Pseudomonas Fluorescens Strain Research Articles

Evaluation of Siderophore Production by Different Promising Microbial Isolates

Indian alkaline soils are deficient in iron due to high pH, high calcium carbonate, highly permeable coarse textured soils, and soils low in organic carbon content. This study is carried out to increase the iron use efficiency of soil by using promising microbial isolates. Production of siderophore by promising microbial isolates is a greatest invention which help in increasing uptake of iron. A short-term laboratory experiment was carried “To evaluate the siderophore productions by different promising microbial isolates using chrome azurol S assay technique”. Ten microbial isolates were inoculated on plate as well as in broth medium. Plates were observed for orange halo formation around the bacterial growth. The size of orange halo around the colony of each microbial isolates was measured. The broth cultures inoculated with inoculum, incubated at 28 ± 20C for 24-72 hr with constant shaking at 120 rpm. After the incubation, the culture broths were centrifuged at 10,000 rpm for 10 min. The cell free supernatants were subjected to quantitative estimation of siderophores by CAS-shuttle, absorbance was measured at 630 nm against a reference consisting of 0.5 ml of uninoculated broth and 0.5 ml of CAS reagent. Obtained results indicated that in both plate and broth assays medium inoculated with strain Pseudomonas fluorescens show significantly higher orange halo formation around the growth and maximum siderophore content in aliquot. Inoculation of this plant growth promoting microbial isolates will be the great achievement in replacing chemical fertilizers in agriculture.

The presence of the plant pathogen Fusarium graminearum as a soil inoculum enhances the rhizosphere survival of bacterial biocontrol strains aimed at the pathogen

AbstractThe serious wheat pathogen Fusarium graminearum causes both root rot and head blight. Some classical biocontrol tests were first used to explore the biocontrol ability of 39 Pseudomonas fluorescens strains. The five most antifungal strains B4, P13, UTPf127, UTPf125 and UTPf105 were selected to screen known antifungal antibiotic genes and greenhouse experiments. The ability of bacteria to colonize wheat rhizosphere and their effect on plant growth in the presence and absence of soil F. graminearum inoculum was studied under greenhouse conditions. Overall, biocontrol bacteria populations were significantly higher in both wheat endo‐and ectorhizosphere of pathogen‐inoculated soil than in healthy soil. The population of all strains differently decreased with time. On day 28, endorhizosphere populations of strain B4 could be detected in inoculated but not healthy soil, while UTPf127 populations remained high in endorhizospheres at all tested times. Isolate B4 and UTPf105 showed the most substantial plant growth in pathogen‐inoculated soil compared to pathogen‐inoculated soil without added bacteria. UTPf127‐treated plants grew better in control soil than when the pathogen was present. In contrast, UTPf125 and P13 showed little effect on plant growth. These results point to complex interactions between pathogen and biocontrol bacteria and suggest that a fungal pathogen in the soil can affect the survival of potential bacterial biological control agents. Additionally, they highlight the importance of screening and evaluating potential biocontrol bacteria against soilborne fungal pathogens by in vivo tests rather than relying on plate screenings.

Pseudomonas fluorescens SP007S Formulations in Controlling Soft Rot Disease and Promoting Growth in Kale

Kale has gained popularity as a healthy food choice due to its rich nutrient profile. However, kale production systems are also affected by various pests and diseases, especially plant pathogenic bacteria, such as Pectobacterium carotovorum. The purpose of this research was to investigate the biocontrol activity of the Pseudomonas fluorescens strain SP007s and develop a formulation that provides stability, long shelf life, and disease control, as well as promoting growth in kale; we expect this formulation to have further commercial applications in the cultivation of kale. The results indicated that a unique mixture of paper sludge, sugar sludge, and glycerol at 40% relative humidity promoted SP007 survival for 6 months at room temperature (30 °C) with measures of 5.92 × 106 CFU/g. This treatment maintained the control efficacy of P. carotovorum in infected soil within 28 days of soil drenching. We evaluated the SP007s formula for controlling soft rot disease in greenhouse conditions, and our results revealed that it can reduce the disease in kale by 65.2% and promotes growth in terms of canopy width, shoot height, number of leaves per plant, fresh weight, and dry weight, which were superior to the control. In addition, the formula can induce the accumulation of endogenous salicylic acid and phenolic compounds, as well as a systemic acquired resistance pathway in the plant defense system. Therefore, the formula of SP007s can be a promising novel biocontrol formula for use in kale production, as it promotes plant growth and acts against P. carotovorum causal soft rot disease.

