Polymyxa Strain Research Articles

Fusaricidins, Polymyxins and Volatiles Produced by Paenibacillus polymyxa Strains DSM 32871 and M1.

Paenibacilli are efficient producers of potent agents against bacterial and fungal pathogens, which are of great interest both for therapeutic applications in medicine as well as in agrobiotechnology. Lipopeptides produced by such organisms play a major role in their potential to inactivate pathogens. In this work we investigated two lipopeptide complexes, the fusaricidins and the polymyxins, produced by Paenibacillus polymyxa strains DSM 32871 and M1 by MALDI-TOF mass spectrometry. The fusaricidins show potent antifungal activities and are distinguished by an unusual variability. For strain DSM 32871 we identified numerous yet unknown variants mass spectrometrically. DSM 32871 produces polymyxins of type E (colistins), while M1 forms polymyxins P. For both strains, novel but not yet completely characterized polymyxin species were detected, which possibly are glycosylated. These compounds may be of interest therapeutically, because polymyxins have gained increasing attention as last-resort antibiotics against multiresistant pathogenic Gram-negative bacteria. In addition, the volatilomes of DSM 32781 and M1 were investigated with a GC–MS approach using different cultivation media. Production of volatile organic compounds (VOCs) was strain and medium dependent. In particular, strain M1 manifested as an efficient VOC-producer that exhibited formation of 25 volatiles in total. A characteristic feature of Paenibacilli is the formation of volatile pyrazine derivatives.

Epiphytic Bacteria from Sweet Pepper Antagonistic In Vitro to Ralstonia solanacearum BD 261, a Causative Agent of Bacterial Wilt

Biological control of plant pathogens, particularly using microbial antagonists, is posited as the most effective, environmentally-safe, and sustainable strategy to manage plant diseases. However, the roles of antagonists in controlling bacterial wilt, a disease caused by the most devastating and widely distributed pathogen of sweet peppers (i.e., R. solanacearum), are poorly understood. Here, amplicon sequencing and several microbial function assays were used to depict the identities and the potential antagonistic functions of bacteria isolated from 80 red and green sweet pepper fruit samples, grown under hydroponic and open soil conditions, with some plants, fungicide-treated while others were untreated. Amplicon sequencing revealed the following bacterial strains: Bacillus cereus strain HRT7.7, Enterobacter hormaechei strain SRU4.4, Paenibacillus polymyxa strain SRT9.1, and Serratia marcescens strain SGT5.3, as potential antagonists of R. solanacearum. Optimization studies with different carbon and nitrogen sources revealed that maximum inhibition of the pathogen was produced at 3% (w/v) starch and 2,5% (w/v) tryptone at pH 7 and 30 °C. The mode of action exhibited by the antagonistic isolates includes the production of lytic enzymes (i.e., cellulase and protease enzymes) and siderophores, as well as solubilization of phosphate. Overall, the results demonstrated that the maximum antimicrobial activity of bacterial antagonists could only be achieved under specific environmental conditions (e.g., available carbon and nitrogen sources, pH, and temperature levels), and that bacterial antagonists can also indirectly promote crop growth and development through nutrient cycling and siderophore production.

Efektivitas Isolat-Isolat Bacillus sebagai Pengendali Penyakit Bulai dan Pemacu Pertumbuhan Tanaman Jagung pada Kondisi Terkontrol

The main disease in maize is downy mildew caused by the fungus Peronosclerospora spp.. This pathogen can cause yield losses of up to 100%. Therefore, efforts to control this disease are continuously carried out, including technical culture, assembly of resistant plants, and use of synthetic fungicides. At the farm level, the use of metalaxyl, synthetic fungicides is the most common practice. On the other hand, it has been reported that some Peronosclerospora groups are starting to become resistant to metalaxyl. These problems lead to the need for alternative controls, for example with biological agents. Biological agents from bacterial groups have been developed to control plant disease, but for downy mildew is still limited. The purpose of this study is to screen and test Bacillus spp. ability to suppress downy mildew and promote the growth of maize. The assay was carried out on seeds by invitro to investigate growth-promoting reactions and also testing under controlled conditions in greenhouses to investigate the suppression ability of downy mildew disease development. The results showed B. polymyxa strain BP18, Bacillus subtilis strain BS41, Bacillus sp. strain BT1, and Bacillus sp. strains can stimulate the growth of corn seedlings and suppress downy mildew. The best isolate in suppressing downy mildew was Bacillus sp. strain BT1 with the smallest AUDPC value (3.94) and the highest protection index (82.71%). It is hoped that these results will find potential isolates and have the potential to be developed into biopesticides and biofertilizers.

