Characterization of Native Bacteria and Their Utilization of Algal Extracellular Products by a Mixed-Substrate Kinetic Model

Abstract

Assimilation and mineralization og 14C labelled extracellular products (EOC) by native bacterial populations were followed in a diel study and from early spring through autumn in two eutrophic Danish lakes. Kinetic analyses according to a mixed-substrate kinetic model always revealed linear kinetics. The method was found useful in unveiling in situ specific algal-bacterial associations mediated through the release of EOC from the primary producers. Further, bacterial adaptation toward the phycosphere of Microcystis aeruginosa could be detected by following the shift in X-intercepts for the lines of net uptake and respiration during the development of a bloom of M. aeruginosa. By simultaneous measurements of particulate primary production, EOC release and transport of EOC to the bacteria by a differential filtration technique, it is shown that the method presented does not generally estimate changes in the kinetic parameters, but does reveal qualitative changes. It is concluded that the mixed-substrate method is a powerful approach for elucidating specific algal-bacterial associations in situ, even in highly complex eutrophic environments.