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.