Pantoea Vagans Research Articles

16S rRNA-based Metagenomic Analysis of Beeswax-coated Saba Banana (Musa × paradisiaca) Pseudostem

Bananas are one of the most popular fruits, and their production generates significant agricultural waste. Banana pseudostems, a by-product of the banana industry, are being investigated as a renewable and biodegradable alternative to synthetic food packaging materials. However, these pseudostems have the potential to harbor harmful bacteria due to their natural fiber composition. Therefore, this study analyzes the effect of beeswax coating on the microbial communities in banana pseudostems. The microbial community is analyzed through a metagenomics approach that targets the 16S rRNA gene of the Saba banana (Musa × paradisiaca) pseudostem. Two experimental conditions were considered: pseudostem with beeswax coating and pseudostem without beeswax coating. The findings indicate that the microbial communities in all samples are primarily composed of the phyla Proteobacteria, Cyanobacteria, and Firmicutes. The dominant species found in uncoated banana pseudostem is Pantoea sp. At-9b, Escherichia coli, Synechococcus sp. JA-3-3-Ab, Pantoea vagans, and Klebsiella pneumoniae. The dominant species found in beeswax-coated banana pseudostem is Synechococcus sp. JA-3-3-Ab, Pseudanabaena sp. PCC 7367, Chroococcidiopsis thermalis, Priestia megaterium, and Ammonifex degensii. The Chao1, Shannon, Simpson, and Equitability indices indicate that the species richness, diversity, and evenness in the uncoated banana pseudostem are higher than in the beeswax-coated banana pseudostem. The degree of similarity between bacterial populations found in uncoated banana pseudostem and beeswax-coated banana pseudostem is around 53.9%.

Exploring the Organic Acid Secretion Pathway and Potassium Solubilization Ability of Pantoea vagans ZHS-1 for Enhanced Rice Growth.

Soil potassium deficiency is a common issue limiting agricultural productivity. Potassium-solubilizing bacteria (KSB) show significant potential in mitigating soil potassium deficiency, improving soil quality, and enhancing plant growth. However, different KSB strains exhibit diverse solubilization mechanisms, environmental adaptability, and growth-promoting abilities. In this study, we isolated a multifunctional KSB strain ZHS-1, which also has phosphate-solubilizing and IAA-producing capabilities. 16S rDNA sequencing identified it as Pantoea vagans. Scanning electron microscopy (SEM) showed that strain ZHS-1 severely corroded the smooth, compact surface of potassium feldspar into a rough and loose state. The potassium solubilization reached 20.3 mg/L under conditions where maltose was the carbon source, sodium nitrate was the nitrogen source, and the pH was 7. Organic acid metabolism profiling revealed that strain ZHS-1 primarily utilized the EMP-TCA cycle, supplemented by pathways involving pantothenic acid, glyoxylic acid, and dicarboxylic acids, to produce large amounts of organic acids and energy. This solubilization was achieved through direct solubilization mechanisms. The strain also secreted IAA through a tryptophan-dependent metabolic pathway. When strain ZHS-1 was inoculated into the rhizosphere of rice, it demonstrated significant growth-promoting effects. The rice plants exhibited improved growth and root development, with increased accumulation of potassium and phosphorus. The levels of available phosphorus and potassium in the rhizosphere soil also increased significantly. Additionally, we observed a decrease in the relative abundance of Actinobacteria and Proteobacteria in the rice rhizosphere soil, while the relative abundance of genera associated with acid production and potassium solubilization, such as Gemmatimonadota, Acidobacteria, and Chloroflexi, as well as Cyanobacteria, which are beneficial to plant growth, increased. These findings contribute to a deeper understanding of the potassium solubilization mechanisms of strain ZHS-1 and highlight its potential as a plant growth-promoting rhizobacteria.

Unveiling resilience: coelomic fluid bacteria’s impact on plant metabolism and abiotic stress tolerance

