Cultivable and metagenomic approach to study the combined impact of nanogypsum and Pseudomonas taiwanensis on maize plant health and its rhizospheric microbiome.

In the present study we examined the effect of nanogypsum and Pseudomonas taiwanensis strain BCRC 17751on plant and soil health using conventional and metagenomics approaches. Soil physicochemical properties and agronomical parameters of maize plants were reported to be better when applied with nanogypsum and bacterial inoculum together. When compared to control a significant increase in total bacterial counts, nitrogen, phosphorus, potassium (NPK) solubilizing bacterial population and soil enzyme activities (fluorescein diacetate, alkaline phosphatase, dehydrogenase, ß-glucosidase, arylesterase and amylase) was reported in treatments. The metagenomics studies revealed dominance of beneficial bacteria such as Proteobacteria, Bacteriodetes, Planctomycetes, Acidobacteria and Nitrospirae in treated soil. On the other hand some novel bacterial diversity was also reported in treated soil which was evident from presence of taxonomically unclassified sequences. Hence, it can be concluded that combined application of nanogypsum and Pseudomonas taiwanensis in maize help in improving the structure and function of soil which affects the plant health without causing any toxic effect. However, in situ validation of the prescribed treatment is required under field conditions on different crops in order to give maximum benefits to the farmers and the environment.

Evaluation of Pseudomonas sp. for its multifarious plant growth promoting potential and its ability to alleviate biotic and abiotic stress in tomato (Solanum lycopersicum) plants.

1-Aminocyclopropane-1-carboxylate (ACC) deaminase activity is one of the most beneficial traits of plant growth promoting (PGP) rhizobacteria responsible for protecting the plants from detrimental effects of abiotic and biotic stress. The strain S3 with ACC deaminase activity (724.56 nmol α-ketobutyrate mg-1 protein hr-1) was isolated from rhizospheric soil of turmeric (Curcuma longa), a medicinal plant, growing in Motihari district of Indian state, Bihar. The halotolerant strain S3, exhibited optimum growth at 8% (w/v) NaCl. It also exhibited multiple PGP traits such as indole acetic acid production (37.71 µg mL-1), phosphate solubilization (69.68 mg L-1), siderophore, hydrocyanic acid (HCN) and ammonia production as well as revealed antagonism against Rhizoctonia solani. The potential of isolated strain to alleviate salinity stress in tomato plants was investigated through pots trials by inoculating strain S3 through-seed bacterization, soil drenching, root dipping as well as seed treatment + soil drenching. The strain S3 inoculated through seed treatment and soil drenching method led to improved morphological attributes (root/shoot length, root/shoot fresh weight and root/shoot dry weight), photosynthetic pigment content, increased accumulation of osmolytes (proline and total soluble sugar), enhanced activities of antioxidants (Catalase and Peroxidase) and phenolic content in salt stressed tomato plants. The biochemical characterisation, FAMEs analysis and 16S rRNA gene sequencing revealed that strain S3 belongs to the genus Pseudomonas. The overall findings of the study revealed that Pseudomonas sp. strain S3 can be explored as an effective plant growth promoter which stimulate growth and improve resilience in tomato plants under saline condition.

Characterization of methyl-accepting chemotaxis proteins (MCPs) for amino acids in plant-growth-promoting rhizobacterium Pseudomonas protegens CHA0 and enhancement of amino acid chemotaxis by MCP genes overexpression.

Pseudomonas protegens CHA0, known as plant-growth-promoting rhizobacterium, showed positive chemotactic responses toward proteinaceous L-amino acids. Genomic analysis revealed that P. protegens CHA0 possesses four putative chemoreceptors for amino acids (designated CtaA, CtaB, CtaC, and CtaD, respectively). Pseudomonas aeruginosa PCT2, a mutant defective in chemotaxis to amino acids, harboring a plasmid containing each of ctaA, ctaB, ctaC, and ctaD showed chemotactic responses to 20, 4, 4, and 11 types of amino acids, respectively. To enhance chemotaxis toward amino acids, we introduced the plasmids containing ctaA, ctaB, ctaC, or ctaD into P. protegens CHA0. By overexpression of the genes, we succeeded in enhancing chemotaxis toward more than half of the tested ligands. However, unexpectedly, the P. protegens CHA0 transformants showed unchanged or decreased responses to some amino acids when compared to wild-type CHA0. We speculate that alternation of expression of a chemoreceptor may affect the abundance of other chemoreceptors. ABBREVIATIONS: cDNA: complementary DNA; LBD: ligand-binding domain; MCP: methyl-accepting chemotaxis protein; PDC: PhoQ/DcuS/CitA; PGPR: plant-growth-promoting rhizobacteria; qRT-PCR: quantitative reverse transcription PCR.

