Pseudomonas Isolates Research Articles

Comparative Multi-Omics Survey Reveals Novel Specialized Metabolites and Biosynthetic Gene Clusters Under GacS Control in Pseudomonas donghuensis Strain SVBP6.

In Pseudomonas donghuensis SVBP6, isolated from an agricultural field, the well-conserved Gac-Rsm pathway upregulates biosynthesis of the antifungal compound 7-hydroxytropolone (7-HT). However, 7-HT does not fully explain the strain's Gac-Rsm-dependent antimicrobial activity. Here, we combined comparative transcriptomic, proteomic, and metabolomic approaches to identify novel GacS-dependent biosynthetic gene clusters (BGC) and/or extracellular specialized metabolites. Our data revealed a broad impact of GacS on gene expression and extracellular metabolite profile of SVBP6. At both the mRNA and polypeptide levels, specialized metabolism was the main affected functional category in the gacS mutant. The major extracellular MS/MS spectral families promoted by GacS were fatty acid amides, fatty acids, and alkaloids. GacS was required for the production of the antimicrobial compound pseudoiodinine and to activate expression of the corresponding BGC. We also detected GacS-dependent production of 2,3,4-trihydro-β-carboline-1-one, which may add to the antimicrobial arsenal of SVBP6. Furthermore, transcriptomics and proteomics pinpointed several GacS-activated BGCs that had escaped in silico genome mining tools. Altogether, comparative multi-omics analyses of gacS loss-of-function mutants in Pseudomonas isolates are a promising strategy to uncover bioactive metabolites and/or their BGCs. Discovery of novel natural products is important for harnessing the potential of microbiota to improve crop plant growth and health.

Impact of bioinoculants on growth enhancement, physicochemical characteristics, biochemical profiles, and enzymatic defense mechanisms in tomato (Lycopersicum esculentum)

The excessive use of fungicides in agriculture causes challenges like pathogen resistance, soil and water contamination, and potential health risks. Sustainable options like Pseudomonas spp. and yeast are being explored as bioinoculants to promote plant growth and inhibit fungal proliferation. 87 isolates, comprising 36 fluorescent Pseudomonas spp. and 51 yeast isolates were obtained from healthy fruits and vegetables. Yeast (YFSL) and Pseudomonas (PFSL) isolates significantly (p < 0.05) inhibited the in-vitro growth of Fusarium solani and Drechslera sp. Experiments in a screen house for 90 days used a randomized block design to study the effects of bioinoculants on plant and fruit health. Moreover, plants and fruits treated with these bioinoculants showed increased levels of salicylic acid (66.14%), total phenolic content (59.67%), chlorophyll (24.31%), carbohydrates (40.38%), phosphorus (0.24%), and antioxidant activity (90%). The treatments displayed higher levels of plant defensive enzymes, chitinase (0.09 mg/h/protein) and β-1-3-glucanase (0.093 mg/h/protein). The increased concentrations of antioxidant enzymes like SOD (0.07 U/L), POD (0.23 U/L), and APX (0.24 U/L) were also observed in the fruits of bio-inoculated plants. However., the difference in results was non-significant (P ≤ 0.05). This study demonstrates the Efficacy of bioinoculants in improving plant growth, compositional characteristics, and antioxidant activities while reducing losses in tomato plants and fruits.

Bioremediation of hydrocarbon pollutants by Pseudomonas putida under optimal conditions

Background: The extreme toxicity of petroleum products to human and environmental health, particularly when linked to large-scale unintentional spills, has made them one of the most serious and current environmental pollution issue. Petroleum products are a complex mixture of hydrocarbons.Methods: Oil-contaminated soil samples were gathered and utilized to isolate hydrocarbon-degrading bacterial isolates. The bacterial isolates possessing bioremediation capabilities were identified using phenotypic determination and biochemical properties. The Optimal conditions including incubation period, temperature, different pH values and different carbon sources were studied for bioremediation of crude oil by bacterial isolates.Result: In Wasit province of Iraq, Pseudomonas putida, P. fluorescens, and P. aeruginosa isolated from soil samples tainted with petroleum hydrocarbons. Pseudomonas putida have more ability for bioremediation of crude oil (68%) compared to P. aeruginosa and P. fluorescens (47%, 58%) respectively. The results of optical density (600nm), biomass and (E24%) index for Pseudomonas putida were (1.080, 1.98 and 60%) respectively. The Optimal conditions (incubation period, temperature, different pH values and different carbon sources) were studied for bioremediation of crude oil by Pseudomonas putida by using liquid BHM supplemented with 1% crude oil. The result of this study showed that the incubation period of 9 days was the optimum for bioremediation of hydrocarbons which was 88.33%. The optimum temperature and pH were 35 °C and 7 respectively. The carbon source (glucose and fructose) was optimal for hydrocarbon bioremediation.Conclusion: This bacterial isolate Pseudomonas putida can be use in petroleum hydrocarbon bioremediation process.Keywords: Pseudomonas putida; Bioremediation; Optical density

