Plant growth promoting endophyte Burkholderia contaminans NZ antagonizes phytopathogen Macrophomina phaseolina through melanin synthesis and pyrrolnitrin inhibition

Functional and Genomic Potential of Burkholderia contaminans PB_AQ24 Isolate for Boosting the Growth of Bamboo Seedlings in Heavy Metal Contaminated Soils

The present study investigated the genomic and functional potential of Burkholderia contaminans PB_AQ24, a bacterial strain isolated from the municipal solid waste dumpsite, for boosting the growth of Dendrocalamus strictus (Male bamboo) seedlings. The isolated strain exhibited high potency for metal solubilization and ACC (1-Aminocyclopropane-1-carboxylate) deaminase activity. Its genome harbored diverse genes responsible for nitrogen and phosphorus utilization (trpABCDES, iaaH, acdS, pstABCS, phoAUD, pqqABCDE, kdpABC, gln, and nirBD) and also an abundance of heavy metal tolerant genes (ftsH, hptX, iscX-fdx-hscAB-iscAUR, mgtA, corA, and copC). Seeds priming experiments carried out in heavy metal contaminated soils (such as waste dumpsite soil (WDS), fly ash dumpsite soil (FAS) and natural garden soil (NGS control)) augmented with Burkholderia contaminans sp. PB_AQ24 showed 85% sustenance of seedlings in WDS and 80% in FAS. The study thus highlighted the potential features in isolated bacterial strain Burkholderia sp. PB_AQ24 (NCBI accession no. JAQOUG000000000), which could boost the growth of bamboo seedlings in heavy metal contaminated soils and may be applied for restoration and rejuvenation of contaminated sites.

Investigating the properties and antibacterial, antioxidant, and cytotoxicity activity of postbiotics derived from Lacticaseibacillus casei on various gastrointestinal pathogens in vitro and in food models

Background

Postbiotics comprise soluble compounds freed from the structure of destroyed bacteria or created by living bacteria. Such byproducts provide the host with enhanced biological function as well as specific physiological consequences. This research aims to examine the characteristics and possible health advantages of Lacticaseibacillus (L.) casei-derived postbiotics.

Methods

The antibacterial effects of postbiotics derived from L. casei were examined in vitro against various infectious gastrointestinal agents, as well as pasteurized milk and minced beef. Postbiotic activity potential was evaluated using disc-diffusion agar, minimum inhibitory concentration, minimum bactericidal concentration, and well-diffusion agar methods. Postbiotics were tested for antioxidant activity against 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radicals. Additionally, the total phenolic and flavonoid content of the postbiotics was determined. The colorimetric MTT was used to investigate the potential cytotoxicity of postbiotics. The chemical makeup of the postbiotics was also determined using gas chromatography/mass spectrometry.

Results

The antibacterial capacity was mostly related to pyrrolo[1,2-a] pyrazine-1,4-dione, benzoic acid, and laurostearic acid. Gram-positive microbes were more influenced by microbial byproducts in vitro than Gram-negative bacteria (P<0.05). The minimum effective concentrations of postbiotics were found to be much greater in ground beef and milk in the Listeria monocytogenes-inoculated model than with other bacteria (P<0.05). Postbiotics also show high antioxidant activity. Postbiotics generated from L. casei had the greatest concentrations of phenolic (99.46 mg GAE/g) and flavonoid (17.46 mg QE/g) constituents. Postbiotics had no influence on the viability of human foreskin fibroblasts at any dose.

Conclusion

Lactobacillus spp. postbiotics, particularly L. casei, were recommended for use as antioxidants, antimicrobials, and preservatives in both the food and pharmaceuticals sector for their beneficial effects and biological properties.

