influenced under the conditions tested. An overall description of some of the mechanisms involved in the DaG20 adaptation to molybdate-stress conditions is discussed

Nair, R. R., Silveira, C. M., Diniz, M. S., Almeida, M. G., Moura, J. J. G., and Rivas, M. G., Changes in metabolic pathways of Desulfovibrio alaskensis G20 cells induced by molybdate excess, Journal of Biological Inorganic Chemistry, 2015, 20, 311-322.

Molybdate is a specific inhibitor for sulfate-reducing bacteria. Sodium molybdate (980 mg/L) added to artificial wastewater decreased sulfate reducing bacteria by a factor of 103 and sulfate reduction
Yamamoto-Ikemoto, R., Matsui, S., Komori, T., Ecological Interactions Among Denitrification, Poly-P Accumulation, Sulfate Reduction, And Filamentous Sulfur Bacteria In Activated-Sludge, Water Science And Technology , 1994, 30 , 201-210.

Mier, J.l., Ballester, A., Gonzalez, F., Blazquez, M.l., Gomez, E.,The Influence Of Metallic-Ions On The Activity Of Sulfolobus BC, Journal Of Chemical Technology And Biotechnology, 1996, 65, 272-280.

Sodium molybdate inhibited sulfate reduction by human gut sulfate-reducing bacteria causing an accumulation of ethanol and malonate and reducing the rate of utilization of lactate.

Willis, C.L., Cummings, J.H., Neale, G., Gibson, G.R., Nutritional aspects of dissimilatory sulfate reduction in the human large intestine, Current Microbiology, 1997, 35, 294-298.

When sodium molybdate (20 mmol l -1)was added to a sediment slurry, sulfate reduction was completely stopped and mainly acetate was accumulated. From the third day after the addition of molybdate methane was produced while accumulated acetate was consumed. The maximum rate of methane production was 1.2-1.9 micromol ml -1 day -1.

Fukui, M., Suh, J., Yonezawa, Y., Urushigawa, Y., Major substrates for microbial sulfate reduction in the sediments of Ise Bay, Japan, Ecological Research,1997, 12, 201-209.
Gardner, A. W. and Hall-Patch, P. K., J. Nutr., 1962, 84, 31.

Biogas produced during anaerobic treatment of sulfate containing wastes, such as distillery waste, invariably contains around 1-3% (v/v) H2S. Sodium molybdate inhibits sulfate reduction and H2S production. A single dose of 3 mM molybdate inhibited production of H2S for 9 days. Continuous dosing of 3 mM molybdate inhibited H2S production for only 11 days. Methane production declined from day 66.

Ranade, DR, Dighe, AS, Bhirangi, SS, Panhalkar, VS, Yeole, TY Evaluation of the use of sodium molybdate to inhibit sulphate reduction during anaerobic digestion of distillery waste, Bioresource Technology, 1999, 68, 287-291

The culture growth of the sulfate-reducing bacterium Desulfovibrio desulfuricans and the rate of sulfate reduction were reduced in contact with sputter-deposited Mo thin films and Mo powder. Mo formed molybdate, molybdenum disulfide, oxoMo(V) cysteine and thiocyanato complexes.

Chen, G., Ford, T.E., Clayton, C.R., Interaction of sulfate-reducing bacteria with molybdenum dissolved from sputter-deposited molybdenum thin films and pure molybdenum powder, Journal Of Colloid And Interface Science, 1998, 204, 237-246.

See also

Lomans, B.P., OpdenCamp, H.J.M., Pol, A., vanderDrift, C., Vogels, G.D., Role of methanogens and other bacteria in degradation of dimethyl sulfide and methanethiol in anoxic freshwater sediments, Applied And Environmental Microbiology, 1999, 65, 2116-2121.

Sodium nitrite and ammonium molybdate inhibit production of H2 S by sulfate-reducing bacteria. The amounts of inhibitor required to stop production of H2S from water associated with an oil field in containment of sulfate reducing bacteria depends on the composition and metabolic state of the microbial community. a pure culture of the sulfate-reducing bacterium and a consortium of sulfate reducing bacteria, 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 H 2S by Desulfovibrio sp. 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 sulfate-reducing bacterium, 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.

