Detection of quorum sensing signal molecules and identification of an autoinducer synthase gene among biofilm forming clinical isolates of Acinetobacter spp

Background

Quorum sensing is a term that describes an environmental sensing system that allows bacteria to monitor their own population density which contributes significantly to the size and development of the biofilm. Many gram negative bacteria use N-acyl-homoserine lactones as quorum sensing signal molecules. In this study, we sought to find out if the biofilm formation among clinical isolates of Acinetobacter spp. is under the control of autoinducing quorum sensing molecules.

Methodology/Principal Findings

Biofilm formation among clinical isolates of Acinetobacter spp. was assessed and the production of signal molecules were detected with Chromobacterium violaceum CV026 biosensor system. Characterisation of autoinducers was carried out by mass spectrometric analysis. We have also reported the identification of an autoinducer synthase gene, abaΙ among the isolates that produce quorum sensing signal molecules and have reported that the mutation in the abaI gene influences their biofilm forming capabilities. Using a microtitre-plate assay it was shown that 60% of the 50 Acinetobacter spp. isolates significantly formed biofilms. Further detection with the biosensor strain showed that some of these isolates produced long chain signal molecules. Mass spectrometric analysis revealed that five of these isolates produced N-decanoyl homoserine lactone and two isolates produced acyl-homoserine lactone with a chain length equal to C₁₂. The abaΙ gene was identified and a tetracycline mutant of the abaΙ gene was created and the inhibition in biofilm formation in the mutant was shown.

Conclusions/Significance

These data are of great significance as the signal molecules aid in biofilm formation which in turn confer various properties of pathogenicity to the clinical isolates including drug resistance. The use of quorum sensing signal blockers to attenuate bacterial pathogenicity is therefore highly attractive, particularly with respect to the emergence of multi antibiotic resistant bacteria.     

Concentrations of Indole-3-acetic Acid and Its Esters in Avena and Zea

An isotope-dilution method has been developed for the assay of free indole-3-acetic acid and ester indole-3-acetic acid as measured by indole-3-acetic acid liberated by mild alkaline hydrolysis. Application of this method to seedlings of Avena sativa and Zea mays indicates the upper limit of free indole-3-acetic acid in Avena to be about 16 μg per kg and in Zea, about 24 μg. The amount of 1 n alkali-labile indole-3-acetic acid in Zea is about 330 μg per kg and there is very little 1 n alkali-labile IAA in Avena. A chemical characterization of the indole-3-acetic acid of Avena and a confirmation of the chemical characterization of the indole-3-acetic acid of Zea is presented.     

Biosynthesis of Auxin by the Gram-Positive Phytopathogen Rhodococcus fascians Is Controlled by Compounds Specific to Infected Plant Tissues

The role and metabolism of indole-3-acetic acid in gram-negative bacteria is well documented, but little is known about indole-3-acetic acid biosynthesis and regulation in gram-positive bacteria. The phytopathogen Rhodococcus fascians, a gram-positive organism, incites diverse developmental alterations, such as leafy galls, on a wide range of plants. Phenotypic analysis of a leafy gall suggests that auxin may play an important role in the development of the symptoms. We show here for the first time that R. fascians produces and secretes the auxin indole-3-acetic acid. Interestingly, whereas noninfected-tobacco extracts have no effect, indole-3-acetic acid synthesis is highly induced in the presence of infected-tobacco extracts when tryptophan is not limiting. Indole-3-acetic acid production by a plasmid-free strain shows that the biosynthetic genes are located on the bacterial chromosome, although plasmid-encoded genes contribute to the kinetics and regulation of indole-3-acetic acid biosynthesis. The indole-3-acetic acid intermediates present in bacterial cells and secreted into the growth media show that the main biosynthetic route used by R. fascians is the indole-3-pyruvic acid pathway with a possible rate-limiting role for indole-3-ethanol. The relationship between indole-3-acetic acid production and the symptoms induced by R. fascians is discussed.     

Structure-activity relationship of cinnamaldehyde analogs as inhibitors of AI-2 based quorum sensing and their effect on virulence of Vibrio spp

Background

Many bacteria, including Vibrio spp., regulate virulence gene expression in a cell-density dependent way through a communication process termed quorum sensing (QS). Hence, interfering with QS could be a valuable novel antipathogenic strategy. Cinnamaldehyde has previously been shown to inhibit QS-regulated virulence by decreasing the DNA-binding ability of the QS response regulator LuxR. However, little is known about the structure-activity relationship of cinnamaldehyde analogs.

