Evidence for Intracellular and Extracellular Dimethylsulfoniopropionate (DMSP) Lyases and DMSP Uptake Sites in Two Species of Marine Bacteria

Abstract

The kinetics of dimethylsulfoniopropionate (DMSP) uptake and dimethylsulfide (DMS) production from DMSP in two bacterial species, Alcaligenes sp. strain M3A, an isolate from estuarine surface sediments, and Pseudomonas doudoroffii, from seawater, were investigated. In Alcaligenes cells induced for DMSP lyase (DL) activity, DMS production occurred without DMSP uptake. In DL-induced suspensions of P. doudoroffii, uptake of DMSP preceded the production of DMS, indicating an intracellular location of DL; intracellular DMSP levels reached ca. 7 mM. DMSP uptake rates in noninduced cells showed saturation at three concentrations (K(inft) [transport] values, 3.4, 127, and 500 (mu)M). In DL-induced cells of P. doudoroffii, DMSP uptake rates increased ca. threefold (V(infmax), 0.022 versus 0.065 (mu)mol of DMSP taken up min(sup-1) mg of cell protein(sup-1)), suggesting that the uptake binding proteins were inducible. DMSP uptake and DL activity in P. doudoroffii were both inhibited by CN(sup-), 2,4-dinitrophenol, and membrane-impermeable thiol-binding reagents, further indicating active uptake of DMSP by cell surface components. The respiratory inhibitors had limited or no effect on DL activity by the Alcaligenes sp. Of the structural analogs of DMSP tested for their effect on DMSP metabolism, glycine betaine (GBT), but not methyl-3-mercaptopropionic acid (MMPA), inhibited DMSP uptake by P. doudoroffii, suggesting that GBT shares a binding protein with DMSP and that MMPA is taken up at a separate site. Two models of DMSP uptake, induction, and DL location found in marine bacteria are presented.