The synergy of halotolerant PGPB and mauran mitigates salt stress in tomato (Solanum lycopersicum) via osmoprotectants accumulation.

Salinity stress is one of the major abiotic factors limiting sustainable agriculture. Halotolerant plant growth-promoting bacteria (PGPB) increased salt stress tolerance in plants, but the mechanisms underlying the tolerance are poorly understood. This study investigated the PGP activity of four halotolerant bacteria under salinity stress and the tomato salt-tolerance mechanisms induced by the synergy of these bacteria with the exopolysaccharide (EPS) mauran. All PGPB tested in this study were able to offer a significant improvement of tomato plant biomass under salinity stress; Peribacillus castrilensis N3 being the most efficient one. Tomato plants treated with N3 and the EPS mauran showed greater tolerance to NaCl than the treatment in the absence of EPS and PGPB. The synergy of N3 with mauran confers salt stress tolerance in tomato plants by increasing sodium transporter genes' expression and osmoprotectant content, including soluble sugars, polyols, proline, GABA, phenols and the polyamine putrescine. These osmolytes together with the induction of sodium transporter genes increase the osmotic adjustment capacity to resist water loss and maintain ionic homeostasis. These findings suggest that the synergy of the halotolerant bacterium N3 and the EPS mauran could enhance tomato plant growth by mitigating salt stress and could have great potential as an inductor of salinity tolerance in the agriculture sector.

Roseovarius bejariae sp. nov., a moderately halophilic bacterium isolated from a hypersaline steep-sided river bed.

An aerobic, Gram-stain-negative ovoid, designated as strain A21T, was isolated using the dilution-to-extinction method from a soil sample taken from Rambla Salada, an athalassohaline habitat located in Murcia (south-eastern Spain). Strain A21T is non-motile, has a respiratory metabolism and grows at NaCl concentrations within the range 0.5-15 % (w/v) [optimum, 5 % (w/v)], at 5-35 °C (optimum, 28 °C) and at pH 6-8 (optimum, pH 7.0). This strain is positive for catalase activity, oxidase activity and nitrate reduction. The 16S rRNA gene sequence indicates that it belongs to the genus Roseovarius in the class Alphaproteobacteria. The most closely related species are Roseovarius pacificus and Roseovarius halotolerans to which the strain A21T shows 16S rRNA gene sequence similarity values of 98.06 and 97.7 %, respectively. The average nucleotide identity in blast and digital DNA-DNA hybridization values between strain A21T and R. pacificus LMG 24575T are 76.8 and 21 %, respectively. The DNA G+C content based on the genome is 61.28 mol%. The major fatty acids (>5 % of the total fatty acids) of strain A21T are C18 : 1 ω7c/C18 : 1 ω6c and C16 : 0. The only detected isoprenoid quinone in strain A21T is ubiquinone 10 (Q-10). The polar lipid profile contains phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and three unidentified polar lipids. Based on the phylogenetic, genotypic, phenotypic and chemotaxonomic data, the strain represents a novel species of the genus Roseovarius, for which the name Roseovarius bejariae sp. nov. is proposed. Strain A21T (=CECT 9817T=LMG 31311T) is the type strain.

Roseovarius ramblicola sp. nov., a moderately halophilic bacterium isolated from saline soil in Spain.

Strain D15T was isolated from a soil sample taken from Rambla Salada (Murcia), south-eastern Spain, by using the dilution-to-extinction method. The strain, a Gram-stain-negative aerobic bacteria, is non-motile, ovoid- or rod-shaped, catalase- and oxidase-positive, and grows at NaCl concentrations within the range 0.5-10 % (w/v) [optimum 3 % (w/v)], at 5-30 °C (optimum 28 °C) and at pH 6-9 (optimum pH 7.0). The 16S rRNA gene sequence indicates that it belongs to the genus Roseovarius in the class Alphaproteobacteria. Its closest relatives are Roseovarius tolerans EL-172T and Roseovarius azorensis SSW084T, to which the strain shows 16S rRNA gene-sequence similarity values of 96.1 and 95.3 %, respectively. The DNA G+C content is 63 mol%. The major fatty acids (>5 % of the total fatty acids) of strain D15T are C18 : 1ω7c, C16 : 0 and C12 : 0. The only detected isoprenoid quinone of strain D15T is ubiquinone 10 (Q-10). The polar lipid profile contains phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, aminolipid and three polar lipids. Based on the phylogenetic, genotypic, phenotypic and chemotaxonomic data, the strain represents a novel species of the genus Roseovarius, for which the name Roseovarius ramblicola sp. nov. is proposed. Strain D15T (=CECT 9424=LMG 30322) is the type strain.