Plant Growth Promoting Rhizobacteria (PGPR) induced protection: A plant immunity perspective

Plant-environment interactions, particularly biotic stress, are increasingly essential for global food security due to crop losses in the dynamic environment. Therefore, understanding plant responses to biotic stress is vital to mitigate damage. Beneficial microorganisms and their association with plants can reduce the damage associated with plant pathogens. One such group is PGPR (Plant growth-promoting rhizobacteria), which influences plant immunity significantly by interacting with biotic stress factors and plant signalling compounds. This review explores the types, metabolism, and mechanisms of action of PGPR, including their enzyme pathways and the signalling compounds secreted by PGPR that modulate gene and protein expression during plant defence. Furthermore, the review will delve into the crosstalk between PGPR and other plant growth regulators and signalling compounds, elucidating the physiological, biochemical, and molecular insights into PGPR's impact on plants under multiple biotic stresses, including interactions with fungi, bacteria, and viruses. Overall, the review comprehensively adds to our knowledge about PGPR's role in plant immunity and its application for agricultural resilience and food security.

Anti-Aflatoxigenic Burkholderia contaminans BC11-1 Exhibits Mycotoxin Detoxification, Phosphate Solubilization, and Cytokinin Production

The productivity and quality of agricultural crops worldwide are adversely affected by disease outbreaks and inadequate nutrient availability. Of particular concern is the potential increase in mycotoxin prevalence due to crop diseases, which poses a threat to food security. Microorganisms with multiple functions have been favored in sustainable agriculture to address such challenges. Aspergillus flavus is a prevalent aflatoxin B1 (AFB1)-producing fungus in China. Therefore, we wanted to obtain an anti-aflatoxigenic bacterium with potent mycotoxin detoxification ability and other beneficial properties. In the present study, we have isolated an anti-aflatoxigenic strain, BC11-1, of Burkholderia contaminans, from a forest rhizosphere soil sample obtained in Luzhou, Sichuan Province, China. We found that it possesses several beneficial properties, as follows: (1) a broad spectrum of antifungal activity but compatibility with Trichoderma species, which are themselves used as biocontrol agents, making it possible to use in a biocontrol mixture or individually with other biocontrol agents in an integrated management approach; (2) an exhibited mycotoxin detoxification capacity with a degradation ratio of 90% for aflatoxin B1 and 78% for zearalenone, suggesting its potential for remedial application; and (3) a high ability to solubilize phosphorus and produce cytokinin production, highlighting its potential as a biofertilizer. Overall, the diverse properties of BC11-1 render it a beneficial bacterium with excellent potential for use in plant disease protection and mycotoxin prevention and as a biofertilizer. Lastly, a pan-genomic analysis suggests that BC11-1 may possess other undiscovered biological properties, prompting further exploration of the properties of this unique strain of B. contaminans. These findings highlight the potential of using the anti-aflatoxigenic strain BC11-1 to enhance disease protection and improve soil fertility, thus contributing to food security. Given its multiple beneficial properties, BC11-1 represents a valuable microbial resource as a biocontrol agent and biofertilizer.

Employing Genomic Tools to Explore the Molecular Mechanisms behind the Enhancement of Plant Growth and Stress Resilience Facilitated by a Burkholderia Rhizobacterial Strain

The rhizobacterial strain BJ3 showed 16S rDNA sequence similarity to species within the Burkholderia genus. Its complete genome sequence revealed a 97% match with Burkholderia contaminans and uncovered gene clusters essential for plant-growth-promoting traits (PGPTs). These clusters include genes responsible for producing indole acetic acid (IAA), osmolytes, non-ribosomal peptides (NRPS), volatile organic compounds (VOCs), siderophores, lipopolysaccharides, hydrolytic enzymes, and spermidine. Additionally, the genome contains genes for nitrogen fixation and phosphate solubilization, as well as a gene encoding 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The treatment with BJ3 enhanced root architecture, boosted vegetative growth, and accelerated early flowering in Arabidopsis. Treated seedlings also showed increased lignin production and antioxidant capabilities, as well as notably increased tolerance to water deficit and high salinity. An RNA-seq transcriptome analysis indicated that BJ3 treatment significantly activated genes related to immunity induction, hormone signaling, and vegetative growth. It specifically activated genes involved in the production of auxin, ethylene, and salicylic acid (SA), as well as genes involved in the synthesis of defense compounds like glucosinolates, camalexin, and terpenoids. The expression of AP2/ERF transcription factors was markedly increased. These findings highlight BJ3's potential to produce various bioactive metabolites and its ability to activate auxin, ethylene, and SA signaling in Arabidopsis, positioning it as a new Burkholderia strain that could significantly improve plant growth, stress resilience, and immune function.