Development of a defined compost system for the study of plant-microbe interactions.

Plant growth promoting rhizobacteria can improve plant health by providing enhanced nutrition, disease suppression and abiotic stress resistance, and have potential to contribute to sustainable agriculture. We have developed a sphagnum peat-based compost platform for investigating plant-microbe interactions. The chemical, physical and biological status of the system can be manipulated to understand the relative importance of these factors for plant health, demonstrated using three case studies: 1. Nutrient depleted compost retained its structure, but plants grown in this medium were severely stunted in growth due to removal of essential soluble nutrients - particularly, nitrogen, phosphorus and potassium. Compost nutrient status was replenished with the addition of selected soluble nutrients, validated by plant biomass; 2. When comparing milled and unmilled compost, we found nutrient status to be more important than matrix structure for plant growth; 3. In compost deficient in soluble P, supplemented with an insoluble inorganic form of P (Ca3(PO4)2), application of a phosphate solubilising Pseudomonas strain to plant roots provides a significant growth boost when compared with a Pseudomonas strain incapable of solubilising Ca3(PO4)2. Our findings show that the compost system can be manipulated to impose biotic and abiotic stresses for testing how microbial inoculants influence plant growth.

Inoculation of pqqE gene inhabiting Pantoea and Pseudomonas strains improves the growth and grain yield of wheat with a reduced amount of chemical fertilizer.

OBJECTIVE: The present study was performed to examine the role of pqqE inhabiting rhizobacteria in organic acid production and relationship of the organic acids with phosphate solubilization by the bacteria in vitro as well as in vivo. METHODS AND RESULTS: The pqqE gene was PCR amplified and sequenced in genomic DNA of Pantoea sp. WP-5 and Pseudomonas sp. NN-4. Nucleotide sequence obtained from WP-5 and NN-4 showed maximum sequence similarity (88 and 89%, respectively) with the pqqE gene of Pseudomonas fluorescens strain CMR12a (KM251420). Deduced amino acid sequence from pqqE gene of Pseudomonas sp. NN-4 and Pantoea sp. WP-5 showed 75 and 93% similarity, respectively, with protein pyrroloquinoline quinone. Phosphate solubilization and acid production assay were quantified on spectrophotometer and high-profile liquid chromatograph, respectively, by each bacterial strain. Both strains produced organic acids such as acetic, citric, gluconic, succinic and malic acid and lowered the pH of Pikovskaya broth medium under laboratory conditions. Phosphate solubilization by Pantoea sp. WP-5 was 311 ± 4 and 204 ± 3 µg ml-1 in the culture medium supplemented with glucose and sucrose as carbon source, respectively. Pseudomonas sp. NN-4 solubilized 176 ± 3 and 298 ± 5 µg ml-1 phosphate in Pikovskaya broth medium under similar conditions. In field experiments conducted during two consecutive years, the concentration of acetic acid and gluconic acid was higher in root exudates of plants treated with Pantoea sp. WP-5 at 30% reduced doses of nitrogen (N)- and phosphorus (P)-based chemical fertilizers as compared to non-inoculated plants. Values of chlorophyll contents, crop growth rate, leaf area index, straw yield and P contents were recorded higher in plants inoculated with Pantoea sp. WP-5 and Pseudomonas sp. NN-4 as compared to non-inoculated control. Grain yield was increased by 10-12% due to inoculation with Pantoea sp. WP-5 and Pseudomonas sp. NN-4 over non-inoculated control in the field experiments. CONCLUSIONS: These results lead to the conclusions that the rhizobacteria inhabiting pqqE gene produced organic acids and solubilized the phosphate in vitro. On inoculation to wheat plants in field experiments, these strains produced the organic acids, solubilized the phosphate, and improved the P uptake and productivity of wheat. SIGNIFICANCE AND IMPACT OF THE STUDY: The Pantoea sp. WP-5 and Pseudomonas sp. NN-4 are the potential candidates for inoculation to wheat as phosphate solubilizer even with reduced chemical fertilizer dose. The inoculation of the strains may enhance grain yield and net income of the farmer even with less chemical fertilizer application. This practice will be helpfull inminimizing environmental pollution.

