OLIGOSACCHARIDE DEGRADATION BY ANAEROBIC MARINE-BACTERIA - CHARACTERIZATION OF AN EXPERIMENTAL SYSTEM TO STUDY POLYMER DEGRADATION IN SEDIMENTS

Enrichment of bacteria from anoxic marine sediments on specific carbohydrates yielded a reproducible model system with which to compare the degradation of a set of structurally related substrates. The goal was to approximate the diversity of natural mixed microbial populations while reducing the complexity of studying the degradation of specific substrates in sediments. Structurally related substrates were used to compare the influence of substrate size, chemical linkage, and stereochemistry on carbohydrate degradation. Headspace gases (CO2, H-2, CH4, H2S) were monitored by gas chromatography, and carbohydrate substrates were separated and quantified with high-pressure Liquid chromatography. The sequence of transformations observed in the cultures is consistent with the sequential substrate degradation expected in a consortium of anaerobic bacteria, and the transfer of carbon from substrates through to end products was followed quantitatively. A series of experiments showed that mixed cultures of marine bacteria distinguish between even small, closely related substrates that do not require extracellular hydrolysis prior to uptake. A galactose-beta(1,3)-arabinose disaccharide (GLA) was degraded at half the rate of seven other similar disaccharides and three larger oligosaccharides. Results from transfer cultures indicate that the ability to degrade GLA probably is not widespread among bacteria. Although neither the component monomers of GLA nor its beta(1,3) linkage is uncommon in marine environments, its specific combination of a hexose and a pentose may not fit standard carbohydrate transport systems in bacteria. Substrate structural features clearly can have a significant effect on degradation rates, even at molecular weights below the direct transport size limit.