Effect of exopolysaccharides of Paenibacillus polymyxa rhizobacteria on physiological and morphological variables of wheat seedlings.

Paenibacillus polymyxa is a promising plant-growth-promoting rhizobacterium that associates with a wide range of host plants, including agronomically important ones. Inoculation of wheat seedlings with P. polymyxa strains CCM 1465 and 92 was found to increase the mitotic index of the root cells 1.2- and 1.6-fold, respectively. Treatment of seedlings with the exopolysaccharides (EPSs) of these strains increased the mitotic index 1.9-fold (P. polymyxa CCM 1465) and 2.8-fold (P. polymyxa 92). These increases indicate activation of cell division in the root meristems. Analysis of the morphometric variables of the seedlings showed that P. polymyxa CCM 1465, P. polymyxa 92, and their EPSs promoted wheat growth, increasing root and shoot length up to 22% and root and shoot dry weight up to 28%, as compared with the control. In addition, both strains were found to intensely colonize the seedling root surface. Thus, P. polymyxa EPSs are active metabolites that, along with whole cells, are responsible for the contact interactions of the bacteria with wheat roots and are implicated in the induction of plant responses to these interactions. The strains used in this work are of interest for further study to broaden the existing understanding of the mechanisms of plant-bacterial interactions and to develop effective biofertilizers for agricultural purposes.

Genome Sequence of Paenibacillus polymyxa Strain HOB6, Isolated from Hemp Seed Oil.

ABSTRACTPaenibacillus polymyxa strain HOB6 was isolated from hemp seed oil. The strain displays antimicrobial activity against fungal pathogens and has potential for development as a biopesticide against cannabis diseases. Its genome was sequenced and annotated, uncovering the ability to encode the biosynthetic pathways for antimicrobial lanthipeptides and nonribosomal peptides.

Molecular-genetic identification of microorganism strains isolated from activated sludge based on an analysis of nucleotide sequences of the 16s rRNA gene

A molecular-genetic identification of four bacterial strains isolated from activated sludge of urban wastewater treatment plants (Ulan-Ude) and the industrial enterprise OJSC “Selenginsky Pulp and Paper Mill” (Selenginsk) was carried out. Bacterial strains were identified by a capillary sequencer ABI 3130XL Genetic Analyzer (Applied Biosystems) using 16S primers 27F and 1492R at the Genomics Collective Use Center of the Institute of Chemical Biology and Fundamental Medicine, SB RAS, Novosibirsk. The results were obtained using the method of determination of the direct nucleotide sequence of a 16S rRNA fragment followed by comparison of the nucleotide identity with the sequences deposited in the international database GenBank. Bacterial strains isolated from activated sludge were identified according to the GenBank database: strain B 1.1 corresponds to Paenibacillus dendritiformis strain P411 (similarity 99.93%), strains B 1.2 and B 1.3 correspond to Bacillus licheniformis strain PB399 (similarity 86 and 100%, respectively), strain P 1.1 corresponds to the Paenibacillus polymyxa strain ISSDS-85 (similarity 99.86%). The biochemical properties of the identified strains were determined: amylolytic, proteolytic and lipolytic activity; the ability to ferment carbohydrates in Hiss’ nutrient medium; the ability to form ammonia, urea and nitrate reduction. The bacterial strains isolated from activated sludge may be promising for the destruction of wastewater pollutants. On their basis, it is planned to create a consortium of microorganisms for the destruction of protein and fatty pollutants in wastewater.

