Enhancement of antibacterial and growth-promoting effects of Paenibacillus polymyxa by optimizing its fermentation process.

AIMS: We aimed to enhance the antibacterial and growth-promoting effects of Paenibacillus polymyxa by improving the yield of spores, lipopeptides and indole-3-acetic acid (IAA) in the fermentation process. METHODS AND RESULTS: Through medium optimization by the response surface method and feeding fermentation, the number of spores reached 2.37 × 109  cfu ml-1 with an increase of 38%, the content of lipopeptides reached 60.8 mg L-1 with an increase of 89%, and the content of IAA reached 24.3 mg L-1 with an increase of 176%, respectively, comparing with the original (un-optimized) culture conditions. The fermentation culture of P. polymyxa from the optimized medium and feeding fermentation resulted in higher colonization of P. polymyxa in soils than that from the original culture during the 49 days for testing. Comparing with the supernatant of the original culture, the supernatant of the P. polymyxa culture from the optimized medium and feeding fermentation showed enhanced antibacterial effects and plant growth-promoting effects. The enhanced antibacterial effect was shown as the increase of the inhibition zone by 59%, 45% and 26% against Ralstonia solanacearum, Erwinia carotovora and Xanthomonas campestris. The enhanced growth-promoting effects on tomato and strawberry plants were the increase of plant height by 47% and 5%, root length by 23% and 15% and root weight by 65% and 110%. CONCLUSIONS: The combination of medium optimization and feeding fermentation effectively improved the yield of spores, lipopeptides and IAA. Lipopeptides and IAA lead to enhanced antibacterial and plant growth-promoting effects of the P. polymyxa product. SIGNIFICANCE AND IMPACT OF THIS STUDY: The optimized fermentation method significantly improved the yield of spores, lipopeptides and IAA, thus providing theoretical and technical support for enhancing the antibacterial and growth-promoting effects of P. polymyxa products in agriculture.

Isolation and characterization of antagonistic Paenibacillus polymyxa HX-140 and its biocontrol potential against Fusarium wilt of cucumber seedlings.

OBJECTIVE: The aim of this study is to evaluate the efficacy of the strain Paenibacillus polymyxa HX-140, isolated from the rhizosphere soil of rape, to control Fusarium wilt of cucumber seedlings caused by Fusarium oxysporum f. sp. cucumerinum. RESULTS: Strain HX-140 was able to produce protease, cellulase, ß-1,3-glucanase and antifungal volatile organic compounds. An in vitro dual culture test showed that strain HX-140 exhibited broad spectrum antifungal activity against soil-borne plant pathogenic fungi. Strain HX-140 also reduced the infection of Fusarium wilt of cucumber seedlings by 55.6% in a greenhouse pot experiment. A field plot experiment confirmed the biocontrol effects and further revealed that antifungal activity was positively correlated with inoculum size by the root-irrigation method. Here, inoculums at 106 107 and 108 cfu/mL of HX-140 bacterial suspension reduced the incidence of Fusarium wilt of cucumber seedling by 19.5, 41.1, and 50.9%, respectively. CONCLUSIONS: Taken together, our results suggest that P. polymyxa HX-140 has significant potential in the control of Fusarium wilt and possibly other fungal diseases of cucumber.

Interactional mechanisms of Paenibacillus polymyxa SC2 and pepper (Capsicum annuum L.) suggested by transcriptomics.