Environmental Monitoring of Nebraska Ready-to-eat Meat Processing Establishments Resulted in the Isolation of Listeria Alongside Pseudomonas Highly Resistant to Quaternary Ammonia Sanitizer

Robust environmental monitoring for Listeria monocytogenes often may not be feasible for small and very small meat processors in the United States due to the limitations in finances, staffing, or expertise. Three small/very small processors in Nebraska were sampled using sponge applicators in nonfood contact surface areas to determine if biofilm and sanitizer resistance behaviors of Pseudomonas could relate to the prevalence of L. monocytogenes and Listeria spp. in ready-to-eat meat processing environments. Samples were 3.3% (3/90) positive for L. monocytogenes, and 12.2% (11/90) of samples were positive for Listeria spp. Pseudomonas spp. were also isolated. When Listeria spp. and Pseudomonas spp. were assayed for biofilm production and resistance to a quaternary ammonia sanitizer, multiple isolates belonging to both genera capable of forming biofilms were identified. Four Pseudomonas spp. isolates resisted the 200 ppm manufacturer-recommended sanitizer concentration for food contact surface sanitation, and one Pseudomonas spp. isolated from a drain sample that was also positive for L. monocytogenes demonstrated a sanitizer minimum bactericidal concentration of 1000 ppm. These findings further support the need for monitoring of small and very small meat processors for L. monocytogenes as well as highlight the need to identify other bacteria in these processing environments, like Pseudomonas, that are resistant to environmental stressors.

Potentiality of Formulated Pseudomonas Fluorescens and Bacillus Subtilis for the Management of Sheath Blight Disease of Rice Under Field Condition

Rice production is severely affected by sheath blight disease in Bangladesh which is caused by a fungus Rhizoctonia solani that is still merely managed by synthetic chemical fungicides. In this study, different isolates of Pseudomonas fluorescens and Bacillus subtilis were evaluated to assess their inhibitory effects against R. solani both in- vitro and field condition following dual culture method in order to formulate technique for the management of sheath blight of rice. Among all the isolates, P. fluorescens (Pf- 7 and Pf- 8) and B. subtilis (Bs-17 and Bs-21) showed the highest in –vitro mycelial growth suppression of the pathogen. Based on the in-vitro mycelial growth suppression performance, fourteen treatments combinations, either single or in consortia of antagonistic bacteria in talc-based formulations were applied by root dipping. All the formulated bacterial isolates showed significant reduction in disease and severity compared to untreated control and chemical fungicide. At 90 DAT, both the disease incidence and severity were found lowest in T11 (31.67 % and 37.33 % respectively) where the seedlings were treated for 24 hours with consortium of Pf-7 + Pf- 8 formulated in talc followed by in T12 (32.00 % and 38.00 %) where the seedlings were treated for 24 hours with consortium of Bs-17 + Bs-21 formulated in talc respectively. Vegetative and yield parameters were also significantly increased in both T11 and T12. The highest yield as well as Benefit Cost Ratio (BCR) were found in T11 (2.50 kg/ m2 and 2.20) followed by T12 (2.49 kg/m2 and 2.18). Thus, the consortia of bacterial isolates (Pseudomonas fluorescens and Bacillus subtilis) with seedling dipping time for 24 hour represents a promising alternative to chemical fungicides for the management of sheath blight of rice in field condition. J Bangladesh Agril Univ 22(3): 342-351, 2024

The microbiome of continuous wheat rotations: minor shifts in bacterial and archaeal communities but a source for functionally active plant-beneficial bacteria