Methodology/Principal Findings

By evaluating the QS inhibitory activity of a series of cinnamaldehyde analogs, structural elements critical for autoinducer-2 QS inhibition were identified. These include an α,β unsaturated acyl group capable of reacting as Michael acceptor connected to a hydrophobic moiety and a partially negative charge. The most active cinnamaldehyde analogs were found to affect the starvation response, biofilm formation, pigment production and protease production in Vibrio spp in vitro, while exhibiting low cytotoxicity. In addition, these compounds significantly increased the survival of the nematode Caenorhabditis elegans infected with Vibrio anguillarum, Vibrio harveyi and Vibrio vulnificus.

Conclusions/Significance

Several new and more active cinnamaldehyde analogs were discovered and they were shown to affect Vibrio spp. virulence factor production in vitro and in vivo. Although ligands for LuxR have not been identified so far, the nature of different cinnamaldehyde analogs and their effect on the DNA binding ability of LuxR suggest that these compounds act as LuxR-ligands.     

Enzymatic Esterification of Indole-3-acetic Acid to myo-Inositol and Glucose

Incubation of mature sweet corn kernels of Zea mays in dilute solutions of ¹⁴C-labeled indole-3-acetic acid leads to the formation of ¹⁴C-labeled esters of myo-inositol, glucose, and glucans. Utilizing this knowledge it was found that an enzyme preparation from immature sweet corn kernels of Zea mays catalyzed the CoA- and ATP-dependent esterification of indole-3-acetic acid to myo-inositol and glucose. The esters formed were 2-O-(indole-3-acetyl)-myo-inositol, 1-dl-1-O-(indole-3-acetyl)-myo-inositol, di-O-(indole-3-acetyl)-myo-inositol, tri-O-(indole-3-acetyl)-myo-inositol, 2-O-(indole-3-acetyl)-d-glucopyranose, 4-O-(indole-3-acetyl)-d-glucopyranose and 6-O-(indole-3-acetyl)-d-glycopyranose. An assay system was developed for measuring esterification of ¹⁴C-labeled indole-3-acetic acid by ammonolysis of the esters followed by isolation and counting the radioactive indole-3-acetamide.     

Detection of quorum-sensing-related molecules in <Emphasis Type="Italic">Vibrio scophthalmi</Emphasis>

Background  

Cell-to-cell communication (also referred to as quorum sensing) based on N-acyl-homoserine lactones (AHLs) is a widespread response to environmental change in Gram-negative bacteria. AHLs seem to be highly variable, both in terms of the acyl chain length and in the chemical structure of the radicals. Another quorum sensing pathway, the autoinducer-2-based system, is present both in Gram-positive and Gram-negative bacteria. In this study the presence of signal molecules belonging to both quorum sensing signalling pathways was analysed in the marine symbiotic species Vibrio scophthalmi.     

Ectopic expression and functional characterization of type III polyketide synthase mutants from <Emphasis Type="Italic">Emblica officinalis</Emphasis> Gaertn

Key message

Functional characterization and ectopic expression studies of chalcone synthase mutants implicate the role of phenylalanine in tailoring the substrate specificity of type III polyketide synthase.

Abstract

Chalcone synthase (CHS) is a plant-specific type III polyketide synthase that catalyzes the synthesis of flavonoids. Native CHS enzyme does not possess any functional activity on N-methylanthraniloyl-CoA, which is the substrate for acridione/quinolone alkaloid biosynthesis. Here, we report the functional transformation of chalcone synthase protein from Emblica officinalis (EoCHS) to quinolone and acridone synthase (ACS) with single amino acid substitutions. A cDNA of 1173 bp encoding chalcone synthase was isolated from E. officinalis and mutants (F215S and F265V) were generated by site-directed mutagenesis. Molecular modeling studies of EoCHS did not show any active binding with N-methylanthraniloyl-CoA, but the mutants of EoCHS showed strong affinity to the same. As revealed by the modeling studies, functional analysis of CHS mutants showed that they could utilize p-coumaroyl-CoA as well as N-methylanthraniloyl-CoA as substrates and yield active products such as naringenin, 4-hydroxy 1-methyl 2(H) quinolone and 1,3-dihydroxy-n-methyl acridone. Exchange of a single amino acid in EoCHS (F215S and F265V) resulted in functionally active mutants that preferred N-methylanthraniloyl-CoA over p-coumaroyl-CoA. This can be attributed to the increase in the relative volume of active sites in mutants by mutation. Moreover, metabolomic and MS analyses of tobacco leaves transiently expressing mutant genes showed high levels of naringenin, acridones and quinolone derivatives compared to wild-type CHS. This is the first report demonstrating the functional activity of EoCHS mutants with N-methylanthraniloyl-CoA and these results indicate the role of phenylalanine in altering the substrate specificity and in the evolution of type III PKSs.