BACKGROUND: Paenibacillus polymyxa SC2, a bacterium isolated from the rhizosphere soil of pepper (Capsicum annuum L.), promotes growth and biocontrol of pepper. However, the mechanisms of interaction between P. polymyxa SC2 and pepper have not yet been elucidated. This study aimed to investigate the interactional relationship of P. polymyxa SC2 and pepper using transcriptomics. RESULTS: P. polymyxa SC2 promotes growth of pepper stems and leaves in pot experiments in the greenhouse. Under interaction conditions, peppers stimulate the expression of genes related to quorum sensing, chemotaxis, and biofilm formation in P. polymyxa SC2. Peppers induced the expression of polymyxin and fusaricidin biosynthesis genes in P. polymyxa SC2, and these genes were up-regulated 2.93- to 6.13-fold and 2.77- to 7.88-fold, respectively. Under the stimulation of medium which has been used to culture pepper, the bacteriostatic diameter of P. polymyxa SC2 against Xanthomonas citri increased significantly. Concurrently, under the stimulation of P. polymyxa SC2, expression of transcription factor genes WRKY2 and WRKY40 in pepper was up-regulated 1.17-fold and 3.5-fold, respectively. CONCLUSIONS: Through the interaction with pepper, the ability of P. polymyxa SC2 to inhibit pathogens was enhanced. P. polymyxa SC2 also induces systemic resistance in pepper by stimulating expression of corresponding transcription regulators. Furthermore, pepper has effects on chemotaxis and biofilm formation of P. polymyxa SC2. This study provides a basis for studying interactional mechanisms of P. polymyxa SC2 and pepper.

Molecular changes associated with spontaneous phenotypic variation of Paenibacillus polymyxa, a commonly used biocontrol agent, and temperature-dependent control of variation.

There has been a growing interest in deploying plant growth-promoting rhizobacteria (PGPR) as a biological control agent (BCA) to reduce the use of agrochemicals. Spontaneous phenotypic variation of PGPR, which causes the loss of traits crucial for biocontrol, presents a large obstacle in producing commercial biocontrol products. Here, we report molecular changes associated with phenotypic variation in Paenibacillus polymyxa, a PGPR widely used for biocontrol worldwide, and a simple cultural change that can prevent the variation. Compared to B-type (non-variant) cells of P. polymyxa strain E681, its phenotypic variant, termed as F-type, fails to form spores, does not confer plant growth-promoting effect, and displays altered colony and cell morphology, motility, antagonism against other microbes, and biofilm formation. This variation was observed in all tested strains of P. polymyxa, but the frequency varied among them. RNA-seq analysis revealed differential regulation of many genes involved in sporulation, flagella synthesis, carbohydrate metabolism, and antimicrobial production in F-type cells, consistent with their pleiotropic phenotypic changes. F-type cells's sporulation was arrested at stage 0, and the key sporulation gene spo0A was upregulated only in B-type cells. The phenotypic variation could be prevented by altering the temperature for growth. When E681 was cultured at 20 °C or lower, it exhibited no variation for 7 days and still reached ~ 108 cfu/mL, the level sufficient for commercial-scale production of biocontrol products.

The Status of Soil Microbiome as Affected by the Application of Phosphorus Biofertilizer: Fertilizer Enriched with Beneficial Bacterial Strains.

Regarding the unfavourable changes in agroecosystems resulting from the excessive application of mineral fertilizers, biopreparations containing live microorganisms are gaining increasing attention. We assumed that the application of phosphorus mineral fertilizer enriched with strains of beneficial microorganisms contribute to favourable changes in enzymatic activity and in the genetic and functional diversity of microbial populations inhabiting degraded soils. Therefore, in field experiments conditions, the effects of phosphorus fertilizer enriched with bacterial strains on the status of soil microbiome in two chemically degraded soil types (Brunic Arenosol - BA and Abruptic Luvisol - AL) were investigated. The field experiments included treatments with an optimal dose of phosphorus fertilizer (without microorganisms - FC), optimal dose of phosphorus fertilizer enriched with microorganisms including Paenibacillus polymyxa strain CHT114AB, Bacillus amyloliquefaciens strain AF75BB and Bacillus sp. strain CZP4/4 (FA100) and a dose of phosphorus fertilizer reduced by 40% and enriched with the above-mentioned bacteria (FA60). The analyzes performed included: the determination of the activity of the soil enzymes (protease, urease, acid phosphomonoesterase, ß-glucosidase), the assessment of the functional diversity of microorganisms with the application of BIOLOGTM plates and the characterization of the genetic diversity of bacteria, archaea and fungi with multiplex terminal restriction fragment length polymorphism and next generation sequencing. The obtained results indicated that the application of phosphorus fertilizer enriched with microorganisms improved enzymatic activity, and the genetic and functional diversity of the soil microbial communities, however these effects were dependent on the soil type.