ABSTRACT Earthworms’ coelomic fluid (CF) has been discovered to possess properties that promote plant development. In particular, the earthworm’s coelomic fluid-associated bacteria (CFB) are the primary factor influencing the plants’ response. To investigate this, we used bacteria isolated from the CF and selected based on different plant growth-promoting traits, in a mesocosm ecosystem that includes plants. This experiment aimed to assess their impact on the metabolism of plants growing under abiotic stress environments (alkaline soil and nitrogen (N), phosphate (P), and potassium (K) deficit) and compare the lipid profiles of plants under the various treatments. We used seven different bacterial species isolated from the CF of Aporrectodea molleri and as a plant model Zea mays L. For the metabolomic analysis method, we used gas chromatography-mass spectrometry lipidomic. After observing the metabolomic profiles, we found that a few molecular pathways are involved in how plants react to bacterial biostimulants. The bacterial isolates belonging to Pantoea vagans, Pseudomonas aeruginosa, Bacillus paramycoides, and Bacillus thuringiensis have led to a significant increase in synthesizing several metabolites belonging to various chemical categories. Contrary to predictions, abiotic stress did not cause a drop in the composition and concentration of lipids in plants treated with the CFB, demonstrating the rigidity of the protective mechanisms. The statistical analysis based on the Pearson method revealed a positive significant correlation between plant growth parameters (length of the aerial part, surface of the leaves, and biomass) and some metabolites belonging to fatty acids, carboxylic acids, benzene derivatives, and alkanes. Moreover, the standard metabolic components of all treatments in much higher concentrations during bacterial treatments than the control treatment suggests that the bacteria have stimulated the overexpression of these metabolic components. According to these results, we could assume that plants treated with CFB exhibit an adaptability of abiotic stress defense mechanisms, which may be attributed to the upregulation of genes involved in lipid biosynthesis pathways.

Production of Seedlings of Corymbia citriodora Inoculated with Endophytic Bacteria

This study aimed to evaluate the effect of inoculants of endophytic bacteria producing indoleacetic acid (IAA) on the physiological quality of seeds and the production of seedlings of Corymbia citriodora (Hook.) KD Hill & LAS Johnson. In the physiological quality test of the seeds, the treatments used were individual inoculation with Priestia megaterium, Exiguobacterium sibiricum, Pantoea vagans strain 45URP4-1, and Bacillus sp.; joint effect of the four strains (mix); inoculation only with the carrier (cassava starch and activated charcoal); carrier with 1.0 μg mL−1 of IAA; and non-inoculated control without IAA and without a carrier. In the production of seedlings in a greenhouse, the treatments were the same, except for the mix, which was replaced by P. vagans strain 7URP1-6 (Pvs7), as inoculation with the mix increased the number of abnormal seedlings. In the physiological quality test of seeds, seeds inoculated with the bacteria individually did not have the physiological quality impaired and the carrier created a microenvironment around the seeds, benefiting germination percentage, germination speed index, average germination time, and average germination speed. In the greenhouse, seedlings inoculated with Pvs7, P. megaterium and E. sibiricum were taller, with a larger stem diameter and dry mass of shoot, roots, and total. Seeds inoculated with E. sibiricum had higher averages for height, chlorophyll b content, and shoot and total dry mass, as well as a greater ability to colonize the rhizosphere and roots of C. citriodora, resulting in the production of higher-quality seedlings. Inoculation of seeds of C. citriodora with endophytic bacteria proved to be a promising alternative for plant development.

Pantoea vagans causing soft rot disease in Agave angustifolia, in Mexico

AbstractIn Mexico, agave (Agave angustifolia Haw.) crops stand out regionally due to their socioeconomic, agroecological and cultural importance. It is the most important raw material in the elaboration of two relevant alcoholic beverages: tequila and mezcal. Nevertheless, this crop is susceptible to phytopathological threats mainly fungi and bacteria, both having a massive impact in yearly production. In this paper, we describe an agave disease consisting in reddish chlorotic lesions along the leaf bases resulting in tissue degradation and producing soft rot (softening tissue and firmness loss). Fast‐growing yellow and mucoid bacteria colonies were isolated from the lesions in BK agar. Microscopic analysis resulted in a Gram‐negative bacilli. Pathogenic tests resulted showed identical symptoms to the initial ones in natural maguey host plants as well as in the selected model Aloe vera L. showing more aggressive soft rot symptoms. It is important to highlight that in the selected plant model (Aloe vera), the symptoms arose faster and more aggressively. Biochemical and molecular analysis of the bacterial isolate identifies it as Pantoea vagans, a species not previously documented in this crop. Although all bacterial infections in plants are treated in similar ways, accurate identification could translate into targeted prevention. The detection of Pantoea vagans is considered a relevant problem given the symptoms it causes. We conclusively reported a 37% infection incidence rate, which can mean significant economic losses. However, the role of the genus Pantoea in agave rot has been poorly studied. Therefore, this report shows the identification of a new Pantoea species bounded to agave cultivars in Malinalco municipality, state of Mexico.

Contribution of Native Plasmids of Pantoea vagans C9-1 to Epiphytic Fitness and Fire Blight Management on Apple and Pear Flowers and Fruits.

