title: Periplasmic PQQ-dependent glucose oxidation in free-living and symbiotic rhizobia.
abstract: The expression of the pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenase (GDH) of Rhizobium tropici CIAT899 and Sinorhizobium meliloti RCR2011 was investigated under different nutrient-limiting conditions in continuous cultures, under different conditions of phosphate availability, and in S. meliloti bacteroids. The presence of free PQQ in alfalfa root exudates has also been assayed. It was shown that apo-GDH or holoenzyme was actively synthesized by these rhizobia, with the concomitant production of gluconate from glucose, under certain environmental conditions. GDH activity was also detected in bacteroids from alfalfa root nodules inoculated with either S. meliloti RCR2011 or 102F34. It was also shown that free PQQ was present in root exudates of alfalfa, but its production is ascribed to the activity of Erwinia sp., a normal contaminant of these seeds.
authors.affiliation: Centro de Investigación y Desarrollo en Fermentaciones Industriales CINDEFI (CONICET-UNLP), Calles 47 y 115 (1900) La Plata, Argentina.
authors.forename: C E
authors.initials: CE
authors.lastname: Bernardelli
authors.forename: M F
authors.initials: MF
authors.lastname: Luna
authors.forename: M L
authors.initials: ML
authors.lastname: Galar
authors.forename: J L
authors.initials: JL
authors.lastname: Boiardi
mesh_terms: D003470:Culture Media; D005947:Glucose / Q000378:metabolism*; D005948:Glucose Dehydrogenases / Q000378:metabolism*; D000455:Medicago sativa / Q000382:microbiology; D010084:Oxidation-Reduction; D045542:PQQ Cofactor; D019897:Periplasm / Q000201:enzymology*; D018517:Plant Roots / Q000737:chemistry / Q000382:microbiology; D015363:Quinolones / Q000032:analysis; D011809:Quinones / Q000032:analysis; D012231:Rhizobium / Q000201:enzymology* / Q000254:growth & development; D016962:Sinorhizobium meliloti / Q000201:enzymology* / Q000254:growth & development; D013559:Symbiosis
chemical_list: D003470:Culture Media; D015363:Quinolones; D011809:Quinones; D045542:PQQ Cofactor; D005948:Glucose Dehydrogenases; C033955:glucose dehydrogenase (pyrroloquinoline-quinone); D005947:Glucose