Continuous wheat cropping often leads to yield decline, with suspected causes including increased pathogen susceptibility, decreased root growth, or low nutrient use efficiency, though the exact causes remain unknown. Here, we investigated soil and root-associated bacterial and archaeal communities in wheat under rotation versus continuous cultivation, monitored fungal pathogen presence, and used beneficial bacteria to mitigate Gaeumannomyces tritici (Ggt) symptoms in greenhouse experiments. Sampling was conducted at two field sites with different soil textures over two years and at two plant developmental stages, capturing site-specific and seasonal fluctuations. By cultivation, 767 bacterial isolates were screened for plant-beneficial traits. Amplicon sequencing revealed minor effects on community structure due to wheat rotational position but pronounced effects related to site, year, and microhabitat. Rhizoplane isolates with plant-beneficial traits were mainly Flavobacterium, Microbacterium, Pedobacter, Pseudomonas, Stenotrophomonas, and Variovorax. Continuous wheat rotations showed the highest proportion of bacteria with fungal antagonistic potential, indicating plant roots’ recruitment of beneficial bacteria. Introducing Ggt in the greenhouse experiment altered the bacterial and archaeal community, confirming field study results and demonstrating that applying beneficial bacteria early in the season at the seedling stage can control Ggt and improve plant growth. This study highlights the dynamic nature of wheat's below-ground bacterial and archaeal community, influenced by soil type, season, and microhabitat, with wheat rotation playing a minor role. In addition, it confirms the potential of selected Bacillus and Pseudomonas isolates, whether used individually or in consortia, for microbe-assisted mitigation of yield decline in intensive wheat production.

Multifunctional fluorescent Pseudomonas: effects on maize development and tools for their selection

Maize is one of the most cultivated cereals worldwide. Despite the low nutrient availability in the soil, high amounts of fertilizers are applied causing economic and environmental impacts. Then, Plant Growth Promoting Rhizobacteria (PGPR) as Fluorescent Pseudomonas can be utilized as an alternative. The present work aims to analyze the effect of Pseudomonas isolates on maize development and production and verify the relationship between growth mechanisms and IAA production. Sixteen Pseudomonas isolates were tested in vitro to produce IAA, ACC deaminase, siderophores, and solubilize Fe and Al phosphates. Three isolates (CBSAL02, CBSAL05, and CBSAL06) were selected for the field experiment, in which an A. brasilense inoculant was the control, generating five treatments with four replications. More than 50% of the isolates demonstrated the tested mechanisms. Only CBSAL05 did not produce siderophore or could fix N. Inoculations with A. brasilense and Pseudomonas isolates increased leaf N content among the selected isolates. The CBSAL06 isolate increased productivity, thus demonstrating the potential use as an inoculant.

Description of three new Pseudomonas species isolated from aquarium fish: Pseudomonas auratipiscis sp. nov., Pseudomonas carassii sp. nov. and Pseudomonas ulcerans sp. nov

Pseudomonas species constitute a significant group of pathogens in aquarium fish and frequently cause haemorrhagic septicaemia. This study conducted a taxonomic characterization of Pseudomonas isolates from aquarium fish exhibiting deep ulceration and general disease signs. A polyphasic approach was employed to ascertain the taxonomic affiliation of the strains. The overall genome relatedness indices of digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI) between the strains and the other members of the genus Pseudomonas were found to be below the established thresholds of 70 and 95–96%, respectively. Whole-genome based phylogenetic analysis revealed that strains 119PT and 120P were closely related to P. arcuscaelestis. Strain 137PT was related to P. peradeniyensis, while strains 147PT and 148P were closely related to P. japonica. The morphological, physiological, and biochemical characteristics of the strains and the genome relatedness indices of dDDH and ANI below the established thresholds confirmed the classification of the strains as three novel species. Genome analyses of the strains were also conducted to determine their biosynthesis-related gene clusters, virulence features and ecological distribution patterns. Based on polyphasic characterization, the strains 119PT, 120P, 137PT, 147PT, and 148P are novel species within the genus Pseudomonas, for which the following names are proposed: Pseudomonas auratipiscis sp. nov., with the strain 119PT as the type strain (=DSM 117162 T, =LMG 33381T); Pseudomonas carassii sp. nov., with the strain 137PT as the type strain (=DSM 117060T, =LMG 33378T); and Pseudomonas ulcerans sp. nov. 147PT, as the type strain (=DSM 117163T, =LMG 33377T).