Pantoea vagans C9-1 (C9-1) is a biological control bacterium that is applied to apple and pear trees during bloom for suppression of fire blight, caused by Erwinia amylovora. Strain C9-1 has three megaplasmids: pPag1, pPag2, and pPag3. Prior bioinformatic studies predicted these megaplasmids have a role in environmental fitness and/or biocontrol efficacy. Plasmid pPag3 is part of the large Pantoea plasmid (LPP-1) group that is present in all Pantoea spp. and has been hypothesized to contribute to environmental colonization and persistence, while pPag2 is less common. We assessed fitness of C9-1 derivatives cured of pPag2 and/or pPag3 on pear and apple flowers and fruit in experimental orchards. We also assessed the ability of a C9-1 derivative lacking pPag3 to reduce populations of E. amylovora on flowers and disease incidence. Previously, we determined that tolerance to stresses imposed in vitro was compromised in derivatives of C9-1 lacking pPag2 and/or pPag3; however, in this study, the loss of pPag2 and/or pPag3 did not consistently reduce the fitness of C9-1 on flowers in orchards. Over the summer, pPag3 contributed to survival of C9-1 on developing apple and pear fruit in two of five trials, whereas loss of pPag2 did not significantly affect survival of C9-1. We also found that loss of pPag3 did not affect C9-1's ability to reduce E. amylovora populations or fire blight incidence on apple flowers. Our findings partially support prior hypotheses that LPP-1 in Pantoea species contributes to persistence on plant surfaces but questions whether LPP-1 facilitates host colonization.

First Report of Bacterial Necrosis Caused by Pantoea vagans in Mango in China.

Mango (Mangifera indica L.) is one of the most important tropical fruits in China. Bacterial black spot is one of the primary factors limiting mango production and thus leads to huge economic losses (Bie et al. 2022). In June 2020, necrotic symptoms similar to bacterial black spot was observed with incidence 30% to 65% on mango cultivar Yuwen, Jinhuang, Tainong and Guifei in Baise, Guangxi, China. Typically, the lesions began as chlorotic spots that coalesced into an irregular shape, becoming black and slightly raised, with a yellow halo. Thirteen diseased samples collected from five orchards were cut into approximately 5-mm pieces, sterilized for 10 s with 75% ethanol, soaked with 2% NaClO for 1 min, and rinsed in sterilized water three times. The samples were then homogenized and a 10-fold serial dilution was made before plating onto Lysogeny broth (LB) agar. After incubation at 28°C for 3 days, one representative colony that was beige to yellow in color, round, convex and smooth with entire margins from each orchard was selected for further study. Genomic DNA was extracted to amplify the 16S rRNA gene (Lane et al. 1991). The resulting 16S rRNA sequences were compared in GenBank using BLASTn and shared at least 99% identity with Pantoea spp.. Furthermore, six housekeeping genes fusA, gyrB, leuS, pyrG, rplB and rpoB partial sequences of five isolates were amplified and sequenced (Delétoile et al. 2009). The sequences were deposited in GenBank (16S rRNA: OL413424 to OL413246, OP225727-OP225728; leuS: OL441796, OL441798 to OL441801; fusA, gyrB, leuS, pyrG, rplB and rpoB: OP272638-OP272662). The five bacterial isolates were classified as P. vagans based on the phylogenetic tree of the concatenated sequences and sequences derived from different Pantoea reference isolates inferred by maximum-likelihood using MegaX software (Kumar et al. 2018). Biochemical tests showed the isolates were Gram-negative, oxidase negative, and hydrogen oxidase positive, and could use D-glucose, D-fructose, L-rhamnose, D-galactose and D-mannitose as a carbon resource (Bradbury, 1986). Pathogenicity tests were performed on mango cv. Yuwen. The representative isolate was inoculated by infiltration with sterile needleless syringes on healthy leaves and spraying onto slightly scratched leaves with bacterial suspensions (OD600=0.1) respectively (Kutschera, et al. 2019). A Xanthomonas citri pv. mangiferaeindicae (Xcm) suspension and sterilized water were used as positive and negative controls, respectively. Inoculated plants were kept with 90 ± 5% relative humidity and 28 ± 1°C in the greenhouse for 1 week. Black to brown necrotic symptoms were observed on all leaves inoculated by infiltration except the negative control. These were observed in plants inoculated by spraying only after 2 weeks. Bacteria re-isolated from diseased tissues were consistent with the inoculated isolates and identified as P. vagans, fulfilling Koch's postulates. To date, P. vagans have been isolated from eucalyptus with bacterial blight and dieback, and maize with brown stalk rot (Brady et al. 2009). However, to our knowledge, this is the first report of P. vagans causing bacterial necrosis on mango in China. It was also found that some of the diseased samples were coinfected with P. vagans and Xcm in our investigation. Therefore, it is necessary to further study the infection mechanisms of this pathogen.

