Pseudomonas Graminis Research Articles

Pseudomonas petrae sp. nov. isolated from regolith samples in Antarctica

A polyphasic taxonomic approach was used to characterize the four strains P2653T, P2652, P2498, and P2647, isolated from Antarctic regolith samples. Initial genotype screening performed by PCR fingerprinting based on repetitive sequences showed that the isolates studied formed a coherent cluster separated from the other Pseudomonas species. Identification results based on 16S rRNA gene sequences showed the highest sequence similarity with Pseudomonas graminis (99.7%), which was confirmed by multilocus sequence analysis using the rpoB, rpoD, and gyrB genes. Genome sequence comparison of P2653T with the most related P. graminis type strain DSM 11363T revealed an average nucleotide identity of 92.1% and a digital DNA-DNA hybridization value of 46.6%. The major fatty acids for all Antarctic strains were C16:0, Summed Feature 3 (C16:1ω7c/C16:1ω6c) and Summed Feature 8 (C18:1ω7c/C18:1ω6c). The predominant respiratory quinone was Q-9, and the major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, and phosphatidylglycerol. The regolith strains could be differentiated from related species by the absence of arginine dihydrolase, ornithine and lysine decarboxylase and by negative tyrosine hydrolysis. The results of this polyphasic study allowed the genotypic and phenotypic differentiation of four analysed strains from the closest related species, which confirmed that the strains represent a novel species within the genus Pseudomonas, for which the name Pseudomonas petrae sp. nov. is proposed with P2653T (CCM 8850T = DSM 112068T = LMG 30619T) as the type strain.

Antibacterial and Adsorption Properties of Sulfonated GO-PVDF Nanocomposite Ultrafiltration Membranes for Environmental Applications

The application of nanocomposite materials in membrane bioreactors (MBRs) is attractive because of their great potential to enhance the filtration performance and antifouling. This study modified polyvinylidene fluoride (PVDF) ultrafiltration membranes using graphene oxide (GO) and sulfonation GO (SGO). The antibacterial properties of nanocomposite membranes were tested using three Gram-negative bacterial species (Pantoea agglomerans, Escherichia coli, and Pseudomonas graminis). The results showed that PVDF-GO and PVDF-SGO ultrafiltration (UF) membranes had significantly nontoxic properties (>95%, significance at p<0.0001), indicating that it was innocuous to bacterial growth. On the other hand, the nanoparticles (NPs) (GO and SGO) had approximately 50% antibacterial activity based on the viability tests, disc diffusion, and TEM analysis. The performance of membranes was examined using a pure water prermeabilty flux test. The water flux of the PVDF-SGO membrane (720 Lm−2 h−1) significantly increased compared with that of the GO membrane (428 Lm−2 h−1). Furthermore, the PVDF-SGO membrane had a 65.2% removal of methylene blue (MB), indicating that the SGO incorporated in the membrane enhanced the absorption capacity of heterocyclic aromatic compounds such as MB. The nanocomposite membranes (PVDF-GO and PVDF-SGO) are more sustainable than the PVDF membrane and are promising materials for MBRs because they have higher permeability and absorption capacity, and re harmless to bacterial activity.

Microbial Diversity in the Phyllosphere and Rhizosphere of an Apple Orchard Managed under Prolonged "Natural Farming" Practices.

Microbial diversity in an apple orchard cultivated with natural farming practices for over 30 years was compared with conventionally farmed orchards to analyze differences in disease suppression. In this long-term naturally farmed orchard, major apple diseases were more severe than in conventional orchards but milder than in a short-term natural farming orchard. Among major fungal species in the phyllosphere, we found that Aureobasidium pullulans and Cryptococcus victoriae were significantly less abundant in long-term natural farming, while Cladosporium tenuissimum predominated. However, diversity of fungal species in the phyllosphere was not necessarily the main determinant in the disease suppression observed in natural farming; instead, the maintenance of a balanced, constant selection of fungal species under a suitable predominant species such as C. tenuissimum seemed to be the important factors. Analysis of bacteria in the phyllosphere revealed Pseudomonas graminis, a potential inducer of plant defenses, predominated in long-term natural farming in August. Rhizosphere metagenome analysis showed that Cordyceps and Arthrobotrys, fungal genera are known to include insect- or nematode-infecting species, were found only in long-term natural farming. Among soil bacteria, the genus Nitrospira was most abundant, and its level in long-term natural farming was more than double that in the conventionally farmed orchard.