Sunflower meal ethanol solute powder as an upcycled value-product to prolong food shelf life

In this study the potential of sunflower meal ethanol-wash powder (SEWP) to be used as antimicrobial agent in liquid foods was investigated. SEWP represents the waste of the main process of protein isolation from industrially produced sunflower meal. The washing liquids remaining after treatment of the sunflower meal with 75% aqueous ethanol solution were collected and turned into powder rich in bioactive compounds. Due to its recognized properties, different concentrations (2.5 and 5% w/v) of SEWP were first tested in vitro against Alicyclobacillus acidoterrestris and a cocktail of Pseudomonas putida and Pseudomonas fluorescens strains, using appropriate culture media. Then, the SEWP antimicrobial efficacy was tested on two real food matrices differing in their composition. Soymilk, rich in proteins, and apple juice, composed mainly of carbohydrates, were used as food models. Concentrations equal to 1%, 1.5%, 2%, 2.5%, 5% and 7.5% (w/v) SEWP were tested in the juice, whereas the sole three highest concentrations were tested in the soymilk. Both beverages were pre-inoculated with different spoilage bacteria. The same mix of Pseudomonas spp. and A. acidoterrestris strain used for the in vitro test were employed to contaminate the soymilk and the apple juice, respectively. In vitro results showed moderate effects of SEWP against selected target microorganisms. On the contrary, two completely different microbial evolutions were recorded in the soymilk and apple juice. The three concentrations of SEWP were slightly effective against spoilage of soymilk, whereas all the concentrations used in the juice were sufficient to completely inhibit microbial growth of A. acidoterrestris. The shelf life of the apple juice supplemented with 1% SEWP was extended for more than 21 days. Considering both the antimicrobial efficacy and the sensory properties of the juice, the lowest SEWP concentration (1% w/v) demonstrated the best result as a bioprotectant. Overall results imply dependence of SEWP antimicrobial efficiency on food composition and a need of preliminary evaluation of the product if used as an antimicrobial agent in the food industry.

Exploitation of indigenous fluorescent pseudomonads against stem and pod rot of groundnut caused by <i>Sclerotium rolfsii</i>

Stem and pod rot of groundnut is an economically important soil borne disease caused by Sclerotium rolfsii Sacc. The present study aimed to evaluate the indigenous bacterial bio control agent Pseudomonas fluorescens strains having multiple traits related to bio control and plant growth promoting activity. Healthy rhizospheric soil from groundnut field was collected from different North Karnataka districts. Nineteen strains of P. fluorescens were isolated by serial dilution technique on King’s B medium. The antagonistic potential of nineteen strains was tested against S. rolfsii by using dual culture technique. The per cent inhibition was highly variable among the nineteen strains of P. fluorescens ranging from 2.59 to 75.18 per cent. Maximum mycelial inhibition of S. rolfsii was recorded by the strain PF-2 (75.18%) followed by PF-3 (72.96%), PF-6 (69.62%) and least inhibition was recorded by PF-13 (2.59%). Five superior strains of P. fluorescens showed fluorescens under UV light, yellowish green pigmentation, rod shaped cells under microscope. Five superior strains were subjected for various biochemical tests and all the isolates were positive for biochemical characterization such as Gram staining, endospore production, catalase, starch hydrolysis, urease test, casein hydrolysis and gelatin liquefy action and negative for KOH and in dole test. Further, these strains were subjected for plant growth promoting traits such as HCN production, IAA production, siderophore production and volatile compounds production. Among these, the strainsviz., PF-2 and PF-3 were scored as strong with respect to antagonism and growth promotion. The strainsPF-6, PF-7 and PF-10 were scored as moderate with light brown colour. Among the tested strains of P. fluorescens, the isolates PF-2 and PF-3 were recorded higher production of siderophore, isolates PF-6, PF-7 and PF-10 showed moderate production of siderophore. The strain PF-2 of P. fluorescens showed highest per cent of mycelial inhibition of S. rolfsii indicating higher production of volatile compounds, followed by PF-3 and PF-6. Whereas, the least mycelial inhibition was recorded by the isolate PF-10 indicating less production of volatile compounds.