Plant growth-promoting rhizobacterium, Paenibacillus polymyxa CR1, upregulates dehydration-responsive genes, RD29A and RD29B, during priming drought tolerance in arabidopsis.

In recent decades, drought has become a global problem for food security and agricultural production. A variety of strategies have been developed to enhance drought tolerance, but largely unsuccessful since most drought-responsive genes (DRGs) stimulate a stomata closure and in turn suppress plant growth and yield. To access if and/or how plants could enhance drought tolerance without trading off growth and development, we screened and isolated a plant growth-promoting rhizobacterium, Paenibacillus polymyxa CR1, capable of 1) priming drought tolerance and concurrently 2) increasing root growth in plants, e.g., Arabidopsis and soybean. In parallel, we uncovered that P. polymyxa CR1 3) induces the expression of two DRGs, Response to Desiccation (RD)29A and RD29B, 4) of which pattern upregulations are controlled by a diurnal rhythm. Besides, RD29A and RD29B act as 5) 'memory' genes; their transcript levels are increased to a greater extent when plants encountered P. polymyxa CR1 for the second time compared to an initial exposure. In line with these findings, T-DNA insertion mutant Arabidopsis of RD29A or RD29B displayed enhanced susceptibility to drought, without any change in stomata behaviors or growth rates, than wild-type plants. Hence, we conclude that RD29A or RD29B are unique, efficacious generic materials that can potentially aid in upgrading the plants own survival capacity against drought without reducing yield potential.

Pan-genome analysis of Paenibacillus polymyxa strains reveals the mechanism of plant growth promotion and biocontrol.

Rapid development of gene sequencing technologies has led to an exponential increase in microbial sequencing data. Genome research of a single organism does not capture the changes in the characteristics of genetic information within a species. Pan-genome analysis gives us a broader perspective to study the complete genetic information of a species. Paenibacillus polymyxa is a Gram-positive bacterium and an important plant growth-promoting rhizobacterium with the ability to produce multiple antibiotics, such as fusaricidin, lantibiotic, paenilan, and polymyxin. Our study explores the pan-genome of 14 representative P. polymyxa strains isolated from around the world. Heap's law model and curve fitting confirmed an open pan-genome of P. polymyxa. The phylogenetic and collinearity analyses reflected that the evolutionary classification of P. polymyxa strains are not associated with geographical area and ecological niches. Few genes related to phytohormone synthesis and phosphate solubilization were conserved; however, the nif cluster gene associated with nitrogen fixation exists only in some strains. This finding is indicative of nitrogen fixing ability is not stable in P. polymyxa. Analysis of antibiotic gene clusters in P. polymyxa revealed the presence of these genes in both core and accessory genomes. This observation indicates that the difference in living environment led to loss of ability to synthesize antibiotics in some strains. The current pan-genomic analysis of P. polymyxa will help us understand the mechanisms of biological control and plant growth promotion. It will also promote the use of P. polymyxa in agriculture.

Isolation and Characterization of Plant Growth-Promoting Endophytic Bacteria Paenibacillus polymyxa SK1 from Lilium lancifolium.

