Interactions and Insertion of Escherichia coli Hfq into Outer Membrane Vesicles as Revealed by Infrared and Orientated Circular Dichroism Spectroscopies.

The possible carrier role of Outer Membrane Vesicles (OMVs) for small regulatory noncoding RNAs (sRNAs) has recently been demonstrated. Nevertheless, to perform their function, these sRNAs usually need a protein cofactor called Hfq. In this work we show, by using a combination of infrared and circular dichroism spectroscopies, that Hfq, after interacting with the inner membrane, can be translocated into the periplasm, and then be exported in OMVs, with the possibility to be bound to sRNAs. Moreover, we provide evidence that Hfq interacts with and is inserted into OMV membranes, suggesting a role for this protein in the release of sRNA outside the vesicle. These findings provide clues to the mechanism of host-bacteria interactions which may not be defined solely by protein-protein and protein-outer membrane contacts, but also by the exchange of RNAs, and in particular sRNAs.

Bacterial diversity and community structure in the rhizosphere of the halophyte Halocnemum strobilaceum in an Algerian arid saline soil.

Hypersaline ecosystems host a particular microbiota, which can be specifically recruited by halophytes. In order to broaden our knowledge of hypersaline ecosystems, an in natura study was conducted on the microbiota associated with the halophyte Halocnemum strobilaceum from alkaline-saline arid soil in Algeria. We collected and identified a total of 414 strains isolated from root tissues (RT), root-adhering soil (RAS), non-adhering rhizospheric soil (NARS) and bulk soil (BS) using different NaCl concentrations. Our data showed that halophilic and halotolerant bacterial isolates in BS and the rhizosphere belonged to 32 genera distributed in Proteobacteria (49%), Firmicutes (36%), Actinobacteria (14%) and Bacteroidetes (1%). Bacterial population size and species diversity were greatly increased in the rhizosphere (factor 100). The reservoir of diversity in BS was dominated by the genera Bacillus and Halomonas. Bacillus/Halomonas ratio decreased with the proximity to the roots from 2.2 in BS to 0.3 at the root surface. Salt screening of the strains showed that species belonging to nine genera were able to grow up to 5.1 M NaCl. Thus, we found that H. strobilaceum exerted a strong effect on the diversity of the recruited microbiota with an affinity strongly attributed to the genus Halomonas.

Production and Characterization of a Novel Exopolysaccharide from Ramlibacter tataouinensis.

The current study examines the desiccation-resistant Ramlibacter tataouinensis TTB310T as a model organism for the production of novel exopolysaccharides and their structural features. This bacterium is able to produce dividing forms of cysts which synthesize cell-bound exopolysaccharide. Initial experiments were conducted on the enrichment of cyst biomass for exopolysaccharide production under batch-fed conditions in a pilot-scale bioreactor, with lactate as the source of carbon and energy. The optimized medium produced significant quantities of exopolysaccharide in a single growth phase, since the production of exopolysaccharide took place during the division of the cysts. The exopolysaccharide layer was extracted from the cysts using a modified trichloroacetic acid method. The biochemical characterization of purified exopolysaccharide was performed by gas chromatography, ultrahigh-resolution mass spectrometry, nuclear magnetic resonance, and Fourier-transform infrared spectrometry. The repeating unit of exopolysaccharide was a decasaccharide consisting of ribose, glucose, rhamnose, galactose, mannose, and glucuronic acid with the ratio 3:2:2:1:1:1, and additional substituents such as acetyl, succinyl, and methyl moieties were also observed as a part of the exopolysaccharide structure. This study contributes to a fundamental understanding of the novel structural features of exopolysaccharide from a dividing form of cysts, and, further, results can be used to study its rheological properties for various industrial applications.

Metataxonomics of Tunisian phosphogypsum based on five bioinformatics pipelines: Insights for bioremediation.

Phosphogypsum (PG) is an acidic by-product from the phosphate fertilizer industry and it is characterized by a low nutrient availability and the presence of radionuclides and heavy metals which pose a serious problem in its management. Here, we have applied Illumina MiSeq sequencing technology and five bioinformatics pipelines to explore the phylogenetic communities in Tunisian PG. Taking One Codex as a reference method, we present the results of 16S-rDNA-gene-based metataxonomics abundances with four other alternative bioinformatics pipelines (MetaGenome Rapid Annotation using Subsystem Technology (MG-RAST), mothur, MICrobial Community Analysis (MICCA) and Quantitative Insights into Microbial Ecology (QIIME)), when analyzing the Tunisian PG. Importantly, based on 16S rDNA datasets, the functional capabilities of microbial communities of PG were deciphered. They suggested the presence of PG autochthonous bacteria valorizable into (1) removal of radioactive elements and toxic heavy metals, (2) promotion of plant growth, (3) oxidation and (4) reduction of sulfate. These bacteria can be explored further for applications in the bioremediation of by-products, like PG, by different processes.

