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Abstract

Endogenous carbon reserves such as poly-beta-hydroxy alkanoate (PHA) can sustain microbial viability during conditions of nutrient deprivation. Microbial extracellular enzyme activities under one set of environmental 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 changes in environmental conditions were imposed upon river biofilms by transferring them between three rivers of acid, circum-neutral and alkaline pH. The findings supported the hypothesis; each of the transfers resulted in reduced PHA levels, while the physiology of the biofilm (metabolic activity, population density, phosphatase & glucosidase activities) acclimated to the environmental conditions of the recipient site. The greatest PHA depletion was observed when the magnitude of the imposed change resulted in an inability of phosphatase enzyme to respond to the change. The implicit greater dependence on the reserves of PHA, is similarly consistent with the hypothesis.