Isolation, characterization, and genetic manipulation of cold-tolerant, manganese-oxidizing Pseudomonas sp. strains.

Manganese-oxidizing bacteria (MnOB) produce Mn oxide minerals that can be used by humans for bioremediation, but the purpose for the bacterium is less clear. This study describes the isolation and characterization of cold-tolerant MnOB strains isolated from a compost pile in Morris, Minnesota, USA: Pseudomonas sp. MS-1 and DSV-1. The strains were preliminarily identified as members of species Pseudomonas psychrophila by 16S rRNA analysis and a multi-locus phylogenetic study using a database of 88 genomes from the Pseudomonas genus. However, the average nucleotide identity between these strains and the P. psychrophila sp. CF149 type strain was less than 93%. Thus, the two strains are members of a novel species that diverged from P. psychrophila. DSV-1 and MS-1 are cold tolerant; both grow at 4°C but faster at 24°C. Unlike the mesophilic MnOB P. putida GB-1, both strains are capable of robustly oxidizing Mn at low temperatures. Both DSV-1 and MS-1 genomes contain homologs of several Mn oxidation genes found in P. putida GB-1 (mnxG, mcoA, mnxS1, mnxS2, and mnxR). Random mutagenesis by transposon insertion was successfully performed in both strains and identified genes involved in Mn oxidation that were similar to those found in P. putida GB-1. Our results show that MnOB can be isolated from compost, supporting a role for Mn oxidation in plant waste degradation. The novel isolates Pseudomonas spp. DSV-1 and MS-1 both can oxidize Mn at low temperature and likely employ similar mechanisms and regulation as P. putida GB-1.IMPORTANCEBiogenic Mn oxides have high sorptive capacity and are strong oxidants. These two characteristics make these oxides and the microbes that make them attractive tools for the bioremediation of wastewater and contaminated environments. Identifying MnOB that can be used for bioremediation is an active area of research. As cold-tolerant MnOB, Pseudomonas sp. DSV-1 and MS-1 have the potential to expand the environmental conditions in which biogenic Mn oxide bioremediation can be performed. The similarity of these organisms to the well-characterized MnOB P. putida GB-1 and the ability to manipulate their genomes raise the possibility of modifying them to improve their bioremediation ability.

Evaluation of rhizospheric Pseudomonas spp. for the management of Fusarium wilt of tomato in Cholistan, Pakistan

Agriculture plays a crucial role in national development, food security, and poverty reduction. Despite its importance, the agricultural sector's contribution to GDP is gradually decreasing. Fusarium wilt, caused by Fusarium oxysporum f.sp. lycopersici, has significantly hindered tomato production globally. Tomato (Lycopersicon esculentum Mill.), a widely grown vegetable, is threatened by various pathogens, with Fusarium wilt being particularly damaging due to yield and quality loss. Synthetic chemicals are commonly used to control Fusarium wilt in tomatoes, but these chemicals are harmful to the environment and human health due to their toxicity and persistence. This has prompted researchers to develop eco-friendly alternatives. In preliminary tests, 10 isolates of Pseudomonas spp. were evaluated in vitro against Fusarium oxysporum. Four isolates that effectively inhibited the growth of F. oxysporum were chosen for further experimentation. A greenhouse study revealed that two bacterial isolates, IUB310 and Mad1230, significantly reduced disease severity by 69.2% and 65%, respectively. Plant growth-promoting rhizobacteria from the Pseudomonas family not only combat pathogens but also induce systemic resistance in plants by strengthening cell walls and triggering defensive proteins and compounds. The results clearly highlight the significance of Pseudomonas strains in suppressing F. oxysporum and promoting plant growth, indicating their potential use in managing Fusarium wilt in tomato cultivation.

