Oxalic acid is often accumulated as a metabolic end-product in plant cells either as the free acid, as sodium and potassium oxalate, or precipitated as an insoluble salt most commonly calcium oxalate. Deposits of calcium oxalate occur as microscopic crystals in many different organs and tissues a wide variety of plant taxa. Their accumulated amount varies among species and may comprise up to 85 % of dry weight of some plants [1]. In the animal kingdom oxalate and its salts are presented in urine and blood of mammals. Much of the oxalate in animals originates from the oxalate ingested with plant material, although mammals through the oxidation of glyoxlate and ascorbate synthesize minute amounts.
Many fungi, belonging to Ascomycetes, Basidiomycetes and Zygomycetes, a few Lichens [2] and slime mold genera Perichaena and Dianema [3] produce calcium oxalate crystals during some phase of their life cycle. Accumulation of oxalate by fungi, particularly in Aspergillus, Penicillium and Mucor species is of such an order that these fungi could be used for industrial fermentation for oxalate. On the death and decay of plants containing oxalate, the soil where its chelating properties will prove toxic and interfere with plant growth. Nevertheless, as oxalate does not seem to accumulate significantly in soils and in the litter below oxalate-bearing plants, it can be postulated that it is rapidly catabolised aerobically by soil microorganisms. Oxalic acid is naturally occurring, highly oxidized organic compound with powerful chelating activity.
At high concentrations, oxalic acid causes death in humans and animals due to its corrosive effects. In smaller amounts, oxalic acid causes a variety of pathological disorders, including hyperoxaluria, pyridoxine deficiency, cardiomyopathy, cardiac conductance disorders, calcium oxalate stones and renal failure [4]. This condition is thought to result due to a failure in the conversion of glyoxylate arising from the oxidative decarboxylation of glycine in to formate, or in the reconversion of glyoxlate in to glycine by glutamate-glycine transaminase. The excess of glyoxlate formed in these cases is oxidized to oxalate. Aggregation of calcium salts of oxalate and phosphate may cause formation of mineral deposits in the kidney and urinary tracts and the process of stone formation is known as urolithiasis. In man and animals oxalate is a non-essential toxic end product of metabolism and is excreted unchanged in mine, since there are no known naturally occurring enzymes in vertebrates capable of degrading oxalate. There is an interesting suggestion that treatment of kidney stones could probably be attempted with oxalate degrading microbes (Oxalobacter formigenes).Recently (2002) Ixion Biotechnology, Inc.,(Alachua, FL) has been issued a new patent (US 6,355,242) relating to the treatment or prevention of oxalate-related disease in animals through the delivery of oxalate-degrading bacteria and enzymes.
Oxalate is detoxified (catabolized) via the action of two enzymatic proteins, formyl coenzyme A transferase (encoded by the frc gene) and oxalyl coenzyme A decarboxylase (encoded by the oxc gene), contained in the cytosol of Oxalobacter formigenes that colonizes the human intestinal tract. It is speculated that oxalate-degrading bacteria decrease oxalate absorption from the intestines and their absence in the gastrointestinal tract correlates with the formation of calcium-oxalate urolithiasis.
Though all oxalate-utilizing microorganisms may play important role in the carbon cycle aerobic, oxalate-decomposing bacteria will be discussed in the following paragraphs. A limited number of aerobic bacteria were described, which are able to utilize oxalate as sole carbon and energy source.[Methylobacterium] extorquens was the first described oxalate-degrading bacteria [5]. However, the taxonomic position of this organism and other pink-pigmented, facultative methylotrophs (PPFM) was uncertain. Thus, they were subsequently assigned to several different genera (e.g., Vibrio, Pseudomonas, Protomonas) until it was proposed that PPFMs be grouped in the genus Methylobacterium and that Protomonas extorquens be classified as [Methylobacterium] extorquens [6]. "[Pseudomonas] oxalaticus" is most popular oxalate-decomposing bacterium described in the literature and was initially named Vibrio oxalaticus by Bhat and Barker, 1948 [7]. Jenni et al., (1988) showed that Pseudomonas oxalaticus Ox1 phenotypically and genomically related to Ralstonia eutropha (formerly Alcaligenes eutrophus) [8, 9]. Sahin et al.[19] described the strain Ox1 in the Genus Ralstonia as Ralstonia oxalatica comb. nov. This organism was subsequently assigned to several different genera (e.g., pseudomonas, Alcaligenes, Ralstonia and Wautersia) finally Cupriavidus as C. oxalaticus by Vandamme and Coenye (2004).
Tamer(1982), was isolated 27 strains of mesophilic, non-hydrogen lithotrophic oxalate-oxidizers belonging to genera Ralstonia, Alcaligenes, Pseudomonas and Methylobacterium from soil litter close to oxalate excreting plants Rumex,Oxalis and Arum sp. [14]. He was obtained a new yellow pigmented bacterial strains using oxalate as the sole carbon end energy source from litter of Mesenbryanthemum sp. not resembling any previously known yellow pigmented oxalate oxidizers and designed as Pseudomonassp. Tamer et al.[20] described these yellow pigmented strains in the novel Genus Oxalicibacterium as Oxalicibacterium flavum.
