Utilization of algal polysaccharides by human colonic bacteria, in axenic culture or in association with hydrogenotrophic microorganisms.

The ability of different hydrolytic bacteria from the human colon to grow on various algal polymers (carrageenans, Palmaria palmata xylan, ulvan, desulphated ulvan and laminaran) was investigated and the interactions between Bacteroides thetaiotaomicron and H2-utilizing microorganisms (one methanogenic archaea and an acetogenic bacterium) were studied during laminaran degradation. None of the algal polysaccharides supported the growth of any of the hydrolytic species tested, except for laminaran, which allowed substantial growth of B thetaiotaomicron. This suggested that bacterial consortia were involved in algal polymer breakdown rather than one specific bacterial species. The presence of H2-utilizing microorganisms did not increase the extent of laminaran degradation by B thetaiotaomicron. Whereas the decrease in formate and H2 concentrations attested to their utilization by both hydrogenotrophic microorganisms, the large increase in acetate production observed in the coculture with acetogenic bacteria was mainly due to acetogenic fermentation of sugars released during laminaran hydrolysis.