Virulence Attenuation of Pectobacterium carotovorum Using N-Acyl-homoserine Lactone Degrading Bacteria Isolated from Potato Rhizosphere

Abstract

Several soil bacteria were found to degrade N-Acylhomoserine lactones (NAHLs), thereby interfering with the bacterial quorum sensing system. In this research, fifteen strains of NAHL degrading rhizobacteria were isolated from potato rhizosphere. Based on phenotypic characteristics and 16S rDNA sequence analyses, the strains were identified as members of genera Bacillus, Streptomyces, Arthrobacter, Pseudomonas and Mesorhizobium. All tested isolates were capable to degrade both synthetic and natural NAHL produced by Pectobacterium carotovorum subsp. carotovorum (Pcc) strain EMPCC. In quorum quenching experiments selected isolates, especially Mesorhizobium sp., were markedly reduced the pathogenicity of Pcc strain EMPCC in potato tubers and totally suppressed tissue maceration on potato tubers. These led to consider the latter as a useful biocontrol agent against Pectobacterium spp.Keywords: Mesorhizobium, NAHLs, Pectobacterium carotovorum, Quorum sensing Many bacterial species employ complex communication systems that link cell density and gene expression to regulate a broad range of biological functions (Fuqua et al., 2001;Miller and Bassler, 2001). Such cell-to-cell communication, termed quorum sensing (QS), depends on the production, diffusion, and recognition of small signal molecules. Bacteria recognize the changes in their population density by sensing the concentrations of signal molecules, which are accumulated as bacterial cells proliferate. NAcyl-homoserine lactones (NAHLs), also known as autoinducers, are widely conserved signal molecules that are present in the quorum-sensing systems of many gramnegative bacteria. Bacteria release, detect, and respond to accumulation of these signal molecules resulting in synchronizing expression of diverse biological functions including bioluminescence, antibiotic synthesis, biofilm formation, swarming, plasmid conjugation, siderophore production and production of virulence determinants (Whitehead et al., 2001). Since pathogenicity or pathogenicity-associated functions are controlled by QS in some major plant and animal pathogens, it has been proposed that the QS system could be an appropriate novel target for biological control agents or drugs in order to attenuate and limit virulence (Faure and Dessaux, 2007). Anti-QS mechanisms have been employed by inhibiting the synthesis or perception of the NAHL signal, as well as its enzymatic degradation by wild-type bacteria and eukaryotes, and genetically modified organisms (Molina et al., 2003;Rasmussen and Givskov, 2006).The NAHL-degrading enzymatic activities were initially discovered in a few bacterial species (Dong et al., 2000;Leadbetter and Greenberg, 2000). However, they have now been reported in Proteobacteria belonging to the Agrobacterium, Bosea, Commamonas, Delftia, Ochrobactrum, Pseudomonas, Ralstonia, Sphingopyxis and Variovorax genera (d'Angelo-Picard et al., 2005;Flagan et al., 2003;Huang et al., 2003;Jafra et al., 2006;Leadbetter and Greenberg, 2000;Lin et al., 2003;Park et al., 2003;Uroz et al., 2003). In...

Taxonomy, Physiology, and Natural Products of Actinobacteria

“…In addition to direct toxic effects on other microbes, nitrous oxide production by Streptomyces has been suggested to activate plant defenses, improving the plant's protection against pathogens (597). Recently, Mahmoudi et al (559) reported that streptomycetes can degrade the signaling compounds that coordinate the expression of genes required for pathogenicity in Pectobacterium carotovorum, suggesting a further mechanism for disease suppression. In addition, the production of chitinases or plant growth-promoting compounds has been reported to contribute to disease suppression by some Streptomyces isolates (598)(599)(600)(601).…”

“…The Actinobacteria are widely recognized for their potential in biocontrol (553-555) because they are important producers of bioactive compounds (556). Over the past 50 years, there have been many studies on the mechanisms by which Actinobacteria might inhibit pathogens in soil, including antibiosis, nutrient competition, production of degradative enzymes, nitrous oxide production, and quorum quenching (557)(558)(559). Their adaptability to different environments in the rhizosphere makes them a strong competitor.…”

Anti-quorum Sensing Effetcs of Ethanolic Crude Extract ofAnethum graveolensL.

“…carotovorum (1×10 6 CFU/ ml) and 15 μl plant extract (Dill extract) 15 . Agria) were washed with tap water, surface-sterilized with sodium hypochlorite (5 %) and were then rinsed using sterile water after air-drying under sterile conditions.…”

Potential of Bioremediation and PGP Traits in Streptomyces as Strategies for Bio-Reclamation of Salt-Affected Soils for Agriculture

“…However, the major traits of Actinobacteria are the production of a wide variety of bioactive compounds [108] and many well-known mechanisms by which they inhibit plant pathogens in the soil. Some of these mechanisms include antibiosis, nutrient competition, quorum quenching, and production of degradative enzymes and nitrous oxide [109,110].…”