Use of native plants and their associated bacteria rhizobiomes to remediate-restore Draa Sfar and Kettara mining sites, Morocco.

Soil and mine tailings are unreceptive to plant growth representing an imminent threat to the environment and resource sustainability. Using indigenous plants and their associated rhizobacteria to restore mining sites would be an eco-friendly solution to mitigate soil-metal toxicity. Soil prospection from Draa Sfar and Kettara mining sites in Morocco was carried out during different seasons for native plant sampling and rhizobacteria screening. The sites have been colonized by fifteen tolerant plant species having different capacities to accumulate Cu, Zn, and P in their shoots/root systems. In Draa Sfar mine, Suaeda vera J.F. Gmel., Sarcocornia fruticosa (L.) A.J. Scott., and Frankenia corymbosa Desf. accumulated mainly Cu (more than 90 mg kg-1), Atriplex halimus L. accumulated Zn (mg kg-1), and Frankenia corymbosa Desf. accumulated Pb (14 mg kg-1). As for Kettara mine, Aizoon canariense L. mainly accumulated Zn (270 mg kg-1), whereas Forsskalea tenacissima L. was the best shoot Cu accumulator with up to 50 mg kg-1, whereas Cu accumulation in roots was 21 mg kg-1. The bacterial screening revealed the strains' abilities to tolerate heavy metals up to 50 mg kg-1 Cu, 250 mg kg-1 Pb, and 150 mg kg-1 Zn. Isolated strains belonged mainly to Bacillaceae (73.33%) and Pseudomonadaceae (10%) and expressed different plant growth-promoting traits, alongside their antifungal activity. Results from this study will provide an insight into the ability of native plants and their associated rhizobacteria to serve as a basis for remediation-restoration strategies.

P2CS: updates of the prokaryotic two-component systems database.

The P2CS database (http://www.p2cs.org/) is a comprehensive resource for the analysis of Prokaryotic Two-Component Systems (TCSs). TCSs are comprised of a receptor histidine kinase (HK) and a partner response regulator (RR) and control important prokaryotic behaviors. The latest incarnation of P2CS includes 164,651 TCS proteins, from 2758 sequenced prokaryotic genomes. Several important new features have been added to P2CS since it was last described. Users can search P2CS via BLAST, adding hits to their cart, and homologous proteins can be aligned using MUSCLE and viewed using Jalview within P2CS. P2CS also provides phylogenetic trees based on the conserved signaling domains of the RRs and HKs from entire genomes. HK and RR trees are annotated with gene organization and domain architecture, providing insights into the evolutionary origin of the contemporary gene set. The majority of TCSs are encoded by adjacent HK and RR genes, however, 'orphan' unpaired TCS genes are also abundant and identifying their partner proteins is challenging. P2CS now provides paired HK and RR trees with proteins from the same genetic locus indicated. This allows the appraisal of evolutionary relationships across entire TCSs and in some cases the identification of candidate partners for orphan TCS proteins.

Remote Biodegradation of Ge-Imogolite Nanotubes Controlled by the Iron Homeostasis of Pseudomonas brassicacearum.

The toxicity of high-aspect-ratio nanomaterials (HARNs) is often associated with oxidative stress. The essential nutrient Fe may also be responsible of oxidative stress through the production of reactive oxygen species. In the present study, it has been examined to what extent adding Fenton reaction promoting Fe impacted the toxicity of an alumino-germanate model HARN. Structural addition of only 0.95% wt Fe to Ge-imogolite not only alleviated the toxicity observed in the case of Fe-free nanotubes but also stimulated bacterial growth. This was attributed to the metabolization of siderophore-mobilized Fe from the nanotube structure. This was evidenced by the regulation of the homeostasis-monitoring intracellular Fe levels. This was accompanied by a biodegradation of the nanotubes approaching 40%, whereas the Fe-free nanomaterial remained nearly untouched.

