Endophytic Bacterial Strains Research Articles

Genome Sequence Resource of Bacillus velezensis Strain HC-8, a Native Bacterial Endophyte with Biocontrol Potential Against the Honeysuckle Powdery Mildew Causative Pathogen Erysiphe lonicerae var. lonicerae.

Genome Sequence Resource of Bacillus velezensis Strain HC-8, a Native Bacterial Endophyte with Biocontrol Potential Against the Honeysuckle Powdery Mildew Causative Pathogen Erysiphe lonicerae var. lonicerae.

Bioprospects of Endophytic Bacteria in Plant Growth Promotion and Ag-Nanoparticle Biosynthesis.

In this study, five endophytic bacterial strains, namely Rhizobium pusense (MS-1), Bacillus cereus MS-2, Bacillus flexus (MS-3), Methylophilus flavus (MS-4), and Pseudomonas aeruginosa (MS-5), were used to investigate their potential role in the enhancement of growth yields of two types of tomato varieties, viz. hybrid and local, and in the biosynthesis of silver nanoparticles (AgNPs). The inoculation of bacterial strains enhanced the root and shoot length, biomass, and leaf chlorophyll contents. The fruit weight of the tomato (kg/plant) was also higher in the bacteria inoculated plants of both hybrid and local varieties than in the control (untreated). A significant increase was recorded in the fruit yield (g/plant) in all the treatments, whereas Methylophilus flavus (MS-4) inoculated plants yielded nearly 2.5 times more fruit weight compared to the control in the hybrid variety and two times higher in the local variety. The response to M. flavus as a microbial inoculant was greater than to the other strains. Biosynthesis of Ag nanoparticles was also carried out using all five endophytic bacterial strains. The weakest producers of AgNPs were Rhizobium pusense (MS-1) and Methylophilus flavus (MS-4), while Bacillus cereus MS-2, Bacillus flexus (MS-3), and Pseudomonas aeruginosa (MS-5) were strong producers of AgNPs. Nanoparticles were further characterized using high-resolution scanning electron microscopy (HR-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV-Vis spectrophotometry, and X-ray diffraction (XRD) analysis, and revealed cuboidal shaped AgNPs in the Bacillus cereus MS-2 strain. In addition, the biosynthesized AgNPs showed antibacterial activity against various pathogenic and endophytic bacterial strains.

Bioactivities evaluation of an endophytic bacterial strain Bacillus velezensis JRX-YG39 inhabiting wild grape

BackgroundBotrytis cinerea can cause serious disease on lots of plant hosts during growth and postharvest storage. Biocontrol is known to be eco-friendly methods to control pathogens. Plant endophytic bacteria are generally considered as beneficial organisms, since they can promote plant growth and enhance plant immune system. Thus, screening biological control agents is very important for sustainable plant protection.ResultsFifty-six endophytic bacteria were obtained from wild grape. Sixteen isolates and their extracts exhibited significant antifungal activity against B. cinerea. Particularly, strain JRX-YG39 with the strongest inhibition ability had a broad-spectrum antifungal activity. Combining 16S rDNA analysis and the phylogenetic results based on gyrA and gyrB genes, JRX-YG39 was assigned as Bacillus velezensis. JRX-YG39 could produce bioactive VOCs and obviously depressed mycelia growth of B. cinerea. It was confirmed that VOCs released by JRX-YG39 could significantly promote growth and induce defense of Arabidopsis thaliana. Thirty-one bioactive secondary metabolites were further identified from JRX-YG39 culture by gas chromatography–mass spectrometry analysis. Dibutyl phthalate, a potential antifungal substance, was the major compound accounting for 78.65%.ConclusionsB. velezensis JRX-YG39 has wide broad-spectrum antagonistic activity and significant plant promotion activity. Hence, B. velezensis JRX-YG39 will provide a valuable constituent of modern agricultural practice as biofertilizers and biocontrol agents.