Nemati, M., Mazutinec, T. J., Jenneman, G. E., and Voordouw, G., Control of biogenic H2S production with nitrite and molybdate, Journal of Industrial Microbiology & Biotechnology, 2001, 26, 350-355.

See also

Pareek, S., Azuma, J., Shimizu , Y., and Matsui, S., Hydrolysis of newspaper polysaccharides under sulfate reducing and methane producing conditions, Biodegradation, 2000, 11, 229-237.
Robertson, W.J., Franzmann, P. D., and Mee, B. J., Spore-forming, Desulfosporosinus-like sulphate-reducing bacteria from a shallow aquifer contaminated with gasoline, Journal of Applied Microbiology, 2000, 88, 248-259.
Scholten, J.C.M., Conrad, R., and Stams, A. J. M., Effect of 2-bromo-ethane sulfonate, molybdate and chloroform on acetate consumption by methanogenic and sulfate-reducing populations in freshwater sediment, Fems Microbiology Ecology, 2000, 32, 35-42.

A single dose of 3 mM molybdate inhibited production of H2S for 9 days from distillery waste which had a sulfate content of 10 g /l. Continuous dosing of 3 mM molybdate inhibited H2S production for only 11 days after which H2S was again produced, while methane production declined from day 66.

Ranade, D.R., Dighe, A.S., Bhirangi, S.S., Panhalkar, V.S., Yeole, T.Y. Evaluation of the use of sodium molybdate to inhibit sulphatereduction during anaerobic digestion of distillery waste Bioresource Technology, 1999, 68, 3, 287-291.
Mier, J.l., Ballester, A., Gonzalez, F., Blazquez, M.l., Gomez, E.,The Influence Of Metallic-Ions On The Activity Of Sulfolobus BC, Journal Of Chemical Technology And Biotechnology, 1996, 65, 272-280.

Bacteria may reduce molybdate to MoS2 . D. desulfuricans suspended in bicarbonate buffer solution with lactate or dihydrogen as the electron donor reduces molybdenum(VI) in the presence of sulfide to MoS2 , which precipitates. Enzymatic reduction of Mo( VI) by sulfate-reducing bacteria may contribute to the accumulation of Mo(IV) in anaerobic environments. These organisms may be useful for removing soluble Mo from contaminated water.

Tucker M.D., Barton L.L., Thomson B.M., Reduction and immobilization of molybdenum by Desulfovibrio desulfuricans, Journal Of Environmental Quality, 1997, 26, 1146-1152.

The characterization of a novel Mo-Fe protein (MorP) associated with a system that responds to Mo in Desulfovibrio alaskensis is reported. Biochemical characterization shows that MorP is a periplasmic homomultimer of high molecular weight (260 ± 13 kDa) consisting of 16-18 monomers of 15321.1 ± 0.5 Da. The UV/visible absorption spectrum of the as-isolated protein shows absorption peaks around 280, 320, and 570 nm with extinction coefficients of 18700, 12800, and 5000 M-1 cm-1, respectively. Metal content, EXAFS data and DFT calculations support the presence of a Mo-2S-[2Fe-2S]-2S-Mo cluster. Analysis of the available genomes from Desulfovibrio species shows that the MorP encoding gene is located downstream of a sensor and a regulator gene. This type of gene arrangement, called two component system, is used by the cell to regulate diverse physiological processes in response to changes in enviromental conditions. Increase of both gene expression and protein production was observed when cells were cultured in the presence of 45 mu M molybdenum. Involvement of this system in Mo tolerance of sulfate reducing bacteria is proposed.

Rivas, M. G., Carepo, M. S. P., Mota, C. S., Korbas, M., Durand, M. C., Lopes, A. T., Brondino, C. D., Pereira, A. S., George, G. N., Dolla, A., Moura, J. J. G., and Moura, I., Molybdenum Induces the Expression of a Protein Containing a New Heterometallic Mo-Fe Cluster in Desulfovibrio alaskensis, Biochemistry, 2009, 48, 873-882.