Phyto-Inhibitory and Antimicrobial Activity of Brown Propolis from Romania.

The objective of this paper was to study the phyto-inhibitory and antimicrobial activity of brown propolis collected from the counties of four regions in Romania. The main physico-chemical and functional properties of 16 samples of propolis from different landforms of geographical regions were determined. Their antimicrobial activities were established against 5 bacterial strains (Pseudomonas fluorescens, Bacillus subtilis, Bacillus cereus, Escherichia coli, and Proteus mirabilis) and 5 fungal strains (Alternaria alternata, Cladosporium cladosporioides, Fusarium oxysporum, Mucor racemosus, and Aspergillus niger). Simultaneously, the phyto-inhibitory effect of propolis samples on different cereals was highlighted: hexaploid bread wheat (Triticum aestivum), maize (Zea mays L.), oats (Avena sativa L.), and barley (Hordeum vulgare L.). Correlations between the antioxidant activity and total flavonoid and phenol content of the propolis samples were identified, respectively, and the statistical analysis highlighted that the diameter of the inhibition zone was influenced by the strain type (bacterial and fungal) and the geographical regions of propolis. Principal component analysis (PCA) indicated that out of seven principal components, only two exhibited > 0.5. Pearson's correlation coefficient showed a low and moderate positive linear relationship between the diameter of the inhibition zone and the flavonoid and phenol concentration of the propolis samples.

Bioluminescence resonance energy transfer biosensor for measuring activity of a protease secreted by Pseudomonas fluorescens growing in milk

Bacterial proteases are sporadic contributors to milk spoilage, reducing the quality of ultra-heat treated (UHT) milk and other dairy products. Current methods for measuring bacterial protease activity in milk are insensitive and too slow to be used in routine testing in dairy processing plants. We have designed a novel bioluminescence resonance energy transfer (BRET)-based biosensor to measure the activity of proteases secreted by bacteria in milk. The BRET-based biosensor is highly selective for bacterial protease activity compared with other proteases tested, notably including plasmin, which is abundant in milk. It incorporates a novel peptide linker that is selectively cleaved by P. fluorescens AprX proteases. The peptide linker is flanked by green fluorescent protein (GFP2) at the N-terminus and a variant Renilla luciferase (RLuc2) at the C-terminus. Complete cleavage of the linker by bacterial proteases from Pseudomonas fluorescens strain 65, leads to a 95% decrease in the BRET ratio. We applied an azocasein-based calibration method to the AprX biosensor using standard international enzyme activity units. In a 10-min assay, the detection limit for AprX protease activity in buffer was equivalent to 40 pg/mL (≈0.8 pM, 22 μU/mL) and 100 pg/mL (≈2pM, 54 μU/mL) in 50% (v/v) full fat milk. The EC50 values were 1.1 ± 0.3 ng/mL (87 μU/mL) and 6.8 ± 0.2 ng/mL (540 μU/mL), respectively. The biosensor was approximately 800x more sensitive than the established FITC-Casein method in a 2-h assay, the shortest feasible time for the latter method. The protease biosensor is sensitive and fast enough to be used in production settings. It is suitable for measuring bacterial protease activity in raw and processed milk, to inform efforts to mitigate the effects of heat-stable bacterial proteases and maximise the shelf-life of dairy products.

Isolation and characteristics of Pseudomonas fluorescens to inhibit Phytophthora palmivora causing rot disease in durian

Plant growth promoting Rhizobacteria (PGPR) have long been selected as biocontrol agents for plants. The PGPR are beneficial bacteria that live in plant roots and enhance plant growth by various of mechanisms. The PGPR have many species of the bacterial genus Pseudomonas, in which the Pseudomonas fluorescens strains is suitable for application as a biocontrol agent due to its abundance in natural soil and plant root systems. Pseudomonas fluorescens strains have important characteristics such as the ability to adhere to soil particles and to rhizomes, the ability to synthesize antibiotics, and to produce hydrolytic enzymes. Furthermore, P. fluorescens strains also possess plant growth promoting characteristics such as proteolysis, phosphate solubilization, iron chelation, and phytohormone production. Durian is a crop that has been expanded in Southeast Asian countries but the rate of durians infected with root, stem and fruit rot caused by P. palmivora is quite large. In this study, five native P. fluorescens isolates were isolated from 70 soil and rhizome samples collected from 10 durian growing provinces and evaluated for their ability to antagonize P. palmivora in petri plates. These isolates were gram negative, small, single isolated rods without sporulation when observed under microscope. All of them tested positive for catalase test, oxidase test, starch hydorolysis, gelatine liquefaction, H2S, citrate utilization and negative with indole, Voges-proskauers, methyl red. All of 5 native P. fluorescens isolates were capable of phosphate solubilizing activity, N2 fixation, siderophore and IAA production. The study showed that P. fluorescens P. fDN strain was able to inhibit P. palmivora causing rot disease in durian with 51.85% inhibition of radial growth.