Biosynthesis and Characterization of Zinc Nanoparticles Using Strains of Pseudomonas and Actinobacteria

Research was carried out at the Green Nanotechnology Laboratory, University of Agricultural Sciences, Dharwad, Karnataka, with a specific emphasis on the biosynthesis of zinc nanoparticles using Pseudomonas and Actinobacteria. Collection and screening of Pseudomonas and Actinobacterial isolates were done at Microbial Genetics Laboratory, Department of Agricultural Microbiology, UAS, Dharwad. The ZnNPswere biosynthesized and characterized through UV-Visible spectroscopy, Particle Size Analyzer (PSA), Scanning Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS), X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The ZnNPs synthesized through Pseudomonas(AUDP209) and Actinobacteria(AUDT636)isolates exhibited peak values at 365 and 374 nm, with average sizes of 48.7 nm and 54.9 nm, respectively.SEM images revealed the spherical shape of the biosynthesized ZnNPs, while EDX confirmed the zinc ions presence in the biosynthesized samples and the crystalline structure of the ZnNPswas confirmed by XRD.FTIR spectroscopy confirmed the organic compounds present in the microbial extracts responsible for the capping and stabilizing agents for biosynthesis of ZnNPs.

Taxonomy of Pseudomonas spp. determines interactions with Bacillus subtilis.

There is a strong interest in the microbial ecology field to predict interaction among microorganisms, whether two microbial isolates will promote each other's growth or compete for resources. Numerous studies have been performed based on surveying the available literature or testing phylogenetically diverse sets of species in synthetic communities. Here, a high throughput screening has been performed using 720 Pseudomonas isolates, and their impact on the biofilm formation of Bacillus subtilis was tested. The aim was to determine whether a majority of Pseudomonas will promote or inhibit the biofilms of B. subtilis in the co-cultures. This study reports that Pseudomonas taxonomy is a good predictor of interaction outcome, and only a minority of Pseudomonas isolates promote Bacillus biofilm establishment.

The Etiological and Antimicrobial Susceptibility Profiles of the Bacteria Obtained from Ovine Caseous Lymphadenitis Cases in the Çankırı Region, Türkiye.

Sheep caseous lymphadenitis (CLA) causes significant economic losses in the livestock sector by causing a loss in the quantity and quality of animal products and a loss in the breeding value of animals. Although the primary agent in CLA's etiology is Corynebacterium pseudotuberculosis, some other opportunistic microorganisms also play a role. Therefore, the control and treatment of CLA necessitates the identification of the relevant etiological agents. This study aimed to conduct an in vitro culture and molecular characterization (PCR analysis and 16S rRNA sequencing) of the bacteria involved in sheep CLA cases reported in the Çankırı province of Türkiye and determine the antibiotic susceptibility of the case isolates. In total, 82 (16.4%) of 500 sheep in five farms were diagnosed with CLA. Following the culture of the superficial abscesses samples, C. pseudotuberculosis was identified in 30 (36.59%) as a result of PCR, Pseudomonas spp. in 8 (9.76%), and Enterobacter cancerogenus in 1 (1.22%), as a result of 16S rRNA sequencing. These data revealed extensive heterogeneity among the Pseudomonas isolates, with hints of derivation from a common ancestry for some and phylogenetic similarity to isolates from Germany, Malaysia, and India. In contrast to the high susceptibility to cefoperazone and lincomycin, the high resistances of C. pseudotuberculosis and Pseudomonas spp. isolates to cephalothin, ceftiofur, cloxacillin, amoxicillin, and bacitracin were remarkable. Based on these findings, it was concluded that for an effective treatment and control of ovine CLA cases, there is a need to consider the possible involvement of opportunistic bacteria other than the primary causative agent, C. pseudotuberculosis. It also contributed to increasing the country-specific sequence data and establishing new taxa from a universal perspective.

Aflatoxin B1 Control by Various Pseudomonas Isolates.

The climate-change-coupled fungal burden in crop management and the need to reduce chemical pesticide usage highlight the importance of finding sustainable ways to control Aspergillus flavus. This study examines the effectiveness of 50 Pseudomonas isolates obtained from corn rhizospheres against A. flavus in both solid and liquid co-cultures. The presence and quantity of aflatoxin B1 (AFB1) and AFB1-related compounds were determined using high-performance liquid chromatography-high resolution mass spectrometry analysis. Various enzymatic- or non-enzymatic mechanisms are proposed to interpret the decrease in AFB1 production, accompanied by the accumulation of biosynthetic intermediates (11-hydroxy-O-methylsterigmatocystin, aspertoxin, 11-hydroxyaspertoxin) or degradation products (the compounds C16H10O6, C16H14O5, C18H16O7, and C19H16O8). Our finding implies the upregulation or enhanced activity of fungal oxidoreductases and laccases in response to bacterial bioactive compound(s). Furthermore, non-enzymatic reactions resulted in the formation of additional degradation products due to acid accumulation in the fermented broth. Three isolates completely inhibited AFB1 or any AFB1-related compounds without significantly affecting fungal growth. These bacterial isolates supposedly block the entire pathway for AFB1 production in the fungus during interaction. Apart from identifying effective Pseudomonas isolates as potential biocontrol agents, this work lays the foundation for exploring new bacterial bioactive compounds.