Biotic and abiotic transformation of amino acids in cloud water: experimental studies and atmospheric implications

Abstract. The interest in organic nitrogen and particularly in quantifying and studying the fate of amino acids (AAs) has been growing in the atmospheric-science community. However very little is known about biotic and abiotic transformation mechanisms of amino acids in clouds. In this work, we measured the biotransformation rates of 18 amino acids with four bacterial strains (Pseudomonas graminis PDD-13b-3, Rhodococcus enclensis PDD-23b-28, Sphingomonas sp. PDD-32b-11, and Pseudomonas syringae PDD-32b-74) isolated from cloud water and representative of this environment. At the same time, we also determined the abiotic (chemical, OH radical) transformation rates within the same solutions mimicking the composition of cloud water. We used a new approach by UPLC–HRMS (ultra-performance liquid chromatography–high-resolution mass spectrometry) to quantify free AAs directly in the artificial-cloud-water medium without concentration and derivatization. The experimentally derived transformation rates were used to compare their relative importance under atmospheric conditions with loss rates based on kinetic data of amino acid oxidation in the aqueous phase. This analysis shows that previous estimates overestimated the abiotic degradation rates and thus underestimated the lifetime of amino acids in the atmosphere, as they only considered loss processes but did not take into account the potential transformation of amino acids into each other.

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

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. The bacterial communities associated with leaves and fruits of four local Serbian plum cultivars (Požegača, Ranka, Čačanska Lepotica and Čačanska 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. 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. 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 modulations of Pseudomonas graminis in response to H2O2 in cloud water

In cloud water, microorganisms are exposed to very strong stresses especially related to the presence of reactive oxygen species including H2O2 and radicals, which are the driving force of cloud chemistry. In order to understand how the bacterium Pseudomonas graminis isolated from cloud water respond to this oxidative stress, it was incubated in microcosms containing a synthetic solution of cloud water in the presence or in the absence of H2O2. P. graminis metabolome was examined by LC-MS and NMR after 50 min and after 24 hours of incubation. After 50 min, the cells were metabolizing H2O2 while this compound was still present in the medium, and it was completely biodegraded after 24 hours. Cells exposed to H2O2 had a distinct metabolome as compared to unexposed cells, revealing modulations of certain metabolic pathways in response to oxidative stress. These data indicated that the regulations observed mainly involved carbohydrate, glutathione, energy, lipid, peptides and amino-acids metabolisms. When cells had detoxified H2O2 from the medium, their metabolome was not distinguishable anymore from unexposed cells, highlighting the capacity of resilience of this bacterium. This work illustrates the interactions existing between the cloud microbial metabolome and cloud chemistry.

Assessing water-assisted UV-C light and its combination with peroxyacetic acid and Pseudomonas graminis CPA-7 for the inactivation and inhibition of Listeria monocytogenes and Salmonella enterica in fresh-cut ‘Iceberg’ lettuce and baby spinach leaves