Paenibacillus polymyxa is a plant growth-promoting rhizobacterium that has immense potential to be used as an environmentally friendly replacement of chemical fertilizers and pesticides. In the present study, Paenibacillus polymyxa SK1 was isolated from bulbs of Lilium lancifolium. The isolated endophytic strain showed antifungal activities against important plant pathogens like Botryosphaeria dothidea, Fusarium oxysporum, Botrytis cinerea, and Fusarium fujikuroi. The highest percentage of growth inhibition, i.e., 66.67 ± 2.23%, was observed for SK1 against Botryosphaeria dothidea followed by 61.19 ± 3.12%, 60.71 ± 3.53%, and 55.54 ± 2.89% against Botrytis cinerea, Fusarium fujikuroi, and Fusarium oxysporum, respectively. The metabolite profiling of ethyl acetate fraction was assessed through the UHPLC-LTQ-IT-MS/MS analysis, and putative identification was done with the aid of the GNPS molecular networking workflow. A total of 29 compounds were putatively identified which included dipeptides, tripeptides, cyclopeptides (cyclo-(Leu-Leu), cyclo(Pro-Phe)), 2-heptyl-3-hydroxy 4-quinolone, 6-oxocativic acid, anhydrobrazilic acid, 1-(5-methoxy-1H-indol-3-yl)-2-piperidin-1-ylethane-1,2-dione, octadecenoic acid, pyochelin, 15-hydroxy-5Z,8Z,11Z, 13E-eicosatetraenoic acid, (Z)-7-[(2R,3S)-3-[(2Z,5E)-Undeca-2,5-dienyl]oxiran-2-yl]hept-5-enoic acid, arginylasparagine, cholic acid, sphinganine, elaidic acid, gossypin, L-carnosine, tetrodotoxin, and ursodiol. The high antifungal activity of SK1 might be attributed to the presence of these bioactive compounds. The isolated strain SK1 showed plant growth-promoting traits such as the production of organic acids, ACC deaminase, indole-3-acetic acid (IAA), siderophores, nitrogen fixation, and phosphate solubilization. IAA production was strongly correlated with the application of exogenous tryptophan concentrations in the medium. Furthermore, inoculation of SK1 enhanced plant growth of two Lilium varieties, Tresor and White Heaven, under greenhouse condition. In the light of these findings, the P. polymyxa SK1 may be utilized as a source of plant growth promotion and disease control in sustainable agriculture.

The impact of Paenibacillus polymyxa HY96-2 luxS on biofilm formation and control of tomato bacterial wilt.

The focus of this study was to investigate the effects of luxS, a key regulatory gene of the autoinducer-2 (AI-2) quorum sensing (QS) system, on the biofilm formation and biocontrol efficacy against Ralstonia solanacearum by Paenibacillus polymyxa HY96-2. luxS mutants were constructed and assayed for biofilm formation of the wild-type (WT) strain and luxS mutants of P. polymyxa HY96-2 in vitro and in vivo. The results showed that luxS positively regulated the biofilm formation of HY96-2. Greenhouse experiments of tomato bacterial wilt found that from the early stage to late stage postinoculation, the biocontrol efficacy of the luxS deletion strain was the lowest with 50.70 ± 1.39% in the late stage. However, the luxS overexpression strain had the highest biocontrol efficacy with 75.66 ± 1.94% in the late stage. The complementation of luxS could restore the biocontrol efficacy of the luxS deletion strain with 69.84 ± 1.09% in the late stage, which was higher than that of the WT strain with 65.94 ± 2.73%. Therefore, we deduced that luxS could promote the biofilm formation of P. polymyxa HY96-2 and further promoted its biocontrol efficacy against R. solanacearum.

Genome analysis of Paenibacillus polymyxa A18 gives insights into the features associated with its adaptation to the termite gut environment.

Paenibacillus polymyxa A18 was isolated from termite gut and was identified as a potential cellulase and hemicellulase producer in our previous study. Considering that members belonging to genus Paenibacillus are mostly free-living in soil, we investigated here the essential genetic features that helped P. polymyxa A18 to survive in gut environment. Genome sequencing and analysis identified 4608 coding sequences along with several elements of horizontal gene transfer, insertion sequences, transposases and integrated phages, which add to its genetic diversity. Many genes coding for carbohydrate-active enzymes, including the enzymes responsible for woody biomass hydrolysis in termite gut, were identified in P. polymyxa A18 genome. Further, a series of proteins conferring resistance to 11 antibiotics and responsible for production of 4 antibiotics were also found to be encoded, indicating selective advantage for growth and colonization in the gut environment. To further identify genomic regions unique to this strain, a BLAST-based comparative analysis with the sequenced genomes of 47 members belonging to genus Paenibacillus was carried out. Unique regions coding for nucleic acid modifying enzymes like CRISPR/Cas and Type I Restriction-Modification enzymes were identified in P. polymyxa A18 genome suggesting the presence of defense mechanism to combat viral infections in the gut. In addition, genes responsible for the formation of biofilms, such as Type IV pili and adhesins, which might be assisting P. polymyxa A18 in colonizing the gut were also identified in its genome. In situ colonization experiment further confirmed the ability of P. polymyxa A18 to colonize the gut of termite.

