Genetic neighborhoods of the genes (tmoXWV) that encode the TMAO transporter (red) among representative genome-sequenced marine bacteria. All genes colored black have no confirmed functional relationship with TMAO metabolism. α, Alphaproteobacteria; δ, Deltaproteobacteria; γ, Gammaproteobacteria; GMA, γ-glutamylmethylamide; NMG, N-methylglutamate.