Microbial degradation of oxalate in the gastrointestinal tracts of rodents and ruminants

Abstract

<p>White laboratory rats from only one of five commercial breeders tested harbored populations of colonic oxalate-degrading bacteria. An obligately anaerobic, oxalate-degrading bacterium, Oxalobacter formigenes strain OxCR6, isolated from these rats colonized the ceca and colons of other rats which did not harbor O. formigenes. Colonization only occurred in rats that were fed diets that contained 3.0 or 4.5% sodium oxalate. After colonization, the rates of oxalate degradation in cecal and colonic contents from rats fed a diet with 4.5% sodium oxalate increased by 19 and 40 times, respectively. In these colonized rats, strain OxCR6 attained concentrations of 10[superscript]8/g (dry weight) of cecal contents. Strains of O. formigenes isolated from the cecal contents of swine, guinea pigs, and wild rats and from human feces also colonized the ceca of laboratory rats; a ruminal strain failed to colonize the rat cecum. The ability to implant O. formigenes into the indigenous intestinal flora of the adult laboratory rat should provide an animal model in which the influence of O. formigenes on the fate of dietary oxalate in mammals can be studied;Selection of oxalate-degrading bacteria may account for the increased rates of oxalate degradation observed in ruminants adapted to diets high in oxalate. A culture medium that contained minerals, 14 mM CaCl[subscript]2, 0.1% yeast extract, 20% filter-sterilized rumen fluid, 20 mM sodium oxalate, and agar was used to enumerate oxalate-degrading anaerobes in sheep ruminal contents. Viable counts of oxalate degraders and rates of oxalate degradation in the ruminal contents from sheep fed diets containing 2.2% oxalate averaged 3.4 x 10[superscript]8/g and 8.2 [mu]mol/g per h, respectively. When the dietary oxalate level was reduced to 1.5%, counts increased to 6.3 x 10[superscript]8/g, but rates decreased to 5.8 [mu]mol/g per h. When sheep were returned to pre-adaptive diets (0.8% oxalate), counts and rates decreased to 6.3 x 10[superscript]7/g and 2.7 [mu]mol/g per h, respectively. Thus, ruminal rates of oxalate degradation are influenced by the level of oxalate in the diet; however, more work is needed to define the relationships between these rates, counts of oxalate degraders, and dietary oxalate levels.</p>