Paenibacillus polymyxa biofilm polysaccharides antagonise Fusarium graminearum.

Fusarium Head Blight (FHB) caused by Fusarium graminearum pathogens constitutes a major threat to agricultural production because it frequently reduces the yield and quality of the crop. The disease severity is predicted to increase in various regions owing to climate change. Integrated management where biocontrol plays an important role has been suggested in order to fight FHB. P. polymyxa A26 is known to be an effective antagonist against F. graminearum. Deeper understanding of the mode of action of P. polymyxa A26 is needed to develop strategies for its application under natural settings in order to effectively overcome the pathogenic effects. This study aims to re-evaluate a former study and reveal whether compounds other than non-ribosomal antibiotic lipopeptides could be responsible for the antagonistic effect, despite what is often reported. Wheat seedlings were grown to maturity and the spikes infected with the pathogen under greenhouse conditions. The development of FHB infection, quantified via the disease incidence severity and 100-kernel weight, was strongly correlated (r > 0.78, p < 0.01) with the content of the polysaccharide component D-glucuronic acid in the biofilm. Furthermore, while increased inoculum density from 106 to 108 cells/ml did not affect wild type performance, a significant increase was observed with the P. polymyxa mutant deficient in nonribosomal lipopeptide synthesis. Our results show that P. polymyxa A26 biofilm extracellular polysaccharides are capable of antagonizing F. graminearum and that the uronate content of the polysaccharides is of critical importance in the antagonism.

Plant growth promotion and suppression of bacterial leaf blight in rice by Paenibacillus polymyxa Sx3.

The effects and mechanisms of Paenibacillus polymyxa Sx3 on growth promotion and the suppression of bacterial leaf blight in rice were evaluated in this study. The results from a plate assay indicated that Sx3 inhibited the growth of 20 strains of Xanthomonas oryzae pv. oryzae (Xoo). Rice seedling experiments indicated that Sx3 promoted plant growth and suppressed bacterial leaf blight. In addition, bacteriological tests showed that Sx3 was able to fix nitrogen, solubilize phosphate and produce indole acetic acid, indicating that various mechanisms may be involved in the growth promotion by Sx3. The culture filtrate of P. polymyxa Sx3 reduced bacterial growth, biofilm formation and disrupted the cell morphology of Xoo strain GZ 0005, as indicated by the transmission and scanning electron microscopic observations. In addition, MALDI-TOF MS analysis revealed that Sx3 could biosynthesize two types of secondary metabolites fusaricidins and polymyxin P. In summary, this study clearly indicated that P. polymyxa Sx3 has strong in vitro and in vivo antagonistic activity against Xoo, which may be at least partially attributed to its production of secondary metabolites. SIGNIFICANCE AND IMPACT OF THE STUDY: Antagonistic bacteria can grow well in their originating environment. However, it is unclear whether antagonistic bacteria were able to survive in different ecological environments. This study revealed that Paenibacillus polymyxa Sx3 isolated from rhizosphere soil of cotton significantly promoted the plant growth and suppressed bacterial leaf blight in rice. Therefore, it could be inferred that P. polymyxa Sx3 has the potential to be used as biocontrol agents in plants grown in different ecological environments.

A plant growth-promoting bacterium alters the microbial community of continuous cropping poplar trees' rhizosphere.