The effectiveness of ultraviolet C light (UV-C) delivered in water (WUV) or in peroxyacetic acid (PAA) for the inactivation and inhibition of L. monocytogenes and S. enterica in ready-to-eat ‘Iceberg lettuce’ and baby spinach leaves, was evaluated throughout chilled storage in modified atmosphere packaging (MAP). The inhibition of pathogen's growth by sequential pretreatments with UV-C in PAA and then biocontrol using Pseudomonas graminis CPA-7 was assessed during MAP storage at 5 °C and upon a breakage of the cold-storage chain. In fresh-cut lettuce, 0 1 kJ/m2 UV-C, in water or in 40 mg/L PAA, inactivated both pathogens by up to 2.1 ± 0.7 log10, which improved the efficacy of water-washing by up to 1.9 log10 and showed bacteriostatic effects on both pathogens. In baby spinach leaves, the combination of 0 3 kJ/m2 UV-C and 40 mg/L PAA reduced S. enterica and L. monocytogenes populations by 1.4 ± 0.2 and 2.2 ± 0.3 log10 respectively, which improved water-washing by 0.8 ± 0.2 log10. Combined treatments (0.1 or 0 3 kJ/m2 WUV and 40 mg/L PAA) inactivated both pathogens in the process solution from lettuce or spinach single sanitation, respectively. Pretreating lettuce with UV-C in PAA reduced L. monocytogenes and S. enterica's growth by up to 0.9 ± 0.1 log10 with respect to the PAA-pretreated control after 6 d at 5 °C in MAP. Upon a cold-chain breakage, CPA-7 prevented S. enterica growth in PAA-pretreated lettuce, whereas showed no effect on L. monocytogenes in any of both matrices. Low-dose UV-C in PAA is a suitable preservation strategy for improving the safety of ready-to-eat leafy greens and reducing the risk of cross contamination.

Fabrication and characterization of anti-fouling and non-toxic polyvinylidene fluoride -Sulphonated carbon nanotube ultrafiltration membranes for membrane bioreactors applications

The ultrafiltration (UF) membrane in membrane bioreactor (MBR) technology is the most suitable in a wastewater treatment plant (WWTP). In MBR systems, bacteria consume organic waste for energy to survive. Hence, the membranes should be non-toxic to the bacteria but still possess antifouling capability. In this study, carbon nanotube (CNT)- and sulphonated CNT (SCNT)-blended ultrafiltration polyvinylidene fluoride (PVDF) membranes were fabricated with the aim of conserving the bacterial population. The successful sulphonation of CNTs was observed by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The porosity of PVDF-CNT and -SCNT membranes was 81 and 84%, respectively. The mean pore size was 50 and 60nm, respectively, and the corresponding water flux experiment was 360.43 and 680Lm−2h−1. The fouling recovery ratio (FRR) of the CNTs and SCNTs were 72.74 and 83.52%, respectively. In addition, the BSA (bovine serum albumin) rejection was 90% in the PVDF-SCNT. The CNTs and SCNTs (150μg/mL) had a significant antibacterial effect against Escherichia coli, Pantoea agglomerans, and Pseudomonas graminis isolated from full scale MBR with 60% cell viability. On the other hand, PVDF-CNT and -SCNT membranes were nontoxic (90%, p<0.0001) to the bacterial population. Therefore, the fabricated UF membranes have sustainable antifouling properties and are non-toxic to bacteria. This study suggests that PVDF-CNT and -SCNT are promising materials for MBR systems in WWTPs.

Evaluation of Pseudomonas graminis CPA-7 as a biopreservation method for fresh-cut pear: Physicochemical, enzymatic, and nutritional quality.

Biological preservation methods with bacterial antagonists have emerged as alternatives to chemical sanitizers for extending shelf-life and reducing the population of pathogenic microorganisms. In addition, calcium plays an important role in maintaining the quality of fruit, and postharvest calcium treatments might determine the potential of fruit for processing. The objective of this work was to evaluate the effect of the postharvest application of calcium and biopreservation with the CPA-7 strain of Pseudomonas graminis on the quality parameters of fresh-cut pears. After harvest, whole pears were dipped in calcium chloride solution (1%, w/v) or water (control) for 10 min at 25 ℃ and stored for five months at temperatures ranging from 0 to -0.5 ℃. Both batches of fruit were minimally processed and dipped in a solution containing CPA-7 and an antioxidant solution or kept untreated, and both groups were stored at 4 ℃ for six days. The postharvest calcium treatment had no remarkable effect on the quality of the whole and fresh-cut pears. The enzymatic activities (PPO, PME and PG) related to browning and softening were constant in fresh-cut pears after storage, and the application of P. graminis CPA-7 had a positive effect on the activity of PPO. Finally, a combined effect of the biocontrol agent and calcium treatment was not demonstrated.