Production of (2R,3R)-butanediol by Paenibacillus polymyxa PM 3605 from crude glycerol supplemented with sugarcane molasses

2,3-Butanediol (2,3-BDO) is a chemical platform used in several applications, such as cosmetics, medicines, polymers, and fuels. Its levo-isomer is used as an antifreeze agent of industrial interest. Glycerol has been extensively investigated to produce 2,3-BDO by different bacteria. However, few studies involving Paenibacillus polymyxa and glycerol have been conducted so far. In this study, biodiesel-derived glycerol was used for the 2,3-BDO production by P. polymyxa PM 3605. About 14.5 g/L of 2,3-BDO was obtained from 50 g/L of crude glycerol in shaken flasks at 37 °C and 200 rpm. By supplementing the glycerol-containing medium with 10 g/L of sugarcane molasses, the final 2,3-BDO production was enhanced to up to 19 g/L. This was the highest 2,3-BDO titer produced by the P. polymyxa strain from crude glycerol as the main carbon source, and sugarcane molasses as a secondary substrate, until now. The selectivity of levo-2,3-BDO was high, and the production of meso-2,3-BDO and acetoin were not detected. As 2,3-BDO metabolism is dependent on strict oxygen control to ensure a microaerobic condition, the production found here has potential for improvement, indicating that the glycerol use by P. polymyxa PM 3605 is promising for the levo-2,3-BDO synthesis.

Comparative and Functional Analyses of Two Sequenced Paenibacillus polymyxa Genomes Provides Insights Into Their Potential Genes Related to Plant Growth-Promoting Features and Biocontrol Mechanisms.

Many bacteria belonging to Paenibacillus polymyxa are plant growth-promoting rhizobacteria (PGPR) with the potential to promote plant growth and suppress phytopathogens and have been used as biological control agents (BCAs). However, the growth promotion and biocontrol mechanisms of P. polymyxa have not been thoroughly elucidated thus far. In this investigation, the genome sequences of two P. polymyxa strains, ZF129 and ZF197, with broad anti-pathogen activities and potential for growth promotion were comparatively studied. Comparative and functional analyses of the two sequenced P. polymyxa genomes showed that the ZF129 genome consists of one 5,703,931 bp circular chromosome and two 79,020 bp and 37,602 bp plasmids, designated pAP1 and pAP2, respectively. The complete genome sequence of ZF197 consists of one 5,507,169 bp circular chromosome and one 32,065 bp plasmid, designated pAP197. Phylogenetic analysis revealed that ZF129 is highly similar to two P. polymyxa strains, HY96-2 and SQR-21, while ZF197 is highly similar to P. polymyxa strain J. The genes responsible for secondary metabolite synthesis, plant growth-promoting traits, and systemic resistance inducer production were compared between strains ZF129 and ZF197 as well as other P. polymyxa strains. The results indicated that the variation of the corresponding genes or gene clusters between strains ZF129 and ZF197 may lead to different antagonistic activities of their volatiles or cell-free supernatants against Fusarium oxysporum. This work indicates that plant growth promotion by P. polymyxa is largely mediated by phytohormone production, increased nutrient availability and biocontrol mechanisms. This study provides an in-depth understanding of the genome architecture of P. polymyxa, revealing great potential for the application of this bacterium in the fields of agriculture and horticulture as a PGPR.

The Bio-Synthesis of Three Metal Oxide Nanoparticles (ZnO, MnO2, and MgO) and Their Antibacterial Activity Against the Bacterial Leaf Blight Pathogen.

Xanthomonas oryzae pv. oryzae (Xoo) is the most infectious pathogen of rice, which causes bacterial leaf blight (BLB) disease. However, the accumulation of chemical or antibiotic resistance of Xoo necessitate the development of its alternative control. In this study, we biologically synthesize three metal oxide nanoparticles (ZnO, MnO2, and MgO) using rhizophytic bacteria Paenibacillus polymyxa strain Sx3 as reducing agent. The biosynthesis of nanoparticles was confirmed and characterized by using UV-vis spectroscopy, XRD, FTIR, EDS, SEM, and TEM analysis. The UV Vis reflectance of the nanoparticle had peaks at 385, 230, and 230 nm with an average crystallite particle size 62.8, 18.8, and 10.9 nm for ZnO, MnO2, and MgO, respectively. Biogenic ZnO, MnO2, and MgO nanoparticles showed substantial significant inhibition effects against Xoo strain GZ 0006 at a concentration of 16.0 μg/ml, for which the antagonized area was 17, 13, and 13 mm and the biofilm formation was decreased by 74.5, 74.4, and 80.2%, respectively. Moreover, the underlining mechanism of nanoparticles was inferred to be in relation to the reactive oxygen species based on their antibacterial efficiency and the deformity in the cell wall phenomenon. Overall, an attractive and eco-friendly biogenic ZnO, MnO2, and MgO nanoparticles were successfully produced. Altogether, the results suggest that the nanoparticles had an excellent antibacterial efficacy against BLB disease in rice plants, together with the increase in growth parameter and rice biomass. In conclusion, the synthesized nanoparticles could serve as an alternative safe measure in combatting the antibiotic-resistant of Xoo.