Levering proteomic analysis of Pseudomonas fluorescens mediated resistance responses in tomato during pathogenicity of Fusarium oxysporum f. sp. oxysporum

The tomato, one of the world’s most extensively cultivated and consumed vegetable crops is negatively impacted by various pathogens. This study aimed to observe the differentially expressed proteins in tomato samples in plant–pathogen-biocontrol interactions. The fungal pathogen associated with wilted plants were isolated and identified based on its morphological and molecular characteristics. Fourteen strains of Pseudomonas fluorescens from agricultural soils were identified and described using biochemical assays, molecular analyses, and screening for antagonistic ability against the Fusarium wilt pathogen. Results demonstrated that the potential of P. fluorescens (TPf12) positively influenced the expression of antagonism against tomato wilt disease. A total of 14 proteins expressed differently were revealed in the 2D-PAGE-MS investigation. Proteins such as nucleoside diphosphate kinase, phenylalanine ammonia-lyase, protein kinase family protein, Ser/Thr protein kinase-like are unchanged in FOL pathogen interaction, but up-regulated in FOL + TPf12 treated roots, and lipid transfer-like protein, and phenylalanine ammonia-lyase were down-regulated in FOL infested roots and upregulated in FOL + TPf12 treated tomato roots. Phenylalanine ammonia-lyase protein expression is commonly found in TPf12 bioenriched roots, and FOL + TPf12 treated roots, indicating its role in response to the application of TPf12 in tomato. A GC–MS analysis was performed to detect the bioactive metabolites synthesized by TPf12. Molecular docking investigations were conducted using the maestro’s GLIDE docking module of the Schrodinger Software program. Among the secondary metabolites, Cyclohexanepropanoic acid, 2-oxo-, methyl ester (CAS), and 3-o-(4-o-Beta-D-Galactopyranosyl-Beta-D-Galactopyraosyl)-2-Acetylamino-2-Deoxy-D-Galactose were shown to be top-ranked with a least docking score against each differently expressed proteins. The profiled molecules expressed differently due to plant-pathogen-biocontrol interactions may be directly or incidentally involved in the wilt disease resistance of tomato plants.

Triclocarban-contaminated wastewater treatment by innovative hybrid moving entrapped bead activated sludge reactor (HyMER): Continuous performance and computational dynamic simulation analysis

Triclocarban (TCC) has been used in consumer products and is a widespread contaminant in municipal wastewater treatment systems that ultimately accumulates in natural receiving water and soil. This work aims to apply an innovative hybrid moving entrapped bead activated sludge reactor (named “HyMER”) that integrates entrapped TCC-degrading microbes and freely suspended activated sludge to treat TCC-contaminated wastewater. A previously isolated TCC-degrading bacterium (Pseudomonas fluorescens strain MC46, called MC46) and barium alginate entrapment were applied. The synthetic TCC-contaminated wastewater treatment (with TCC concentration of 10 mg/L) was performed using 20-cycle fed-batch reactor operation with feeding times of 12 and 24 h and cycle times of 13 and 25 h. The results indicated that the HyMER effectively reduced chemical oxygen demand by up to 80 and 95 % and TCC by up to 53 and 83 %, respectively, with feeding times of 12 and 24 h. Three TCC degradation intermediate products were found—3,4-dichloroaniline, 4-chloroaniline, and aniline. Scanning electron microscopic analysis revealed shorter cells and bacterial appendage development as cell adaptations against TCC and its intermediates. The live/dead assay indicated high survival of entrapped MC46 in toxic conditions, with up to 84 % viable cells. Based on computational fluid dynamic analysis, no entrapped cell agglomeration showed in the reactor, indicating the potential application of HyMER for real wastewater treatment. These results exhibit the feasibility of HyMER and its applicability for future toxic wastewater treatment.