Evaluation of Antifungal Activity of Endophytic Bacillus spp. and Identification of Secondary Metabolites Produced Against the Phytopathogenic Fungi

Endophytic bacteria serve as a rich source of diverse antimicrobial compounds. Recently, there has been a growing interest in utilizing endophytic Bacillus spp. as biological agents against phytogenic fungi, owing to their potential to produce a wide range of antimicrobial substances. The objective of this research was to investigate the protective abilities of 15 endophytic Bacillus spp. isolated from previous study from wheat plant, against the phytopathogenic fungi, Fusarium graminearum and Macrophomina phaseolina. A dual culture plate assay was conducted as a preliminary analysis, revealing that 7 out of 15 endophytic Bacillus spp. demonstrated inhibition against one or both of the phytopathogenic fungi used in this study. All seven endophytes were further assessed for the presence of diffusible antifungal metabolites. The cultures were grown in potato dextrose broth for 120 h, and the cell-free supernatant was extracted and analyzed using the cup plate method. The methanolic extract yielded similar results to the dual culture plate analysis, except for WL2-15. Additionally, deformities in the mycelial structure were examined under the light microscope upon exposure to methanolic extract. Furthermore, the analysis and identification of metabolites were carried out via gas chromatography-mass spectrometry of methanolic extract from selected seven endophytic Bacillus spp. The chromatogram revealed the presence of some major peaks such as tridecanoic acid, methyl ester, hydroperoxide, 1-methylbutyl, 9-octadecenamide, (z)-, hexane-1,3,4-triol, 3,5-dimethyl- tetradecanoic acid. To the best of our knowledge, this is the first report of these biocontrol agents in endophytic Bacillus spp. Interestingly, volatile organic compound production was also seen in all the isolates against the phytopathogenic fungi.

Fungal-Bacterial Combinations in Plant Health under Stress: Physiological and Biochemical Characteristics of the Filamentous Fungus Serendipita indica and the Actinobacterium Zhihengliuella sp. ISTPL4 under In Vitro Arsenic Stress

Fungal-bacterial combinations have a significant role in increasing and improving plant health under various stress conditions. Metabolites secreted by fungi and bacteria play an important role in this process. Our study emphasizes the significance of secondary metabolites secreted by the fungus Serendipita indica alone and by an actinobacterium Zhihengliuella sp. ISTPL4 under normal growth conditions and arsenic (As) stress condition. Here, we evaluated the arsenic tolerance ability of S. indica alone and in combination with Z. sp. ISTPL4 under in vitro conditions. The growth of S. indica and Z. sp. ISTPL4 was measured in varying concentrations of arsenic and the effect of arsenic on spore size and morphology of S. indica was determined using confocal microscopy and scanning electron microscopy. The metabolomics study indicated that S. indica alone in normal growth conditions and under As stress released pentadecanoic acid, glycerol tricaprylate, L-proline and cyclo(L-prolyl-L-valine). Similarly, d-Ribose, 2-deoxy-bis(thioheptyl)-dithioacetal were secreted by a combination of S. indica and Z. sp. ISTPL4. Confocal studies revealed that spore size of S. indica decreased by 18% at 1.9 mM and by 15% when in combination with Z. sp. ISTPL4 at a 2.4 mM concentration of As. Arsenic above this concentration resulted in spore degeneration and hyphae fragmentation. Scanning electron microscopy (SEM) results indicated an increased spore size of S. indica in the presence of Z. sp. ISTPL4 (18 ± 0.75 µm) compared to S. indica alone (14 ± 0.24 µm) under normal growth conditions. Our study concluded that the suggested combination of microbial consortium can be used to increase sustainable agriculture by combating biotic as well as abiotic stress. This is because the metabolites released by the microbial combination display antifungal and antibacterial properties. The metabolites, besides evading stress, also confer other survival strategies. Therefore, the choice of consortia and combination partners is important and can help in developing strategies for coping with As stress.

