Acetobacter diazotrophicus possesses a pyrroloquinoline quinone-linked glucose dehydrogenase (PQQ-GDH). The enzyme seemingly belongs to the type II PQQ-GDH enzymes and, at least under the culture conditions tested, the organism synthesizes enough PQQ to saturate the ape-enzyme. The synthesis of this enzyme is stimulated when the organism is grown under N-2-fixing conditions. It is proposed that this enzyme may play an important role in providing extra energy in N-2-fixing cells.