Safranin-O-Mediated Photodynamic Inactivation of Microorganisms Reduces Milk Contaminating Bacteria Count and Prevented New Cases of Mastitis

The objectives of this study were to evaluate the antimicrobial capacity of the photosensitizer (PS) safranin-O (Sf), through antimicrobial photodynamic therapy (PDTa), against strains of Pseudomonas fluorescens (PV1, PVh, and PC3) and Staphylococcus aureus (SV1, SV3, SV5, SC5, SC6, and SC8) isolated from milk from cows and goats and the biofilm formation on equipment. To evaluate the effectiveness of the formulation, studies were carried out through in situ applications of the Sf hydrogel as post-dipping in lactating cows and goats. Antibiogram tests showed the resistance of Staphylococcus aureus isolates to ampicillin, trimethoprim, and tetracycline. In the in vitro assays in bovine milk, the PDTa reduced the P. fluorescens (PV1) counts by 17.4% (p<0.05). In goat milk, the PDTa reduced the growth of S. aureus by up to 24.43% (SC8) (p<0.05), and for P. fluorescens (PC3), the inactivation was 50.25%. In biofilm formation, there were reduction of 66.66% (SV1) and 38.27% (SC5) in the adhesion of S. aureus to stainless steel coupons. For in situ applications, photoactivated Sf maintained bacterial counts in bovine milk similar to the control treatment (lactic acid). During the experimental period (28 days), there were reductions of 23.23% and 28.85% in staphylococci and Pseudomonas spp. in cow’s milk and 76.13% for Pseudomonas spp. in goat milk (p<0.05). There was no significant difference in goat milk’s somatic cell count (CCS). These results indicate that photoactivated Sf can help reduce milk contamination and maintain the health of the mammary gland.

Fungi Associated with the Spoilage of Sweet Orange (Citrus sinensis) Fruits and their Management by Bio-Control Agents

Different Sweet Orange fruits (Citrus Sinensis) rot fungi were isolated from rotted fruits.These were Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, Penicillium digitatum. During pathogenicity test two fungi Aspergillus niger and Penicillium digitatum were proved to be most pathogenic. The Aspergillus niger fungi during dual culture with Bacillus substilis, Bacillus substilis srtain2, Pseudomonas fluorescens, Pseudomonas aeruginosa , Bacillus methylotrophicus, Bacillus cereus, Bacillus aryabhattai and Streptomyces strain showed different level of inhibation zones. Bacillus cereus was the most effective and caused 71.5% inhibition and Pseudomonas aeruginosa was least 53.28% and others Bacillus substilis, Bacillus substilis srtain2, Pseudomonas fluorescens, Bacillus methylotrophicus , Bacillus aryabhattai ,and Streptomyces caused 68.05%, 64.00%, 70.25%, 59.37%, 57.75% and, 55.25%, respectively. Penicillium digitatum fungi during dual culture with Bacillus substilis, Bacillus substilis srtain2, Pseudomonas fluorescens, Pseudomonas aeruginosa , Bacillus methylotrophicus, Bacillus cereus, Bacillus aryabhattai and Streptomyces strain showed different level of inhibation zones. Bacillus cereus was the most effective and caused 69.25% inhabition and Pseudomonas aeruginosa was least 51.75% respectively. During experiment on fruits the most effective biocontrol agent Bacillus cereus and Streptomyces strain were tested on fruits and it was found that Bacillus cereus and Streptomyces strain were effectively control the rot by Aspergillus niger and showed data 49.45%, 43.55%. During experiment on fruits the most effective biocontrol agent Bacillus cereus and Streptomyces strain were tested on fruits and it was found that Bacillus cereus and Streptomyces strain were effectively control the rot by Penicillium digitatum and showed data (51.62%, 45.67%). Experiment were performed for protective and curative effects. During protective effect the two biocontrol agents Bacillus methylotrophicus and Bacillus cereus reduced the percentage rottenig by 64.74% and 57.52% respectively in case of Aspergillus niger and in case of Penicillium digitatum the effect of two Biocontrol agents Bacillus methylotrophicus and Bacillus cereus caused 59.37% and 54.63% respectively reducuction in decaying. During the Curative effect the two biocontrol agents Bacillus methylotrophicus and Bacillus cereus reduced the rottenig percentage 62.53% and 55.84% respectively in case of Aspergillus niger but in case of Penicillium digitatum the effect of the Biocontrol agents Bacillus methylotrophicus and Bacillus cereus caused 58.29% and 51.99% respectively reducuction in decaying. Use of Biocontrol agents as protective is better than the curative.

