Nature of Incorporated 14C-Labeled Material Retained by Sulfuric Acid Fixed Bacteria in Pure Cultures and in Natural Aquatic Populations

Abstract

The levels of 14C-substrates (glutamic acid, alanine, glucose, and uracil) retained by aquatic bacteria in pure cultures and natural marine and fresh water samples after fixation with 2 N sulfuric acid (H2SO4 to reduce pH to 2) were found to be identical to the amount of 14C-labeled material associated with cold 10% trichloroacetic acid (TCA) precipitates collected on filters. Both TCA and H2SO4 were also equally effective in driving CO2 from solution. In heterotrophic potential studies, therefore, the 14C activity associated with natural bacterial populations collected on membrane filters after H2SO4 fixation represents macromolecules only, and not free substrate pools or low molecular weight metabolites.