Characterization and identification of plant growth promoting endophytic bacterial strain IU10

Growing evidence has suggested that plant growth-promoting endophytic bacteria can regulate, which can be used as biofertilizers, bio-stimulants, and biocontrol agent. In the present study, Bacillus subtills IU10 was isolated from plants and was subjected to advanced chromatography and spectroscopic techniques for the extraction and isolation of indole-3-acetic acid (IAA). Up to 10 ?g/mL of IAA was quantified in the bacterial extract using the [2H2]-IAA internal standards in GC-MS analysis. PVK agar containing Ca3(PO4)2 was used to measure the ability of IU10 to solubilize phosphate. The clear zones formed by phosphate solubilization were measured to assess the phosphate solubilization potential. Azurol-S (CAS) medium was used for measuring siderophore production. The orange halo circles were measured to quantify the siderophore production. Endophytic IU10 inoculated plants showed significantly improvement root to shoot length, biomass and chlorophyll as compared to control. The data indicates that IU10 produce phytohormones, siderophore and immobilize nutrients could be used as biofertilizer. Keywords: phytohormones, nutrient immobilization, growth promotion, endophytes.

Characterization, enzymatic and biochemical properties of endophytic bacterial strains of the medicinal plant Ajuga turkestanica (Rgl.) Brig (Lamiaceae)

This research work aims to isolate endophytic bacteria from the Ajuga turkestanica plant that have plant growth promoting properties. The microscopic, enzymatic and biochemical properties of the isolated endophytic bacteria are described. Twelve isolates of endophytic bacteria were isolated by standard microbiological methods. Isolated endophytic bacteria were identified by (MALDI-TOF MS). Endophytic bacteria isolated from the plant were detected in MALDI-TOF MS. Bacterial isolates were dominated by endophytic bacteria belonging to the genus Bacillus, Pseudomonas, Siccibacter. When the growth-enhancing properties of cultivated plants used in sustainable agriculture were studied, the isolated bacterial strains showed positive results in siderophor, ammonia, indole acetic acid production, and nitrogen fixation properties. Numerous endophytic bacteria have been found to have the enzymatic activity of oxidase, catalase, amylase, lecithinase and lipase. The results showed that endophytic bacteria isolated from the plant A. turkestanica are have plant stimulating properties which can be shown as a candidate for the production of bioinoculants individually or as part of a consortium.

Genomic Analysis of Endophytic Bacillus-Related Strains Isolated from the Medicinal Plant Origanum vulgare L. Revealed the Presence of Metabolic Pathways Involved in the Biosynthesis of Bioactive Compounds.

Multidrug-resistant pathogens represent a serious threat to human health. The inefficacy of traditional antibiotic drugs could be surmounted through the exploitation of natural bioactive compounds of which medicinal plants are a great reservoir. The finding that bacteria living inside plant tissues, (i.e., the endophytic bacterial microbiome) can influence the synthesis of the aforementioned compounds leads to the necessity of unraveling the mechanisms involved in the determination of this symbiotic relationship. Here, we report the genome sequence of four endophytic bacterial strains isolated from the medicinal plant Origanum vulgare L. and able to antagonize the growth of opportunistic pathogens of cystic fibrosis patients. The in silico analysis revealed the presence of gene clusters involved in the production of antimicrobial compounds, such as paeninodin, paenilarvins, polymyxin, and paenicidin A. Endophytes’ adaptation to the plant microenvironment was evaluated through the analysis of the presence of antibiotic resistance genes in the four genomes. The diesel fuel degrading potential was also tested. Strains grew in minimum media supplemented with diesel fuel, but no n-alkanes degradation genes were found in their genomes, suggesting that diesel fuel degradation might occur through other steps involving enzymes catalyzing the oxidation of aromatic compounds.