Impact of Pseudomonas graminis strain CPA-7 on respiration and ethylene production in fresh-cut ‘Golden delicious’ apple according to the maturity stage and the preservation strategy

The effect of the biocontrol agent (BCA) Pseudomonas graminis CPA-7 on the accumulation of CO2 and ethylene (C2H4) in fresh-cut apples at two maturity stages was evaluated in refrigerated conditions. Factors involved in the preservation strategy applied upon commercial conditions such as the antioxidant (AOX) treatment and the storage system were included in the analysis. Regardless of the maturity stage, the BCA reduced C2H4 levels within the MAP atmosphere in AOX-untreated apples wedges, by 29 and 43% in immature and mature apples, respectively. Nevertheless, the addition of ascorbate as antioxidant counteracted this effect. In vitro tests suggested that the reduction of C2H4 levels was not associated to the uptake of this molecule by CPA-7. Interestingly, in non-inoculated samples AOX treatment showed contradictory effects on C2H4 production in MAP conditions by significantly reducing C2H4 levels in immature apples (by 23%) while increasing it in mature ones (by 40%). Similarly, CPA-7 had opposite effects on the CO2 accumulation pattern depending on the storage system or the fruit maturity stage. In this sense, CPA-7 was associated to a higher fruit respiratory activity at an advanced maturity stage yet without inducing the fruit fermentative metabolism or altering the fruit quality during a week of refrigerated storage. Overall, these results show that CPA-7 may contribute to the maintenance of the microbiological and physicochemical quality of fresh-cut apple by modulating the fruit ethylene production and/or respiration.

Discovery of Phloeophagus Beetles as a Source of Pseudomonas Strains That Produce Potentially New Bioactive Substances and Description of Pseudomonas bohemica sp. nov.

Antimicrobial resistance is a worldwide problem that threatens the effectiveness of treatments for microbial infection. Consequently, it is essential to study unexplored niches that can serve for the isolation of new microbial strains able to produce antimicrobial compounds to develop new drugs. Bark beetles live in phloem of host trees and establish symbioses with microorganisms that provide them with nutrients. In addition, some of their associated bacteria play a role in the beetle protection by producing substances that inhibit antagonists. In this study the capacity of several bacterial strains, isolated from the bark beetles Ips acuminatus, Pityophthorus pityographus Cryphalus piceae, and Pityogenes bidentatus, to produce antimicrobial compounds was analyzed. Several isolates exhibited the capacity to inhibit Gram-positive and Gram-negative bacteria, as well as fungi. The genome sequence analysis of three Pseudomonas isolates predicted the presence of several gene clusters implicated in the production of already described antimicrobials and moreover, the low similarity of some of these clusters with those previously described, suggests that they encode new undescribed substances, which may be useful for developing new antimicrobial agents. Moreover, these bacteria appear to have genetic machinery for producing antitumoral and antiviral substances. Finally, the strain IA19T showed to represent a new species of the genus Pseudomonas. The 16S rRNA gene sequence analysis showed that its most closely related species include Pseudomonas lutea, Pseudomonas graminis, Pseudomonas abietaniphila and Pseudomonas alkylphenolica, with 98.6, 98.5 98.4, and 98.4% identity, respectively. MLSA of the housekeeping genes gyrB, rpoB, and rpoD confirmed that strain IA19T clearly separates from its closest related species. Average nucleotide identity between strains IA19T and P. abietaniphila ATCC 700689T, P. graminis DSM 11363T, P. alkylphenolica KL28T and P. lutea DSM 17257T were 85.3, 80.2, 79.0, and 72.1%, respectively. Growth occurs at 4-37°C and pH 6.5-8. Optimal growth occurs at 28°C, pH 7–8 and up to 2.5% NaCl. Respiratory ubiquinones are Q9 (97%) and Q8 (3%). C16:0 and in summed feature 3 are the main fatty acids. Based on genotypic, phenotypic and chemotaxonomic characteristics, the description of Pseudomonas bohemica sp. nov. has been proposed. The type strain is IA19T (=CECT 9403T = LMG 30182T).