Design Defines the Effects of Nanoceria at a Low Dose on Soil Microbiota and the Potentiation of Impacts by the Canola Plant.

Soils act as nanoceria sinks via agricultural spreading and surface waters. Canola plants were grown for one month in soil spiked with nanoceria (1 mg·kg(-1)). To define the role of nanomaterials design on environmental impacts, we studied nanoceria with different sizes (3.5 or 31 nm) and coating (citrate). We measured microbial activities involved in C, N, and P cycling in the rhizosphere and unplanted soil. Bacterial community structure was analyzed in unplanted soil, rhizosphere, and plant roots by 454-pyrosequencing of the 16S rRNA gene. This revealed an impact gradient dependent on nanomaterials design, ranging from decreased microbial enzymatic activities in planted soil to alterations in bacterial community structure in roots. Particle size/aggregation was a key parameter in modulating nanoceria effects on root communities. Citrate coating lowered the impact on microbial enzymatic activities but triggered variability in the bacterial community structure near the plant root. Some nanoceria favored taxa whose closest relatives are hydrocarbon-degrading bacteria and disadvantaged taxa frequently associated in consortia with disease-suppressive activity toward plant pathogens. This work provides a basis to determine outcomes of nanoceria in soil, at a dose close to predicted environmental concentrations, and to design them to minimize these impacts.

Pyoverdine and histicorrugatin-mediated iron acquisition in Pseudomonas thivervalensis.

The genome of Pseudomonas thivervalensis LMG 21626(T) has been sequenced and a genomic, genetic and structural analysis of the siderophore mediated iron acquisition was undertaken. Pseudomonas thivervalensis produces two structurally new siderophores, pyoverdine PYOthi which is typical for P. thivervalensis strains and a closely related strain, and the lipopeptidic siderophore histicorrugatin which is also detected in P. lini. Histicorrugatin consists out of an eight amino acid long peptide which is linked to octanoic acid. It is structurally related to the siderophores corrugatin and ornicorrugatin. Analysis of the proteome for TonB-dependent receptors identified 25 candidates. Comparison of the TonB-dependent receptors of P. thivervalensis with the 17 receptors of its phylogenetic neighbor, P. brassicacearum subsp. brassicacearum NFM 421, showed that NFM 421 shares the same set of receptors with LMG 21626(T), including the histicorrugatin receptor. An exception was found for their cognate pyoverdine receptor which can be explained by the observation that both strains produce structurally different pyoverdines. Mass analysis showed that NFM 421 did not produce histicorrugatin, but the analogue ornicorrugatin. Growth stimulation assays with a variety of structurally distinct pyoverdines produced by other Pseudomonas species demonstrated that LMG 21626(T) and NFM 421 are able to utilize almost the same set of pyoverdines. Strain NFM 421 is able utilize two additional pyoverdines, pyoverdine of P. fluorescens Pf0-1 and P. citronellolis LMG 18378(T), these pyoverdines are probably taken up by the FpvA receptor of NFM 421.

Small regulatory RNAs and the fine-tuning of plant­bacteria interactions.

Small regulatory RNAs (sRNAs) play a key role in many physiological and adaptive responses in bacteria. Faced with rapidly changing environments, it is more advantageous for bacteria to use sRNA-mediated responses than regulation by protein transcriptional factors, as sRNAs act at the post-transcriptional level and require less energy and time for their synthesis and turnover. The use of RNA deep sequencing has provided hundreds of sRNA candidates in different bacterial species that interact with plants. Here, we review the most recent results for the involvement of bacterial sRNAs in beneficial as well as deleterious plant­bacteria interactions. We describe the current view for the role of sRNAs, which are suggested to improve competition for both niches and resources in plant-interacting bacteria. These sRNAs also help plant-associated bacteria individually adapt to the rapidly changing conditions to which they are exposed, during different stages of this interaction.

Aged TiO2-based nanocomposite used in sunscreens produces singlet oxygen under long-wave UV and sensitizes Escherichia coli to cadmium.