Potential of N2-fixing endophytic bacteria isolated from maize roots as biofertiliser to enhance soil fertility, N uptake, and yield of Zea mays L. cultivated in alluvial soil in dykes

This study aimed to (i) select the endophytic bacteria from maize roots for their N2-fixing ability and (ii) evaluate the efficacy of potent indigenous bacterial strains on soil fertility, nitrogen (N) uptake, and growth and yield of maize. A total of 31 maize root samples were collected from An Giang province in Vietnam to isolate the bacteria. The pot experiment was conducted in nine treatments: (i) 100% N of the recommended fertiliser formula (RFF), (ii) 85% N of RFF, (iii) 70% N of RFF, (iv) 55% N of RFF, (v) 85% N of RFF plus a mixture of two potent strains of nitrogen-fixing endophytic bacteria (NFEB), (vi) 70% N of RFF plus a mixture of two potent strains of NFEB, (vii) 25% N of RFF plus a mixture of two potent strains of NFEB, (viii) 0% N of RFF plus a mixture of two potent strains of NFEB, and (ix) 0% N of RFF. The experiment was conducted in the greenhouse to collect soil and plant samples at harvest and observe their growth and agronomic parameters. The results showed that two acid-resistant endophytic bacterial strains were selected and identified as Enterobacter cloacae ASD-21 and E. cloacae ASD-48. At 85% N level, a mixture of the two endophytic bacteria strains was applied as biofertilisers and proved their ability to significantly enhance NH4+ content and N uptake, with an increase of 14.8 mg NH4+ kg-1 and 0.26 g N pot-1, respectively. A mixture of the two potent strains of NFEB produced higher values in plant height, stem diameter, cob length, and cob diameter compared to 100% N of RFF. It replaced 15% N of RFF but still maintained the maize grain yield

Differential response of two endophytic bacterial strains inoculation on biochemical and physiological parameters of Bacopa monnieriL. under arsenic stress conditions

The accumulation of arsenic (As), in medicinal herbs, is detrimental due to its adverse effects on plant metabolism and consumer health. The present study aims to examine the ameliorative effect of two arsenate [As(V)] reducing endophytic bacterial strains (CIMAP-A4 and BAC-7) on As induced photo-toxicity in Bacopa monnieri. The inoculation of BAC-7 and CIMAP-A4 in As contaminated soil showed an increase in biomass (26 and 84%) and reduced As accumulation in plant tissue (42% and 88%) respectively. Strain CIMAP-A4 improved tolerance index, arsenate reductase activity, plant nutrient uptake (Zn, Mg, Ca), and non-protein thiol synthesis than BAC-7 under As stress.The indole acetic acid production and biofilm formation potential under As(V) stress (10 mg L−1) only in CIMAP-A4 could be the reason for the higher ameliorating effect. The strain CIMAP-A4 was identified as Paenibacillus sp. and could be a good option for As-induced stress mitigation in plants and successful bioremediation.

Antagonistic and growth-promoting potential of multifarious bacterial endophytes against Fusarium wilt of chickpea

BackgroundChickpea is the most important legume crop in India, and its productivity is significantly lowered due to biotic constraints such as wilt caused by Fusarium oxysporum f. sp. ciceris. Endophytes help plants to thrive better under stress conditions by regulating plant hormones and inducing systemic resistance. The aim of the present study was to identify chickpea root bacterial endophytes having antagonistic ability for the management of the Fusarium wilt.ResultsTwenty endophytic bacterial strains were isolated from the susceptible and resistant chickpea cultivar, amongst which 35% bacterial endophytes gave positive results for siderophore and 15% isolates were HCN producers, whereas 55% showed good growth on ACC-supplemented medium. Based upon 16S rRNA phylogenetic analysis, efficient endophytic bacterial isolates CRBE1, CRBE3 and CRBE7 were identified as Priestia megaterium, Brucella haematophila and Microbacterium paraoxydans, respectively. Bacterial endophyte CRBE7 and CRBE3 showed pronounced antagonistic activity against Fusarium oxysporum f. sp. ciceris under in vitro conditions. Inoculation of chickpea with isolated bacterial endophytes alone and in combination through seed priming resulted in significant biocontrol activity against Fusarium wilt of chickpea under screenhouse conditions. Biopriming of chickpea seeds alone with CRBE3 and as consortium of CRBE3 + CRBE7 upsurged the phenol content in susceptible and resistant chickpea varieties JG 62 and HC 3, which indicated the role of promising endophytes as potential bio-agents under in vivo conditions.ConclusionsChickpea root bacterial endophytes Priestia megaterium (CRBE1), Brucella haematophila (CRBE3) and Microbacterium paraoxydans (CRBE7) exhibiting antagonistic activity could be incorporated in integrated disease management module against Fusarium wilt of chickpea.