Bacterial communities of plum phyllosphere and characterization of indigenous antagonistic Bacillus thuringiensis R3/3 isolate.

AIMS: The characterization of bacterial communities diversity on four local plum cultivars in two phenological stages using culture-dependent and culture-independent methods and screening among culturable plum community for indigenous bacteria active against phytopathogens. METHODS AND RESULTS: The bacterial communities associated with leaves and fruits of four local Serbian plum cultivars (Pozegaca, Ranka, Cacanska Lepotica and Cacanska Rodna) were investigated in two phenological stages during early (May) and late (July) fruit maturation. Metagenomic approach revealed Methylobacterium, Sphingomonas and Hymenobacter as dominant genera. The most frequently isolated representatives with cultivable approach were pseudomonads with Pseudomonas syringae and Pseudomonas graminis, the most likely resident species of plum community. Antagonistic Bacillus thuringiensis R3/3 isolate from plum phyllosphere had ability to produce exoenzymes, reduce the growth of phytopathogenic bacteria in co-culture environment and show quorum quenching activity. CONCLUSIONS: Plum cultivar and growth season contribute to the structure of the bacterial community associated with plum. Plum phyllosphere is good source of antagonists effective against phytopathogens. SIGNIFICANCE AND IMPACT OF STUDY: Knowledge of bacterial communities on plum will have an impact on studies related to phyllosphere ecology and biocontrol. The indigenous antagonistic isolate, B. thuringiensis R3/3, from plum could be further investigated for its potential use in biological control of plum diseases.

Metabolic and Genomic Traits of Phytobeneficial Phenazine-Producing Pseudomonas spp. Are Linked to Rhizosphere Colonization in Arabidopsis thaliana and Solanum tuberosum.

Bacterial rhizosphere colonization is critical for phytobeneficial rhizobacteria such as phenazine-producing Pseudomonas spp. To better understand this colonization process, potential metabolic and genomic determinants required for rhizosphere colonization were identified using a collection of 60 phenazine-producing Pseudomonas strains isolated from multiple plant species and representative of the worldwide diversity. Arabidopsis thaliana and Solanum tuberosum (potato) were used as host plants. Bacterial rhizosphere colonization was measured by quantitative PCR using a newly designed primer pair and TaqMan probe targeting a conserved region of the phenazine biosynthetic operon. The metabolic abilities of the strains were assessed on 758 substrates using Biolog phenotype microarray technology. These data, along with available genomic sequences for all strains, were analyzed in light of rhizosphere colonization. Strains belonging to the P. chlororaphis subgroup colonized the rhizospheres of both plants more efficiently than strains belonging to the P. fluorescens subgroup. Metabolic results indicated that the ability to use amines and amino acids was associated with an increase in rhizosphere colonization capability in A. thaliana and/or in S. tuberosum The presence of multiple genetic determinants in the genomes of the different strains involved in catabolic pathways and plant-microbe and microbe-microbe interactions correlated with increased or decreased rhizosphere colonization capabilities in both plants. These results suggest that the metabolic and genomic traits found in different phenazine-producing Pseudomonas strains reflect their rhizosphere competence in A. thaliana and S. tuberosum Interestingly, most of these traits are associated with similar rhizosphere colonizing capabilities in both plant species.IMPORTANCE Rhizosphere colonization is crucial for plant growth promotion and biocontrol by antibiotic-producing Pseudomonas spp. This colonization process relies on different bacterial determinants which partly remain to be uncovered. In this study, we combined a metabolic and a genomic approach to decipher new rhizosphere colonization determinants which could improve our understanding of this process in Pseudomonas spp. Using 60 distinct strains of phenazine-producing Pseudomonas spp., we show that rhizosphere colonization abilities correlated with both metabolic and genomic traits when these bacteria were inoculated on two distant plants, Arabidopsis thaliana and Solanum tuberosum Key metabolic and genomic determinants presumably required for efficient colonization of both plant species were identified. Upon further validation, these targets could lead to the development of simple screening tests to rapidly identify efficient rhizosphere colonizers.

Effects of plant growth-promoting bacteria on EDTA-assisted phytostabilization of heavy metals in a contaminated calcareous soil.