Assessment of soil yeasts Papiliotrema laurentii S-08 and Saitozyma podzolica S-77 for plant growth promotion and biocontrol of Fusarium wilt of brinjal

AIM

This study aimed to determine the efficacy of the soil yeasts Papiliotrema laurentii S-08 and Saitozyma podzolica S-77 for plant growth promotion (PGP) and biocontrol of wilt disease in brinjal plants while applying yeasts individually or as a consortium in pot experiments.

METHODS AND RESULTS

The yeasts were tested for various PGP characteristics and antagonistic activity against the phytopathogen Fusarium oxysporum f. sp. melongenae. Both the yeast isolates demonstrated some PGP attributes as well as inhibited the growth of the phytopathogen. A gas chromatography-mass spectrometry analysis of the yeast metabolites revealed the presence of several antifungal compounds. The pot experiment performed under nursery conditions showed that applying these yeasts, individually or in consortium, decreased the percent disease incidence in brinjal seedlings while significantly enhancing their growth parameters.

CONCLUSION

Papiliotrema laurentii S-08 and S. podzolica S-77 can be used in brinjal plants as plant growth promoters and also as biocontrol agents against the brinjal wilt disease.

Heterologous Biosynthesis of Complex Bacterial Natural Products in Burkholderia gladioli

Bacterial natural products (NPs) are an indispensable source of drugs and biopesticides. Heterologous expression is an essential method for discovering bacterial NPs and the efficient biosynthesis of valuable NPs, but the chassis for Gram-negative bacterial NPs remains inadequate. In this study, we built a Burkholderiales mutant Burkholderia gladioli Δgbn::attB by introducing an integrated site (attB) to inactivate the native gladiolin (gbn) biosynthetic gene cluster, which stabilizes large foreign gene clusters and reduces the native metabolite profile. The growth and successful heterologous production of high-value NPs such as phylogenetically close Burkholderiales-derived antitumor polyketides (PKs) rhizoxins, phylogenetically distant Gammaproteobacteria-derived anti-MRSA (methicillin-resistant Staphylococcus aureus) antibiotics WAP-8294As, and Deltaproteobacteria-derived antitumor PKs disorazols demonstrate that this strain is a potential chassis for Gram-negative bacterial NPs. We further improved the yields of WAP-8294As through promoter insertions and precursor pathway overexpression based on heterologous expression in this strain. This study provides a robust bacterial chassis for genome mining, efficient production, and molecular engineering of bacterial NPs.

An edible coating utilizing Malva sylvestris seed polysaccharide mucilage and postbiotic from Saccharomyces cerevisiae var. boulardii for the preservation of lamb meat