Diverse Virulence Attributes of Pantoea alfalfae sp. nov. CQ10 Responsible for Bacterial Leaf Blight in Alfalfa Revealed by Genomic Analysis.

Alfalfa is widely grown worldwide for its excellent nutritional value. Pantoea species living in alfalfa seeds can easily spread over great distances with frequent trade. However, the pathogenic properties of this dangerous hitchhiker on alfalfa have not been evaluated. Here, we identified the taxonomic status of Pantoea strain CQ10 isolated from the interior of alfalfa seeds based on the whole genome sequence. The diverse virulence attributes of strain CQ10 during host infection were characterized through pathogenicity assays and functional and genomic analyses. We report that strain CQ10 belongs to a novel species in the genus Pantoea, which was phylogenetically close to Pantoea vagans and Pantoea agglomerans. Strain CQ10 caused bacterial leaf blight of alfalfa after inoculation from the roots. We found that strain CQ10 possesses a large number of pathogenic genes involved in shaping the virulence properties during bacteria-host interactions, including motility, biofilm, type VI secretion system, and nutrient acquisition. Compared with P. vagans and P. agglomerans, the unique virulence factors of strain CQ10 were mainly involved in motility and biofilm, which were confirmed by in vitro experiments. Taken together, our results suggest that strain CQ10 is the first Pantoea species to infect alfalfa, and it possesses diverse virulence attributes among which motility and biofilm may be the best weapons.

Chemical and microbiological characterization of two traditional Mongolian high-fat dairy products produced in Xilin Gol, China.

Mongolian butter and Tude are traditional high-fat dairy products produced in Xilin Gol, China, which have unique chemical and microbiological characteristics. Mongolian Tude is made from Mongolian butter, dreg, and flour. In this study, the traditional manufacturing process of Mongolian butter and Tude was investigated for the first time. Mongolian butter was characterized by high-fat content (99.38 ± 0.63%) and high acidity (77.09 ± 52.91°T), whereas Mongolian Tude was considered a high-fat (21.45 ± 1.23%) and high-protein (8.28 ± 0.65%) dairy product obtained by butter, dreg, and flour. Mongolian butter and Tude were proven to be safe for human consumption in terms of benzopyrene content. In addition, Listeria monocytogenes, Staphylococcus aureus, Salmonella, coliforms, and aflatoxin M1 were not detected in the samples. Bacteria and molds were not isolated from Mongolian butter; in contrast, the total count of bacteria and molds in Mongolian Tude was within the range of 4.5 × 102 to 9.5 × 104 and 0 to 2.2 × 105, respectively. Moreover, Lactococcus (41.55%), Lactobacillus (11.05%), Zygosaccharomyces (40.20%), and Pichia (12.90%) were the predominant bacterial and fungal genera, and Lactobacillus helveticus (15.6%), Lactococcus raffinolactis (9.6%), Streptococcus salivarius (8.5%), Pantoea vagans (6.1%), Bacillus subtilis (4.2%), Kocuria rhizophila (3.5%), Acinetobacter johnsonii (3.5%), Zygosaccharomyces rouxii (46.2%), Pichia fermentans (14.7%), and Dipodascus geotrichum (11.7%) were the predominant species in the microbiota of Mongolian Tude. Thus, it can be stated that the microbiota of food products produced by different small families varied significantly. Collectively, the findings presented herein are the first report of chemical and microbiological characterization of products of geographical origin and highlight the need for standardization of manufacturing procedures of Mongolian butter and Tude in the future.

Seeds of Stevia rebaudiana Bertoni as a Source of Plant Growth-Promoting Endophytic Bacteria with the Potential to Synthesize Rebaudioside A.

In this study, a new strain of Pantoea vagans, SRS89, was isolated from surface-sterilized stevia seeds. The isolate was evaluated using morphological, molecular, and biochemical methods. The bacterium was 1.5 μm long, yellowish in color, and classified as Gram-negative. Whole genome sequencing of our strain revealed the presence of a 4,610,019 bp chromosome, and genome annotation resulted in the detection of 4283 genes encoding 4204 putative coding sequences. Phylogenic analysis classified the genome of our strain close to the MP7 and LMG 24199 strains of P. vagans. Functional analysis showed that the highest number of genes within the analyzed bacterium genome were involved in transcription, amino acid transport and metabolism, and carbohydrate transport and metabolism. We also identified genes for enzymes involved in the biosynthesis of carotenoids and terpenoids. Furthermore, we showed the presence of growth regulators, with the highest amount noted for gibberellic acid A3, indole-3-acetic acid, and benzoic acid. However, the most promising property of this strain is its ability to synthesize rebaudioside A; the estimated amount quantified using reversed-phase (RP)-HPLC was 4.39 mg/g of the dry weight of the bacteria culture. The isolated endophytic bacterium may be an interesting new approach to the production of this valuable metabolite.

