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 apo-enzyme. The synthesis of this enzyme is stimulated when the organism is grown under N₂-fixing conditions. It is proposed that this enzyme may play an important role in providing extra energy in N₂-fixing cells.Centro de Investigación y Desarrollo en Fermentaciones Industriales