L-carnitine metabolism in bacteria. A) Schematic representation of the main pathways for L(-)-carnitine metabolization in bacteria. Shaded and striped reactions correspond to the pathways observed in Enterobacteria and Acinetobacter strains, respectively. Reactions in the dashed box correspond to Pseudomonas strains. Enzymes or "systems" involved: 1, γ-butyrobetaine hydroxylase; 2, L-carnitine dehydrogenase; 3, L-carnitine dehydratase; 3a, "carnitinyl-CoA hydrolase"; 4, crotonobetaine reductase; 4a, "γ-butyrobetaine dehydrogenase"; 5, monooxygenase; 6, "carnitine racemase"; 7, D-carnitine dehydrogenase. Adapted from . B) Complete anaerobic biotransformation pathway for trimethylammonium compounds in E. coli. Adapted from . Abbreviations: Crot, crotonobetaine; γ-BB, γ-butyrobetaine, L-Car, L-carnitine; D-Car, D-carnitine; Gly, glycine; 3-dehydro-Car, 3-dehydrocarnitine; Me3N, trimethylamine; Mal, malate; Suc, succinate; CaiT, L-carnitine/γ-butyrobetaine/crotonobetaine protein transporter; CaiA, CaiB, crotonobetaine reduction reaction; CaiB, CoA transferase; CaiC, L-carnitine/γ-butyrobetaine/crotonobetaine CoA ligase; CaiD, enoyl-CoA hydratase or carnitine racemase activity.