A Novel Application of Laser in Biocontrol of Plant Pathogenic Bacteria

The effect of laser radiation has never been tested on the antimicrobial activity of cyanobacterial extracts. In order to investigate this, aqueous extracts from three cyanobacterial strains identified as Thermoleptolyngbya sp., Leptolyngbya sp., and Synechococcus elongatus were exposed to laser radiation. The aqueous extracts both directly exposed to the laser and those derived from pre-exposed biomass were tested for their antimicrobial activity to select the most active extracts under different exposure times and distances from the laser source. Methods: A fixed weight of one-month old cyanobacterial biomass was used in extraction. Another similar biomass was exposed to laser before aqueous extraction. The laser treatment was performed using two distances, 5 and 10 cm, with three exposure times, 4, 16, and 32 min. The antimicrobial assay was performed against the bacterial plant pathogen, whose identity was confirmed by molecular analysis and cell wall structure by a Gram stain. Results: The pathogenic bacterium was identified as Gram-negative Pantoae vagans. The aqueous extract that was not exposed to laser treatment (control) was mostly ineffective against the pathogenic bacterium, whereas a significant increase in the antimicrobial effect was observed for the extract directly exposed to the laser followed by the extract derived from laser-pre-exposed cyanobacterial biomass. In the case of Synechococcus elongatus extracts, the extract that was directly exposed to the laser showed the highest statistically significant antimicrobial activity against Pantoea vagans, with an inhibition zone of 15.5 mm, at 10 cm and 4 min of laser treatment. Conclusions: This is the first report on the effect of laser on enhancing the antimicrobial profile of cyanobacterial extracts. The direct exposure of cyanobacterial extracts to the laser was more effective and biologically safer than exposing the biomass itself prior to extraction. The laser used was a monochromatic red light within the visible range. This radiation increased the antimicrobial activity of cyanobacterial extracts and can be used as an eco-friendly biocontrol strategy.

Assessment of earthworm (Aporrectodea molleri)'s coelomic fluid-associated bacteria on different plant growth-promoting traits and maize germination and seedling growth

Earthworms together with plant growth-promoting bacteria (PGPB) can significantly increase the availability of nutrients and promote plant growth. However, earthworm's associated PGPB are poorly studied concerning their effect as biofertilizers to improve plant growth. In the current study, we aim to demonstrate that earthworm represents a reservoir and vector for PGPB through its coelomic fluid (CF), which is in permanent contact with the rhizosphere. To achieve this objective, 16 identified bacteria, previously, isolated from the (CF) of the earthworm Aporrectodea molleri, were tested for their potential to promote plant growth, in vivo and in vitro, by running 6 tests concerning 6 different PGP (Plant growth-promoting) characters, and co-inoculating maize seeds with potent bacteria. The results revealed that 87% of the CF's associated bacteria, have positive PGP traits. Out of the tested bacteria, 44% showed siderophores production, 25% and 37%, respectively, were positive for phosphate and potassium solubilizing in solid medium. Equally, 69% of the CF isolated bacteria showed phosphate solubilization, potassium solubilization, IAA production and nitrogen fixation abilities in liquid media. Moreover, 2 isolates (12%) inhibited the growth of the phytopathogenic fungus Fusarium oxysporum. Overall, the maize seeds treated with the CF's isolated bacteria LC68 (Buttiauxella gaviniae), LC27 (Pantoea vagans), LC12 (Bacillus thuringiensis) showed the better and, significantly, higher performance in germination speed and percentage, in addition to root and shoot length, and biomass.This work has highlighted that earthworm, in their coelomic fluid, harbour PGPB, which would stimulate plant growth and which could be involved in improving soil fertility.

Integrated Metabarcoding and Culturomic-Based Microbiome Profiling of Rice Phyllosphere Reveal Diverse and Functional Bacterial Communities for Blast Disease Suppression.