Elastin degradation product isodesmosine is a chemoattractant for Pseudomonas aeruginosa.

Previous studies have demonstrated that Pseudomonas aeruginosa PAO1 is chemotactic towards proteinogenic amino acids, however, the chemotaxis response of this strain towards non-proteinogenic amino acids and the specific chemoreceptors involved in this response are essentially unknown. In this study, we analysed the chemotactic response of PAO1 towards two degradation products of elastin, the lysine-rich, non-proteinogenic amino acids, desmosine and isodesmosine. We observed that isodesmosine, a potential biomarker for different diseases, served as a chemoattractant for PAO1. A screen of 251methyl-accepting chemotaxis proteins mutants of PAO1 identified PctA as the chemoreceptor for isodesmosine. We also showed that the positive chemotactic response to isodesmosine is potentially common by demonstrating chemoattraction in 12 of 15 diverse (in terms of source of isolation) clinical isolates, suggesting that the chemotactic response to this non-proteinogenic amino acid might be a conserved feature of acute infection isolates and thus could influence the colonization of potential infection sites.

Shifts in soil chemical properties and bacterial communities responding to biotransformed dry olive residue used as organic amendment.

Dry olive residue (DOR) is a waste product derived from olive oil extraction and has been proposed as an organic amendment. However, it has been demonstrated that a pre-treatment, such as its transformation by saprophytic fungi, is required before DOR soil application. A greenhouse experiment was designed where 0 and 50 g kg(-1) of raw DOR (DOR), Coriolopsis floccosa-transformed DOR (CORDOR) and Fusarium oxysporum-transformed DOR (FUSDOR) were added to soil. Analyses of the soil chemical properties as well as the structure and relative abundance of bacterial and actinobacterial communities were conducted after 0, 30 and 60 days following amendment. The different amendments produced a slight decrease in soil pH and significant increases in carbon fractions, C/N ratios, phenols and K, with these increases being more significant after DOR application. Quantitative PCR assays of the 16S rRNA gene and PLFA analyses showed that all amendments favoured bacterial growth at 30 and 60 days, although actinobacterial proliferation was more evident after CORDOR and FUSDOR application at 60 days. Bacterial and actinobacterial DGGE multivariate analyses showed that the amendments produced structural changes in both communities, especially after 60 days of amendment. PLFA data analysis identified changes in soil microbial communities according to the amendment considered, with FUSDOR and CORDOR being less disruptive than DOR. Finally, integrated analysis of all data monitored in the present study enabled us to conclude that the greatest impact on soil properties was caused by DOR at 30 days and that soil showed some degree of resilience after this time.

Effects of dry olive residue transformed by Coriolopsis floccosa (Polyporaceae) on the distribution and dynamic of a culturable fungal soil community.

Dry olive residue (DOR) is an abundant waste product resulting from a two-phase olive oil extraction system. Due to its high organic and mineral content, this material has been proposed as an organic soil amendment; however, it presents phytotoxic and microtoxic properties. Thus, a pretreatment is necessary before its application to soil. Among the strategies for the bioremediation of DOR is treatment with ligninolytic fungi, e.g. Coriolopsis floccosa. This work aimed to assess the diversity of culturable fungi in a soil of the southeast Iberian Peninsula and to evaluate the short-term impact of untransformed and C. floccosa-transformed DOR on soil mycobiota. A total of 1,733 strains were isolated by the particle filtration method and were grouped among 109 different species using morphological and molecular methods. The majority of isolates were ascomycetes and were concentrated among three orders: Hypocreales, Eurotiales and Capnodiales. The soil amendment with untransformed DOR was associated with a depression in fungal diversity at 30 days and changes in the proportions of the major species. However, when C. floccosa-transformed DOR was applied to the soil, changes in fungal diversity were less evident, and species composition was similar to unamended soil.

Interference of AHL signal production in the phytophatogen Pantoea agglomerans as a sustainable biological strategy to reduce its virulence.