     

The complete genome sequence of Dickeya zeae EC1 reveals substantial divergence from other Dickeya strains and species

Background

Dickeya zeae is a bacterial species that infects monocotyledons and dicotyledons. Two antibiotic-like phytotoxins named zeamine and zeamine II were reported to play an important role in rice seed germination, and two genes associated with zeamines production, i.e., zmsA and zmsK, have been thoroughly characterized. However, other virulence factors and its molecular mechanisms of host specificity and pathogenesis are hardly known.

Results

The complete genome of D. zeae strain EC1 isolated from diseased rice plants was sequenced, annotated, and compared with the genomes of other Dickeya spp.. The pathogen contains a chromosome of 4,532,364 bp with 4,154 predicted protein-coding genes. Comparative genomics analysis indicates that D. zeae EC1 is most co-linear with D. chrysanthemi Ech1591, most conserved with D. zeae Ech586 and least similar to D. paradisiaca Ech703. Substantial genomic rearrangement was revealed by comparing EC1 with Ech586 and Ech703. Most virulence genes were well-conserved in Dickeya strains except Ech703. Significantly, the zms gene cluster involved in biosynthesis of zeamines, which were shown previously as key virulence determinants, is present in D. zeae strains isolated from rice, and some D. solani strains, but absent in other Dickeya species and the D. zeae strains isolated from other plants or sources. In addition, a DNA fragment containing 9 genes associated with fatty acid biosynthesis was found inserted in the fli gene cluster encoding flagellar biosynthesis of strain EC1 and other two rice isolates but not in other strains. This gene cluster shares a high protein similarity to the fatty acid genes from Pantoea ananatis.

Conlusion

Our findings delineate the genetic background of D. zeae EC1, which infects both dicotyledons and monocotyledons, and suggest that D. zeae strains isolated from rice could be grouped into a distinct pathovar, i.e., D. zeae subsp. oryzae. In addition, the results of this study also unveiled that the zms gene cluster presented in the genomes of D. zeae rice isolates and D. solani strains, and the fatty acid genes inserted in the fli gene cluster of strain EC1 were likely derived from horizontal gene transfer during later stage of bacterial evolution.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1545-x) contains supplementary material, which is available to authorized users.     

Sesquiterpene lactone stereochemistry influences herbivore resistance and plant fitness in the field

Background and Aims

Stereochemical variation is widely known to influence the bioactivity of compounds in the context of pharmacology and pesticide science, but our understanding of its importance in mediating plant–herbivore interactions is limited, particularly in field settings. Similarly, sesquiterpene lactones are a broadly distributed class of putative defensive compounds, but little is known about their activities in the field.

Methods

Natural variation in sesquiterpene lactones of the common cocklebur, Xanthium strumarium (Asteraceae), was used in conjunction with a series of common garden experiments to examine relationships between stereochemical variation, herbivore damage and plant fitness.

Key Results

The stereochemistry of sesquiterpene lactone ring junctions helped to explain variation in plant herbivore resistance. Plants producing cis-fused sesquiterpene lactones experienced significantly higher damage than plants producing trans-fused sesquiterpene lactones. Experiments manipulating herbivore damage above and below ambient levels found that herbivore damage was negatively correlated with plant fitness. This pattern translated into significant fitness differences between chemotypes under ambient levels of herbivore attack, but not when attack was experimentally reduced via pesticide.

Conclusions

To our knowledge, this work represents only the second study to examine sesquiterpene lactones as defensive compounds in the field, the first to document herbivore-mediated natural selection on sesquiterpene lactone variation and the first to investigate the ecological significance of the stereochemistry of the lactone ring junction. The results indicate that subtle differences in stereochemistry may be a major determinant of the protective role of secondary metabolites and thus of plant fitness. As stereochemical variation is widespread in many groups of secondary metabolites, these findings suggest the possibility of dynamic evolutionary histories within the Asteraceae and other plant families showing extensive stereochemical variation.     