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, β-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.

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.

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.

Draft genome sequence data of Paenibacillus Polymyxa strain TH2H2, isolated from a tomato flower in Korea.

Members of the genus Paenibacillus are known for their production of useful substances, and some species of the genus are recognized to be plant growth-promoting rhizobacteria. Paenibacillus polymyxa TH2H2, isolated from a tomato flower, had antifungal activity. Here, the draft genome sequence of Paenibacillus polymyxa TH2H2 is reported. The 5,983,104-bp genome, with a G+C content of 45.31%, comprised 5,221 protein-coding genes, 64 ribosomal RNA and 100 transfer RNA. Three intact antibiotic biosynthesis gene clusters were identified using antiSMASH. These encoded the antifungal agent fusaricidin and two antibacterial agents, tridecaptin and polymyxin. Sequence data have been deposited in the DDBJ/ENA/GenBank database under the accession number RPDG01000000. The version described in this paper is RPDG00000000.1. The BioProject ID in the GenBank database is PRJNA505713.

Growth-promoting and disease-suppressing effects of Paenibacillus polymyxa strain YCP16-23 on pepper (Capsicum annuum) plants

Phytophthora blight is the most devastating disease for pepper (Capsicum annuum L.) production and is caused by Phytophthora capsici. Current management strategies are not effective. Our study assessed the multi-trait effects of Paenibacillus polymyxa, which suppresses Phytophthora blight and promotes plant growth in pepper plants. A total of 82 bacterial strains isolated from rhizosphere soil of pepper plants were screened for in vitro inhibition of P. capsici growth. The results revealed that only six strains showed strong antagonistic activity against P. capsici. These six strains were used for controlling Phytophthora blight in pepper by seedling assays under greenhouse conditions. Three strains showed a lower incidence of Phytophthora blight and were used in further growth-promoting and biocontrol studies under greenhouse conditions. Strain YCP16-23 showed >60.0% suppression of P. capsici and significantly promoted growth of pepper plants compared to the untreated control. Based on cultural and morphological characterization and 16S rRNA gene sequencing, strain YCP16-23 was identified as Paenibacillus polymyxa. Strain YCP16-23 demonstrated many characteristics that are beneficial for plants, such as production of α-amylase, ammonia, cellulase, indole-3-acetic acid, pectinase, siderophores, and protease, as well as solubilization of phosphate. In a two-year field trial, strain YCP16-23 exhibited remarkable disease suppressing effect by controlling Phytophthora blight (76.24% and 38.09% in years 2017 and 2018, respectively) compared with the untreated control. Strain YCP16-23 caused disease suppression comparable to the microbial fungicides ‘Cike’ (72.04% and 15.41%) and Fluazinam (80.47% and 5.24%). Overall, the results suggest that strain YCP16-23 could provide protection against Phytophthora blight via direct and indirect modes of action and can be used as a biocontrol agent.

Comparative genome analysis and mining of secondary metabolites of Paenibacillus polymyxa.

Paenibacillus polymyxa is a well-known Gram-positive biocontrol bacterium. It has been reported that many P. polymyxa strains can inhibit bacteria, fungi and other plant pathogens. Paenibacillus polymyxa employs a variety of mechanisms to promote plant growth, so it is necessary to understand the biocontrol ability of bacteria at the genome level. In the present study, thanks to the widespread availability of Paenibacillus genome data and the development of bioinformatics tools, we were able to analyze and mine the genomes of 43 P. polymyxa strains. The strain NCTC4744 was determined not to be P. polymyxa according to digital DNA-DNA hybridization and average nucleotide identity. By analysis of the pan-genome and the core genome, we found that the pan-genome of P. polymyxa was open and that there were 3,192 core genes. In a gene cluster analysis of secondary metabolites, 797 secondary metabolite gene clusters were found, of which 343 are not similar to known clusters and are expected to reveal a large number of new secondary metabolites. We also analyzed the plant growth-promoting genes that were mined and found, surpisingly, that these genes are highly conserved. The results of the present study not only reveal a large number of unknown potential secondary metabolite gene clusters in P. polymyxa, but also suggest that plant growth promotion characteristics are evolutionary adaptations of P. polymyxa to plant-related habitats.