TiO2-based nanocomposite (NC) are widely used as invisible UV protectant in cosmetics. These nanomaterials (NMs) end in the environment as altered materials. We have investigated the properties of T-Lite SF, a TiO2-NC used as sunscreen, after weathering in water and under light. We have examined the formation of ROS and their consequences on cell physiology of Escherichia coli. Our results show that aged-T-Lite SF produced singlet oxygen under low intensity long wave UV and formed hydroxyl radicals at high intensity. Despite the production of these ROS, T-Lite SF had neither effect on the viability of E. coli nor on mutant impaired in oxidative stress, did not induce mutagenesis and did not impair the integrity of membrane lipids, thus seemed safe to bacteria. However, when pre-exposed to T-Lite SF under low intensity UV, cells turned out to be more sensitive to cadmium, a priority pollutant widely disseminated in soil and surface waters. This effect was not a Trojan horse: sensitization of cells was dependent on the formation of singlet oxygen. These results provide a basis for caution, especially on NMs that have no straight environmental toxicity. It is crucial to anticipate indirect and combined effects of environmental pollutants and NMs.

Extraction and Purification of Outer Membrane Vesicles and Their Associated RNAs.

Outer membrane vesicles (OMVs), produced by Gram negative-bacteria and sRNAs, are key players in cell-to-cell communication and interactions of bacteria with the environment. OMVs act as information carriers and encapsulate various molecules such as proteins, lipids, metabolites, and RNAs. OMVs and sRNAs play a broad range of functions from pathogenesis to stress resistance, to biofilm formation and both mediate interkingdom signaling. Various studies indicate that there is a mechanism of intercellular communication mediated by OMV-derived bacterial RNAs that is conserved among certain bacterial species. Here we describe methods for the extraction and purification of vesicles produced by Gram-negative bacteria, such as Pseudomonas brassicacearum and Escherichia coli, and address methods for the extraction of OMVs-derived sRNA and techniques for the analysis of sRNAs.

Insights into Bacterial Extracellular Vesicle Biogenesis, Functions, and Implications in Plant-Microbe Interactions.

Plant-microbe interactions play a crucial role in shaping plant health and survival. In recent years, the role of extracellular vesicles (EVs) in mediating intercellular communication between plants and microbes has emerged as an intriguing area of research. EVs serve as important carriers of bioactive molecules and genetic information, facilitating communication between cells and even between different organisms. Pathogenic bacteria leverage extracellular vesicles (EVs) to amplify their virulence, exploiting their cargo rich in toxins and virulence factors. Conversely, beneficial microbes initiate EV secretion to stimulate plant immune responses and nurture symbiotic relationships. The transfer of EV-packed small RNAs (sRNAs) has been demonstrated to facilitate the modulation of immune responses. Furthermore, harnessing the potential of EVs holds promise for the development of innovative diagnostic tools and sustainable crop protection strategies. This review highlights the biogenesis and functions of EVs in bacteria and their importance in plant defense, and paves the way for future research in this exciting field.

Microcystin influence on soil-plant microbiota: Unraveling microbiota modulations and assembly processes in the rhizosphere of Vicia faba.

Microcystins (MCs) are frequently detected in cyanobacterial bloom-impacted waterbodies and introduced into agroecosystems via irrigation water. They are widely known as phytotoxic cyanotoxins, which impair the growth and physiological functions of crop plants. However, their impact on the plant-associated microbiota is scarcely tackled and poorly understood. Therefore, we aimed to investigate the effect of MCs on microbiota-inhabiting bulk soil (BS), root adhering soil (RAS), and root tissue (RT) of Vicia faba when exposed to 100 µg L-1 MCs in a greenhouse pot experiment. Under MC exposure, the structure, co-occurrence network, and assembly processes of the bacterial microbiota were modulated with the greatest impact on RT-inhabiting bacteria, followed by BS and, to a lesser extent, RAS. The analyses revealed a significant decrease in the abundances of several Actinobacteriota-related taxa within the RT microbiota, including the most abundant and known genus of Streptomyces. Furthermore, MCs significantly increased the abundance of methylotrophic bacteria (Methylobacillus, Methylotenera) and other Proteobacteria-affiliated genera (e.g., Paucibacter), which are supposed to degrade MCs. The co-occurrence network of the bacterial community in the presence of MCs was less complex than the control network. In MC-exposed RT, the turnover in community composition was more strongly driven by deterministic processes, as proven by the beta-nearest taxon index. Whereas in MC-treated BS and RAS, both deterministic and stochastic processes can influence community assembly to some extent, with a relative dominance of deterministic processes. Altogether, these results suggest that MCs may reshape the structure of the microbiota in the soil-plant system by reducing bacterial taxa with potential phytobeneficial traits and increasing other taxa with the potential capacity to degrade MCs.