Non-toxic properties of TiO2 and STiO2 nanocomposite PES ultrafiltration membranes for application in membrane-based environmental biotechnology

In membrane bioreactor (MBR) technology, nanocomposite membrane has a great potential to improve the filtration performance and antifouling. However, antibacterial activity of nanoparticles (NPs) is a significant disadvantage which can be impacted to bacterial growth and microbial community in MBRs. The modified polyethersulfone (PES) ultrafiltration (UF) membranes in the study were prepared by using TiO2 NPs and TiO2 NPs functionalized with sulfonation (STiO2). The antibacterial effect of NPs and non-toxic properties of nanocomposite membranes were examined by using three different Gram-negative bacterial species isolated from a local full scale membrane bioreactor treating municipal wastewater (Escherichia coli, Pantoea agglomerans, and Pseudomonas graminis). Results are revealed that the TiO2 and STiO2 NPs have 60% of antibacterial activity based on disc diffusion, viability tests, and TEM analysis. However, the PES-TiO2 and PES-STiO2 nanocomposite UF membranes showed significantly lower antibacterial activity (<95%, significance at p < 0.0001), indicating innocuous to bacterial growth. This study highlights that the PES-TiO2 and PES-STiO2 nanocomposite membrane is more sustainable than PES membrane and promising materials for MBRs, by taking advantage of non-toxic properties to bacterial growth.

Evaluation of biocontrol capacity of Pseudomonas graminis CPA-7 against foodborne pathogens on fresh-cut pear and its effect on fruit volatile compounds

The application of microorganisms to control the growth of foodborne pathogens is an alternative to the use of chemical additives. In this work, Pseudomonas graminis CPA-7 was tested as a biocontrol agent against Salmonella enterica and Listeria monocytogenes on fresh-cut pear under conditions that simulate its commercial application at 5 ± 1 °C (under a modified atmosphere and antioxidant solution). The quality of the fresh-cut fruit, including the ethanol and acetaldehyde contents and the volatile profile, was determined. After the storage period, the L. monocytogenes population was reduced by 1-log unit by the presence of CPA-7; however, CPA-7 was not found to have antagonistic activity against S. enterica. The fruit quality (total soluble solids content and titratable acidity) was not negatively affected by CPA-7. The ethanol and acetaldehyde contents increased during the shelf-life of the fruit regardless of the presence of CPA-7. Some volatile compounds were key factors for discriminating samples from the two groups (the control group and the group that was inoculated with CPA-7). Some components are common in the volatile profile of pear (methyl acetate, 3-methylbutyl acetate, 1-butanol, 1-hexanol, and hexanal), and thus increases in their contents could enhance consumers flavour perception.

Pseudomonas graminis strain CPA-7 differentially modulates the oxidative response in fresh-cut ‘Golden delicious’ apple depending on the storage conditions

The oxidative response in fresh-cut antioxidant-treated ‘Golden delicious’ apples during chilling storage was differentially modified by the biopreservative bacterium Pseudomonas graminis CPA-7 depending on the storage conditions (passive modified atmosphere packaging (MAP) or air). Results showed that inoculation with CPA-7 had no influence on fruit quality parameters in any of the conditions tested. During the first 24 h both in air and in MAP, ascorbate peroxidase (APX) activity triplicated the initial level in response to CPA-7, reaching up to 4-fold the activity of non-inoculated fruit (control). From 24 h of storage in MAP, polyphenol oxidase (PPO) activity was sharply enhanced in response to CPA-7 attaining values up to 8-fold higher than that of the control at the end of the experiment, yet it was not paired to an increase in browning incidence. Concomitantly, at 24 h of storage in MAP, CPA-7 suppressed peroxidase (POX) and catalase (CAT) activities. Subsequently, after 3 d in such conditions, superoxide dismutase (SOD) and PPO activities were almost duplicated in the presence of CPA-7 compared to the control. On the other hand, when stored in air, POX showed a biphasic induction in response to CPA-7 after 1 d and 6 d of incubation. On day 6, this enzyme duplicated its activity in inoculated samples compared to the control regardless of storage conditions. Inoculation with CPA-7 led to the slowdown of the decline of antioxidant capacity in air, which contrasted with the response upon MAP conditions. These results suggest that CPA-7 may trigger the activation of the fruit defense-response thereby mitigating its oxidative damage. Such activation may play a role as a putative biocontrol mechanism against foodborne pathogen infections.

