Gluconobacter oxydans

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A Microbial Biorealm page on the genus Gluconobacter oxydans

Contents

Classification

Higher order taxa

Bacteria; Proteobacteria; Alphaproteobacteria; Rhodospirillales; Acetobacteraceae; Gluconobacter; oxydans

Species

NCBI: Taxonomy

oxydans

Description and significance

Gluconobacter oxydans, previously known as Acetobacter suboxydans, are Gram-negative rod or oval shaped bacteria ranging from about 0.5 to 0.8mm x to 4.2mm. The name oxy from Gluconobacter oxydans is Latin for 'sharp' and 'acidic', and dans is 'giving'. They tend to have a small genome size because of their limited metabolic abilities. These abilities include partially oxidizing carbohydrates and alcohols through the process of oxidative fermentation, and they can be used for synthesis of Vitamin C, D-gluconis acid and ketogluconic acids[3]. G. oxydans are found in flowers, fruits, garden soil, alcoholic beverages, cider, and soft drinks because they contain strains capable of growing in high concentrations of sugar solutions and low pH values (optimal pH for growth is 5.5-6.0)[2]. Although they are able to grow in extreme conditions, their growth rate is slow and the concentration of mature cells are low. The importance of G. oxydans is its ability to incompletely oxidize carbon substrates such as D-sorbitol, glycerol, D-fructose, and D-glucose for the use in biotechnological instruments[3].

Genome structure

The genome of Gluconobacter oxydans tends to be small in size, ranging about 2240 to 3787kb (Verma et al., 1997). Shapes can be ellipsoidal or rod-shaped with dimensions of 0.5 to 0.8x0.9 to 4.2mm. The total number of genes is 2664, the total number of all DNA molecules is 6, and the total size of all the DNA molecules is 2922384bp. The circular chromosome has a size of 2.7Mb and a total of 2743 reading frames. It contains four plasmids with sizes of 26.6kb, 14.5kb, 13.2kb, and 2.7kb, and a megaplasmid with a size of 163kb. Its G+C content is 61%. G. oxydans is an aerobe which has oxygen as a terminal electron acceptor[4]. The highest growth rate occur at temperatures between 25 to 30 degrees C and it cannot withstand high temperatures above 37 degrees C. G. oxydans are interesting because they cause apples and pears to rot and they thrive in environments with high concentrations of sugar[3].

Cell structure and metabolism

Gluconobacter oxydans has two membranes and no flagella and are thus non-motile. This bacteria usually contains ubiquinone-10 [3]. Since they are aerobes, they must oxidize to get their energy[3]. One method involves oxidation of sugars, aliphatic and cyclic alcohols, and steroids to oxidation product. Another method is through the pentose phosphate pathway where phosphorylation occurs initially then proceeds with oxidation through the pathway. It is suggested that G. oxydans has an incomplete set of tricarboxylic acid cycle (TCA) enzymes because the carbon dioxide produced from glucose was from the pentose phosphate pathway. They possess properties for TCA because they are primarily responsible for the biosynthesis of glutamate, aspartate, and succinate. The main function of G. oxydans is their oxidative capabilites. It uses membrane-bound dehydrogenases to oxidize polyols into ketones and sugars into acids[3]. G. oxydans was first found used as vinegar formation through alcoholic fermentation. Gluconobacter cannot oxidize acetate and lactate to carbon dioxide and water, it goes through an incomplete oxidation of its substrates[3].

Ecology

Gluconobacter oxydans is often found in sugar rich or alcoholic areas. It contributes to the environment by oxidizing sugars, sugar acids, and sugar alcohols. It can cause fruits to rot like rotten apples and pears. G. oxydans can incompletely oxidize substrates under natural conditions.[5] They have membrane-bound dehydrogenases that carry out the process of incomplete oxidation([6]pg 288).

Pathology

Gluconobacter oxydans strains are non-pathogenic to humans or animals, but they cause bacterial rot to apples and pears turning them shades of brown.[2]

Application to Biotechnology

Gluconobacter oxydans is useful for a number of biotechnological applications.

It goes through the process of oxidizing glycerol to dihydroxyacetone(DHA). It uses a membrane-bound glycerol dehydrogenase to oxidize sorbitol, gluconate, and arabitol. G. oxydans contain many membrane-bound dehydrogenases that are very useful for the incomplete oxidation of substrates in biotechnological experiments([6]pg288).

Production of vitamin C, sorbitol, xylitol, and vinegar are aided with the addition of G. oxydans.