Currently, microbial bioactive substances (postbiotics) are considered a promising tool for achieving customer demand for natural preservatives. This study aimed to investigate the effectiveness of an edible coating developed by Malva sylvestris seed polysaccharide mucilage (MSM) and postbiotics from Saccharomyces cerevisiae var. boulardii ATCC MYA-796 (PSB) for the preservation of lamb meat. PSB were synthesized, and a gas chromatograph connected to a mass spectrometer and a Fourier transform infrared spectrometer were used to determine their chemical components and main functional groups, respectively. The Folin-Ciocalteu and aluminium chloride techniques were utilized to assess the total flavonoid and phenolic levels of PSB. Following that, PSB has been incorporated into the coating mixture, which contains MSM, and its potential radical scavenging and antibacterial activities on lamb meat samples were determined after 10 days of 4 °C storage. PSB contains 2-Methyldecane, 2-Methylpiperidine, phenol, 2,4-bis (1,1-dimethyl ethyl), 5,10-Diethoxy-2,3,7,8- tetrahydro-1H,6H-dipyrrolo[1,2-a:1',2'-d] pyrazine, and Ergotaman-3',6',18-trione, 12'-hydroxy-2'-methyl-5'-(phenylmethyl)-, (5'alpha) as well as various organic acids with significant radical scavenging activity (84.60 ± 0.62 %) and antibacterial action toward Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus, Staphylococcus aureus, and Listeria innocua as foodborne pathogens. The edible PSB-MSM coating effectively reduced microbial growth and increased meat shelf life (> 10 days). When PSB solutions were added to the edible coating, the moisture content, pH value, and hardness of the samples were also more successfully maintained (P < 0.05). The PSB-MSM coating inhibited lipid oxidation in meat samples considerably and diminished the formation of primary as well as secondary oxidation intermediates (P < 0.05). Additionally, when MSM + 10 % PSB edible coating was utilized, the sensory properties of the samples were maintained more well during preservation. As a significance, the use of edible coatings based on PSB and MSM is efficient in decreasing microbiological and chemical degradation in lamb meat during preservation.

Characterization of Growth-Promoting Activities of Consortia of Chlorpyrifos Mineralizing Endophytic Bacteria Naturally Harboring in Rice Plants-A Potential Bio-Stimulant to Develop a Safe and Sustainable Agriculture

Eighteen pesticide-degrading endophytic bacteria were isolated from the roots, stems, and leaves of healthy rice plants and identified through 16S rRNA gene sequencing. Furthermore, biochemical properties, including enzyme production, dye degradation, anti-bacterial activities, plant-growth-promoting traits, including N-fixation, P-solubilization, auxin production, and ACC-deaminase activities of these naturally occurring endophytic bacteria along with their four consortia, were characterized. Enterobacter cloacae HSTU-ABk39 and Enterobacter sp. HSTU-ABk36 displayed inhibition zones of 41.5 ± 1.5 mm, and 29 ± 09 mm against multidrug-resistant human pathogenic bacteria Staphylococcus aureus and Staphylococcus epidermidis, respectively. FT-IR analysis revealed that all eighteen isolates were able to degrade chlorpyrifos pesticide. Our study confirms that pesticide-degrading endophytic bacteria from rice plants play a key role in enhancing plant growth. Notably, rice plants grown in pots containing reduced urea (30%) mixed with either endophytic bacterial consortium-1, consortium-2, consortium-3, or consortia-4 demonstrated an increase of 17.3%, 38.6%, 18.2%, and 39.1% yields, respectively, compared to the control plants grown in pots containing 100% fertilizer. GC-MS/MS analysis confirmed that consortia treatment caused the degradation of chlorpyrifos into different non-toxic metabolites, including 2-Hydroxy-3,5,6 trichloropyridine, Diethyl methane phosphonate, Phorate sulfoxide, and Carbonochloridic. Thus, these isolates could be deployed as bio-stimulants to improve crop production by creating a sustainable biological system.

