Bacterial uptake of dissolved organic matter in relation to detrital aggregation in marine and freshwater systems1

Abstract

Microbial uptake of 3 H‐labeled glucose and acetate was studied in water samples from various depths in the Pacific Ocean and Lake Tahoe, California. Microzones of incorporation were identified by comparison of autoradiographic detection of the uptake of 3 H‐labeled organic substrates with scanning electron micrographs of detritus (nonliving particulate matter and associated microflora). In both freshwater and marine systems, immediate (within 4 hr) accumulation of dissolved organic compounds was detected mainly in bacterial cells and filaments. With continued incubation, the label was dispersed throughout detrital particles, with localization greatest in bacteria. Uptake of both substrates by attached microorganisms was significantly higher in the cuphotic than in the aphotic zone as was the extent of detrital aggregation. Autoradiographs show that dissolved organic substrates assimilated by bacteria are linked to the formation of capsular materials, which are important in building detrital aggregates.