Bacterial exopolymer and PHB production in fluctuating ground-water habitats

The physiological response of a strain of ground-water bacteria to short-term fluctuations in the quality of percolating water was followed in a continuous-flow water-saturated soil column. The cells reduced their production of uronic acids-characterized extracellular polysaccharides by more than 50% when pure ground water was enriched with phosphate and glucose but resumed it gradually as the poor growth conditions returned. Bacteria that were sorbed to the mineral particles in the soil column produced more exopolymers-about six times more in pure ground water-than free-living bacteria, but the composition of the polymer was the same. Glucose, mannose and galacturonic acid accounted for about 90% of the carbohydrate. The cells stored about five times more poly-β-hydroxybutyric acid (PHB) in pure than in enriched ground water, and sorbed cells had five times higher concentrations than free-living cells. The quality variations of the ground water were also reflected in the population size of bacteria, which differed by two to four orders of magnitude between poor and enriched conditions.