Molybdenum in Biology - An Essential Trace Element

Molybdenum in bacteria

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.

Sulfate reducing bacteria including inhibition by Mo

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.

Sulfate reducing bacteria including inhibition by Mo

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.

Bacterial reduction of molybdate(VI)

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.

Bacterial reduction of molybdate(VI)

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.

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.