Bacterial reduction of molybdate (VI)

A bacterium reduced molybdate(VI) to molybdenum blue (Mo(V, VI)). Sucrose, maltose, glucose, and glycerol (in decreasing order) supported molybdate reduction after 24 h of incubation. Optimum concentration of sucrose for molybdate reduction was 1.0% (w/v) after 24 h of static incubation. Ammonium sulfate supported molybdate reduction giving the highest amount of molybdenum blue after 24 h of incubation at 0.3% (w/v). The optimum molybdate concentration that supported molybdate reduction was between 15 and 25 mM. Molybdate reduction was optimum at 35 degrees C. Phosphate at concentrations higher than 5 mM strongly inhibited molybdate reduction. The molybdenum blue produced from cellular reduction exhibited a unique absorption spectrum with a maximum peak at 865 nm and a shoulder at 700 nm. The isolate was tentatively identified as Serratia marcescens Strain Dr. Y6

Shukor, M.Y., Habib, S. H. M., Rahman, M. F. A., Jirangon, H., Abdullah, M. P. A., Shamaan, N. A., and Syed, M. A., Hexavalent molybdenum reduction to molybdenum blue by S. marcescens Strain Dr. Y6, Applied Biochemistry and Biotechnology, 2008, 149, 33-43.

Heterotrophicbacteria [bacteria requiring a supply of organic material as food from the environment]can reduce molybdenum (molybdate) to molybdenum blue. With molybdenum (molybdate) in the growth media, bacterial colonies turn to blue; the enzyme responsible has not been purified. As a substrate for the enzyme activity laboratory-prepared 10:4-phosphomolybdate is better than 12-phosphomolybdate by a factor of 13 in the apparent Vmax.

Shukor, M. Y., Rahman, M. F. A., Shamaan, N. A., Lee, C. H., Karim, M. I. A., and Syed, M. A., An improved enzyme assay for molybdenum-reducing activity in bacteria, Applied Biochemistry and Biotechnology, 2008, 144, 293-300.

Molybdate is an essential trace element required by biological systems including the anaerobic sulfate-reducing bacteria (SRB); however, detrimental consequences may occur if molybdate is present in high concentrations in the environment. Molybdate is a structural analog of sulfate and inhibits sulfate respiration of SRB. The growth was followed of Desulfovibrio gigas ATCC 19364, Desulfovibrio vulgaris Hildenborough, Desulfovibrio desulfuricans DSM 642, and D. desulfuricans DSM 27774 in media containing sub-lethal levels of molybdate. The culture fluid became red-brown having absorption peaks at 467, 395 and 314 nm attributed to a molybdate-sulfide complex. Reduction of molybdate with the formation of molybdate disulfide occurs in the periplasm D. gigas and D. desulfuricans DSM 642. The occurrence of poorly crystalline Mo-sulfides in black shale may be due to SRB reduction and selective enrichment of Mo in paleo-seawater.

Biswas, K., Woodards, N., Xu, H. F., and Barton, L., Reduction of molybdate by sulfate-reducing bacteria, Biometals, 2009, 22, 131-139.

The need to isolate efficient heavy metal reducers for cost effective bioremediation has resulted in the isolation of a potent molybdenum-reducing bacterium. The isolate was tentatively identified as Serratia sp. strain DRY5 based on the Biolog GN carbon utilization profiles and partial 16S rDNA molecular phylogeny.

Strain DRY5 produced 2.3 times the amount of Mo-blue than S. marcescens strain Dr.Y6, 23 times more than E. coli K12 and 7 times more than E. cloacae strain 48. Strain DRY5 required 37 °C and pH 7.0 for optimum molybdenum reduction. Carbon sources such as sucrose, maltose, glucose and glycerol, supported cellular growth and molybdate reduction after 24 h of static incubation, The optimum carbon source that supported reduction was sucrose at 1.0% (w/v). Ammonium sulfate, ammonium chloride, glutamic acid, cysteine, and valine supported growth and molybdate reduction with ammonium sulfate as the optimum nitrogen source at 0.2% (w/v). Molybdate reduction was optimally supported by 30 mM molybdate.

