Structural investigation of carboxyinethyl cellulose biodeterioration by Bacillus subtilis subsp subtilis NCIB 3610

摘要

Structural changes of carboxymethyl cellulose (CMC) during biodeterioration with Bacillus subtilis subsp. subtlits NCIB 3610 were studied with small-angle X-ray scattering (SAXS), size exclusion chromatography, and viscosity measurements. Cleavage of CMC polymers changed flow characteristics from those of non-Newtonian pseudoplastic fluid to those of Newtonian fluid. The viscosity decreased from 10 to 1.4 mPas and the concentration of reducing sugar increased by 18-fold. Upon biodeterioration the average radius of gyration decreased from 147 to 123 angstrom; cleaved polymer chains remained in close contact in unstirred medium as reflected by a relatively large apparent radius of gyration. However, such degraded CMC aggregates were easily dispersed with shear stress. The results suggest that biodeterioration mainly affects CMC structural features that are larger than 5 nm. Furthermore, the results also suggest that CMC metabolism and biodeterioration may be decoupled; B. subtilis subsp. subtilis NCIB 3610 produces cellulases that effectively cleave CMC but cannot efficiently utilize hydrolyzed products. There were no structural or theological changes observed in the absence of B. subtilis subsp. subtilis NCIB 3610 growth