Quinolone resistance in absence of selective pressure: the experience of a very remote community in the Amazon forest

Background

Quinolones are potent broad-spectrum bactericidal agents increasingly employed also in resource-limited countries. Resistance to quinolones is an increasing problem, known to be strongly associated with quinolone exposure. We report on the emergence of quinolone resistance in a very remote community in the Amazon forest, where quinolones have never been used and quinolone resistance was absent in 2002.

Methods

The community exhibited a considerable level of geographical isolation, limited contact with the exterior and minimal antibiotic use (not including quinolones). In December 2009, fecal carriage of antibiotic resistant Escherichia coli was investigated in 120 of the 140 inhabitants, and in 48 animals reared in the community. All fluoroquinolone-resistant isolates were genotyped and characterized for the mechanisms of plasmid- and chromosomal-mediated quinolone resistance.

Principal Findings

Despite the characteristics of the community remained substantially unchanged during the period 2002–2009, carriage of quinolone-resistant E. coli was found to be common in 2009 both in humans (45% nalidixic acid, 14% ciprofloxacin) and animals (54% nalidixic acid, 23% ciprofloxacin). Ciprofloxacin-resistant isolates of human and animal origin showed multidrug resistance phenotypes, a high level of genetic heterogeneity, and a combination of GyrA (Ser83Leu and Asp87Asn) and ParC (Ser80Ile) substitutions commonly observed in fluoroquinolone-resistant clinical isolates of E. coli.

Conclusions

Remoteness and absence of antibiotic selective pressure did not protect the community from the remarkable emergence of quinolone resistance in E. coli. Introduction of the resistant strains from antibiotic-exposed settings is the most likely source, while persistence and dissemination in the absence of quinolone exposure is likely mostly related with poor sanitation. Interventions aimed at reducing the spreading of resistant isolates (by improving sanitation and water/food safety) are urgently needed to preserve the efficacy of quinolones in resource-limited countries, as control strategies based only on antibiotic restriction policies are unlikely to succeed in those settings.     

Autoinducer-2 detection among commensal oral streptococci is dependent on pH and boric acid

Autoinducer-2, considered a universal signaling molecule, is produced by many species of bacteria; including oral strains. Structurally, autoinducer-2 can exist bound to boron (borated autoinducer-2). Functionally, autoinducer-2 has been linked to important bacterial processes such as virulence and biofilm formation. In order to test production of autoinducer-2 by a given bacterial strain, a bioassay using marine bioluminescent bacteria Vibrio harveyi as a reporter for autoinducer-2 has been designed. We hypothesize that pH adjustment and addition of boron are required for optimal bioluminescence and accurate autoinducer-2 detection. Using this reporter strain we tested autoinducer-2 activity from two oral commensal species, Streptococcus gordonii DL1 and Streptococcus oralis 34. Spent broth was collected and adjusted to pH 7.5 and supplemented with boric acid prior to measuring autoinducer- 2 activity. Results show that low pH inhibits bioluminescence of the reporter strain, but pH 7.5 allows for bioluminescence induction and proper readings of autoinducer-2 activity. Addition of boric acid also has a positive effect on bioluminescence allowing for a more sensitive detection of autoinducer-2 activity. Our data suggests that although autoinducer-2 is present in spent broth, low pH and/or low levels of boric acid become an obstacle for proper autoinducer-2 detection. For proper autoinducer-2 detection, we propose a protocol using this bioassay to include pH adjustment and boric acid addition to spent broth. Studies on autoinducer-2 activity in several bacteria species represent an important area of study as this universal signaling molecule is involved in critical bacterial phenotypes such as virulence and biofilm formation.     

Bacterial distribution in the rhizosphere of wild barley under contrasting microclimates

Background

All plants in nature harbor a diverse community of rhizosphere bacteria which can affect the plant growth. Our samples are isolated from the rhizosphere of wild barley Hordeum spontaneum at the Evolution Canyon (‘EC’), Israel. The bacteria which have been living in close relationship with the plant root under the stressful conditions over millennia are likely to have developed strategies to alleviate plant stress.