Discovery of the 1-naphthylamine biodegradation pathway reveals a broad-substrate-spectrum enzyme catalyzing 1-naphthylamine glutamylation.

1-Naphthylamine (1NA), which is harmful to human and aquatic animals, has been used widely in the manufacturing of dyes, pesticides, and rubber antioxidants. Nevertheless, little is known about its environmental behavior and no bacteria have been reported to use it as the growth substrate. Herein, we describe a pathway for 1NA degradation in the isolate Pseudomonas sp. strain JS3066, determine the structure and mechanism of the enzyme NpaA1 that catalyzes the initial reaction, and reveal how the pathway evolved. From genetic and enzymatic analysis, a five gene-cluster encoding a dioxygenase system was determined to be responsible for the initial steps in 1NA degradation through glutamylation of 1NA. The γ-glutamylated 1NA was subsequently oxidized to 1,2-dihydroxynaphthalene which was further degraded by the well-established pathway of naphthalene degradation via catechol. A glutamine synthetase-like (GS-like) enzyme (NpaA1) initiates 1NA glutamylation, and this enzyme exhibits a broad substrate selectivity toward a variety of anilines and naphthylamine derivatives. Structural analysis revealed that the aromatic residues in the 1NA entry tunnel and the V201 site in the large substrate-binding pocket significantly influence NpaA1's substrate preferences. The findings enhance understanding of degrading polycyclic aromatic amines, and will also enable the application of bioremediation at naphthylamine contaminated sites.

Plant, bacteria and fungi crosstalk: Direct and indirect biocontrol mechanisms of sugarcane rhizoplane Pseudomonas species against Fusarium wilt

In order to identify an effective rhizoplane Pseudomonas species to combat sugarcane wilt pathogen (Fusarium sacchari), twenty Pseudomonas isolates were obtained from the sugarcane rhizoplane of different genotypes. The three-tier confrontation (direct, indirect and remote) tests revealed antagonistic activity of the bacteria, bacterial non-volatile and volatile compounds. In dual culture assay, SRP19 (46.30%) and SRP20 (39.30%) have shown the highest inhibition against F. sacchari. 16S-23S rDNA sequencing identified them as Pseudomonas chlororaphis subsp. aurantiaca (SRP19) and Pseudomonas aeruginosa (SRP20). Exploration of biocontrol mechanisms revealed the potential roles for IAA production, extracellular enzyme secretion (proteases, cellulases and chitinases), HCN synthesis, siderophore production, pyocyanin or fluorescein production and phosphate solubilization. The molecular analysis revealed the presence of genes (phz, prnD, phlD and pltC) involved in the biosynthesis of antimicrobial peptides like phenazines, pyrrolnitrin, 2,4-diacetyl phloroglucinol and pyoleuteorin, involved in suppressing Fusarium. The antagonistic activity was further confirmed under greenhouse conditions by sett treatment with potential antagonistic isolates, which increased germination and reduced the pre-emergent mortality by 60% and post-emergent seedling mortality by 76% in SRP19 treated pots. The study revealed that the isolate Pseudomonas chlororaphis subsp. aurantiaca strain SRP19 can act as PGPR with both plant growth promoting and pathogen suppressing activity that can be used as an effective biocontrol agent against Fusarium wilt of sugarcane.

Variability in Maize Seed Bacterization and Survival Correlating with Root Colonization by Pseudomonas Isolates with Plant-Probiotic Traits.

