Glycine betaine metabolism in the acetogenic bacterium Acetobacterium woodii.

The quarternary, trimethylated amine glycine betaine (GB) is widespread in nature but its fate under anoxic conditions remains elusive. It can be used by some acetogenic bacteria as carbon and energy source but the pathway of GB metabolism has not been elucidated. We have identified a gene cluster involved in GB metabolism and studied acetogenesis from GB in the model acetogen Acetobacterium woodii. GB is taken up by a secondary active, Na+ coupled transporter of the betaine-choline-carnitine (BCC) family. GB is demethylated to dimethylglycine, the end product of the reaction, by a methyltransferase system. Further conversion of the methyl group requires CO2 as well as Na+ indicating that GB metabolism involves the Wood-Ljungdahl pathway. These studies culminate in a model for the path of carbon and electrons during acetogenensis from GB and a model for the bioenergetics of acetogenesis from GB.