Phyllosphere—the harsh foliar plant part exposed to vagaries of environmental and climatic variables is a unique habitat for microbial communities. In the present work, we profiled the phyllosphere microbiome of the rice plants using 16S rRNA gene amplicon sequencing (hereafter termed metabarcoding) and the conventional microbiological methods (culturomics) to decipher the microbiome assemblage, composition, and their functions such as antibiosis and defense induction against rice blast disease. The blast susceptible rice genotype (PRR78) harbored far more diverse bacterial species (294 species) than the resistant genotype (Pusa1602) that showed 193 species. Our metabarcoding of bacterial communities in phyllomicrobiome revealed the predominance of the phylum, Proteobacteria, and its members Pantoea, Enterobacter, Pseudomonas, and Erwinia on the phyllosphere of both rice genotypes. The microbiological culturomic validation of metabarcoding-taxonomic annotation further confirmed the prevalence of 31 bacterial isolates representing 11 genera and 16 species with the maximum abundance of Pantoea. The phyllomicrobiome-associated bacterial members displayed antifungal activity on rice blast fungus, Magnaporthe oryzae, by volatile and non-volatile metabolites. Upon phyllobacterization of rice cultivar PB1, the bacterial species such as Enterobacter sacchari, Microbacterium testaceum, Pantoea ananatis, Pantoea dispersa, Pantoea vagans, Pseudomonas oryzihabitans, Rhizobium sp., and Sphingomonas sp. elicited a defense response and contributed to the suppression of blast disease. qRT-PCR-based gene expression analysis indicated over expression of defense-associated genes such as OsCEBiP, OsCERK1, and phytohormone-associated genes such as OsPAD4, OsEDS1, OsPR1.1, OsNPR1, OsPDF2.2, and OsFMO in phyllobacterized rice seedlings. The phyllosphere bacterial species showing blast suppressive activity on rice were found non-plant pathogenic in tobacco infiltration assay. Our comparative microbiome interrogation of the rice phyllosphere culminated in the isolation and identification of agriculturally significant bacterial communities for blast disease management in rice farming through phyllomicrobiome engineering in the future.

Characterization of Phosphate Solubilizing Bacterial Endophytes and Plant Growth Promotion In Vitro and in Greenhouse.

Phosphate is one of the most important nutrients for plant growth and development, and only 0.1% of the phosphate in soils is available to plants. Currently, the use of excess phosphate fertilizer has caused surface and ground water pollution and water eutrophication, resulting in algal blooms in lakes and oceans. Therefore, it is imperative to explore alternative ways to solve these problems for sustainable agricultural production and improvement of soil fertility, while protecting the environment. Microorganisms from the rhizosphere and within plants are able to solubilize insoluble soil phosphate, making it available to plants. Five high phosphate solubilizing bacteria from our bacterial endophyte library were chosen for this study and identified as Pantoea vagans IALR611, Pseudomonas psychrotolerans IALR632, Bacillus subtilis IALR1033, Bacillus safensis IALR1035 and Pantoea agglomerans IALR1325. All five bacteria significantly promoted tall fescue growth in vitro. Greenhouse experiments showed that IALR1325 significantly promoted pepper and tomato growth, and IALR632 was the best in promoting tomato growth. In addition, all these bacteria had extracellular acid phosphatase and phytase activities. One of the mechanisms for phosphate solubilization by bacteria is pH reduction caused by gluconic acid production. Our results indicate that P. agglomerans IALR1325 is a promising bacterium for future applications.

Pantoea vagans strain BWL1 controls blue mold in mandarin fruit by inhibiting ergosterol biosynthesis in Penicillium expansum

Penicillium expansum is a major postharvest fungal pathogen of a variety of fruits. Recently, Pen. expansum has been reported to infect citrus fruit; however, the management of Pen. expansum on citrus has not been studied. Pantoea vagans strain BWL1 was isolated from the surface of mandarin fruit. Here, its inhibitory effect on postharvest blue mold on mandarin fruit was evaluated. Pan. vagans inhibited conidial germination and mycelial growth of Pen. expansum. Cell-free fermentation extract of Pan. vagans inhibited the expression of ergC, a gene involved in ergosterol biosynthesis, and decreased the ergosterol content in Pen. expansum, resulting in plasma membrane disruption in the fungal pathogen. In vivo experiments showed that the development of blue mold caused by Pen. expansum on citrus fruit was significantly decreased by treatment with Pan. vagans strain BWL1. These results suggest that Pan. vagans can produce metabolites that exhibit antifungal activity toward Pen. expansum by inhibiting the biosynthesis of ergosterol. The application of Pan. vagans strain BWL1 could be effective for the postharvest management of blue mold in citrus fruit.

Characterisation and Mutagenesis Study of An Alternative Sigma Factor Gene (hrpL) from Erwinia mallotivora Reveal Its Central Role in Papaya Dieback Disease.

