POLY-BETA-HYDROXY ALKANOATE AND THE SUPPORT OF RIVER BIOFILM METABOLISM FOLLOWING RADICAL CHANGES IN ENVIRONMENTAL-CONDITIONS

Endogenous carbon reserves such as poly-beta-hydroxy alkanoate (PHA) c an sustain microbial viability during conditions of nutrient deprivati on. Microbial extracellular enzyme activities under one set of environ mental conditions might be wholly inappropriate for another, and thus PHA might also serve as an energy source as the biofilm acclimates to a changed environment. In order to test this hypothesis, radical chang es in environmental conditions were imposed upon river biofilms by tra nsferring them between three rivers of acid, circum-neutral and alkali ne pH. The findings supported the hypothesis; each of the transfers re sulted in reduced PHA levels, while the physiology of the biofilm (met abolic activity, population density, phosphatase and glucosidase activ ities) acclimated to the environmental conditions of the recipient sit e. The greatest PHA depletion was observed when the magnitude of the i mposed change resulted in an inability of phosphatase enzyme to respon d to the change. The implicit greater dependence on the reserves of PH A, is similarly consistent with the hypothesis.