Fusaricidin-Type Compounds Create Pores in Mitochondrial and Plasma Membranes of Mammalian Cells.

Fusaricidins and related LI-F compounds are effective bactericides and fungicides. Recently, we have found that they are highly toxic to mammalian cells. Here, we studied the effect of fusaricidin-type compounds (FTCs) on the membranes of mammalian cells. Ethanol extracts from Paenibacillus polymyxa strains, RS10 and I/Sim, were fractionated and analyzed by HPLC and mass spectrometry. The effects of FTCs on mitochondrial functions and integrity were studied by standard methods: measurements of swelling, membrane potential (ΔΨm), respiration rate, cytochrome c release, and pore sizes. Superoxide flashes were registered by 3,7-dihydro-2-methyl-6-(4-methoxyphenyl)imidazol[1,2-a]pyrazine-3-one (MCLA). Plasma membrane permeability was assessed by propidium iodide (PI) staining and ATP release. FTCs caused the permeabilization of the inner mitochondria membrane (IMM) to ions and low-molecular-weight (~750 Da) solutes. The permeabilization did not depend on the permeability transition pore (mPTP) but was strongly dependent on ΔΨm. Fusaricidins A plus B, LI-F05a, and LI-F05b–LI-F07b permeabilized IMM with comparable efficiency. They created pores and affected mitochondrial functions and integrity similarly to mPTP opening. They permeabilized the sperm cell plasma membrane to ATP and PI. Thus, the formation of pores in polarized membranes underlays the toxicity of FTCs to mammals. Besides, FTCs appeared to be superior reference compounds for mPTP studies.

Effects of Rhizobacteria on Plant Development, Quality of Flowering and Bulb Mineral Contents in Hyacinthus orientalis L.

Size of bulbs is directly proportional to the quality of the flower, the commercial value of the bulb and getting more bulblet. The research was carried out to evaluate the effects of PGPR on plant growth parameters, flowering, bulb quality and bulb mineral contents in hyacinth (Hyacinthus orientalis L. cv. Aiolos) under greenhouse condition. In the study, there were 5 applications: (T1) Pseudomonas putida strain RCK-42A, (T2) Kluyvera cryocrescens strain RCK-113C, (T3) Paenibacillus polymyxa strain RCK-12E, (T4) Bacillus subtilis strain RCK-17C, and (T5) Control (uninoculated bacteria). The surface-sterilized bulbs were incubated separately by shaking at 80 rpm for two hours at 28 ºC to coat the bulbs with the bacteria. The chlorophyll content (50.02), leaf length (26.03 cm), leaf area (268.38cm2), flower fresh and dry weight (15.54 g and 0.88 g) in T2 (Kluyvera cryocrescens strain RCK-113C) was found as the maximum according to other applications. The highest leaf width (6.37 cm) and the highest floret number were observed in T4. It was shown that the maximum bulb diameter (42.57 mm), bulb length (40.01 mm) and bulb weight (12.01 g) were determined in T2. The maximum N (2.90%), P (1.98%) and Ca (1.74%) were found in T3. Maximum Fe (0.48 mg kg-1), Mn (151.20 mg kg-1) and Zn (35.28 mg kg-1) were found in T1. Use of especially Kluyvera cryocrescens strain RCK-113C and Pseudomonas putida strain RCK-42A bacterial isolates may be effective in maintaining the sustainability of the environment and growing medium in the cultivation of hyacinth and also the development of bio fertilizer.

Chronicle of a Soil Bacterium: Paenibacillus polymyxa E681 as a Tiny Guardian of Plant and Human Health.