The Anti-Listeria Activity of Pseudomonas fluorescens Isolated from the Horticultural Environment in New Zealand

Beneficial bacteria with antibacterial properties are attractive alternatives to chemical-based antibacterial or bactericidal agents. Our study sourced such bacteria from horticultural produce and environments to explore the mechanisms of their antimicrobial properties. Five strains of Pseudomonas fluorescens were studied that possessed antibacterial activity against the pathogen Listeria monocytogenes. The vegetative culture of these strains (Pseudomonas fluorescens-PFR46I06, Pseudomonas fluorescens-PFR46H06, Pseudomonas fluorescens-PFR46H07, Pseudomonas fluorescens-PFR46H08 and Pseudomonas fluorescens-PFR46H09) were tested against Listeria monocytogenes (n = 31), Listeria seeligeri (n = 1) and Listeria innocua (n = 1) isolated from seafood and horticultural sources and from clinical cases (n = 2) using solid media coculture and liquid media coculture. All Listeria strains were inhibited by all strains of P. fluorescens; however, P. fluorescens-PFR46H07, P. fluorescens-PFR46H08 and P. fluorescens-PFR46H09 on solid media showed good inhibition, with average zones of inhibition of 14.8 mm, 15.1 mm and 18.2 mm, respectively, and the other two strains and P. fluorescens-PFR46H09 had a significantly greater zone of inhibition than the others (p < 0.05). There was no inhibition observed in liquid media coculture or in P. fluorescens culture supernatants against Listeria spp. by any of the P. fluorescens strains. Therefore, we hypothesized that the structural apparatus that causes cell-to-cell contact may play a role in the ejection of ant-listeria molecules on solid media to inhibit Listeria isolates, and we investigated the structural protein differences using whole-cell lysate proteomics. We paid special attention to the type VI secretion system (TSS-T6SS) for the transfer of effector proteins or bacteriocins. We found significant differences in the peptide profiles and protein summaries between these isolates' lysates, and PFR46H06 and PFR46H07 possessed the fewest secretion system structural proteins (12 and 11, respectively), while PFR46H08 and PFR46H09 had 18 each. P. fluorescens-PFR46H09, which showed the highest antimicrobial effect, had nine tss-T6SS structural proteins compared to only four in the other three strains.

Promoting Strawberry (Fragaria × ananassa) Stress Resistance, Growth, and Yield Using Native Bacterial Biostimulants

Strawberry production is challenged by several abiotic and biotic stresses, such as drought, soil salinity, and the angular leaf spot (ALS) disease caused by Xanthomonas fragariae. In recent decades, the development of commercial products containing combinations of different Plant-Growth-Promoting (PGP) microorganisms has been one of the main focuses of agricultural research. However, their results are often erratic depending on crop species, environmental conditions, and competition among the different strains or indigenous plant microbiota. The use of beneficial microorganisms selected from the crop-specific microbiota may help overcome this limitation, promoting their utilization for sustainable agriculture. The culturable bacteriota of strawberry plants was screened to identify PGP activities in vitro. Bacterial isolates were tested in vivo on strawberry plants in both optimal and stress (X. fragariae infection or salinity) conditions, allowing the selection of strains of Pseudomonas fluorescens, Stenotrophomonas rhizophila, and Agrobacterium rubi whose application showed a significant increase in plant growth and fruit production (up to seven-fold), even under stress conditions, and the ability to control ALS by over 50%. Potential synergistic effects among PGP isolates were tested by coordinated inoculation. However, plant growth and fruit quality were not promoted, except for fruit weight and size, by coordinate inoculation in comparison to m23 and m27 single-strain treatment.

