Nuclear Magnetic Resonance Analysis of [1- 13 C]Dimethylsulfoniopropionate (DMSP) and [1- 13 C]Acrylate Metabolism by a DMSP Lyase-Producing Marine Isolate of the α-Subclass of Proteobacteria

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Abstract
The prominence of the α-subclass of Proteobacteria in the marine bacterioplankton community and their role in dimethylsulfide (DMS) production has prompted a detailed examination of dimethylsulfoniopropionate (DMSP) metabolism in a representative isolate of this phylotype, strain LFR. [1-13C]DMSP was synthesized, and its metabolism and that of its cleavage product, [1-13C]acrylate, were studied using nuclear magnetic resonance (NMR) spectroscopy. [1-13C]DMSP additions resulted in the intracellular accumulation and then disappearance of both [1-13C]DMSP and [1-13C]β-hydroxypropionate ([1-13C]β-HP), a degradation product. Acrylate, the immediate product of DMSP cleavage, apparently did not accumulate to high enough levels to be detected, suggesting that it was rapidly β-hydroxylated upon formation. When [1-13C]acrylate was added to cell suspensions of strain LFR it was metabolized to [1-13C]β-HP extracellularly, where it first accumulated and was then taken up in the cytosol where it subsequently disappeared, indicating that it was directly decarboxylated. These results were interpreted to mean that DMSP was taken up and metabolized by an intracellular DMSP lyase and acrylase, while added acrylate was β-hydroxylated on (or near) the cell surface to β-HP, which accumulated briefly and was then taken up by cells. Growth on acrylate (versus that on glucose) stimulated the rate of acrylate metabolism eightfold, indicating that it acted as an inducer of acrylase activity. DMSP, acrylate, and β-HP all induced DMSP lyase activity. A putative model is presented that best fits the experimental data regarding the pathway of DMSP and acrylate metabolism in the α-proteobacterium, strain LFR.