Seed treatment with plant growth-promoting bacteria represents the primary strategy to incorporate them into agricultural ecosystems, particularly for crops under extensive management, such as maize. In this study, we evaluated the seed bacterization levels, root colonization patterns, and root competitiveness of a collection of autochthonous Pseudomonas isolates that have demonstrated several plant-probiotic abilities in vitro. Our findings indicate that the seed bacterization level, both with and without the addition of various protectants, is specific to each Pseudomonas strain, including their response to seed pre-hydration. Bacterization kinetics revealed that while certain isolates persisted on seed surfaces for up to 4 days post-inoculation (dpi), others experienced a rapid decline in viability after 1 or 2 dpi. The observed differences in seed bacterization levels were consistent with the root colonization densities observed through confocal microscopy analysis, and with root competitiveness quantified via selective plate counts. Notably, isolates P. protegens RBAN4 and P. chlororaphis subsp. aurantiaca SMMP3 demonstrated effective competition with the natural microflora for colonizing the maize rhizosphere and both promoted shoot and root biomass production in maize assessed at the V3 grown stage. Conversely, P. donghuensis SVBP6 was detected at very low levels in the maize rhizosphere, but still exhibited a positive effect on plant parameters, suggesting a growth-stimulatory effect during the early stages of plant development. In conclusion, there is a considerable strain-specific variability in the maize seed bacterization and survival capacities of Pseudomonas isolates with plant-probiotic traits, with a correlation in their root competitiveness under natural conditions. This variability must be understood to optimize their adoption as inputs for the agricultural system. Our experimental approach emphasizes the critical importance of tailoring seed bacterization treatments for each inoculant candidate, including the selection and incorporation of protective substances. It should not be assumed that all bacterial cells exhibit a similar performance.

First Report of Pseudomonas amygdali pv. morsprunorum causing Bacterial Canker in Sweet Cherry Orchards in Washington State.

In 2023, an outbreak of bacterial canker disease (BCD) in sweet cherry orchards caused significant economic losses to growers and nurseries in the Pacific Northwest, USA (Fig. S1). The cherry industry in Washington State alone is valued at over $800 million (USDA NASS, 2022). BCD poses a recurring threat to the state's sweet cherry [Prunus avium (L.) L.] orchards, especially young and newly planted orchards. Three Pseudomonas species, including P. syringae pv. syringae (Pss), P. amygdali pv. morsprunorum (Pam) (formerly P. syringae pv. morsprunorum Race 1, Psm1), and P. avellanae pv. morsprunorum (formerly P. syringae pv. morsprunorum Race 2, Psm2), have been reported to be associated with BCD in sweet cherries (Hulin et al. 2019). While Pss is widely prevalent in the United States, Pam has only been reported in Michigan (Renick et al., 2008) as well as in Europe, Central America, South Africa and Australia (Hulin et al. 2019) . In 2023, we surveyed more than 60 cherry orchards and collected hundreds of canker samples from newly planted up to 8-year-old trees. BCD prevalence ranged from 40-100% in cherry orchards, leading to the removal of hundreds of thousands of trees. Affected cherry trees exhibited characteristic bacterial canker symptoms, including dead bud, canker, and gummosis (Fig. S1). Bacteria were isolated from canker tissues or ooze on King's B (KB) agar plates (King et al., 1954) and more than 300 fluorescent Pseudomonas isolates were obtained from 12 symptomatic sweet cherry cultivars. PCR results using Pss- and Pam- specific primers (SyrB and Psm1, Table S1) (Sorensen et al., 1998; Kałużna et al., 2016) revealed that 91.9% and 8% isolates were tested positive for SyrB and Psm1, indicating that these isolates potentially belong to Pss and Pam, respectively. Pathogenicity tests using immature cherries cv. Sentina showed that all isolates caused typical necrotic lesions and could be re-isolated and re-identified as Pss and Pam, thus completing Koch's postulates. The identity of three Pam representative isolates (S79, S158, S202) was further confirmed by comparing gyrD and rpoD housekeeping genes as well as 16S rRNA gene sequence with other Pam strains in GenBank (Parkinson et al., 2010; Gomila et al., 2017). Blast searches against GenBank using gyrB (GenBank accession numbers PP357444-PP357446), rpoD (PP357447-PP357449) and 16S rRNA (GenBank accession numbers PP421223-PP421225) gene sequences, ranging from 520 to 859bp, matched those of the Pam isolates (GenBank accession numbers CP026558 or PP218075) with 100% homology and 100% query coverage, further indicating that these isolates are indeed Pam. This represents the first documented record of Pam causing BCD in the Pacific Northwest, USA, suggesting the complexity of the disease, which underscores the need for effective management strategies for cherry growers in the region.