In vitro thrombolytic potential of fibrinolytic enzyme from Brevibacterium sp. isolated from the root of the plant, Aloe castellorum

Cardiovascular diseases (CVDs) like stroke and heart attack are leading causes of mortality worldwide, resulting in about 30% of deaths. The proportion in the Kingdom of Saudi Arabia was 46%. The commercial thrombolytic agents are thus associated with a range of side effects, while bacterially derived fibrinolytic enzymes have no or little side effects. Hence, there is an urgent need to identify novel fibrinolytic enzymes to treat or prevent CVDs. An endophytic bacterial strain producing fibrinolytic enzyme was isolated from the root of the plant Aloe castellorum. Enzyme production was enhanced through a conventional method and a statistical approach. The in vitro lytic activity of blood clots was also assessed. Endangered plant of Aloe castellorum roots, researchers isolated an endophytic strain producing fibrinolytic enzymes. It was identified as Brevibacterium sp. The culture medium was also optimized by a conventional method to screen the factors significant for successful culture. Fibrinolytic enzyme production peaked when Brevibacterium sp. was cultured in the presence of maltose (613 ± 12 U/mL), followed by starch (576 ± 13 U/mL). Among the selected nitrogen sources, yeast extract (642 ± 5.9 U/mL) and beef extract (610 ± 13 U/mL) enhanced enzyme yield relative to that in the control (487 ± 7.2 U/mL). Ionic sources such as Mg2+ (672 ± 10.3 U/mL) and Ca2+ (605 ± 12.3 U/mL) showed enhanced fibrinolytic enzyme production relative to the control (405 ± 13.2 U/mL). Upon employing a two-level full factorial design for examining the significant factors, it was revealed that maltose, yeast extract, and Mg2+ were important (p < 0.05). To enhance thrombolytic agent production using central composite design and response surface methodologies. The fibrinolytic enzyme obtained from Brevibacterium sp. has great potential to lyse blood clots in vitro.

Isolation and Characterization of Endophytes Bacterial Strains of Momordica charantia L. and Their Possible Approach in Stress Management

In the present study, eight endophytic bacterial strains, namely Bacillus licheniformis R1, Bacillus sp. R2, Agrobacterium tumefaciens R6, uncultured bacterium R11, Bacillus subtilis RS3, Bacillus subtilis RS6, uncultured bacterium RS8 and Lysinibacillus fusiformis RS9, were isolated from the root of Momordica charantia L. All the strains, except R6 exhibited positive for IAA production, siderophore production, and phosphate solubilization during plant growth-promoting traits analysis. Strains invariably utilized glucose and sucrose as a carbon source during substrate utilization, while yeast extract, ammonium sulphate, ammonium chloride, glycine, glutamine, and isoleucine as nitrogen sources. In addition, Spectinomycin was found as the most effective during antibiotic sensitivity TEST, followed by Chloramphenicol, Erythromycin, Rifampicin and Kanamycin, while Polymixin B was found least effective, while strains R1, R6, and RS8 were sensitive to all the antibiotics. Strains R1 and RS6 were able to withstand tolerance up to 10% of NaCl. The strains showing resistance against broad-spectrum antibiotics, especially chloramphenicol, can be used in hospital waste management. In addition, strains with a tolerance of 10 % of NaCl can improve plant growth in the saline affected area.

Screening of Antimicrobial Activities and Lipopeptide Production of Endophytic Bacteria Isolated from Vetiver Roots.

