Biodegradation of β-1,4-linked polyglucuronic acid (cellouronic acid)

Biodegradability of beta-1,4-linked polyglucuronic acid (cellouronic acid), which was prepared from regenerated cellulose by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation under aqueous conditions, was examined by enzymatic treatments and incubation treatments with microorganisms collected from some soil samples. Degradation of cellouronic acid was traced by size exclusion chromatography (HPSEC) or total organic carbon (TOC) of the treated products or solutions, respectively. Cellouronic acid was depolymerized by a commercial crude cellulase and decreased in its weight average degree of polymerization from about 1600 to 40 by the cellulase treatment at 20 degreesC for 40 days. C-13-NMR analysis and liquid chromatography of the treated products showed that hydrolysis-type enzymes present in the crude cellulase as contaminants primarily depolymerized cellouronic acid to give glucuronic acid. When aqueous solutions containing cellouronic acid were incubated with soil microorganisms for more than 3 days, the TOC values decreased to less than 20% of the initial value, depending on molecular weight of the cellouronic acid used. The decreasing rate of TOC for cellouronic acid was clearly higher than that of carboxymethylcellulose, which is one of the cellulose derivatives having carboxymethyl substituents. These results imply that cellouronic acid has both biodegradability and metabolizability in the natural environment.