Efficacy of Pseudomonas graminis CPA-7 against Salmonella spp. and Listeria monocytogenes on fresh-cut pear and setting up of the conditions for its commercial application

Pseudomonas graminis CPA-7 has been reported to control foodborne pathogens on fresh-cut apple, peach and melon. The first aim of this study was to assess its antagonistic activity against Salmonella spp. and L. monocytogenes on fresh-cut pear. CPA-7 was able to control both pathogens on fresh-cut pear stored in air conditions at 5, 10 and 20 °C. However, when CPA-7 antagonistic effect was tested by simulating commercial application (with antioxidant solution and passive modified atmosphere packaging), its effect decreased and no reductions of foodborne pathogens were reported at 10 °C. Therefore, the second aim was to optimise the antioxidant solution and the packaging in order to retain its antagonistic capacity. The selected antioxidant solution was 2% ascorbic acid +2% sodium citrate +1% CaCl2 according to growth and effect of CPA-7. Film permeability, which affects gas composition inside fruit packages, influenced CPA-7 efficacy. If the biopreservative strain is used, film has to be sufficiently gas permeable to allow CPA-7 function and at the same time to maintain product quality.

Effect of Pseudomonas graminis strain CPA-7 on the ability of Listeria monocytogenes and Salmonella enterica subsp. enterica to colonize Caco-2 cells after pre-incubation on fresh-cut pear

To further gain insight into the mechanism by which the biopreservative bacterium Pseudomonas graminis CPA-7 develops its antimicrobial activity, we have examined the effect that the prior interaction stablished by this bacterium and two foodborne pathogens on fresh-cut pear, has on their capacity to colonize human epithelial cells (Caco-2 cell line) which is crucial for establishing infection. CPA-7 inhibited the growth of L. monocytogenes and S. enterica subsp. enterica ser. Enteritidis by 5.5 and 3.1 log10, respectively, after 7d of interaction at 10°C. Furthermore, CPA-7 attenuated the adherence of S. enterica to Caco-2 cells by 0.8 log10 regardless of the pre-adaptation on the fruit. Conversely, the adhesiveness of L. monocytogenes was not influenced by the interaction with the antagonist but it was reduced by 0.5 log10 after incubation on the food matrix. Pathogen-antagonist-food matrix interaction was associated to a significant reduction of the relative invasiveness of both pathogens, by 1.3 log10 in the case of L. monocytogenes and to an undetectable level (below 5CFU/g fruit) for S. enterica. CPA-7 can adhere to and internalize into intestinal epithelium which enables it for competition. Its adherence positively correlates to the multiplicity of infection (MOI) with respect to Caco-2 cells, increasing by 0.6 log10 in an MOI range of 0.1:1 to 100:1. For the same levels of inoculum, internalized cells could only be detected after 7d of pre-adaptation in the fruit (pH4.5–5.0). However, the combination of gastrointestinal digestion and habituation on the fruit resulted in a significant reduction of CPA-7 populations (by 2 log10 more after 7d of incubation than on inoculation day) as well as in the decrease of its adhesiveness (by 0.8 log10) and invasiveness (to undetectable levels).