Pantoea agglomerans is considered one of the most ubiquitous and versatile organisms that include strains that induce diseases in various crops and occasionally cause opportunistic infections in humans. To develop effective strategies to mitigate its impact on plant health and agricultural productivity, a comprehensive investigation is crucial for better understanding its pathogenicity. One proposed eco-friendly approach involves the enzymatic degradation of quorum sensing (QS) signal molecules like N-acylhomoserine lactones (AHLs), known as quorum quenching (QQ), offering potential treatment for such bacterial diseases. In this study the production of C4 and 3-oxo-C6HSL was identified in the plant pathogenic P. agglomerans CFBP 11141 and correlated to enzymatic activities such as amylase and acid phosphatase. Moreover, the heterologous expression of a QQ enzyme in the pathogen resulted in lack of AHLs production and the attenuation of the virulence by mean of drastically reduction of soft rot disease in carrots and cherry tomatoes. Additionally, the interference with the QS systems of P. agglomerans CFBP 11141 by two the plant growth-promoting and AHL-degrading bacteria (PGP-QQ) Pseudomonas segetis P6 and Bacillus toyonensis AA1EC1 was evaluated as a potential biocontrol approach for the first time. P. segetis P6 and B. toyonensis AA1EC1 demonstrated effectiveness in diminishing soft rot symptoms induced by P. agglomerans CFBP 11141 in both carrots and cherry tomatoes. Furthermore, the virulence of pathogen notably decreased when co-cultured with strain AA1EC1 on tomato plants.

Potential of the quorum-quenching and plant-growth promoting halotolerant Bacillus toyonensis AA1EC1 as biocontrol agent.

The use of fertilizers and pesticides to control plant diseases is widespread in intensive farming causing adverse effects together with the development of antimicrobial resistance pathogens. As the virulence of many Gram-negative phytopathogens is controlled by N-acyl-homoserine lactones (AHLs), the enzymatic disruption of this type of quorum-sensing (QS) signal molecules, mechanism known as quorum quenching (QQ), has been proposed as a promising alternative antivirulence therapy. In this study, a novel strain of Bacillus toyonensis isolated from the halophyte plant Arthrocaulon sp. exhibited numerous traits associated with plant growth promotion (PGP) and degraded a broad range of AHLs. Three lactonases and an acylase enzymes were identified in the bacterial genome and verified in vitro. The AHL-degrading activity of strain AA1EC1 significantly attenuated the virulence of relevant phytopathogens causing reduction of soft rot symptoms on potato and carrots. In vivo assays showed that strain AA1EC1 significantly increased plant length, stem width, root and aerial dry weights and total weight of tomato and protected plants against Pseudomonas syringae pv. tomato. To our knowledge, this is the first report to demonstrate PGP and QQ activities in the species B. toyonensis that make this strain as a promising phytostimulant and biocontrol agent.

Corrigendum: Identification of volatile organic compounds in extremophilic bacteria and their effective use in biocontrol of postharvest fungal phytopathogens.

[This corrects the article DOI: 10.3389/fmicb.2021.773092.].

Evolution of Antibiotic Resistance in Escherichia coli and Klebsiella pneumoniae from Urine Cultures.

OBJECTIVE: Determine the evolution of antibiotic resistance of symptomatic bacteriuria caused by Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) in Granada. MATERIAL AND METHOD: A descriptive retrospective study was carried out, including antibiograms of urine cultures in which microorganisms identified as E. coli and K. pneumoniae, were isolated in the Microbiology laboratory of the Hospital Universitario Virgen de las Nieves (Granada, Spain) between January 2016 and June 2021. RESULTS: E. coli was the most frequent isolate (10,048) and its resistance to ampicillin (59.45%) and ticarcillin (59.59%), and the increase to cefepime (15.07%) and amoxicillin-clavulanic acid (17.67%) is noteworthy. K. pneumoniae (2222) is notable for resistance to Fosfomycin (27.91%) and an increase to ciprofloxacin (37.79%) and amoxicillin-clavulanic acid (36.63%). Resistance is generally higher in hospitalized patients, males, and adults. CONCLUSIONS: Antibiotic resistance to the studied Enterobacteriaceae is on the rise, requiring empirical treatment targeted to the population area.

Pseudomonas aeruginosa PAO1 Is Attracted to Bovine Bile in a Novel, Cystic Fibrosis-Derived Bronchial Epithelial Cell Model.