The exploration of certain microbial resources such as beneficial endophytic microorganisms is considered a promising strategy for the discovery of new antimicrobial compounds for the pharmaceutical industries and agriculture. Thirty-one endophytic bacterial strains affiliated with Bacillus, Janthinobacterium, Yokenella, Enterobacter, Pseudomonas, Serratia, and Microbacterium were previously isolated from vetiver (Chrysopogon zizanioides (L.) Roberty) roots. These endophytes showed antifungal activity against Fusarium graminearum and could be a source of antimicrobial metabolites. In this study, in particular, using high-throughput screening, we analyzed their antagonistic activities and those of their cell-free culture supernatants against three species of Fusarium plant pathogens, a bacterial strain of Escherichia coli, and a yeast strain of Saccharomyces cerevisiae, as well as their capacity to produce lipopeptides. The results showed that the culture supernatants of four strains close to B. subtilis species exhibited antimicrobial activities against Fusarium species and E. coli. Using mass spectrometry analyses, we identified two groups of lipopeptides (surfactins and plipastatins) in their culture supernatants. Whole-genome sequencing confirmed that these bacteria possess NRPS gene clusters for surfactin and plipastatin. In vitro tests confirmed the inhibitory effect of plipastatin alone or in combination with surfactin against the three Fusarium species.

Isolation and Characterization of Bacillus velezensis Strain P2-1 for Biocontrol of Apple Postharvest Decay Caused by Botryosphaeria dothidea.

Botryosphaeria dothidea causes apple ring rot, which is among the most prevalent postharvest diseases of apples and causes significant economic loss during storage. In this study, we investigated the biocontrol activity and possible mechanism of Bacillus velezensis strain P2-1 isolated from apple branches against B. dothidea in postharvest apple fruit. The results showed strain P2-1, one of the 80 different endophytic bacterial strains from apple branches, exhibited strong inhibitory effects against B. dothidea growth and resulted in hyphal deformity. B. velezensis P2-1 treatment significantly reduced the ring rot caused by B. dothidea. Additionally, the supernatant of strain P2-1 exhibited antifungal activity against B. dothidea. Re-isolation assay indicated the capability of strain P2-1 to colonize and survive in apple fruit. PCR and qRT-PCR assays revealed that strain P2-1 harbored the gene clusters required for biosynthesis of antifungal lipopeptides and polyketides. Strain P2-1 treatment significantly enhanced the expression levels of pathogenesis-related genes (MdPR1 and MdPR5) but did not significantly affect apple fruit qualities (measured in fruit firmness, titratable acid, ascorbic acid, and soluble sugar). Thus, our results suggest that B. velezensis strain P2-1 is a biocontrol agent against B. dothidea-induced apple postharvest decay. It acts partially by inhibiting mycelial growth of B. dothidea, secreting antifungal substances, and inducing apple defense responses.

The Employment of Endophytic Bacteria for Phytodegradation of Pyridine

Pyridine is considered a heterocyclic aromatic chemical that is poisonous and carcinogenic to a variety of living species. The use of plant and endophytic- bacteria to improve the efficiency of pollutants extraction is considered a viable technique since the endophytic bacteria help in the adaptation of the plant itself in various ecosystems and have significant ecological importance because they improve the soil fertility and quality. This research aims to stimulate the pyridine phytodegradation by Phragmites australis plants using the endophytic bacterial strain, Acinetobacter by inoculation these bacterial cells to the plants to see if it might increase plant growth and pyridine phytodegradation. In the present study, the system of pyridine phytodegradation basins with the vertical subsurface flow (VSSF) was adopted, since this system has better ventilation. In addition, the retention time is several hours due to the penetration of water molecules to the layers of packing materials of the basin, which have a relatively high hydraulic conductivity. After conducting the experiments, samples were collected and tests were done to find out the optimum conditions. The results were recorded as 40 plants of P. australis/m2 of VSSF systems; bacterial cells concentration, 250 mg/L; pyridine concentration, 400 mg/L; temperature, 35 °C and pH, 8±2 for 10 hrs incubation duration. As a result, endophytic bacteria can break down toxic organic substances in combination with certain plants. When the endophytic bacterium, Acinetobacter was not used to enhance the role of Phragmites australis plants in the pyridine-phytodegradation process, the rate of phytodegradation was reduced to less than 30% at a pyridine concentration of 700 mg/L, indicating the importance of this endophytic bacterium in the pyridine phytodegradation process.