Ammoniiphilus oxalaticus andA. oxalativorans are, ammonium-dependent, obligately oxalotrophic
and haloalkalitolarant bacteria that were recently described. Ammoniiphilus strains were isolated from the rhizosphere of sorrel (Rumex acetosa)and from decaying wood respectively. Assimilation of oxalate proceeded by a variant of the serine pathway [15], other known oxalate-oxidizers assimilates oxalates via the glycolate or serine pathways.
A few calcium oxalate-decomposing Streptomyces [27] and fungi species were isolated and showed that oxalate utilization are useful substrates for differentiation of Streptomycessp.[16, 17].
Oxalic acid is the only possible compound in which two carboxyl groups are joined directly; for this reason oxalic acid is one of the strongest organic acids. Unlike other carboxylic acids (except formic acid), it is readily oxidized; this makes it useful as a reducing agent for photography, bleaching, and ink removal. Oxalic acid is usually prepared by heating sodium formate with sodium hydroxide to form sodium oxalate, which is converted to calcium oxalate and treated with sulfuric acid to obtain free oxalic acid.
Biological production of high amounts of oxalic acid is of interest for biohydrometallurgical applications. Because oxalic acid may be used to solubilise heavy metals from ores and minerals [18]. Aerobic oxalate-oxidizers may be used to removal oxalates from waste water and soil. Unfortunately, while a considerable number of oxalate-degrading bacteria have been isolated, information is limited regarding their interactions with other microbes or activities, with metals or other inhibitory compounds.
Several plant pathogenic fungi(such as Botrytis cinerea, Sclerotinia sclerotiorum and Phytophtora infenstans)produce oxalic acid, an essential component of the infection process. Strains of oxalate-degrading bacteria have been recently used to protect a model host plant from infection by oxalate-producing fungal pathogens. Future applications are to develop transgenic plants that are resistant to oxalate-producing fungal pathogens.
OXALATE-DEGRADING HYDROGEN (Knallgas) BACTERIA
The hydrogen-oxidizing bacteria, often called "the Knallgas bacteria", are a physiologic group of aerobic, chemolithoautotrophic bacteria. Among hydrogen-oxidizing bacteria the ability to utilize oxalate as sole carbon and energy source is also shared by Variovorax paradoxus, Xanthobacter autotrophicus and Ralstonia eutropha [13]. Oxalate utilizing strains belonged to the genus Alcaligenes phenotypically showed close relationship with hydrogen-oxidizing Ralstonia eutropha[14].
A review written by the author is suggested to researchers for the general information about oxalatotrophic bacteria [21].
KIDNEY STONES AND NANOBACTERIA
In 1996, researchers from Turkey (22) and Finland (23) reported that newly discovered bacteria called Nanobacteria, cause kidney stones. Researchers in Formosa report finding a common intestinal bacteria called Proteus and another often sexually transmitted bacteria called Ureaplasma in kidney stones (24).
CALCIUM CARBONATE PRECIPITATION BY OXALATE DEGRADING BACTERIA
There is increasing evidence that the Ca oxalate cycle is a major pathway in calcite biomineralisation. This was shown with different oxalate accumulating plants, such as iroko trees [25] and Cactaceae. Huge amounts of Ca oxalate are formed in the biosphere, essentially by plants and fungi. However, net accumulation occurs neither in soils nor in the geological record. The fate of oxalate in natural systems remains unclear, although oxalate catabolism by bacteria is a well-recorded phenomenon. A similar pathway can be drawn for citrate in the rhizosphere of citrate-secreting plants.
Aerobic degradation of oxalates leads to the formation of carbonate ions, which will react with calcium released during the consumption of calcium oxalate by bacteria. The transformation of oxalate into carbonate results in a pH increase which allows the calcium carbonate precipitation. Studies on the oxalate-carbonate cycle showed that the production of calcium carbonate by oxalate-degrading bacteria [26]. Some strains produce mainly calcite, whereas other strains preferentially produce vaterite a polymorph of calcium carbonate. It seems that exopolysaccharides (EPS) and some types of homo- or hetero-polypeptides are strongly linked to the differential calcium carbonate crystallization.
Strategies for preventing calcium oxalate stones
First edition: Feb. 1997, and 7th updated: 29 Sept. 2005
CONTACT
Dr. Nurettin Sahin; Mugla University, Egitim Fakultesi, Biyoloji Egitimi ABD., TR-48170 Kotekli, Mugla-TURKEY. e-mail:oxalate2000 [at] yahoo.com
Suggested citation for this site: Sahin, N. Decomposition of Oxalate by Microorganisms. Last update Sept 29, 2005. URL:http://www.oocities.org/oxalate2000