The objective of this research was to determine the combined effects of ethylenediaminetetraacetic acid (EDTA) and plant growth-promoting rhizobacteria (PGPR) on the phytostabilization of Cd, Pb, and Zn by corn and chemical fractionation of these elements in soil. Three heavy metal-resistant bacteria (P18, P15, and P19) were selected. All strains, belonging to the fluorescent pseudomonads, exhibited plant growth-promoting properties, including phosphorus solubilization and production of siderophore, indole acetic acid, and 1-aminocyclopropane-1-carboxylic acid deaminase. Applying EDTA individually or in combination with bacterial strains (P18 and P15) significantly increased shoot biomass. The highest dry shoot biomass was recorded in the combined treatment of EDTA and P15-inoculated pots. Application of EDTA in PGPR-inoculated pots increased concentrations of heavy metals in corn shoots and roots compared to the control. The highest concentration of Zn in corn root and shoot was observed in P15 + EDTA treatment, which were 2.0-fold and 1.3-fold higher than those in the untreated soil. Results of chemical speciation showed that the co-application of EDTA and fluorescent pseudomonads strains increased the bioavailability of Zn, Pb, and Cd by their redistribution from less soluble fractions to water-soluble forms. It was concluded that bacterial inoculation could improve the efficiency of EDTA in phytostabilization of heavy metals from multi-metal contaminated soils.

Development of plant-microbe phytoremediation system for petroleum hydrocarbon degradation: An insight from alkb gene expression and phytotoxicity analysis.

Aim of present work was to assess in-planta association potential of isolated endophytic bacterial strain Pseudomonas sp. (J10) (KY608252) with two cultivars of Lolium perenne L. (small & jumbo) and Arabidopsis thaliana L. for total petroleum hydrocarbon (TPH) degradation, alkane monooxygenase (alkb) gene expression and phytotoxicity analysis. A plant-microbe phytoremediation system was established to investigate the bacteria's ability to colonize the plant body and quantification of alkb gene to help withstand TPH stress in soil as well as in hydroponics. A real-time PCR method was developed to analyze bacterial colonization and survival within the plant body. Analysis revealed that J10 efficiently colonized all the tested plant species and expressed alkb gene under hydrocarbon stress ranging between 3.7 × 102-3.9 × 106 in A. thaliana and L. perenne (small), respectively. The colonization was more pronounced in soil as compared to hydroponic system. J10 inoculation reduced phytotoxicity and suggested that inoculation had a positive effect on plant growth under stress conditions as compared to control. L. perenne (small) showed significant TPH removal efficiency (45.6%) followed by L. perenne jumbo (24.5%) and A. thaliana (6.2%). In hydroponics, L. perenne (small) degraded about 28.2% TPH followed by L. perenne (jumbo) as 24.4%. Potential of the indigenously isolated plant endophytes may be exploited further for phytoremediation efficiency and industrial applications.

Pseudomonas species isolated from tobacco seed promote root growth and reduce lead contents in Nicotiana tobacum K326.

Endophytic bacteria are generally helpful for plant growth and protection. We isolated from tobacco seeds three Pseudomonas strains (K03, Y04, and N05) that could produce siderophores, indole-3-acetic acid, and 1-aminocyclopropane-1-carboxylate deaminase, fix nitrogen, dissolve phosphorus and potassium, and tolerate heavy metals. In pot experiments, the three isolated strains significantly promoted root growth and increased the root enzyme activity in Nicotiana tobacum K326. Furthermore, bacterial inoculations increased the proportion of residual lead (Pb) by 8.36%-51.63% and decreased the total Pb content by 3.28%-6.38% in the contaminated soil during tobacco planting, compared with uninoculated soils. An effective decrease in Pb content was also found in tobacco leaves with bacterial inoculations. K03 inoculation decreased the Pb content in the upper leaves by 49.80%, and Y04 inoculation had the best effect, decreasing the Pb content in the middle leaves by 70.12%. Additionally, soil pH and root activity had significant effects on transformation and translocation of Pb. The study suggested that in response to Pb pollution in soil, a reasonable application of endophytes (e.g., Pseudomonas) might be a promising approach in promoting tobacco growth and reducing Pb content in tobacco, while simultaneously enhancing Pb stabilization in soils.

Pseudomonas sp. AF-54 containing multiple plant beneficial traits acts as growth enhancer of Helianthus annuus L. under reduced fertilizer input.