Plant growth promoting endophytic Pseudomonas aeruginosa RD10 isolated from water hyacinth for phenol degradation

A total of twelve endophytic bacteria were isolated from the root of E. crassipes. All these bacterial strains were analyzed for phenol degradation potential. Twelve endophytic bacteria were subjected to polyphenol resistance analysis and all showed phenol tolerance up to 300 ppm. Among the twelve bacterial strains, the strain RD10 was resistant up to 800 ppm, and reduced growth were observed at higher concentrations. The plant growth-promoting properties of endophytic bacterial strains were analyzed. Among the isolated bacterial strain, only five strains produced ACC deaminase. IAA production was detected in seven bacterial isolates, while siderophore production was determined from only five bacterial strains. Among the isolated endophytes, the strain RD10 exhibited ACC deaminase, IAA, and siderophore activity in submerged fermentation. ACC deaminase production of 125.2 ± 4.8 m/ml was shown by strain RD10 and IAA production was 89.7 ± 5.1 μg/ml. Moreover, maximum siderophore production was observed (53.9 ± 4.9% siderophore units) in strain RD3. Catechol 2,3-dioxygenase activity of the bacterial strains was analyzed. Catechol 2,3 dioxygenase activity ranges from 0.03 ± 0.01 U/mg to 35.2 ± 1.1 U/mg. Phenol degradation by the isolated endophytes was studied and the initial phenol concentration was 500 ppm. The strain RD1 degraded 1.2 ± 0.2% phenol and more than 50% phenol degradation was observed in strains RD3, RD4, RD6, RD7, RD9, RD10, and RD11, respectively. The endophytic bacterial strain was Gram-negative, rodshaped and motile. It was non-spore-forming bacteria, capsulated and, showed a positive reaction to oxidase and catalase. In MacConkey agar medium, strain RD10 forms smooth and flat colonies, and the diameter of the colonies ranged from 2 to 3 mm. The colonies have an alligator skin-like appearance on top view and have regular margins. The strain RD10 was streaked on blood agar medium and the strain RD10 produced strong pigmentation on blood agar. Antibiotic sensitivity of strain RD10 against various antibiotics in terms of zone of inhibition was analyzed. The endophytic strain RD10 was sensitive to all selected antibiotics. Based on biochemical characters, pigment analysis and, molecular characterization, the strain was confirmed as P. aeruginosa RD10. In this study, P. aeruginosa RD10 was cultured at 400, 500 and, 600 mg/l phenol concentration for 96 h. Optimum growth was achieved at 500 mg/l concentration and an inhibitory effect was observed at 600 mg/l phenol concentration. The results confirmed that the selected strain can withstand and grow well at 500 mg/l phenol concentration. The strain RD10 was cultured at various incubation temperatures with 500 mg/l phenol concentration. Optimization of environmental factors can lead to maximum degradation of phenol. The results revealed that phenol degradation was influenced by temperature. The highest phenol degradation was achieved at 30 °C in Erlenmeyer flask culture and decreased at high temperatures. P. aeruginosa RD10 could degrade phenol at pH 5.5 (10.2 ± 0.5% removal), at pH 6.0, 15.4 ± 1.1% of the phenol was degraded after incubation for 72 h at 30 °C. Phenol removal (%) declined to 70.4 ± 2.9% at higher initial pH value (9.0).

Molecular and Biochemical Characterization, Antimicrobial Activity, Stress Tolerance, and Plant Growth-Promoting Effect of Endophytic Bacteria Isolated from Wheat Varieties.

Endophytic bacteria have been utilized as an alternative source to chemical fertilizers and pesticides to enhance plant productivity and defense mechanisms against biotic and abiotic stress. Five endophytic bacterial strains were isolated from the seeds of three different Pakistani wheat varieties (Ghaneemat-e-IBGE, Atta-Habib, and Siren). The isolated strains AH-1, S-5, S-7, GI-1, and GI-6 showed phylogenetic similarity with Bacillus altitudinis, B. aryabhattai, B. wiedmannii, Pseudomonas aeruginosa, and Burkholderia gladioli, respectively. All strains showed catalase activity (except AH-1) and Indole-3-acetic acid production, with the highest concentration (16.77 μg·mL−1) found for GI-6, followed by S-5 (11.5 μg·mL−1), nitrogen assimilation (except S-7), phosphorus solubilization (except S-7 and AH-1), and ability to produce siderophores, with maximum productions for GI-6 (31 ± 3.5 psu) and GI-1 (30 ± 2.9 psu). All five analyzed strains possessed antimicrobial activity, which was particularly strong in GI-6 and S-5 against Klebsiella pneumonia, Escherichia coli, and Bacillus subtilis. Increasing salinity stress with NaCl negatively affected the bacterial growth of all isolates. However, strains GI-6 and S-5 showed salt tolerance after three days of incubation. A drought tolerance test resulted in a negative impact of poly ethylene glycol on bacterial growth, which was, however, less pronounced in GI-6 strain. The GI-6 strain revealed growth-promoting effects on inoculated wheat plants.