The optimum concentration of phosphate for molybdate reduction was 5 mM when molybdate concentration was fixed at 30 mM. Molybdate reduction was totally inhibited at 100 mM phosphate.

Mo-blue produced by this strain shows a unique characteristic absorption spectrumwith a maximum peak at 865 nm and a shoulder at 700 nm. Dialysis tubing experiment showed that 95.42% of Mo-blue was found in the dialysis tubing suggesting that the molybdate reduction seen in this bacterium was catalyzed by enzyme(s). The characteristics of isolate DRY5 suggest that it would be useful in the bioremediation of molybdenum-containing waste.

Rahman, M. F. A., Shukor, M. Y., Suhaili, Z., Mustafa, S., Shamaan, N. A., and Syed, M. A., Reduction of Mo(VI) by the bacterium Serratia sp strain DRY5, Journal of Environmental Biology, 2009, 30, 65-72.

Enzymatic reduction of molybdate

The bacterium Acinetobacter calcoaceticus strain Dr. Y12 reduced molybdate optimally under conditions of low dissolved oxygen, 37 °C , pH 6.5. The electron donors glucose, fructose, maltose and sucrose supported molybdate reduction to molybdenum-blue after 1 d of incubation, glucose and fructose supporting the highest production. Optimum molybdenum-blue production was reached at 20 mmol/L molybdate and 5 mmol/L phosphate; increasing phosphate inhibited the reduction. In the uv-visible spectrum absorbance of the 865 nm peak and 700 nm shoulder increaed with increasing molybdenum-blue. Metal ions (2 mmol/L final concentration) inhibited the reduction (% inhibition): chromium (88), cadmium (53), copper (80), mercury (100), lead (20). Respiratory inhibitors, antimycin A, rotenone, sodium azide and cyanide did not inhibit molybdenum-blue production, suggesting that the electron transport system is not a site of molybdate reduction

Shukor, M. Y., Rahman, M. F., Suhaili, Z., Shamaan, N. A., and Syed, M. A., Hexavalent Molybdenum Reduction to Mo-blue by Acinetobacter calcoaceticus, Folia Microbiologica, 2010, 55, 137-143.

Reduction of molybdate to molybdenum blue by Klebsiella sp strain hkeem

A novel molybdate-reducing bacterium, tentatively identified as Klebsiella sp. strain hkeem and based on partial 16s rDNA gene sequencing and phylogenetic analysis, has been isolated. Strain hkeem produced 3 times more molybdenum blue than Serratia sp. strain Dr.Y8; the most potent Mo-reducing bacterium isolated to date. Molybdate was optimally reduced to molybdenum blue using 4.5 mM phosphate, 80 mM molybdate and using 1% (w/v) fructose as a carbon source. Molybdate reduction was optimum at 30 degrees C and at pH 7.3. The molybdenum blue produced from cellular reduction exhibited absorption spectrum with a maximum peak at 865 nm and a shoulder at 700 nm. Inhibitors of electron transport system such as antimycin A, rotenone, sodium azide, and potassium cyanide did not inhibit the molybdenum-reducing enzyme. Mercury, silver, and copper at 1 ppm inhibited molybdenum blue formation in whole cells of strain hkeem. ((c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Lim, H. K., Syed, M. A., and Shukor, M. Y., Reduction of molybdate to molybdenum blue by Klebsiella sp strain hkeem, Journal of Basic Microbiology, 2012, 52, 296-305.

Bacterial hydrogen production using a molybdenum enzyme

Rhodobacter sphaeroides O.U.001 is one of the candidates for photobiological hydrogen production among purple non-sulfur bacteria. Hydrogen is produced by Mo-nitrogenase from organic acids such as malate or lactate. A hupSL in frame deletion mutant strain was constructed without using any antibiotic resistance gene. The hydrogen production potential of the R. sphaeroides O.U.001 and its newly constructed hupSL deleted mutant strain in acetate media was evaluated and compared with malate containing media. The hupSL(-) R. sphaeroides produced 2.42 l H2/l culture and 0.25 l H2/l culture in 15 mM malate and 30 mM acetate containing media, respectively, as compared to the wild type cells which evolved 1.97 l H2/l culture and 0.21 l H2/l culture in malate and acetate containing media, correspondingly. According to the results, hupSL- R. sphaeroides is a better hydrogen producer but acetate alone does not seem to be an efficient carbon source for photo-heterotrophic H2 production by R. sphaeroides.