Plant growth promoting rhizobacteria (PGPR) are capable to increase the growth and yield of crops in eco-friendly and sustainable manner. To evaluate the response of sunflower towards inoculation with PGPR, a sunflower root associated bacterium AF-54 isolated from Diyar Gali Himalayan Mountain region, Azad Jammu and Kashmir (AJK), identified as Pseudomonas sp. by 16S rRNA sequence analysis and was characterized using polyphasic approach. The bacterium produced 23.9 µgmL-1 indole-3-acetic acid in tryptophan-supplemented medium, showed 44.28 nmoles mg-1 protein h-1 nitrogenase activity through acetylene reduction assay and released 48.80 µg mL-1 insoluble phosphorus in Pikovskaya's broth. During P-solubilization, the pH of the Pikovskaya's medium decreased from 7 to 3.04 due to the production of acetic acid, malic acid and gluconic acid. Pseudomonas sp. AF-54 showed metabolic versatility by utilizing 79 carbon sources from BIOLOG GN2 plates and resistance to many antibiotics. Furthermore, it inhibited the growth of Fusarium oxysporum in dual culture assay. To evaluate the plant-inoculation response, series of experiments conducted in hydroponic, sterilized soil and fields at AJK, and Faisalabad where inoculated plants with reduced fertilizer showed a significant increase in growth, yield, oil contents and achene NP uptake as compared to non-inoculated control. AF-54 showed extensive root colonization in sterilized and non-sterile conditions documented through yfp-labeling and fluorescent in situ hybridization coupled with confocal laser scanning microscopy. This study concludes that the Pseudomonas sp. strain AF-54 containing multiple plant growth promoting traits can be a potential candidate for biofertilizer production to enhance sunflower crop yield with reduced application of chemical (NP) fertilizers.

Mn accumulation in a submerged plant Egeria densa (Hydrocharitaceae) is mediated by epiphytic bacteria.

Many aquatic plants act as biosorbents, removing and recovering metals from the environment. To assess the biosorbent activity of Egeria densa, a submerged freshwater macrophyte, plants were collected monthly from a circular drainage area in Lake Biwa basin and the Mn concentrations of the plants were analysed. Mn concentrations in these plants were generally above those of terrestrial hyperaccumulators, and were markedly higher in spring and summer than in autumn. Mn concentrations were much lower in plants incubated in hydroponic medium at various pH levels with and without Mn supplementation than in field-collected plants. The precipitation of Mn oxides on the leaves was determined by variable pressure scanning electron microscopy-energy dispersive X-ray analysis and Leucoberbelin blue staining. Several strains of epiphytic bacteria were isolated from the field-collected E. densa plants, with many of these strains, including those of the genera Acidovorax, Comamonas, Pseudomonas and Rhizobium, found to have Mn-oxidizing activity. High Mn concentrations in E. densa were mediated by the production of biogenic Mn oxide in biofilms on leaf surfaces. These findings provide new insights into plant epidermal bacterial flora that affect metal accumulation in plants and suggest that these aquatic plants may have use in Mn phytomining.

Microbial cooperation in the rhizosphere improves liquorice growth under salt stress.

Liquorice (Glycyrrhiza uralensis Fisch.) is one of the most widely used plants in food production, and it can also be used as an herbal medicine or for reclamation of salt-affected soils. Under salt stress, inhibition of plant growth, nutrient acquisition and symbiotic interactions between the medicinal legume liquorice and rhizobia have been observed. We recently evaluated the interactions between rhizobia and root-colonizing Pseudomonas in liquorice grown in potting soil and observed increased plant biomass, nodule numbers and nitrogen content after combined inoculation compared to plants inoculated with Mesorhizobium alone. Several beneficial effects of microbes on plants have been reported; studies examining the interactions between symbiotic bacteria and root-colonizing Pseudomonas strains under natural saline soil conditions are important, especially in areas where a hindrance of nutrients and niches in the rhizosphere are high. Here, we summarize our recent observations regarding the combined application of rhizobia and Pseudomonas on the growth and nutrient uptake of liquorice as well as the salt stress tolerance mechanisms of liquorice by a mutualistic interaction with microbes. Our observations indicate that microbes living in the rhizosphere of liquorice can form a mutualistic association and coordinate their involvement in plant adaptations to stress tolerance. These results support the development of combined inoculants for improving plant growth and the symbiotic performance of legumes under hostile conditions.

