METABOLIC CHANGES ASSOCIATED WITH BIOFILM FORMATION IN AN UNDISTURBEDMEDITERRANEAN STREAM

Respiratory activity (ETS), ectoenzymatic activity (beta-glucosidase a nd beta-xylosidase) and photosynthetic C-14-bicarbonate incorporation in the biofilm were measured in a shaded stream during a colonization sequence (43 days) on artificial substrates (unglazed clay tiles) and compared with older (aged) tiles. In the first five days bacterial den sities and ectoenzyme activities showed a sharp increase. After two we eks, algal density, chlorophyll and productivity increased moderately. Chlorophyll did not reach similar values to those of the aged biofilm s until the last day of colonization. Photosynthetic activity seemed t o be relevant to the heterotrophs metabolism during substrate coloniza tion, as could be deduced from the significant correlation between bet a-glucosidase and C-14-bicarbonate incorporation, algal cell densities and chlorophyll. Respiratory activity (ETS) decreased in the older bi ofilms, accordingly to their higher algal and bacterial density. Young er biofilms (up to 8 days old) showed higher ETS activity per cell, in dicating a fast response of microorganisms to substrate availability.