Tracking atrazine degradation in soil combining 14C-mineralisation assays and compound-specific isotope analysis

The quantification of pesticide dissipation in agricultural soil is challenging. In this study, we investigated atrazine biodegradation in both liquid and soil experiments bioaugmented with distinct atrazine-degrading bacterial isolates. This was achieved by combining 14C-mineralisation assays and compound-specific isotope analysis of atrazine. In liquid experiments, the three bacterial isolates mineralised over 40% of atrazine, demonstrating their potential for extensive degradation. However, the kinetics of mineralisation and degradation varied among the isolates. Carbon stable isotope fractionation was similar for Pseudomonas isolates ADPT34 and ADP2T0, but slightly higher for Chelatobacter SR27. In soil experiments, atrazine primarily degraded into atrazine-desethyl, while atrazine-hydroxy was mainly observed in experiments with SR27. Atrazine mineralisation in soil by ADPT34 and SR27 exceeded 40%, whereas ADP2T0 exhibited a mineralisation rate of 10%. In experiments with ADPT34 and SR27, atrazine 14C-residues were predominantly found in the non-extractable fraction, whereas they accumulated in the extractable fraction in the experiment with ADP2T0. Compound-specific isotope analysis (CSIA) relies on changes of stable isotope ratios and holds potential to evaluate herbicide transformation in soil. CSIA of atrazine indicated atrazine biodegradation in water and solvent extractable soil fractions and varied between 29% and 52%, depending on the bacterial isolate. Despite atrazine degradation in both soil fractions, a significant portion of atrazine residues persisted, depending on the bacterial degrader, initial cell concentration, and mineralisation and degradation rates. Overall, our approach can aid in quantifying atrazine persistence and degradation in soil, and in optimizing bioaugmentation strategies for remediating soils contaminated with persistent herbicides.

Silver nanoparticle with potential antimicrobial and antibiofilm efficiency against multiple drug resistant, extensive drug resistant Pseudomonas aeruginosa clinical isolates

BackgroundThe study aims to investigate the effect of combining silver nanoparticles (AGNPs) with different antibiotics on multi-drug resistant (MDR) and extensively drug resistant (XDR) isolates of Pseudomonas aeruginosa (P. aeruginosa) and to investigate the mechanism of action of AGNPs.MethodsAGNPs were prepared by reduction of silver nitrate using trisodium citrate and were characterized by transmission electron microscope (TEM) in addition to an assessment of cytotoxicity. Clinical isolates of P. aeruginosa were collected, and antimicrobial susceptibility was conducted. Multiple Antibiotic Resistance (MAR) index was calculated, and bacteria were categorized as MDR or XDR. Minimum inhibitory concentration (MIC) of gentamicin, ciprofloxacin, ceftazidime, and AGNPs were determined. The mechanism of action of AGNPs was researched by evaluating their effect on biofilm formation, swarming motility, protease, gelatinase, and pyocyanin production. Real-time PCR was performed to investigate the effect on the expression of genes encoding various virulence factors.ResultsTEM revealed the spherical shape of AGNPs with an average particle size of 10.84 ± 4.64 nm. AGNPS were safe, as indicated by IC50 (42.5 µg /ml). The greatest incidence of resistance was shown against ciprofloxacin which accounted for 43% of the bacterial isolates. Heterogonous resistance patterns were shown in 63 isolates out of the tested 107. The MAR indices ranged from 0.077 to 0.84. Out of 63 P. aeruginosa isolates, 12 and 13 were MDR and XDR, respectively. The MIC values of AGNPs ranged from 2.65 to 21.25 µg /ml. Combination of AGNPs with antibiotics reduced their MIC by 5–9, 2–9, and 3-10Fold in the case of gentamicin, ceftazidime, and ciprofloxacin, respectively, with synergism being evident. AGNPs produced significant inhibition of biofilm formation and decreased swarming motility, protease, gelatinase and pyocyanin production. PCR confirmed the finding, as shown by decreased expression of genes encoding various virulence factors.ConclusionAGNPs augment gentamicin, ceftazidime, and ciprofloxacin against MDR and XDR Pseudomonas isolates. The efficacy of AGNPs can be attributed to their effect on the virulence factors of P. aeruginosa. The combination of AGNPs with antibiotics is a promising strategy to attack resistant isolates of P. aeruginosa.