Phosphatidylcholine affects the secretion of the alkaline phosphatase PhoA in Pseudomonas strains.

Pseudomonas aeruginosa ATCC 27853 and Pseudomonas sp. 593 use the phosphatidylcholine synthase pathway (Pcs-pathway) for the biosynthesis of phosphatidylcholine (PC). Both bacterial strains contain the phoA and lapA genes encoding alkaline phosphatases (ALP) and display strong ALP activities. The PhoA and LapA enzymes are thought to be independently secreted via the Xcp and Hxc type II secretion system (T2SS) subtypes, in which the Hxc system may act as a complementary mechanism when the Xcp pathway becomes limiting. Inactivation of the pcs gene in both bacteria abolished PC synthesis and resulted in approximately 50% less ALP activity in the cell-free culture. Analysis by western blotting showed that LapA protein content in the wild type and the pcs- mutant was unchanged in the cytoplasmic, periplasmic or extracellular protein fractions. In contrast, the PhoA protein in the pcs- mutant was less prevalent among extracellular proteins but was more abundant in the periplasmic protein fraction compared to the wild type. Semi- quantitative reverse transcriptase PCR showed that phoA, lapA and 12 xcp genes were equally expressed at the transcriptional level in both the wild types and the pcs- mutants. Our results demonstrate that the absence of PC in bacterial membrane phospholipids does not interfere with the transcription of the phoA and lapA genes but primarily affects the export of PhoA from the cytoplasm to the extracellular environment via the Xcp T2SS.

Biocontrol of the Potato Blackleg and Soft Rot Diseases Caused by Dickeya dianthicola.

Development of protection tools targeting Dickeya species is an important issue in the potato production. Here, we present the identification and the characterization of novel biocontrol agents. Successive screenings of 10,000 bacterial isolates led us to retain 58 strains that exhibited growth inhibition properties against several Dickeya sp. and/or Pectobacterium sp. pathogens. Most of them belonged to the Pseudomonas and Bacillus genera. In vitro assays revealed a fitness decrease of the tested Dickeya sp. and Pectobacterium sp. pathogens in the presence of the biocontrol agents. In addition, four independent greenhouse assays performed to evaluate the biocontrol bacteria effect on potato plants artificially contaminated with Dickeya dianthicola revealed that a mix of three biocontrol agents, namely, Pseudomonas putida PA14H7 and Pseudomonas fluorescens PA3G8 and PA4C2, repeatedly decreased the severity of blackleg symptoms as well as the transmission of D. dianthicola to the tuber progeny. This work highlights the use of a combination of biocontrol strains as a potential strategy to limit the soft rot and blackleg diseases caused by D. dianthicola on potato plants and tubers.

Shortening the course of antibiotic treatment in the intensive care unit.

Effective antimicrobial stewardship is an increasingly important concern for healthcare providers globally. Antibiotics are frequently prescribed for patients who develop sepsis in the intensive care unit and traditionally courses are prolonged, with uncertain benefit and probable harm. There is little evidence to support many guidelines recommending between 10 and 14 days, and a number of studies suggest substantially shorter courses of less than 7 days may suffice. Safely reducing course length is likely to depend on a number of preconditions, including thorough eradication of any septic foci; optimization of serum antibiotic concentrations, particularly when there is physiological derangement; and use of novel biomarkers such as procalcitonin. The critical care environment is well suited to this aim as patients are closely monitored. With these measures in place, it is reasonable to believe short antibiotic courses can safely be used for the majority of intensive care infections.

The induction of Ethylene response factor 3 (ERF3) in potato as a result of co-inoculation with Pseudomonas sp. R41805 and Rhizophagus irregularis MUCL 41833 - a possible role in plant defense.