Cystic fibrosis (CF) is a life-threatening, inherited, multi-organ disease that renders patients susceptible throughout their lives to chronic and ultimately deteriorating protracted pulmonary infections. Those infections are dominated in adulthood by the opportunistic pathogen, Pseudomonas aeruginosa (Pa). As with other advancing respiratory illnesses, people with CF (pwCF) also frequently suffer from gastroesophageal reflux disease (GERD), including bile aspiration into the lung. GERD is a major co-morbidity factor in pwCF, with a reported prevalence of 35-81% in affected individuals. Bile is associated with the early acquisition of Pa in CF patients and in vitro studies show that it causes Pa to adopt a chronic lifestyle. We hypothesized that Pa is chemoattracted to bile in the lung environment. To evaluate, we developed a novel chemotaxis experimental system mimicking the lung environment using CF-derived bronchial epithelial (CFBE) cells which allowed for the evaluation of Pa (strain PAO1) chemotaxis in a physiological scenario superior to the standard in vitro systems. We performed qualitative and quantitative chemotaxis tests using this new experimental system, and microcapillary assays to demonstrate that bovine bile is a chemoattractant for Pa and is positively correlated with bile concentration. These results further buttress the hypothesis that bile likely contributes to the colonization and pathogenesis of Pa in the lung, particularly in pwCF.

Peribacillus castrilensis sp. nov.: A Plant-Growth-Promoting and Biocontrol Species Isolated From a River Otter in Castril, Granada, Southern Spain.

A strictly aerobic, chemoheterotrophic, endospore-forming, Gram-positive, rod-shaped bacterial strain N3T was isolated from the feces of a river otter in Castril (Granada, southern Spain). It is halotolerant, motile, and catalase-, oxidase-, ACC deaminase-, and C4- and C8-lipase-positive. It promotes tomato plant growth and can reduce virulence in Erwinia amylovora CECT 222T and Dickeya solani LMG 25993T through interference in their quorum-sensing systems, although other antagonistic mechanisms could also occur. A phylogenetic analysis of the 16S rRNA gene sequence as well as the phenotypic and phylogenomic analyses indicated that the strain N3T is a novel species of the genus Peribacillus, with the highest 16S rRNA sequence similar to that of Bacillus frigoritolerans DSM 8801T (99.93%) and Peribacillus simplex DSM 1321T (99.80%). Genomic digital DNA-DNA hybridization (dDDH) between the strain N3T and Bacillus frigoritolerans DSM 8801T and Peribacillus simplex was 12.8 and 69.1%, respectively, and the average nucleotide identity (ANIb) of strain N3T and Bacillus frigoritolerans DSM 8801T and Peribacillus simplex was 67.84 and 93.21%, respectively. The genomic G + C content was 40.3 mol%. Its main cellular fatty acids were anteiso-C15:0 and iso-C15:0. Using 16S rRNA phylogenetic and in silico phylogenomic analyses, together with the chemotaxonomic and phenotypic data, we demonstrated that the type strain N3T (=CECT 30509T = LMG 32505T) is a novel species of the genus Peribacillus and the name Peribacillus castrilensis sp. nov. is proposed.

The Arginine Catabolism-Derived Amino Acid l-ornithine Is a Chemoattractant for Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a common, opportunistic bacterial pathogen among patients with cystic fibrosis, asthma, and chronic obstructive pulmonary disease. During the course of these diseases, l-ornithine, a non-proteinogenic amino acid, becomes more abundant. P. aeruginosa is chemotactic towards other proteinogenic amino acids. Here, we evaluated the chemotaxis response of P. aeruginosa towards l-ornithine. Our results show that l-ornithine serves as a chemoattractant for several strains of P. aeruginosa, including clinical isolates, and that the chemoreceptors involved in P. aeruginosa PAO1 are PctA and PctB. It seems likely that P. aeruginosa's chemotactic response to l-ornithine might be a common feature and thus could potentially contribute to pathogenesis processes during colonization and infection scenarios.

Identification of Volatile Organic Compounds in Extremophilic Bacteria and Their Effective Use in Biocontrol of Postharvest Fungal Phytopathogens.

Phytopathogenic fungal growth in postharvest fruits and vegetables is responsible for 20-25% of production losses. Volatile organic compounds (VOCs) have been gaining importance in the food industry as a safe and ecofriendly alternative to pesticides for combating these phytopathogenic fungi. In this study, we analysed the ability of some VOCs produced by strains of the genera Bacillus, Peribacillus, Pseudomonas, Psychrobacillus and Staphylococcus to inhibit the growth of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Fusarium solani, Monilinia fructicola, Monilinia laxa and Sclerotinia sclerotiorum, in vitro and in vivo. We analysed bacterial VOCs by using GC/MS and 87 volatile compounds were identified, in particular acetoin, acetic acid, 2,3-butanediol, isopentanol, dimethyl disulphide and isopentyl isobutanoate. In vitro growth inhibition assays and in vivo experiments using cherry fruits showed that the best producers of VOCs, Bacillus atrophaeus L193, Bacillus velezensis XT1 and Psychrobacillus vulpis Z8, exhibited the highest antifungal activity against B. cinerea, M. fructicola and M. laxa, which highlights the potential of these strains to control postharvest diseases. Transmission electron microscopy micrographs of bacterial VOC-treated fungi clearly showed antifungal activity which led to an intense degeneration of cellular components of mycelium and cell death.