AIMS: We aimed to develop a biological agent that regulates the microbial community structure of the poplar rhizosphere and alleviates the effects of continuous poplar cropping. METHODS AND RESULTS: Poplar rhizosphere soils were treated with or without Paenibacillus polymyxa CP-S316 microbial fermentation medium. Real-time polymerase chain reaction was performed to measure bacteria and fungi in both groups, and microbial communities were analysed by metabarcoding. In fungi, the operational taxonomic units, abundance-based coverage estimator and Chao index of the CP-S316-treated group were significantly lower than those in the control check (CK) group. In bacteria, the proportions of Bacillus in the CP-S316 and CK groups were 5·20 and 2·38%, respectively, whereas those of Rhizoctonia were 2·20 and 5·82% respectively. The diameter at breast height, culturable bacteria and total bacteria of poplars treated with CP-S316 exceeded those in the CK group. CONCLUSIONS: Our data confirmed that CP-S316 could improve the microbial community structure of poplar rhizosphere and promote the growth of poplars. SIGNIFICANCE AND IMPACT OF THE STUDY: Research aimed at alleviating continuous cropping obstacles and promoting poplar growth via biocontrol agents is uncommon. We analysed the community structures of bacteria and fungi in rhizosphere soil to illustrate the use of CP-S316 for poplar cropping for improving plant health in the continuous cropping of poplar trees.

An endophytic strain of genus Paenibacillus isolated from the fruits of Noni (Morinda citrifolia L.) has antagonistic activity against a Noni's pathogenic strain of genus Aspergillus.

Endophytes are microbes capable of colonizing the tissues of healthy plants and subsequently establishing a harmonious relationship with their hosts. In this research, the endophytic strain Paenibacillus sp. NEB was isolated from fruits of healthy Noni (Morinda citrifolia L.). Strain NEB was identified as Paenibacillus polymyxa using MALDI-TOF Mass Spectrometry. Pathogenic fungal strain NP-1 was isolated from Noni fruits infected by smut, and was identified as Aspergillus aculeatus by polyphasic taxonomy basing on morphological identification, and ITS-5.8S rDNA and ß-tubulin gene phylogenetic analyses. Through the antagonistic test against the pathogenic strain Aspergillus aculeatus NP-1, the results showed that strain NEB had a good antagonistic activity against smut pathogen of Noni. By sequencing with Illumina HiSeq 2000, the draft genome of Paenibacillus sp. NEB was acquired, and 3 CDSs for glucanases were annotated and potentially correlated to the antagonistic activity of this strain. Using realtime-PCR method with specific primers to amplify the biocontrol gene, ß-1,3-1,4- glucanase gene (gluB), it was found in Paenibacillus polymyxa NEB. This study would provide a theoretical and microbial basis for the rationally developing and using Noni beneficial microbial inoculants against its pathogenic strain in the future.

Positive and negative regulation of transferred nif genes mediated by indigenous GlnR in Gram-positive Paenibacillus polymyxa.

Ammonia is a major signal that regulates nitrogen fixation in most diazotrophs. Regulation of nitrogen fixation by ammonia in the Gram-negative diazotrophs is well-characterized. In these bacteria, this regulation occurs mainly at the level of nif (nitrogen fixation) gene transcription, which requires a nif-specific activator, NifA. Although Gram-positive and diazotrophic Paenibacilli have been extensively used as a bacterial fertilizer in agriculture, how nitrogen fixation is regulated in response to nitrogen availability in these bacteria remains unclear. An indigenous GlnR and GlnR/TnrA-binding sites in the promoter region of the nif cluster are conserved in these strains, indicating the role of GlnR as a regulator of nitrogen fixation. In this study, we for the first time reveal that GlnR of Paenibacillus polymyxa WLY78 is essentially required for nif gene transcription under nitrogen limitation, whereas both GlnR and glutamine synthetase (GS) encoded by glnA within glnRA operon are required for repressing nif expression under excess nitrogen. Dimerization of GlnR is necessary for binding of GlnR to DNA. GlnR in P. polymyxa WLY78 exists in a mixture of dimers and monomers. The C-terminal region of GlnR monomer is an autoinhibitory domain that prevents GlnR from binding DNA. Two GlnR-biding sites flank the -35/-10 regions of the nif promoter of the nif operon (nifBHDKENXhesAnifV). The GlnR-binding site Ⅰ (located upstream of -35/-10 regions of the nif promoter) is specially required for activating nif transcription, while GlnR-binding siteⅡ (located downstream of -35/-10 regions of the nif promoter) is for repressing nif expression. Under nitrogen limitation, GlnR dimer binds to GlnR-binding siteⅠ in a weak and transient association way and then activates nif transcription. During excess nitrogen, glutamine binds to and feedback inhibits GS by forming the complex FBI-GS. The FBI-GS interacts with the C-terminal domain of GlnR and stabilizes the binding affinity of GlnR to GlnR-binding site Ⅱ and thus represses nif transcription.

