The relationship between dissolved organic matter cycling and bacterioplankton in freshwater environments

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We have succeeded to the isolation of many of dominant but unculturable freshwater bacterioplankton clusters/subclusters from the freshwater lakes and a river. These isolates were strongly dependent on the carboxylic acids as carbon source. Freshwater bacterioplankton subclusters (PnecC and PnecD) have shown the niche separation by the difference of main source of carboxylic acids in the field (photodegradation of humic substances or primary production). In addition, the production of chromophoric dissolved organic matter which has terrestrial humic-like fluorescence by part of freshwater clusters/subclusters was observed in the cultivation experiments. The contribution of freshwater bacterioplankton to carbon cycle has been partly cleared due to the cultivation-based approach using pure strains.