Effects of Natural Antimicrobials on Xanthomonas Strains Growth

The aim of this work was to investigate the most promising natural antimicrobials effective for the growth suppression of Xanthomonas spp. bacteria. The research objects were Xanthomonas spp. strains isolated from tubers and stem of plants growing in Lithuania: Xanthomonas translucens NRCIB X6, X. arboricola NRCIB X7, NRCIB X8, NRCIB X9, and NRCIB X10; the supernatants of lactic acid bacteria Lactococcus lactis strains 140/2, 57, and 768/5, Lactobacillus helveticus strains 14, 148/3, R, and 3, Lb. reuteri 3 and 7, Streptococcus thermophilus 43, Enterococcus faecium 59-30 and 41-2; endophytic bacterial strains Bacillus, Pseudomonas, and Paenibacillus spp.; and essential oils of lavender (Lavandula angustifolia), grapefruit (Citrus paradisi), pine (Pinus sylvestris), thyme (Thymus vulgaris), rosemary (Rosmarinus officinalis), peppermint (Mentha piperita), lemon (Citrus limetta), aqueous extracts of blueberries (Vaccinium myrtillus), and cranberries (Vaccinium vitis-idaea). The antimicrobial activity of tested substances was determined by agar diffusion method. Supernatants of Lb. reuteri strain 7 and Lb. helveticus strains 14, R, 3, and 148/3 were found to have a high antimicrobial activity against Xanthomonas spp. bacteria strains when compared to the positive control—1.0% copper sulfate (diameter of inhibition zones was 28.8 ± 0.7 mm). The diameter of inhibition zones of supernatants ranged from 23.3 ± 0.6 mm to 32.0 ± 0.1 mm. Thyme (2.0%) and lavender (2.0%) essential oils inhibited the growth of Xanthomonas spp. strains. The diameter of the inhibition zones was from 14.7 ± 0.8 mm to 22.8 ± 0.9 mm. The aqueous extracts of blueberries had a weak antimicrobial activity. The diameter of inhibition zones ranged from 11.0 ± 0.2 mm to 13.0 ± 0.2 mm.

Root-Derived Endophytic Diazotrophic Bacteria Pantoea cypripedii AF1 and Kosakonia arachidis EF1 Promote Nitrogen Assimilation and Growth in Sugarcane.

Excessive, long-term application of chemical fertilizers in sugarcane crops disrupts soil microbial flora and causes environmental pollution and yield decline. The role of endophytic bacteria in improving crop production is now well-documented. In this study, we have isolated and identified several endophytic bacterial strains from the root tissues of five sugarcane species. Among them, eleven Gram-negative isolates were selected and screened for plant growth-promoting characteristics, i.e., production of siderophores, indole-3-acetic acid (IAA), ammonia, hydrogen cyanide (HCN), and hydrolytic enzymes, phosphorus solubilization, antifungal activity against plant pathogens, nitrogen-fixation, 1-aminocyclopropane-1-carboxylic acid deaminase activity, and improving tolerance to different abiotic stresses. These isolates had nifH (11 isolates), acdS (8 isolates), and HCN (11 isolates) genes involved in N-fixation, stress tolerance, and pathogen biocontrol, respectively. Two isolates Pantoea cypripedii AF1and Kosakonia arachidis EF1 were the most potent strains and they colonized and grew in sugarcane plants. Both strains readily colonized the leading Chinese sugarcane variety GT42 and significantly increased the activity of nitrogen assimilation enzymes (glutamine synthetase, NADH glutamate dehydrogenase, and nitrate reductase), chitinase, and endo-glucanase and the content of phytohormones gibberellic acid, indole-3-acetic acid, and abscisic acid. The gene expression analysis of GT42 inoculated with isolates of P. cypripedii AF1 or K. arachidis EF1 showed increased activity of nifH and nitrogen assimilation genes. Also, the inoculated diazotrophs significantly increased plant nitrogen content, which was corroborated by the 15N isotope dilution analysis. Collectively, these findings suggest that P. cypripedii and K. arachidis are beneficial endophytes that could be used as a biofertilizer to improve plant nitrogen nutrition and growth of sugarcane. To the best of our knowledge, this is the first report of sugarcane growth enhancement and nitrogen fixation by Gram-negative sugarcane root-associated endophytic bacteria P. cypripedii and K. arachidis. These strains have the potential to be utilized as sugarcane biofertilizers, thus reducing nitrogen fertilizer use and improving disease management.