Methodology/Principal Findings

We studied distribution of culturable bacteria in the rhizosphere of H. spontaneum and characterized the bacterial 1-aminocyclopropane-1-carboxylate deaminase (ACCd) production, biofilm production, phosphorus solubilization and halophilic behavior. We have shown that the H. spontaneum rhizosphere at the stressful South Facing Slope (SFS) harbors significantly higher population of ACCd producing biofilm forming phosphorus solubilizing osmotic stress tolerant bacteria.

Conclusions/Significance

The long-lived natural laboratory ‘EC’ facilitates the generation of theoretical testable and predictable models of biodiversity and genome evolution on the area of plant microbe interactions. It is likely that the bacteria isolated at the stressful SFS offer new opportunities for the biotechnological applications in our agro-ecological systems.     

Effects of natural and chemically synthesized furanones on quorum sensing in <Emphasis Type="Italic">Chromobacterium violaceum</Emphasis>

Background  

Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions:     

Metabolism of Indole-3-Acetic Acid by Pericarp Discs from Immature and Mature Tomato (Lycopersicon esculentum Mill)

[1′-¹⁴C, ¹³C₆]Indole-3-acetic acid was infiltrated into immature pericarp discs from fruits of tomato (Lycopersicon esculentum Mill., cv Moneymaker). After a 24-h incubation period the discs were extracted with methanol and the partially purified extract was analyzed by reversed-phase high-performance liquid chromatography-radiocounting. Five metabolite peaks (1-5) were detected and subsequently analyzed by combined high-performance liquid chromatography-frit-fast atom bombardment-mass spectrometry. The metabolite 4 fraction was found to contain [¹³C₆]-indole-3-acetylaspartic acid, and analysis of metabolite 5 identified [¹³C₆]indole-3-acetyl-β-d-glucose. The other metabolites could not be identified, but alkaline hydrolysis studies and gel permeation chromatography indicated that metabolites 1 and 3 were both amide conjugates with a molecular weight of approximately 600. Studies with radiolabeled indole-3-acetic acid, indole-3-acetylaspartic acid, and indole-3-acetyl-β-d-glucose demonstrated that in immature pericarp indole-3-acetic acid is deactivated primarily via metabolism to indole-3-acetylaspartic acid, which is further converted to metabolites 1, 2, and 3. In mature, pink pericarp discs, indole-3-acetic acid is converted more extensively to its glucosyl conjugate. Conjugation of indole-3-acetic acid to indole-3-acetylaspartic acid appears to be dependent upon protein synthesis because it is inhibited by cycloheximide. In contrast, cycloheximide has little effect on the further conversion of indole-3-acetylaspartic acid to metabolites 1, 2, and 3.     

The Staphylococcus aureus Autoinducer-2 Synthase LuxS Is Regulated by Ser/Thr Phosphorylation