Simple SummaryErwinia mallotivora is the causal agent of papaya dieback disease in Malaysia, and its pathogenicity is less appreciated, especially from the molecular perspective. Our previous investigations proved that the hrpL/rpoE gene was one of the significant differentially expressed genes (DEGs) during early infection of E. mallotivora in papaya, suggesting this particular gene is important for infection. In this study, an in-depth analysis was performed using bioinformatics software on hrpL from E. mallotivora (EmhrpL) and its encoded protein (EmHrpL) obtaining crucial information including the conserved function and sequence motif, protein structural similarity with related homologs, and the possibility of being inhibited by a cognate inhibitor. Moreover, knockout (insertional mutational on DNA sequence) of the hrpL gene had caused mutant E. mallotivora (ΔEmhrpL) to be avirulent in four-month-old papaya plants. Here, the conclusion was that EmHrpL is indeed a necessary factor in E. mallotivora pathogenicity, and the findings on the potential inhibitor of this protein are useful for future studies to formulate a papaya dieback disease management programme.The alternative sigma (σ) factor E, RpoE or HrpL, has been reported to be involved in stress- and pathogenicity-related transcription initiation in Escherichia coli and many other Gram-negative bacteria, including Erwinia spp. and Pseudomonas spp. A previous study identified the hrpL/rpoE transcript as one of the significant differentially expressed genes (DEGs) during early E. mallotivora infection in papaya and those data serve as the basis of the current project. Here, the full coding DNA sequence (CDS) of hrpL from E. mallotivora (EmhrpL) was determined to be 549 bp long, and it encoded a 21.3 kDa HrpL protein that possessed two highly conserved sigma-70 (σ70) motifs—σR2 and σR4. Nucleotide sequence alignment revealed the hrpL from E. mallotivora shared high sequence similarity to rpoE/hrpL from E. tracheiphila (83%), E. pyrifoliae (81%), and E. tasmaniensis (80%). Phylogenetics analysis indicated hrpL from E. mallotivora to be monophyletic with rpoEs/hrpLs from Pantoea vagans, E. herbicola, and E. tracheiphila. Structural analysis postulated that the E. mallotivora’s alternative σ factor was non-transmembranic and was an extracytoplasmic function (ECF) protein—characteristics shared by other σ factors in different bacterial species. Notably, the protein–protein interaction (PPI) study through molecular docking suggested the σ factor could be possibly inhibited by an anti-σ. Finally, a knockout of hrpL in E. mallotivora (ΔEmhrpL) resulted in avirulence in four-month-old papaya plants. These findings have revealed that the hrpL is a necessary element in E. mallotivora pathogenicity and also predicted that the gene can be inhibited by an anti-σ.

Bacterial Diversity and Antibiotic Susceptibility of Sparus aurata from Aquaculture.

In a world where the population continues to increase and the volume of fishing catches stagnates or even falls, the aquaculture sector has great growth potential. This study aimed to contribute to the depth of knowledge of the diversity of bacterial species found in Sparus aurata collected from a fish farm and to understand which profiles of diminished susceptibility to antibiotics would be found in these bacteria that might be disseminated in the environment. One hundred thirty-six bacterial strains were recovered from the S. aurata samples. These strains belonged to Bacillaceae, Bacillales Family XII. Incertae Sedis, Comamonadaceae, Enterobacteriaceae, Enterococcaceae, Erwiniaceae, Micrococcaceae, Pseudomonadaceae and Staphylococcaceae families. Enterobacter sp. was more frequently found in gills, intestine and skin groups than in muscle groups (p ≤ 0.01). Antibiotic susceptibility tests found that non-susceptibility to phenicols was significantly higher in gills, intestine and skin samples (45%) than in muscle samples (24%) (p ≤ 0.01) and was the most frequently found non-susceptibility in both groups of samples. The group of Enterobacteriaceae from muscles presented less decreased susceptibility to florfenicol (44%) than in the group of gills, intestine and skin samples (76%). We found decreased susceptibilities to β-lactams and glycopeptides in the Bacillaceae family, to quinolones and mupirocin in the Staphylococcaceae family, and mostly to β-lactams, phenicols and quinolones in the Enterobacteriaceae and Pseudomonadaceae families. Seven Enterobacter spp. and five Pseudomonas spp. strains showed non-susceptibility to ertapenem and meropenem, respectively, which is of concern because they are antibiotics used as a last resort in serious clinical infections. To our knowledge, this is the first description of species Exiguobacterium acetylicum, Klebsiella michiganensis, Lelliottia sp. and Pantoea vagans associated with S. aurata (excluding cases where these bacteria are used as probiotics) and of plasmid-mediated quinolone resistance qnrB19-producing Leclercia adecarboxylata strain. The non-synonymous G385T and C402A mutations at parC gene (within quinolone resistance-determining regions) were also identified in a Klebsiella pneumoniae, revealing decreased susceptibility to ciprofloxacin. In this study, we found not only bacteria from the natural microbiota of fish but also pathogenic bacteria associated with fish and humans. Several antibiotics for which decreased susceptibility was found here are integrated into the World Health Organization list of “critically important antimicrobials” and “highly important antimicrobials” for human medicine.