Bioprospecting and Challenges of Plant Microbiome Research for Sustainable Agriculture, a Review on Soybean Endophytic Bacteria

This review evaluates oilseed crop soybean endophytic bacteria, their prospects, and challenges for sustainable agriculture. Soybean is one of the most important oilseed crops with about 20-25% protein content and 20% edible oil production. The ability of soybean root-associated microbes to restore soil nutrients enhances crop yield. Naturally, the soybean root endosphere harbors root nodule bacteria, and endophytic bacteria, which help increase the nitrogen pool and reclamation of another nutrient loss in the soil for plant nutrition. Endophytic bacteria can sustain plant growth and health by exhibiting antibiosis against phytopathogens, production of enzymes, phytohormone biosynthesis, organic acids, and secondary metabolite secretions. Considerable effort in the agricultural industry is focused on multifunctional concepts and bioprospecting on the use of bioinput from endophytic microbes to ensure a stable ecosystem. Bioprospecting in the case of this review is a systemic overview of the biorational approach to harness beneficial plant-associated microbes to ensure food security in the future. Progress in this endeavor is limited by available techniques. The use of molecular techniques in unraveling the functions of soybean endophytic bacteria can explore their use in integrated organic farming. Our review brings to light the endophytic microbial dynamics of soybeans and current status of plant microbiome research for sustainable agriculture.

Insights into the Biocontrol Function of a Burkholderia gladioli Strain against Botrytis cinerea

Pathogenic fungi are the main cause of yield loss and postharvest loss of crops. In recent years, some antifungal microorganisms have been exploited and applied to prevent and control pathogenic fungi. In this study, an antagonistic bacteria KRS027 isolated from the soil rhizosphere of a healthy cotton plant from an infected field was identified as Burkholderia gladioli by morphological identification, multilocus sequence analysis, and typing (MLSA-MLST) and physiobiochemical examinations. KRS027 showed broad spectrum antifungal activity against various phytopathogenic fungi by secreting soluble and volatile compounds. KRS027 also has the characteristics of plant growth promotion (PGP) including nitrogen fixation, phosphate, and potassium solubilization, production of siderophores, and various enzymes. KRS027 is not only proven safe by inoculation of tobacco leaves and hemolysis test but also could effectively protect tobacco and table grapes against gray mold disease caused by Botrytis cinerea. Furthermore, KRS027 can trigger plant immunity by inducing systemic resistance (ISR) activated by salicylic acid- (SA), jasmonic acid- (JA), and ethylene (ET)-dependent signaling pathways. The extracellular metabolites and volatile organic compounds (VOCs) of KRS027 affected the colony extension and hyphal development by downregulation of melanin biosynthesis and upregulation of vesicle transport, G protein subunit 1, mitochondrial oxidative phosphorylation, disturbance of autophagy process, and degrading the cell wall of B. cinerea. These results demonstrated that B. gladioli KRS027 would likely become a promising biocontrol and biofertilizer agent against fungal diseases, including B. cinerea, and would promote plant growth. IMPORTANCE Searching the economical, eco-friendly and efficient biological control measures is the key to protecting crops from pathogenic fungi. The species of Burkholderia genus are widespread in the natural environment, of which nonpathogenic members have been reported to have great potential for biological control agents and biofertilizers for agricultural application. Burkholderia gladioli strains, however, need more study and application in the control of pathogenic fungi, plant growth promotion, and induced systemic resistance (ISR). In this study, we found that a B. gladioli strain KRS027 has broad spectrum antifungal activity, especially in suppressing the incidence of gray mold disease caused by Botrytis cinerea, and can stimulate plant immunity response via ISR activated by salicylic acid- (SA), jasmonic acid- (JA), and ethylene (ET)-dependent signaling pathways. These results indicate that B. gladioli KRS027 may be a promising biocontrol and biofertilizer microorganism resource in agricultural applications.