Crop Protection against Botrytis cinerea by Rhizhosphere Biological Control Agent Bacillus velezensis XT1.

This study aims to evaluate the use of Bacillus velezensis strain XT1 as a plant growth-promoting rhizobacterium (PGPR) and biocontrol agent against B. cinerea in tomato and strawberry plants. Foliar and radicular applications of strain XT1 increased plant total biomass as compared to the control and B. cinerea-infected plants, with root applications being, on the whole, the most effective mode of treatment. Applications of the bacterium were found to reduce infection parameters such as disease incidence and severity by 50% and 60%, respectively. We analyzed stress parameters and phytohormone content in order to evaluate the capacity of XT1 to activate the defense system through phytohormonal regulation. Overall, the application of XT1 reduced oxidative damage, while the H2O2 and malondialdehyde (MDA) content was lower in XT1-treated and B. cinerea-infected plants as compared to non-XT1-treated plants. Moreover, treatment with XT1 induced callose deposition, thus boosting the response to pathogenic infection. The results of this study suggest that the signaling and activation pathways involved in defense mechanisms are mediated by jasmonic acid (JA) and ethylene hormones, which are induced by preventive treatment with XT1. The study also highlights the potential of preventive applications of strain XT1 to activate defense mechanisms in strawberry and tomato plants through hormone regulation.

Biological Control of Verticillium Wilt on Olive Trees by the Salt-Tolerant Strain Bacillus velezensis XT1.

Verticillium wilt, caused by the pathogen Verticillium dahliae, is extremely devastating to olive trees (Olea europea). Currently, no successful control measure is available against it. The objective of this work was to evaluate the antifungal activity of Bacillus velezensis XT1, a well-characterized salt-tolerant biocontrol strain, against the highly virulent defoliating V. dahliae V024. In vitro, strain XT1 showed to reduce fungal mycelium from 34 to 100%, depending on if the assay was conducted with the supernatant, volatile compounds, lipopeptides or whole bacterial culture. In preventive treatments, when applied directly on young olive trees, it reduced Verticillium incidence rate and percentage of severity by 54 and ~80%, respectively. It increased polyphenol oxidase (PPO) activity by 395%, indicating an enhancement of disease resistance in plant tissues, and it decreased by 20.2% the number of fungal microsclerotia in soil. In adult infected trees, palliative inoculation of strain XT1 in the soil resulted in a reduction in Verticillium symptom severity by ~63%. Strain XT1 is biosafe, stable in soil and able to colonize olive roots endophytically. All the traits described above make B. velezensis XT1 a promising alternative to be used in agriculture for the management of Verticillium wilt.

Effects of Halophyte Root Exudates and Their Components on Chemotaxis, Biofilm Formation and Colonization of the Halophilic Bacterium Halomonas Anticariensis FP35T.

Increase in soil salinity poses an enormous problem for agriculture and highlights the need for sustainable crop production solutions. Plant growth-promoting bacteria can be used to boost the growth of halophytes in saline soils. Salicornia is considered to be a promising salt-accumulating halophyte for capturing large amounts of carbon from the atmosphere. In addition, colonization and chemotaxis could play an important role in Salicornia-microbe interactions. In this study, the role of chemotaxis in the colonization of the halophilic siredophore-producing bacteria, Halomonas anticariensis FP35T, on Salicornia hispanica plants was investigated. The chemotactic response of FP35T to Salicornia root exudates showed optimum dependence at a salt concentration of 5 % NaCl (w/v). Oleanolic acid, the predominant compound in the exudates detected by HPLC and identified by UPLC-HRMS Q-TOF, acts as a chemoattractant. In vitro experiments demonstrated the enhanced positive effects of wild-type H. anticariensis strain FP35T on root length, shoot length, germination and the vigour index of S. hispanica. Furthermore, these positive effects partially depend on an active chemotaxis system, as the chemotaxis mutant H. anticariensis FP35 ΔcheA showed reduced plant growth promotion for all the parameters tested. Overall, our results suggest that chemotaxis responses to root exudates play an important role in interactions between Salicornia and halophilic bacteria, enhance their colonization and boost plant growth promotion. Preliminary results also indicate that root exudates have a positive impact on H. anticariensis FP35T biofilm formation under saline conditions, an effect which totally depends on the presence of the cheA gene.