Genomic and Metabolomic Insights into Secondary Metabolites of the Novel Bacillus halotolerans Hil4, an Endophyte with Promising Antagonistic Activity against Gray Mold and Plant Growth Promoting Potential.

The endophytic bacterial strain Hil4 was isolated from leaves of the medicinal plant Hypericum hircinum. It exhibited antifungal activity against Botrytis cinerea and a plethora of plant growth promoting traits in vitro. Whole genome sequencing revealed that it belongs to Bacillus halotolerans and possesses numerous secondary metabolite biosynthetic gene clusters and genes involved in plant growth promotion, colonization, and plant defense elicitation. The Mojavensin cluster was present in the genome, making this strain novel among plant-associated B. halotolerans strains. Extracts of secreted agar-diffusible compounds from single culture secretome extracts and dual cultures with B. cinerea were bioactive and had the same antifungal pattern on TLC plates after bioautography. UHPLC-HRMS analysis of the single culture secretome extract putatively annotated the consecutively produced antimicrobial substances and ISR elicitors. The isolate also proved efficient in minimizing the severity of gray mold post-harvest disease on table grape berries, as well as cherry tomatoes. Finally, it positively influenced the growth of Arabidopsis thaliana Col-0 and Solanum lycopersicum var. Chondrokatsari Messinias after seed biopriming in vitro. Overall, these results indicate that the B. halotolerans strain Hil4 is a promising novel plant growth promoting and biocontrol agent, and can be used in future research for the development of biostimulants and/or biological control agents.

Seed inhabiting bacterial endophytes of maize promote seedling establishment and provide protection against fungal disease

Bacteria from different crops and plant varieties have been shown to possess enormous growth promotional attributes. The study aimed to investigate the role of the endophytic microbiome of seeds of corn in improving the growth of seedlings of two different varieties of maize crops (K-25 and baby corn). Furthermore, the study also assessed the role of these bacteria in the protection of seedlings from fungal pathogens. Total twenty-three endophytic bacterial strains were isolated from maize seeds and identified using 16S rDNA sequencing. Most of the isolates had the ability to synthesize auxin (70 %) and solubilize phosphate (74 %), while all the isolates showed nitrogen fixation ability. Some isolates also showed antagonistic activity against phytopathogenic fungi including Rhizoctonia solani and Fusarium sp. suggesting their biocontrol potential. The presence of different lipopeptide genes including bacillomycin D, fengycin, iturin A and surfactin was confirmed in some of the isolates. We observed that treating seeds with an antibiotic compromised the seedlings’ growth; however, re-inoculation with endophytic isolates (ZM1/Lysinibacillus sp. and ZM2/Paenibacillus dendritiformis) restored the growth of the seedlings in terms of improved root and shoot development in comparison to non-inoculated controls. The colonization of inoculated bacteria on the root surface was visualized using fluorescent microscopy. Seedling protection assay showed that treated seeds (with ZMW8/ Bacillus velezensis) were protected from fungal infestation (Fusarium verticillioides) even after 12 days of inoculation in comparison to the uninoculated control. The study concludes that indigenous seed-associated bacteria of maize play a major role during seed germination, seedling formation and protect them from phytopathogens.