A Comparative Analysis of Ash Leaf-Colonizing Bacterial Communities Identifies Putative Antagonists of Hymenoscyphus fraxineus.

In the last few years, the alarming spread of Hymenoscyphus fraxineus, the causal agent of ash dieback, has resulted in a substantial threat to native ash stands in central and northern Europe. Since leaves and leaf petioles are the primary infection sites, phyllosphere microorganisms are presumed to interact with the pathogen and are discussed as a source of biocontrol agents. We studied compound leaves from susceptible and visible infection-free trees in four ash stands with a high likelihood of infection to assess a possible variation in the bacterial microbiota, depending on the health status of the trees. The bacterial community was analyzed by culture-independent 16S rRNA gene amplicon sequencing and through the isolation and taxonomic classification of 2,589 isolates using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The bacterial community structure did not show significant differences. However, a set of amplicon sequence variants (ASVs) and MALDI groups belonging to Luteimonas, Aureimonas, Pseudomonas, Bacillus, and Paenibacillus were distinctly increased in tolerant trees, which may be associated with the ability of the tree to resist the pathogen. The most obvious differences were observed for Luteimonas, a genus that is also exclusively present in the healthy core microbiome. In a first in vitro screen of antagonists, approximately 11% of total isolates suppressed the growth of H. fraxineus, but a statistical test with two different H. fraxineus strains confirmed only the antagonistic activity of 8% of these isolates. The antagonistic isolates were assigned to Bacillus velezensis, Pantoea vagans, and Pseudomonas caspiana. Overall, our study provides a set of isolates or phylogenetic groups that might be involved in the process that prevents the penetration and spread of H. fraxineus. In the next step, in planta experiments are required with a longer period of exposure to H. fraxineus to evaluate effective isolates or consortia of isolates acting through direct antagonism or competition or indirectly by inducing resistance.

Pantoea sp. S3W-11의 항균활성과 배양 최적화

In this study, 46 bacteria strains were isolated from water and soil collected from Geumjin-ri, Ganggu-ri and Namseock-ri in Yeongdeok-Gun to screen antibacterial bacteria against various pathogenic bacteria. Among them, strain S3W-11 showed an excellent growth inhibition against methicillin-resistant Staphylococcus aureus, Bacillus cereus and Escherichia coli. As a result of the 16S rRNA gene sequence analysis, strain S3W-11 showed the high similarity with Pantoea vagans LMG 24199<SUP>T</SUP>, Pantoea agglomerans DSM 3493<SUP>T</SUP>, Pantoea conspicua LMG 24534<SUP>T</SUP> 99.64%, 99.58%, 99.18%, respectively. The effects of culture medium composition, temperature, and initial pH on the cell growth and antibacterial activity were confirmed for culture optimization of strain S3W-11. Optimal conditions for growth and antibacterial activity in strain S3W-11 were found to be: YPD medium, 25℃ and pH 6.5. When the strain was cultured in LB, NB, TSB, and R2A media, the antibacterial activity has not been confirmed. Optimal reaction time was 48 h in YPD medium, 100 rpm and 0.3 vvm in 2 L-scale fed-batch fermentation process for antimicrobial activity. Strain S3W-11 can be improved on antibacterial activity in optimal culture conditions (YPD medium, 25℃ and pH 6.5). Therefore, the antibacterial activity of Pantoea sp. S3W-11 had potential as antibiotics for pathogens including MRSA.

Detección e identificación molecular de Pantoea vagans en flores de Dahlia sp.

Las Dalias (Dahlia spp.) son flores nativas de Mesoamérica y endémicas de México. Su consumo como alimento es una práctica antigua, en la actualidad es escasa la información y reglamentación sanitaria para su comercialización y consumo. Al respecto, el objetivo del presente estudio fue identificar morfológica, bioquímica y molecularmente, bacterias de origen entérico asociadas con flores de Dalia. Los resultados de la caracterización morfológica revelaron la predominancia de bacilos cortos Gram negativos. A partir de la observación de la morfología colonial en medios de cultivo selectivos y diferenciales se identificaron como Escherichia coli y Salmonella spp. Sin embargo, el uso de un método comercial automatizado los clasifica como Enterobacter cancerogenus. Debido a que ambas pruebas arrojaron resultados distintos en cuanto a la identidad del microorganismo aislado, no fueron concluyentes. Por lo tanto, se recurrió a la caracterización molecular para la identificación del aislado bacteriano. La bacteria predominante en flores de Dalia, correspondió a Pantoea vagans (Número de acceso CP002206). Éste es el primer reporte de Pantoea vagans aislada de flores de Dalia.