Plant growth-promoting activity and quorum quenching-mediated biocontrol of bacterial phytopathogens by Pseudomonas segetis strain P6.

Given the major threat of phytopathogenic bacteria to food production and ecosystem stability worldwide, novel alternatives to conventional chemicals-based agricultural practices are needed to combat these bacteria. The objective of this study is to evaluate the ability of Pseudomonas segetis strain P6, which was isolated from the Salicornia europaea rhizosphere, to act as a potential biocontrol agent given its plant growth-promoting (PGP) and quorum quenching (QQ) activities. Seed biopriming and in vivo assays of tomato plants inoculated with strain P6 resulted in an increase in seedling height and weight. We detected QQ activity, involving enzymatic degradation of signal molecules in quorum sensing communication systems, against a broad range of N-acylhomoserine lactones (AHLs). HPLC-MRM data and phylogenetic analysis indicated that the QQ enzyme was an acylase. The QQ activity of strain P6 reduced soft rot symptoms caused by Dickeya solani, Pectobacterium atrosepticum and P. carotovorum on potato and carrot. In vivo assays showed that the PGP and QQ activities of strain P6 protect tomato plants against Pseudomonas syringae pv. tomato, indicating that strain P6 could have biotechnological applications. To our knowledge, this is the first report to show PGP and QQ activities in an indigenous Pseudomonas strain from Salicornia plants.

Foliar mycoendophytome of an endemic plant of the Mediterranean biome (Myrtus communis) reveals the dominance of basidiomycete woody saprotrophs.

The true myrtle, Myrtus communis, is a small perennial evergreen tree that occurs in Europe, Africa, and Asia with a circum-Mediterranean geographic distribution. Unfortunately, the Mediterranean Forests, where M. communis occurs, are critically endangered and are currently restricted to small fragmented areas in protected conservation units. In the present work, we performed, for the first time, a metabarcoding study on the spatial variation of fungal community structure in the foliar endophytome of this endemic plant of the Mediterranean biome, using bipartite network analysis as a model. The local bipartite network of Myrtus communis individuals and their foliar endophytic fungi is very low connected, with low nestedness, and moderately high specialization and modularity. Similar network patterns were also retrieved in both culture-dependent and amplicon metagenomics of foliar endophytes in distinct arboreal hosts in varied biomes. Furthermore, the majority of putative fungal endophytes species were basidiomycete woody saprotrophs of the orders Polyporales, Agaricales, and Hymenochaetales. Altogether, these findings suggest a possible adaptation of these wood-decaying fungi to cope with moisture limitation and spatial scarcity of their primary substrate (dead wood), which are totally consistent with the predictions of the viaphytism hypothesis that wood-decomposing fungi inhabit the internal leaf tissue of forest trees in order to enhance dispersal to substrates on the forest floor, by using leaves as vectors and as refugia, during periods of environmental stress.

Silencing of Phytopathogen Communication by the Halotolerant PGPR Staphylococcus equorum Strain EN21.

Increasing world food demand together with soil erosion and indiscriminate use of chemical fertilization highlight the need to adopt sustainable crop production strategies. In this context, a combination of plant growth-promoting rhizobacteria (PGPR) and pathogen management represents a sustainable and efficient alternative. Though little studied, halophilic and halotolerant PGPR could be a beneficial plant growth promotion strategy for saline and non-saline soils. The virulence of many bacterial phytopathogens is regulated by quorum sensing (QS) systems. Quorum quenching (QQ) involves the enzymatic degradation of phytopathogen-generated signal molecules, mainly N-acyl homoserine lactones (AHLs). In this study, we investigate plant growth-promoting (PGP) activity and the capacity of the halotolerant bacterium Staphylococcus equorum strain EN21 to attenuate phytopathogens virulence through QQ. We used biopriming and in vivo tomato plant experiments to analyse the PGP activity of strain EN21. AHL inactivation was observed to reduce Pseudomonas syringae pv. tomato infections in tomato and Arabidopsis plants. Our study of Dickeya solani, Pectobacterium carotovorum subsp. carotovorum and Erwinia amylovora bacteria in potato tubers, carrots and pears, respectively, also demonstrated the effectiveness of QS interruption by EN21. Overall, this study highlights the potential of strain S. equorum EN21 in plant growth promotion and QQ-driven bacterial phytopathogen biocontrol.