Multiphasic Kinetics for D-Glucose Uptake by Assemblages of Natural Marine Bacteria

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Abstract
D-Glucose-6-[3H] uptake kinetics for marine microbial assemblages were multiphasic when the kinetics were determined over a broad concentration range (10-9 to 10-3 M). Maximum uptake velocity (Vmax) and the sum of 1/2 saturation constant (Kt) and ambient glucose concentration (Sn), (Kt + Sn), increased gradually as the range of glucose concentration was increased. In all seawater samples examined the lowest (Kt + Sn) values were 2-5 .times. 10-9 M; highest values were as high as 5.9 .times. 10-4 M. Simple diffusion into algae or bacteria can not explain the non-linearity of kinetics curves. Removal of most algal cells did not change the kinetic pattern and indirect estimates of diffusion into bacteria were too small to have greatly changed the uptake in 1 .times. 10-9-1 .times. 10-5 M range of glucose. The kinetic diversity of marine bacterial assemblages has implications in the cycling of dissolved organic matter in the varied concentration regimes presumably present in production microzones. Turnover times of the glucose pool at elevated concentrations were in the order of 101-103 h, suggesting that episodic high concentrations of substrate would diffuse out of the production microzones before significant uptake. Sustained concentration gradients might attract high Kt high Vmax bacteria which might take up a significant fraction of substrate within the production zone. The observed kinetic diversity points to the need for a modified kinetic approach to account for the diversity of Kt and Vmax.