The Staphylococcus aureus autoinducer-2 (AI-2) producer protein LuxS is phosphorylated by the Ser/Thr kinase Stk1 at a unique position, Thr14. The enzymatic activity of the phosphorylated isoform of LuxS was abrogated compared to that of nonphosphorylated LuxS, thus providing the first evidence of an AI-2-producing enzyme regulated by phosphorylation and demonstrating that S. aureus possesses an original and specific system for controlling AI-2 synthesis.The latest discoveries in the field of microbiology have proven that bacteria communicate between each other. In fact, many bacteria secrete small, diffusible signaling molecules. It is generally assumed that these molecules are used for a process termed “quorum sensing,“ the phenomenon whereby the accumulation of specific, diffusible, low-molecular-weight signal molecules (or “autoinducers”) enables bacteria to sense when the minimal number, or “quorum,” of bacteria for a concerted response to be initiated has been achieved (22). Gram-positive and Gram-negative bacteria use quorum-sensing communication circuits to regulate a diverse array of physiological activities, like symbiosis, virulence, competence, conjugation, antibiotic production, motility, sporulation, and biofilm formation (22).The only presently known quorum-sensing mechanism that appears to be shared by both Gram-positive and Gram-negative bacteria is based on a group of interconvertible, diffusible molecules collectively referred to as autoinducer-2 (AI-2). The LuxS protein required for AI-2 production (19, 26) is a metal-containing enzyme (29) that cleaves S-ribosyl-l-homocysteine (SRH) to generate homocysteine and the AI-2 precursor, 4,5-dihydroxy-2,3-pentanedione (DPD). Outside the cell, unstable DPD undergoes chemical rearrangement that converts the molecule to AI-2, a small molecule able to penetrate membranes and to diffuse in the medium, allowing cross-species quorum sensing.The LuxS/AI-2 system in Staphylococcus aureus, a highly adaptable Gram-positive bacterium responsible for numerous clinical infections, has been analyzed in detail (13, 14, 28). Moreover, the emergence of antibiotic resistance has become a serious concern, especially due to methicillin-resistant S. aureus (MRSA) isolates that are resistant to all available penicillins and other β-lactam antimicrobial drugs (7). One appealing approach to this problem is to target bacterial systems associated with virulence mechanisms, particularly those based on signal transduction. Signal sensing leading to cellular responses must be tightly regulated to allow survival under variable conditions. The prevalent signaling mechanism in prokaryotes works through two-component systems. However, studies of the genomes of various pathogens have revealed a large family of eukaryotic-like Ser/Thr protein kinases (STPKs). It is becoming clear that signaling through Ser/Thr phosphorylation is a critical regulatory mechanism in pathogenic bacteria (16, 25). However, our understanding of S. aureus kinase biology has been seriously hampered by failure to identify relevant kinase substrates.While there is a significant body of published work defining the molecular mechanisms by which bacterial cells communicate, little is currently known about the regulation of the LuxS enzymes. The present study was undertaken to determine if the AI-2 producer protein LuxS might be regulated posttranslationally via STPK-dependent mechanisms.     

The hisC1 gene, encoding aromatic amino acid aminotransferase-1 in Azospirillum brasilense Sp7, expressed in wheat

Background and aims

Production of indole-3-acetic acid (IAA) by Azospirillum brasilense is one of the most important mechanisms underlying the beneficial effects observed in plants after inoculation with this bacterium. This study determined the contribution of the hisC1 gene, which encodes aromatic amino acid aminotransferase-1 (AAT1), to IAA production, and analyzed its expression in the free-living state and in association with the roots of wheat.

Methods

We determined production of IAA and AAT activity in the mutant hisC::gusA-sm ^R . To study the expression of hisC1, a chromosomal gene fusion was analyzed by following β-glucuronidase (GUS) activity in vitro, in the presence of root exudates, and in association with roots.

Results

IAA production in the hisC mutant was not reduced significantly compared to the activity of the wild-type strain. AAT1 activity was reduced by 50% when tyrosine was used as the amino acid donor, whereas there was a 30% reduction when tryptophan was used, compared to the activity of the wild-type strain. Expression of the fusion protein was up-regulated in both logarithmic and stationary phases by several compounds, including IAA, tryptophan, tyrosine, and phenyl acetic acid. We observed the expression of hisC1 in bacteria associated with wheat roots. Root exudates of wheat and maize were able to stimulate hisC1 expression.

Conclusions

The expression data indicate that hisC1 is under a positive feedback control in the presence of root exudates and on plants, suggesting that AAT1 activity plays a role in Azospirillum–plant interactions.     

Biological control of pathogen communication in the rhizosphere: A novel approach applied to potato soft rot due to Pectobacterium atrosepticum

Background and aims

Recent basic knowledge on the regulation of virulence in pectinolytic bacteria revealed pathogen communication via quorum sensing signals as a crucial event for the expression of virulence and the onset of disease symptoms. In this paper, we present and discuss advances in a new biocontrol approach based on the interference of microbial communication involved in the cellular density and microenvironment sensoring.

Methods

This emerging strategy consists in the characterization of the signaling molecules used by the target pathogen, then the use of harmless structural analogs to stimulate plant associated-microflora able to degrade both molecule families.

Results

The biocontrol method has been applied for the first time for the control of Pectobacterium atrosepticum. This psychrotrophic bacterium synthesizes N-acyl-homoserine lactones involved in cell-to-cell communication that triggers soft rot and blackleg of potato. The use of the gamma-caprolactone stimulant promotes the emergence and catabolic activity of Rhodococcus erythropolis antagonistic populations in the potato rhizosphere.

Conclusions

Rhodococcus bacteria have the ability to disrupt the quorum sensing-based communication of P. atrosepticum by degrading N-acyl-homoserine lactone signaling molecules and prevent disease.