Unraveling the interplay between root exudates, microbiota, and rhizosheath formation in pearl millet.

BACKGROUND: The rhizosheath, a cohesive soil layer firmly adhering to plant roots, plays a vital role in facilitating water and mineral uptake. In pearl millet, rhizosheath formation is genetically controlled and influenced by root exudates. Here, we investigated the impact of root exudates on the microbiota composition, interactions, and assembly processes, and rhizosheath structure in pearl millet using four distinct lines with contrasting soil aggregation abilities. RESULTS: Utilizing 16S rRNA gene and ITS metabarcoding for microbiota profiling, coupled with FTICR-MS metabonomic analysis of metabolite composition in distinct plant compartments and root exudates, we revealed substantial disparities in microbial diversity and interaction networks. The ß-NTI analysis highlighted bacterial rhizosphere turnover driven primarily by deterministic processes, showcasing prevalent homogeneous selection in root tissue (RT) and root-adhering soil (RAS). Conversely, fungal communities were more influenced by stochastic processes. In bulk soil assembly, a combination of deterministic and stochastic mechanisms shapes composition, with deterministic factors exerting a more pronounced role. Metabolic profiles across shoots, RT, and RAS in different pearl millet lines mirrored their soil aggregation levels, emphasizing the impact of inherent plant traits on microbiota composition and unique metabolic profiles in RT and exudates. Notably, exclusive presence of antimicrobial compounds, including DIMBOA and H-DIMBOA, emerged in root exudates and RT of low aggregation lines. CONCLUSIONS: This research underscores the pivotal influence of root exudates in shaping the root-associated microbiota composition across pearl millet lines, entwined with their soil aggregation capacities. These findings underscore the interconnectedness of root exudates and microbiota, which jointly shape rhizosheath structure, deepening insights into soil-plant-microbe interactions and ecological processes shaping rhizosphere microbial communities. Deciphering plant-microbe interactions and their contribution to soil aggregation and microbiota dynamics holds promise for the advancement of sustainable agricultural strategies. Video Abstract.

Culturing the desert microbiota.

Over the last 30 years, the description of microbial diversity has been mainly based on culture-independent approaches (metabarcoding and metagenomics) allowing an in-depth analysis of microbial diversity that no other approach allows. Bearing in mind that culture-dependent approaches cannot replace culture-independent approaches, we have improved an original method for isolating strains consisting of "culturing" grains of sand directly on Petri dishes (grain-by-grain method). This method allowed to cultivate up to 10% of the bacteria counted on the surface of grains of the three sites studied in the Great Western Erg in Algeria (Timoudi, Béni Abbès, and Taghit), knowing that on average about 10 bacterial cells colonize each grain. The diversity of culturable bacteria (collection of 290 strains) predicted by 16S rRNA gene sequencing revealed that Arthrobacter subterraneus, Arthrobacter tecti, Pseudarthrobacter phenanthrenivorans, Pseudarthrobacter psychrotolerans, and Massilia agri are the dominant species. The comparison of the culture-dependent and -independent (16S rRNA gene metabarcoding) approaches at the Timoudi site revealed 18 bacterial genera common to both approaches with a relative overestimation of the genera Arthrobacter/Pseudarthrobacter and Kocuria, and a relative underestimation of the genera Blastococcus and Domibacillus by the bacterial culturing approach. The bacterial isolates will allow further study on the mechanisms of tolerance to desiccation, especially in Pseudomonadota (Proteobacteria).

A novel binary pesticidal protein from Chryseobacterium arthrosphaerae controls western corn rootworm by a different mode of action to existing commercial pesticidal proteins.

The western corn rootworm (WCR) Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) remains one of the economically most important pests of maize (Zea mays) due to its adaptive capabilities to pest management options. This includes the ability to develop resistance to some of the commercial pesticidal proteins originating from different strains of Bacillus thuringiensis. Although urgently needed, the discovery of new, environmentally safe agents with new modes of action is a challenge. In this study we report the discovery of a new family of binary pesticidal proteins isolated from several Chryseobacterium species. These novel binary proteins, referred to as GDI0005A and GDI0006A, produced as recombinant proteins, prevent growth and increase mortality of WCR larvae, as does the bacteria. These effects were found both in susceptible and resistant WCR colonies to Cry3Bb1 and Cry34Ab1/Cry35Ab1 (reassigned Gpp34Ab1/Tpp35Ab1). This suggests GDI0005A and GDI0006A may not share the same binding sites as those commercially deployed proteins and thereby possess a new mode of action. This paves the way towards the development of novel biological or biotechnological management solutions urgently needed against rootworms.