Studies on the biocontrol mechanisms of Pseudomonas graminis strain CPA-7 against food-borne pathogens in vitro and on fresh-cut melon

The present study was aimed at gaining insight into the mode of action of the antagonistic bacteria Pseudomonas graminis CPA-7, which has been previously identified as an effective biocontrol agent against Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 on fresh-cut fruit. In vitro experiments did not reveal any antimicrobial or proteolytic activity on solid media or any biosurfactant activity on hydrophobic surfaces. Metabolites produced by CPA-7 in two different culture media and on 'Galia' melon were unable to inhibit L. monocytogenes populations on 'Galia' melon plugs at 25 °C or 5 °C. In contrast, at 25 °C the population of this pathogen on 'Galia' plugs was reduced by 2.1 and 3.3 log-units when co-inoculated with the antagonist in water, after 24 and 48 h, respectively. CPA-7 did not form biofilms after 72 h at 25 °C (OD = 0.03) or at 30 °C (OD = 0.01) on polystyrene plates and the production of alginate was close to the negative control. Studies of nutritional profiles showed high overlap (NOI > 0.9) between CPA-7 and E. coli O157:H7 regarding the use of carboxylic acids. This functional group could also contain putative targets for competiveness between CPA-7 and S. enterica, although overlapping was not restrictive enough (NOI = 0.83).

Whole-Genome Sequence of Pseudomonas graminis Strain UASWS1507, a Potential Biological Control Agent and Biofertilizer Isolated in Switzerland.

We report here the whole-genome shotgun sequence of the strain UASWS1507 of the species Pseudomonas graminis, isolated in Switzerland from an apple tree. This is the first genome registered for this species, which is considered as a potential and valuable resource of biological control agents and biofertilizers for agriculture.

Control of fire blight (Erwinia amylovora) by a novel strain 49M of Pseudomonas graminis from the phyllosphere of apple (Malus spp.)

A bacterial isolate called 49M, showing protective activity against fire blight caused by the bacterium Erwinia amylovora, was selected from a large collection of isolates obtained from the apple phyllosphere and was identified as Pseudomonas graminis, based on its phenotype and sequence analysis of the 16S rRNA and rpoD genes. The efficacy of strain 49M under laboratory and greenhouse conditions to protect apple blossoms and apple terminal shoots was equal or even higher than that of the reference strains A506 of Pseudomonas fluorescens and C9-1 of Pantoea vagans, as well as the bioproducts BlightBan A506, Blossom Protect and Hortocyna 18 SP (streptomycin), used for comparison. However, its activity on pear fruitlets was slightly less effective, but significantly better (over 10 %) than that of BlightBan A506. When strain 49M was introduced onto apple blossoms in orchards, it effectively colonised them during the entire bloom period, in different weather conditions, including rain. The strain showed no pathogenicity towards plant tissue (pear fruitlets, apple blossoms, tobacco leaves) and is therefore, a potential candidate for the development of a new biopesticide against fire blight.

Changes in the quality and antioxidant properties of fresh-cut melon treated with the biopreservative culture Pseudomonas graminis CPA-7 during refrigerated storage

The strain CPA-7 of Pseudomonas graminis, isolated from apple by our group, was reported to reduce the population of foodborne pathogens in minimally processed fruit. The aim of this work was to investigate its effect on physical parameters, visual quality, enzymatic activity, vitamin C content and antioxidant activity of fresh-cut melon during refrigerated storage. CPA-7 treated or untreated fresh-cut melon was packaged under air or modified atmosphere (MAP) and stored at 5 and 10°C for 8 days. Results showed a loss of texture during storage, above all at 10°C. A good visual quality was observed for samples stored at 5°C, although samples treated with the antagonistic strain CPA-7 and stored in air presented the lowest score, whereas those stored at 10°C showed a poor visual appearance and a decrease of lightness. In general, CPA-7 treated samples presented higher POD values than untreated ones at 5°C, and lower values at 10°C. PPO increased during refrigerated storage regardless of the addition of the antagonist. Also, treatment with the antagonistic strain CPA-7 retained the antioxidant activity and vitamin C content of fresh-cut melon during refrigerated storage.