The Road from Host-Defense Peptides to a New Generation of Antimicrobial Drugs.

Host-defense peptides, also called antimicrobial peptides (AMPs), whose protective action has been used by animals for millions of years, fulfill many requirements of the pharmaceutical industry, such as: (1) broad spectrum of activity; (2) unlike classic antibiotics, they induce very little resistance; (3) they act synergically with conventional antibiotics; (4) they neutralize endotoxins and are active in animal models. However, it is considered that many natural peptides are not suitable for drug development due to stability and biodisponibility problems, or high production costs. This review describes the efforts to overcome these problems and develop new antimicrobial drugs from these peptides or inspired by them. The discovery process of natural AMPs is discussed, as well as the development of synthetic analogs with improved pharmacological properties. The production of these compounds at acceptable costs, using different chemical and biotechnological methods, is also commented. Once these challenges are overcome, a new generation of versatile, potent and long-lasting antimicrobial drugs is expected.

Antibacterial activity and probiotic characterization of autochthonous Paenibacillus polymyxa isolated from Anabas testudineus (Bloch, 1792).

Microbial fish pathogens are prevalent in aquaculture. Control of bacterial fish pathogens is important and bio control of pathogenic bacteria is a novel field of study. The aim of this study was to evaluate the antagonistic activity of bacteria isolated from Anabas testudineus against potent fish pathogens. The cellular components/preparations and filtered cell free culture supernatants were effective against six fish pathogens. Altogether 110 strains were isolated from fish proximal and distal intestine, out of which 10 strains were selected through well diffusion method. From them a strain HGA4C having prominent antimicrobial activity was selected as candidate probiotic strain. The whole-cell product, heat-killed whole-cell product and the filtered broth were exhibited bactericidal activity against the tested pathogens. Among them cell free culture supernatant showed maximum inhibition. In addition, isolated candidate probiotic bacterium was capable of producing extracellular enzymes important for the digestion of food ingredients and was effectively grown in fish mucus obtained from Oreochromis niloticus. The strain tolerated gradient of bile juice secreted by the host and effectively produced biofilm. Analysis of 16S rDNA sequence revealed that isolated strain HGA4C was Paenibacillus polymyxa (MF457398.1). Furthermore intraperitoneal injection of the bacterium did not induce any pathological anomalies or mortalities in Oreochromis niloticus and disclosed the safety of this bacterium as a candidate probiotic in aquaculture.

Isolation of a potential biocontrol agent Paenibacillus polymyxa NSY50 from vinegar waste compost and its induction of host defense responses against Fusarium wilt of cucumber.

Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (FOC) is one of the major destructive soil-borne diseases infecting cucumber. In this study, we screened 60 target strains isolated from vinegar waste compost, from which 10 antagonistic strains were identified to have the disease suppression capacity of bio-control agents. The 16S rDNA gene demonstrated that the biocontrol agents were Paenibacillus polymyxa (P. polymyxa), Bacillus amyloliquefaciens (B. amyloliquefaciens) and Bacillus licheniformis (B. licheniformis). Based on the results of antagonistic activity experiments and pot experiment, an interesting strain of P. polymyxa (named NSY50) was selected for further research. Morphological, physiological and biochemical characteristics indicated that this strain was positive for protease and cellulase and produced indole acetic acid (22.21±1.27µg mL-1) and 1-aminocyclopropane-1-carboxylate deaminase (ACCD). NSY50 can significantly up-regulate the expression level of defense related genes PR1 and PR5 in cucumber roots at the early stages upon challenge with FOC. However, the gene expression levels of a set of defense-related genes, such as the plant nucleotide-binding site (NBS)-leucine-rich repeat (LRR) gene family (e.g., Csa001236, Csa09775, Csa018159), 26kDa phloem protein (Csa001568, Csa003306), glutathione-S-transferase (Csa017734) and phenylalanine ammonia-lyase (Csa002864) were suppressed by pretreatment with NSY50 compared with the single challenge with FOC after nine days of inoculation. Of particular interest was the reduced expression of these genes at disease progression stages, which may be required for F. oxysporum dependent necrotrophic disease development.

Paenibacillus polymyxa NSY50 suppresses Fusarium wilt in cucumbers by regulating the rhizospheric microbial community.

Paenibacillus polymyxa (P. polymyxa) NSY50, isolated from vinegar residue substrate, suppresses the growth of Fusarium oxysporum in the cucumber rhizosphere and protects the host plant from pathogen invasion. The aim of the present study was to evaluate the effects of NSY50 application on cucumber growth, soil properties and composition of the rhizospheric soil microbial community after exposure to Fusarium oxysporum. Bacterial and fungal communities were investigated by Illumina sequencing of the 16S rRNA gene and the internal transcribed spacer (ITS) regions (ITS1 and ITS2). The results showed that NSY50 effectively reduced the incidence of Fusarium wilt (56.4%) by altering the soil physico-chemical properties (e.g., pH, Cmic, Rmic, total N and Corg) and enzyme activities, especially of urease and ß-glucosidase, which were significantly increased by 2.25- and 2.64-fold, respectively, relative to the pathogen treatment condition. More specifically, NSY50 application reduced the abundance of Fusarium and promoted potentially beneficial groups, including the Bacillus, Actinobacteria, Streptomyces, Actinospica, Catenulispora and Pseudomonas genera. Thus, our results suggest that NSY50 application can improve soil properties, shift the microbial community by increasing beneficial strains and decreasing pathogen colonization in the cucumber rhizosphere, and reduce the occurrence of cucumber Fusarium wilt, thereby promoting cucumber growth.

Isolation, identification and characterization of Paenibacillus polymyxa CR1 with potentials for biopesticide, biofertilization, biomass degradation and biofuel production.

BACKGROUND: Paenibacillus polymyxa is a plant-growth promoting rhizobacterium that could be exploited as an environmentally friendlier alternative to chemical fertilizers and pesticides. Various strains have been isolated that can benefit agriculture through antimicrobial activity, nitrogen fixation, phosphate solubilization, plant hormone production, or lignocellulose degradation. However, no single strain has yet been identified in which all of these advantageous traits have been confirmed. RESULTS: P. polymyxa CR1 was isolated from degrading corn roots from southern Ontario, Canada. It was shown to possess in vitro antagonistic activities against the common plant pathogens Phytophthora sojae P6497 (oomycete), Rhizoctonia solani 1809 (basidiomycete fungus), Cylindrocarpon destructans 2062 (ascomycete fungus), Pseudomonas syringae DC3000 (bacterium), and Xanthomonas campestris 93-1 (bacterium), as well as Bacillus cereus (bacterium), an agent of food-borne illness. P. polymyxa CR1 enhanced growth of maize, potato, cucumber, Arabidopsis, and tomato plants; utilized atmospheric nitrogen and insoluble phosphorus; produced the phytohormone indole-3-acetic acid (IAA); and degraded and utilized the major components of lignocellulose (lignin, cellulose, and hemicellulose). CONCLUSIONS: P. polymyxa CR1 has multiple beneficial traits that are relevant to sustainable agriculture and the bio-economy. This strain could be developed for field application in order to control pathogens, promote plant growth, and degrade crop residues after harvest.