Palliating Salt Stress in Mustard through Plant-Growth-Promoting Rhizobacteria: Regulation of Secondary Metabolites, Osmolytes, Antioxidative Enzymes and Stress Ethylene.

The severity of salt stress is alarming for crop growth and production and it threatens food security. Strategies employed for the reduction in stress are not always eco-friendly or sustainable. Plant-growth-promoting rhizobacteria (PGPR) could provide an alternative sustainable stress reduction strategy owning to its role in various metabolic processes. In this study, we have used two strains of PGPR, Pseudomonas fluorescens (NAIMCC-B-00340) and Azotobacter chroococcum Beijerinck 1901 (MCC 2351), either singly or in combination, and studied their effect in the amelioration of salt toxicity in mustard cultivar Pusa Jagannath via its influence on plants' antioxidants' metabolism, photosynthesis and growth. Individually, the impact of Pseudomonas fluorescens was better in reducing stress ethylene, oxidative stress, photosynthesis and growth but maximal alleviation was observed with their combined application. MDA and H2O2 content as indicator of oxidative stress decreased by 27.86% and 45.18% and osmolytes content (proline and glycine-betaine) increased by 38.8% and 26.3%, respectively, while antioxidative enzymes (SOD, CAT, APX and GR) increased by 58.40, 25.65, 81.081 and 55.914%, respectively, over salt-treated plants through the application of Pseudomonas fluorescens. The combined application maximally resulted in more cell viability and less damage to the leaf with lesser superoxide generation due to higher antioxidative enzymes and reduced glutathione formation (GSH). Considering the obtained results, we can supplement the PGPR in combination to plants subjected to salt stress, prevent photosynthetic and growth reduction, and increase the yield of plants.

Antagonistic Activity of Pseudomonas fluorescens Strain X1 Against Different Fusaria and it’s In Vivo Analysis Against Fusarium udum Infected Pigeon Pea

A plant growth-promoting rhizobacterial strain, Pseudomonas fluorescens X1 isolated from the garden soil was employed for antagonistic activity against different species of fusaria. Strain X1 inhibited four different fusaria (Fusarium moniliforme, Fusarium oxysporum, Fusarium semitectum and Fusarium udum) in dual culture plate assay, and in broth culture using cell-free culture filtrate. Scanning electron microscopic (SEM) analysis revealed deformation and shrinkage in mycelia of fusaria after treatment with strain X1. Confocal micrographs showed degeneration of nuclei inside the cells of fusaria for the same effect. Strain X1 exhibited maximum antifungal activity, when it was grown in nutrient broth yeast (NBY) medium amended with 1mM NH4MoO4 and 1% glucose. The antifungal extracts eluted from thin-layer chromatography (TLC) followed by high performance liquid chromatography (HPLC) showed two fractions active against different fusaria. Liquid chromatography-mass spectrometry (LCMS) analysis of the two fractions 1 and 2 corresponded to molecular ions at m/z 177.16 and m/z 177.09, respectively. Infra-red (IR) analysis showed five similar absorption bands in both the fractions analysed. In vivo analysis of strain X1 alone and along with fungicide inhibited the growth of F. udum and improved the biomass and growth of pigeon pea. These results indicated that strain X1 could be possibly used as a biocontrol agent to inhibit the growth of soil-borne diseases of different fusaria including F. udum that causes wilting in pigeon pea.

Effects of Bacterial and Fungal Inocula on Biomass, Ecophysiology, and Uptake of Metals of Alyssoides utriculata (L.) Medik.

The inoculation of plants with plant-growth-promoting microorganisms (PGPM) (i.e., bacterial and fungal strains) is an emerging approach that helps plants cope with abiotic and biotic stresses. However, knowledge regarding their synergic effects on plants growing in metal-rich soils is limited. Consequently, the aim of this study was to investigate the biomass, ecophysiology, and metal accumulation of the facultative Ni-hyperaccumulator Alyssoides utriculata (L.) Medik. inoculated with single or mixed plant-growth-promoting (PGP) bacterial strain Pseudomonas fluorescens Migula 1895 (SERP1) and PGP fungal strain Penicillium ochrochloron Biourge (SERP03 S) on native serpentine soil (n = 20 for each treatment). Photosynthetic efficiency (Fv/Fm) and performance indicators (PI) had the same trends with no significant differences among groups, with Fv/Fms > 1 and PI up to 12. However, the aboveground biomass increased 4-5-fold for single and mixed inoculated plants. The aboveground/belowground dry biomass ratio was higher for plants inoculated with fungi (30), mixed (21), and bacteria (17). The ICP-MS highlighted that single and mixed inocula were able to double the aboveground biomass' P content. Mn metal accumulation significantly increased with both single and mixed PGP inocula, and Zn accumulation increased only with single PGP inocula, whereas Cu accumulation increased twofold only with mixed PGP inocula, but with a low content. Only Ni metal accumulation approached the hyperaccumulation level (Ni > 1000 mg/kg DW) with all treatments. This study demonstrated the ability of selected single and combined PGP strains to significantly increase plant biomass and plant tolerance of metals present in the substrate, resulting in a higher capacity for Ni accumulation in shoots.