Biosensors using G. oxydans can be used to measure substrate concentration as a biosensor. With the addition of G. oxydans in microbial biosensors the results of the biosensor response is faster due to the periplasmic localization of PQQ-dependent enzymes([6]pg288). Ehtanol in air, glycerol in fermentation media, and glucose in humans are just a few of the exciting applications currently being researched.

Current Research

Gluconobacter oxydans can be used to convert glycerol to dihydroxyacetone. The study shows the possible production of this organism using agricultural byproducts. Since G. oxydans thrive in environments with high sugar concentrations, the medium used for the growth of G. oxydans cells are corn meal hydrolysate and corn steep liquor instead of sorbitol and yeast which are the usual components found. The results of the experiment found that the optimal medium contained "80 g/L reducing sugar, 25 g/L corn steep liquor, and 10 g/L glycerol. The cell mass was about 4.22 g/L and the glycerol dehydrogenase activity was about 5.23 U/mL. For comparison, the cell mass was about 4.0 g/L and the glycerol dehydrogenase activity was about 5.35 U/mL cultured in sorbitol and yeast extract medium"[7]. Clearly, corn meal hydrolysate and corn steep liquor medium is just as effective in performance as the sorbitol and yeast medium, but cost is 15% less[7].

Another study using G. oxydans is the application of this organism in biosensors. It monitors the bacterial bioconversion of glycerol to 1,3-propanediol. The use of G. oxydans gives high detection performance and high reliability of 1,3-PD detection. 'This system was used to monitor the concentration of 1,3-PD during a real bioprocess. Results from biosensor assays of 1,3-PD in bioprocess samples taken throughout the fermentation were in a very good agreement with results obtained from reference HPLC assays (R squared value equals 0.999)'([6]pg287-294).

A study of varying the many membrane-bound glucose oxidation system in Gluconobacter oxydans increases gluconate and acid accumulation. G. oxydans catalyzes the oxidation of glucose to gluconic acid then to 5-keto-D-gluconic acid, which is useful in industry so the increased production of G. oxydans is important. A mutant strain MF1 was used to help 5-KGA accumulate in the medium, therefore increasing the gluconic acid formation[8].

References

[1]Prust, C., Hoffmeister, M., Liesegang, H., Wiezer, A., Fricke, W. F., Ehrenreich, A., Gottschalk, G. and Deppenmeier, U. (2005) Complete genome sequence of the acetic acid bacterium Gluconobacter oxydans. Nature Biotechnol. 23(2): 195-200 (abstract).

[2]Gupta A, Singh VK, Qazi GN, Kumar A. Gluconobacter oxydans:its biotechnological applications. J Mol Micrcobiol Biotechnol. 2001 Jul.

[3]Sue Macauley, Brian McNeil, and Linda M. Harvey. 'The Genus Gluconobacter and Its Applications in Biotechnology'. Critical Reviews in Biotechnology, 21:1, 1-25.

[4]http://cmr.tigr.org/tigr-scripts/CMR/GenomePage.cgi?org=ntgo01 'Gluconobacter oxydans 621H Genome page', Comprehensive Microbial Resource

[5]Cornelia Gatgens, Ursula Degner, Stephanie Bringer-Meyer, and Ute Herrmann. 'Biotransformation of glycerol to dihydroxyacetone by recombinant Gluconobacter oxydans DSM 2343'. Biotechnological Products and process engineering. April 2007.

[6]Jaroslav Katrlik, Igor Vostiar, Jana Sefcovicoa, Jan Tkac, Vladimir Mastihuba, Milan Valach, Vladimir Stefuca, and Peter Gemeiner. 'A novel microbial biosensor based on cells of Gluconobacter oxydans for the selective determination of 1,3-propanediol in the presence of glycerol and its application to bioprocess monitoring'. Analytical and Bioanalytical Chemistry, Springer-Verlag 2007.

[7]Wei S, Song Q, and Wei D. 'Production of Gluconobacter oxydans cells from low-cost culture medium for conversion of glycerol to dihydroxyacetone'. Prep Biochem Biotechnol, 2007; 37(2):113-21.

[8]Merfort M, Herrmann U, Ha SW, Elfari M, Bringer-Meyer S, Gorisch H, and Sahm H. 'Modification of the membrane-bound glucose oxidation system in Gluconobacter oxydans significantly increases gluconate and 5-keto-D-gluconic acid accumulation'. Biotechnol J, 2006 May;1(5):556-63.


Edited by Lynn S Cheung student of Rachel Larson and Kit Pogliano

edited KMG

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