The Gram-positive rhizosphere bacterium Paenibacillus polymyxa promotes plant growth and produces various antibiotics. Herein, we review research on this species over the past two and a half decades, and focus on the mechanisms of P. polymyxa strain E681, isolated from barley roots in the South Korea in 1995. Strain E681 has outstanding growth-promoting effects on barley, cucumber, pepper, sesame, and Arabidopsis thaliana and produces antimicrobial compounds that protect plants against pathogenic fungi, oomycetes, and bacteria. Induced systemic resistance elicited by treating seeds or roots with strain E681 is a possible mechanism for protecting systemic plant tissues from biotic and other environmental stresses. Genome sequencing has broadened our horizons for antibiotic development and other industrial applications beyond agricultural use. At least six gene clusters for the biosynthesis of antibiotics have been discovered, including polymyxin (pmx), which was recently re-instated as an antibiotic of last resort against Gram-negative drug-resistant bacteria. Three groups of antibiotic synthetases include the gene clusters that encode one for the non-ribosomal peptide polymyxin, fusaricidin, and tridecaptin, another for the lantibiotic paenilan, and the third for a polyketide. We successfully introduced the pmx gene cluster into the surrogate host Bacillus subtilis and created polymyxin derivatives by domain swapping. Furthermore, various E681 derivatives, including a high fusaricidin producer and strains lacking multi-antibiotics production, have been constructed by random mutagenesis and genome engineering. Thus, E681 is an important bacterium that contributes to both plant and human health.

Isolation and identification of a phosphate-solubilizing Paenibacillus polymyxa strain GOL 0202 from durum wheat (Triticum durum Desf.) rhizosphere and its effect on some seedlings morphophysiological parameters

Abstract Paenibacillus polymyxa is a common bacterium, belonging to Plant Growth Promoting Rhizobacteria (PGPR). It is found in soils, roots and rhizosphere of various crop plants especially wheat. This bacterium has a great biotechnological potential in sustainable agriculture. Indeed, in the rhizosphere, P. polymyxa is involved in nitrogen fixation, production of phytohormones, exoplysaccharides, hydrolytic enzymes and antibiotics, in the enhancement of soil porosity and in soil phosphorus solubilization. In this study, we have identified GOL 0202 strain as Paenibacillus polymyxa, isolated from durum wheat (Triticum durum Desf.) rhizosphere collected from arid region soil of Southern. This genomic identification was performed by 16S rRNA gene sequencing. It was shown that this strain possesses an interesting phosphate solubilization activity on NBRIP (National Botanical Research Institute Phosphorus) medium containing tricalcium phosphate (Ca3 (PO4)2). This activity, was recorded over five days, it was negatively correlated with pH medium whose decline was due probably to the release of organic acids. In addition to other activities associated with P. polymyxa, this availability of soluble phosphate has allowed the improvement of durum wheat seedlings growth estimated through dry weight, chlorophylls and proteins contents. Hence, P. polymyxa GOL 0202 could be used for their targeted application as bioinoculant.

Paenibacillus polymyxa Role Involved in Phosphate Solubilization and Growth Promotion of Zea mays Under Abiotic Stress Condition

This investigation is aimed to analyse in vitro phosphate solubilization activity of Paenibacillus polymyxa under abiotic stress condition and their growth promotion potential on maize (Zea mays) seeds including the abilities to antagonize phytopathogens. Performance of this strain is greatly influenced to fix available phosphorus, making it essential to ascertain this strain for improving phosphate-solubilizing ability and alleviating the extreme environmental condition effects. In this study, P. polymyxa was screened on the basis of phosphate-solubilizing bacteria using PVK agar, inorganic phosphate and tricalcium phosphate {Ca3(PO4)2} in order to detect the presence of halo zone, indicating the solubilization occurrence. The strain also exhibited the ability to solubilize the phosphate in varying pH treatment (5–9), temperature (25–35 °C) and heavy metal tolerance (0.02–0.05 M Ni and Zn). The maximum phosphate-solubilizing activity was found to be 2635.3 μg ml−1 after 5 days of incubation with the decrease in pH of the medium from 6.08 to 3.28. The effect of the strain on growth of maize seedlings and its other promoting attributes (cell wall-degrading enzymes, N2 fixation ability and biocontrol activity against Fusarium oxysporum and Botrytis cinerea) were studied. Remarkably, the strain P. polymyxa inoculant resulted in almost twofold greater in fresh weight and shoot length of maize seedlings as compared to others. Paenibacillus polymyxa strain used in this study showed efficient phosphate mineralizing and solubilization ability with the view of utilizing them as inoculant sources in correspondence to boost the fertility of soils.