Efficacy of Bio-Agents and Varietal Screening for Resistance to Alternaria Altarnata Inciting Leaf Blight on Chrysanthemum

In the present investigation, Trichoderma harzianum, T. koningii, T. longibrachiatum, Bacillus subtilis and three strains of Pseudomonas fluorescens were tested in vitro for their efficacy against the chrysanthemum leaf blight causing Alternaria alternata. A screening study was also conducted to identify resistant chrysanthemum sources against the leaf blight disease caused by A. alternata. Amongst the bio-agents investigated, Trichoderma koningii, T. harzianum and T. longibrachiatum completely inhibited the mycelium of A. alternata. P. fluorescens strain- 2 (45.33) and Bacillus subtilis (43.71%) showed the least inhibition. Only one (cv. Red Star) of the ten chrysanthemum varieties tested in vivo for resistance to Alternaria alternata (Red Star) demonstrated a resistant reaction with a disease incidence of 4.90%. Yellow, Multiflora, and Manga red were moderately resistant, with disease incidence ranging from 17.03 to 19.20%. Oliveria white and Charlie were very susceptible to the disease, with disease incidence rates of 55.20 and 76.70 percent, respectively.

Evaluation of the motility and capacity of biofilm production by Pseudomonas fluorescens strains in residual milk.

Pseudomonas fluorescens is known to have the ability to adhere and produce biofilm. The formation of biofilms is enhanced by cellular motility, particularly when mediated by flagella. Biofilm formed on surfaces such as those used for food production act as points of contamination, releasing pathogenic or deteriorating microorganisms and compromising the quality of products. We assessed two strains of Pseudomonas fluorescens PL5.4 and PL7.1, sampled from raw, chilled, buffalo milk, which was obtained from a dairy farm. Twitching and swarming motility assays were performed, in addition to the biofilm production evaluations at a temperature of 7 °C. Regarding the motility assays, only the PL5.4 strain scored positive for the swarming assay. On microplates, both strains presented themselves as strong biofilm producers at 7 °C. The PL5.4 strain was also able to form biofilm on a stainless steel structure and maintain this structure for up to 72 hours at refrigeration. The Pseudomonas fluorescens PL5.4 isolate was identified on the basis of a 99% sequence identity with Pseudomonas fluorescens A506, a strain used as a biocontrol in agriculture. Biofilm-forming bacteria, when adapted to low temperatures, become a constant source of contamination, damaging the production, quality, safety and shelf-life of products.

Production of biological pest control agents on hydrolysates of switchgrass

Recently, biological products have outpaced chemicals for pest control because they are more compatible with the environment, and they offer multiple modes of action not easily overcome by resistance mechanisms. Pseudomonas spp. have been developed as biocontrol agents (BCAs) to replace chemicals no longer effective against dry rot disease and other maladies of postharvest potatoes, including sprouting, late-blight, pink rot, and Pythium leak. It is proposed that Pseudomonas spp., which can use the diverse carbon sources in lignocellulosic hydrolysates, have aptitude as valuable coproducts compatible with lignocellulosic biorefining. Our results showed that three Pseudomonas fluorescens strains could rapidly consume all switchgrass hydrolysate sugars, including the pentoses, and also acetic acid, furfural, and hydroxymethylfurfural. If pH was controlled near neutral and sugar concentrations were kept near 10 g/L to prevent osmotic inhibition, high yields of efficacious BCAs could be obtained on xylose- or glucose-rich fractions and unfractionated switchgrass hydrolysates.