Pyrroloquinoline Quinone Biosynthesis GenepqqC, a Novel Molecular Marker for Studying the Phylogeny and Diversity of Phosphate-Solubilizing Pseudomonads

Abstract

Many root-colonizing pseudomonads are able to promote plant growth by increasing phosphate availability in soil through solubilization of poorly soluble rock phosphates. The major mechanism of phosphate solubilization by pseudomonads is the secretion of gluconic acid, which requires the enzyme glucose dehydrogenase and its cofactor pyrroloquinoline quinone (PQQ). The main aim of this study was to evaluate whether a PQQ biosynthetic gene is suitable to study the phylogeny of phosphate-solubilizing pseudomonads. To this end, two new primers, which specifically amplify the pqqC gene of the Pseudomonas genus, were designed. pqqC fragments were amplified and sequenced from a Pseudomonas strain collection and from a natural wheat rhizosphere population using cultivation-dependent and cultivation-independent approaches. Phylogenetic trees based on pqqC sequences were compared to trees obtained with the two concatenated housekeeping genes rpoD and gyrB. For both pqqC and rpoD-gyrB, similar main phylogenetic clusters were found. However, in the pqqC but not in the rpoD-gyrB tree, the group of fluorescent pseudomonads producing the antifungal compounds 2,4-diacetylphloroglucinol and pyoluteorin was located outside the Pseudomonas fluorescens group. pqqC sequences from isolated pseudomonads were differently distributed among the identified phylogenetic groups than pqqC sequences derived from the cultivation-independent approach. Comparing pqqC phylogeny and phosphate solubilization activity, we identified one phylogenetic group with high solubilization activity. In summary, we demonstrate that the gene pqqC is a novel molecular marker that can be used complementary to housekeeping genes for studying the diversity and evolution of plant-beneficial pseudomonads.

Pseudomonas spp. isolates with high phosphate-mobilizing potential and root colonization properties from agricultural bulk soils under no-till management

“…Release of P from mineral phosphate species is related to the production of organic acids, mainly gluconic acid (Lugtenberg and Kamilova 2009). In fluorescent pseudomonads, gluconic acid production is catalyzed by periplasmic oxidation of glucose by a membrane-bound glucose dehydrogenase and its cofactor, pyrroloquinoline quinone (De Werra et al 2009;Meyer et al 2011). All phosphate-mobilizing pseudomonads isolated in this work decreased the pH of the medium in the quantitative solubilization assay (Table 1), most probably due to gluconic acid production.…”

“…1). These two phylogenetic clusters have been reported to include isolates with strong inorganic phosphate solubilization activity in vitro on NBRIP plates (Browne et al 2009;Meyer et al 2011).…”

“…Taxonomic grouping was based on the work of Ramette et al (2011). Colored strains or isolates follow the definition of Meyer et al (2011), with low (blue), medium (green), or strong (red) phosphate solubilization activity on NBRIP medium Results are mean of three replicates±standard deviation. CFU values were log 10 -transformed prior to statistical analysis.…”

Alleviation of Abiotic and Biotic Stresses in Plants by Azospirillum

“…Similar to nitrogen, phosphorus is an essential element for plants. However, its bioavailability is often low in soils due to its presence as insoluble and complexed forms (Meyer et al 2011 ). As mentioned above, one of the main mechanisms harbored by PGPR to solubilize phosphorus is based on soil acidifi cation via the release of acid compounds as gluconic acid, citric acid, oxalic acid (Richardson et al 2009 ).…”

Regulation of Pyrroloquinoline Quinone-Dependent Glucose Dehydrogenase Activity in the Model Rhizosphere-Dwelling Bacterium Pseudomonas putida KT2440

“…Soil-dwelling pseudomonads have become models for understanding GDH-mediated phosphorus solubilization (1,4,7). Miller et al showed that this activity can be impaired by mutations of the GDH-encoding gene (gcd) or of certain genes in the PQQ biosynthesis pathway from Pseudomonas fluorescens F113 (8).…”