Kars, G., Gunduz, U., Yucel, M., Rakhely, G., Kovacs, K. L., and Eroglu, I., Evaluation of hydrogen production by Rhodobacter sphaeroides OU001 and its hupSL deficient mutant using acetate and malate as carbon sources, International Journal of Hydrogen Energy, 2009, 34, 2184-2190.

Biomass hydrocarbon production

Micronutrient Requirements for Growth and Hydrocarbon Production in the Oil Producing Green Alga Botryococcus braunii (Chlorophyta)

The requirements of micronutrients for biomass and hydrocarbon production in Botryococcus braunii UTEX 572 were studied using response surface methodology. The concentrations of four micronutrients (iron, manganese, molybdenum, and nickel) were manipulated to achieve the best performance of B. braunii in laboratory conditions. The responses of algal biomass and hydrocarbon to the concentration variations of the four micronutrients were estimated by a second order quadratic regression model. Genetic algorithm calculations showed that the optimal level of micronutrients for algal biomass were 0.266 M iron, 0.707 M manganese, 0.624 M molybdenum and 3.38 M nickel. The maximum hydrocarbon content could be achieved when the culture media contained 10.43 M iron, 6.53 M manganese, 0.012 M molybdenum and 1.73 M nickel. The validation through an independent test in a photobioreactor suggests that the modified media with optimised concentrations of trace elements can increase algal biomass by 34.5% and hydrocarbon by 27.4%. This study indicates that micronutrients play significant roles in regulating algal growth and hydrocarbon production, and the response surface methodology can be used to optimise the composition of culture medium in algal culture.

Song, Liang, Qin, Jian G., Su, Shengqi, Xu, Jianhe, Clarke, Stephen, and Shan, Yichu, Micronutrient Requirements for Growth and Hydrocarbon Production in the Oil Producing Green Alga Botryococcus braunii (Chlorophyta), PloS one, 2012, 7, e41459.

Bacteria – Antibacterial activity of molybdenum complexes

Mixed-ligand aroylhydrazone complexes of molybdenum: Synthesis, structure and biological activity

The reaction of the benzoylhydrazone of 2-hydroxybenzaldehyde (H2L) with [MoO2(acac)2] proceeds smoothly in refluxing ethanol to afford an orange complex [MoO2L(C2H5OH)] (1). The substrate binding capacity of 1 has been demonstrated by the formation and isolation of two mononuclear [MoO2L(Q)] {where Q = imidazole (2a) and 1-methylimidazole (2b)} and one dinuclear [(MoO2L)2(Q)] {Q = 4,4'-bipyridine (3)} mixed-ligand oxomolybdenum complex.

All the complexes have been characterized by elemental analysis, magnetic and spectroscopic (IR, UV-Vis and NMR) measurements.

The molecular structures of all the oxomolybdenum(VI) complexes (1, 2a, 2b and 3) have been determined by X-ray crystallography. In each complex, the dianionic planar ligand is coordinated to the metal centre via one enolate oxygen, one phenolate oxygen and an azomethine nitrogen atom.

The complexes have been screened for their antibacterial activity against Escherichia coli, Bacillus and Pseudomonas aeruginosa. The minimum inhibitory concentration of these complexes and their antibacterial activity indicates that compounds 2a and 2b are potential lead molecules for drug designing. (C) 2012 Elsevier Ltd. All rights reserved.

Pasayat, Sagarika, Dash, Subhashree P., Saswati, Majhi, Paresh Kumar, Patil, Yogesh P., Nethaji, M., Dash, Hirak R., Das, Surajit, and Dinda, Rupam, Mixed-ligand aroylhydrazone complexes of molybdenum: Synthesis, structure and biological activity, Polyhedron, 2012, 38, 198-204.

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