A bacterial TMAO transporter

Abstract

Trimethylamine oxide (TMAO) acts as an osmolyte in a wide variety of marine organisms, but little is known about the mechanisms by which it accumulates in certain tissues. To determine whether a TMAO-specific transporter occurs in Nature, we examined a bacterium Aminobacter aminovorans that is known to be able to subsist on methylamine as the sole carbon source. We found that A. aminovorans is also able to grow on TMAO as the sole carbon source, and that it takes up [ 14C]labeled TMAO at a rate of approximately 50 pmol min −1 mg protein −1. TMAO uptake was strongly inhibited by unlabeled TMAO (5 mM) but not by related compounds such as methylamine, betaine or γ-amino- n-butyric acid (GABA), indicating that a TMAO-specific transporter is present. The TMAO transporter appears to have an ATP requirement but no ion exchange requirement. This appears to be the first evidence of a TMAO-specific transporter in any organism. The TMAO-grown cells also expressed transporters that were specific to betaine and trimethylamine. Madin–Darby canine kidney (MDCK) cells, which have a betaine transporter that is also capable of transporting GABA, were unable to take up TMAO.