Simple quantification of bacterial envelope-associated extracellular materials.

We have developed a simple method for distinguishing between bacterial cultures that produce different amount of exopolysaccharide. It is based upon small differences in pellet volume formed by those cultures upon centrifugation. For that we have constructed a special centrifugation tube consisting of two connected chambers: an upper 12 ml chamber connected to a lower capillary chamber. Cells are applied to the upper chamber and following centrifugation, sink to its bottom and are forced into the capillary so that the height they fill can be measured. This procedure has been developed in order to demonstrate differences in volume of centrifugation pellet formed by similar number of Escherichia coli K12 wild type, rpoS mutant and yjbG rpoS double mutant cells. These differences are further shown to be a result of overproduction of colanic acid exopolysaccharide in the mutant strains. We suggest that this simple method can be employed to detect differences in other cell surface structures and to estimate biomass when optical density measurement or microscopic count is not applicable.