Phenotypic switching in Pseudomonas brassicacearum involves GacS- and GacA-dependent Rsm small RNAs.

The plant-beneficial bacterium Pseudomonas brassicacearum forms phenotypic variants in vitro as well as in planta during root colonization under natural conditions. Transcriptome analysis of typical phenotypic variants using microarrays containing coding as well as noncoding DNA fragments showed differential expression of several genes relevant to secondary metabolism and of the small RNA (sRNA) genes rsmX, rsmY, and rsmZ. Naturally occurring mutations in the gacS-gacA system accounted for phenotypic switching, which was characterized by downregulation of antifungal secondary metabolites (2,4-diacetylphloroglucinol and cyanide), indoleacetate, exoenzymes (lipase and protease), and three different N-acyl-homoserine lactone molecules. Moreover, in addition to abrogating these biocontrol traits, gacS and gacA mutations resulted in reduced expression of the type VI secretion machinery, alginate biosynthesis, and biofilm formation. In a gacA mutant, the expression of rsmX was completely abolished, unlike that of rsmY and rsmZ. Overexpression of any of the three sRNAs in the gacA mutant overruled the pleiotropic changes and restored the wild-type phenotypes, suggesting functional redundancy of these sRNAs. In conclusion, our data show that phenotypic switching in P. brassicacearum results from mutations in the gacS-gacA system.

Alliance of proteomics and genomics to unravel the specificities of Sahara bacterium Deinococcus deserti.

To better understand adaptation to harsh conditions encountered in hot arid deserts, we report the first complete genome sequence and proteome analysis of a bacterium, Deinococcus deserti VCD115, isolated from Sahara surface sand. Its genome consists of a 2.8-Mb chromosome and three large plasmids of 324 kb, 314 kb, and 396 kb. Accurate primary genome annotation of its 3,455 genes was guided by extensive proteome shotgun analysis. From the large corpus of MS/MS spectra recorded, 1,348 proteins were uncovered and semiquantified by spectral counting. Among the highly detected proteins are several orphans and Deinococcus-specific proteins of unknown function. The alliance of proteomics and genomics high-throughput techniques allowed identification of 15 unpredicted genes and, surprisingly, reversal of incorrectly predicted orientation of 11 genes. Reversal of orientation of two Deinococcus-specific radiation-induced genes, ddrC and ddrH, and identification in D. deserti of supplementary genes involved in manganese import extend our knowledge of the radiotolerance toolbox of Deinococcaceae. Additional genes involved in nutrient import and in DNA repair (i.e., two extra recA, three translesion DNA polymerases, a photolyase) were also identified and found to be expressed under standard growth conditions, and, for these DNA repair genes, after exposure of the cells to UV. The supplementary nutrient import and DNA repair genes are likely important for survival and adaptation of D. deserti to its nutrient-poor, dry, and UV-exposed extreme environment.

Phytobeneficial traits of rhizobacteria under the control of multiple molecular dialogues.

Pseudomonads play crucial roles in plant growth promotion and control of plant diseases. However, under natural conditions, other microorganisms competing for the same nutrient resources in the rhizosphere may exert negative control over their phytobeneficial characteristics. We assessed the expression of phytobeneficial genes involved in biocontrol, biostimulation and iron regulation such as, phlD, hcnA, acdS, and iron-small regulatory RNAs prrF1 and prrF2 in Pseudomonas brassicacearum co-cultivated with three phytopathogenic fungi, and two rhizobacteria in the presence or absence of Brassica napus, and in relation to iron availability. We found that the antifungal activity of P. brassicacearum depends mostly on the production of DAPG and not on HCN whose production is suppressed by fungi. We have also shown that the two-competing bacterial strains modulate the plant growth promotion activity of P. brassicacearum by modifying the expression of phlD, hcnA and acdS according to iron availability. Overall, it allows us to better understand the complexity of the multiple molecular dialogues that take place underground between microorganisms and between plants and its rhizosphere microbiota and to show that synergy in favour of phytobeneficial gene expression may exist between different bacterial species.