PQQ-LINKED EXTRACELLULAR GLUCOSE-OXIDATION AND CHEMOTAXIS TOWARDS THIS COFACTOR IN RHIZOBIA

The presence of the pyrroloquinoline quinone (PQQ)-dependent glucose d ehydrogenase in several strains of different Rhizobium species and of Bradyrhizobium japonicum was investigated. It was found that most stra ins were only able to synthesize the ape-enzyme, whereas in three stra ins, Rhizobium meliloti 102F34 and Bradyrhizobium japonicum strains US DA110 and USDA138 hole-enzyme activity could be observed. In washed su spensions, however, only Rhizobium meliloti 102F34 produced gluconate from glucose in the absence of added PQQ. All strains showed positive chemotaxis towards PQQ. This chemotaxis could already be observed with nanomolar concentrations of PQQ.