Colonization of plant rhizosphere/roots by beneficial microorganisms (e.g. plant growth promoting rhizobacteria - PGPR, arbuscular mycorrhizal fungi - AMF) confers broad-spectrum resistance to virulent pathogens and is known as induced systemic resistance (ISR) and mycorrhizal-induced resistance (MIR). ISR or MIR, an indirect mechanism for biocontrol, involves complex signaling networks that are regulated by several plant hormones, the most important of which are salicylic acid (SA), jasmonic acid (JA) and ethylene (ET). In the present study, we investigated if inoculation of potato plantlets with an AMF (Rhizophagus irregularis MUCL 41833) and a PGPR (Pseudomonas sp R41805) either alone or in combination, could elicit host defense response genes in the presence or absence of Rhizoctonia Solani EC-1, a major potato pathogen. RT-qPCR revealed the significant expression of ethylene response factor 3 (EFR3) in mycorrhized potato plantlets inoculated with Pseudomonas sp R41805 and also in mycorrhized potato plantlets inoculated with Pseudomonas sp R41805 and challenged with R. solani. The significance of ethylene response factors (ERFs) in pathogen defense has been well documented in the literature. The results of the present study suggest that the dual inoculation of potato with PGPR and AMF may play a part in the activation of plant systemic defense systems via ERF3.

Bioenergetics and the role of soluble cytochromes C for alkaline adaptation in gram-negative alkaliphilic Pseudomonas.

Very few studies have been conducted on alkaline adaptation of Gram-negative alkaliphiles. The reversed difference of H(+) concentration across the membrane will make energy production considerably difficult for Gram-negative as well as Gram-positive bacteria. Cells of the alkaliphilic Gram-negative bacterium Pseudomonas alcaliphila AL15-21(T) grown at pH 10 under low-aeration intensity have a soluble cytochrome c content that is 3.6-fold higher than that of the cells grown at pH 7 under high-aeration intensity. Cytochrome c-552 content was higher (64% in all soluble cytochromes c) than those of cytochrome c-554 and cytochrome c-551. In the cytochrome c-552-dificient mutant grown at pH 10 under low-aeration intensity showed a marked decrease in µ max⁡ [h(-1)] (40%) and maximum cell turbidity (25%) relative to those of the wild type. Considering the high electron-retaining abilities of the three soluble cytochromes c, the deteriorations in the growth of the cytochrome c-552-deficient mutant could be caused by the soluble cytochromes c acting as electron storages in the periplasmic space of the bacterium. These electron-retaining cytochromes c may play a role as electron and H(+) condenser, which facilitate terminal oxidation at high pH under air-limited conditions, which is difficult to respire owing to less oxygen and less H(+).

AM fungi and PGP pseudomonads increase flowering, fruit production, and vitamin content in strawberry grown at low nitrogen and phosphorus levels.

There is increasing interest in the quality of crops because of the implications concerning health, economic revenue, and food quality. Here we tested if inoculation with a mixture of arbuscular mycorrhizal fungi (AMF) and/or two strains of plant growth-promoting bacteria (PGPB), in conditions of reduced chemical inputs, affects the quality and yield of strawberry fruits. Fruit quality was measured by concentrations of soluble sugars, various organic acids, and two vitamins (ascorbic and folic acid). Co-inoculation with the AMF and each of the two PGPB resulted in increased flower and fruit production, larger fruit size, and higher concentrations of sugars and ascorbic and folic acid in comparison with fruits of uninoculated plants. These results provide further evidence that rhizospheric microorganisms affect fruit crop quality and show that they do so even under conditions of reduced chemical fertilization and can thus be exploited for sustainable agriculture.

PPZPMs--a novel group of cyclic lipodepsipeptides produced by the Phytophthora alni associated strain Pseudomonas sp. JX090307--the missing link between the viscosin and amphisin group.

The closely related to the Pseudomonas orientalis strain Pseudomonas sp. acc. no. JX090307 was isolated from hyphae of the phytopathogenic oomycete Phytophthora alni spp. alni. In in-vitro antagonistic tests, the living bacterium JX090307 and its cell extract showed antibiosis activity against different fungal pathogens of forest tree species, particularly against Verticillium dahliae and some strains of P. alni ssp. alni. Investigating the cell extract of JX090307 by means of LC-ESI-Q-TOF-MS and -MS/MS techniques, more than 30 cyclic lipodepsipeptids (CLPs) were found. 24 of them belong to a novel group of CLPs named PPZPM. The cyclic lipodepsidecapeptides PPZPMs are composed of a beta-hydroxy fatty acid linked to a peptide part comprising 10 amino acids, where 8 of them are organized in a cyclic structure. PPZPMs differ from members of the Viscosin and Amphisin group by the number of amino acids forming the cyclic structure. The two main components, PPZPM-1a and PPZPM-2a, were investigated additionally by means of NMR spectroscopy.