Inactivation ofpqqgenes ofEnterobacter intermedium60-2G reduces antifungal activity and induction of systemic resistance

Abstract

Enterobacter intermedium 60-2G, a phosphate solubilizing bacterium, has the ability to induce systemic resistance in plants against soft rot pathogen Erwinia carotovora. Glucose dehydrogenase, an enzyme that utilizes pyrroloquinoline quinone (PQQ) as a cofactor, is required for the synthesis of gluconic acid by E. intermedium 60-2G. Here, we report that the pqqA and pqqB genes are required for phosphate solubilization and induced systemic resistance against a soft rot pathogen in tobacco. Mutations in either the pqqA or pqqB gene abolished the production of 2-ketogluconic acid and eliminated the ability of E. intermedium to solubilize hydroxyapatite. Addition of gluconic acid to the growth media restored the ability of the pqqA mutant to produce 2-ketogluconic acid. Interestingly, both pqqA and pqqB mutants of E. intermedium lost their ability to inhibit the growth of the rice pathogen Magnaporthe grisea KI-409. Additionally, induced systemic resistance against the soft rot pathogen was attenuated in the pqq mutants. These functions were restored by complementation with the wild-type pqq gene cluster. Our findings suggest that PQQ plays an important function in beneficial traits including phosphate solubilization, antifungal activity, and induced systemic resistance of E. intermedium, possibly by acting as a cofactor for several enzymes including glucose dehydrogenase.

Mutations That Disrupt Either thepqqor thegdhGene ofRahnella aquatilisAbolish the Production of an Antibacterial Substance and Result in Reduced Biological Control of Grapevine Crown Gall

“…There are reports that plant growth-promoting bacteria are able to solubilize inorganic and/or organic phosphates in soil, which is dependent on the GDH-PQQ holoenzyme activity (22,36). In addition, transfected PQQ genes enhanced the phenotype of MPS in two rhizobacterial strains, Burkholderia cepacia IS-16 and a Pseudomonas sp.…”

“…Moreover, PQQ-linked GDH was recently shown to be required by Sinorhizobium meliloti for optimal nodulation efficiency and competitiveness on alfalfa roots (4). Several reports claim that the GDH-PQQ holoenzyme is involved in antimicrobial substance production in Pseudomonas fluorescens (17,28,46) and in Enterobacter intermedium (22), respectively. Additionally, it has been reported that PQQ plays a role beyond that of a cofactor of the PQQ-dependent dehydrogenase.…”

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

“…The genes responsible for PQQ production have been cloned and sequenced in several bacterial genera, including Pseudomonas, Methylobacterium, Acinetobacter, Klebsiella, Enterobacter, and Rahnella (5,14,17,36,42). In P. fluorescens B16, the PQQ operon is formed by 11 …”

“…Several studies with bacterial mutants unable to produce PQQ and gluconic acid have demonstrated the intimate relation of the cofactor to phosphate solubilization processes (7,17). Besides its relevant role in P solubilization, PQQ is reported to be a potent growth-promoting factor for bacteria and plants, has antioxidant properties (5), and is directly related to the production of antimicrobial substances (7,14,36) as well as to the induction of systemic plant defenses (17). Hence, the cofactor PQQ has multiple plant beneficial effects.…”

Isolation and Characterization of Oligotrophic Bacteria Possessing Induced Systemic Disease Resistance against Plant Pathogens

“…Additionally, other phenotypic properties of the selected bacterial strains including antifungal, chitin degradation, gelatin degradation, and solubilizing phosphate activity were assessed on the detection agar plates, because the microbial properties are known to involve in biocontrol of plant disease and insect (Han et al, 2008;Kim et al, 2008;Martin and Gundersen-Rindal, 2008). The In vitro antifungal activities of the selected strains were tested by dual inoculation on potato dextrose agar (Difco Inc., Detroit, MI) with plant pathogenic fungi Fusarium oxysporum (KACC NO.…”