Uptake of Cyclic AMP by Natural Populations of Marine Bacteria

The major objective of this study was to describe the mechanism(s) of cyclic AMP uptake by natural populations of marine bacteria. A second objective was to determine whether this uptake could contribute to the intracellular regulatory pool of cyclic AMP. Using high-specific-activity P-labeled cyclic AMP, we found several high-affinity uptake systems. The highest-affinity system had a half-saturation constant of <10 pM. This system was extremely specific for cyclic nucleotides, particularly cyclic AMP. It appeared to meet the criteria for active transport. Uptake of cyclic AMP over a wide concentration range (up to 2 muM) showed multiphasic kinetics, with half-saturation constants of 1 nM and greater. These lower-affinity systems were much less specific for cyclic nucleotides. Although much of the labeled cyclic AMP taken up by the high-affinity systems was metabolized, some remained as intact cyclic AMP within the cells during 1 h of incubation. This suggests that at least some of the bacteria use cyclic AMP dissolved in seawater to augment their intracellular pools.