Unveiling chlorpyrifos mineralizing and tomato plant-growth activities of Enterobacter sp. strain HSTU-ASh6 using biochemical tests, field experiments, genomics, and in silico analyses

The chlorpyrifos-mineralizing rice root endophyte Enterobacter sp. HSTU-ASh6 strain was identified, which enormously enhanced the growth of tomato plant under epiphytic conditions. The strain solubilizes phosphate and grew in nitrogen-free Jensen's medium. It secreted indole acetic acid (IAA; 4.8 mg/mL) and ACC deaminase (0.0076 μg/mL/h) and hydrolyzed chlorpyrifos phosphodiester bonds into 3,5,6-trichloro-2-pyridinol and diethyl methyl-monophosphate, which was confirmed by Gas Chromatography - Tandem Mass Spectrometry (GC-MS/MS) analysis. In vitro and in silico (ANI, DDH, housekeeping genes and whole genome phylogenetic tree, and genome comparison) analyses confirmed that the strain belonged to a new species of Enterobacter. The annotated genome of strain HSTU-ASh6 revealed a sets of nitrogen-fixing, siderophore, acdS, and IAA producing, stress tolerance, phosphate metabolizing, and pesticide-degrading genes. The 3D structure of 28 potential model proteins that can degrade pesticides was validated, and virtual screening using 105 different pesticides revealed that the proteins exhibit strong catalytic interaction with organophosphorus pesticides. Selected docked complexes such as α/β hydrolase-crotoxyphos, carboxylesterase-coumaphos, α/β hydrolase-cypermethrin, α/β hydrolase-diazinon, and amidohydrolase-chlorpyrifos meet their catalytic triads in visualization, which showed stability in molecular dynamics simulation up to 100 ns. The foliar application of Enterobacter sp. strain HSTU-ASh6 on tomato plants significantly improved their growth and development at vegetative and reproductive stages in fields, resulting in fresh weight and dry weight was 1.8-2.0-fold and 1.3-1.6-fold higher in where urea application was cut by 70%, respectively. Therefore, the newly discovered chlorpyrifos-degrading species Enterobacter sp. HSTU-ASh6 could be used as a smart biofertilizer component for sustainable tomato cultivation.

Cow dung extract mediated green synthesis of zinc oxide nanoparticles for agricultural applications

In the present study, zinc oxide nanoparticles (ZnO) were synthesized using cow dung extract to apply sustainable agriculture from rural resources. Studies on their antibacterial potential against E. coli DH 5 alpha indicated lower antimicrobial activities than the bulk Zn and commercial Zn nanoparticles. Compared with control and commercial ZnO nanoparticles, the maximum seed germination, root length, and shoot length were observed after the priming of synthesized ZnO NPs. This study suggests that ZnO may significantly increase seed germination and have lower antimicrobial potential. Further, the lower in-vitro cellular leakage and reactive oxygen species (ROS) production provided new hope for using cow dung extract mediated nanoparticles for agricultural and industrial applications.

Endophytic Burkholderia: Multifunctional roles in plant growth promotion and stress tolerance

The genus Burkholderia has proven potential in improving plant performance. In recent decades, a huge diversity of Burkholderia spp. have been reported with diverse capabilities of plant symbiosis which could be harnessed to enhance plant growth and development. Colonization of endophytic Burkholderia spp. have been extensively studied through techniques like advanced microscopy, fluorescent labelling, PCR based assays, etc., and found to be systemically distributed in plants. Thus, use of these biostimulant microbes holds the promise of improving quality and quantity of crops. The endophytic Burkholderia spp. have been found to support plant functions along with boosting nutrient availability, especially under stress. Endophytic Burkholderia spp. improve plant survival against deadly pathogens via mechanisms like competition, induced systemic resistance, and antibiosis. At the same time, they are reported to extend plant tolerance towards multiple abiotic stresses especially drought, salinity, and cold. Several attempts have been made to decipher the potential of Burkholderia spp. by genome mining, and these bacteria have been found to harbour genes for plant symbiosis and for providing multiple benefits to host plants. Characteristics specific for host recognition and nutrient acquisition were confirmed in endophytic Burkholderia by genomics and proteomics-based studies. This could pave the way for harnessing Burkholderia spp. for biotechnological applications like biotransformation, phytoremediation, insecticidal activity, antimicrobials, etc. All these make Burkholderia spp. a promising microbial agent in improving plant performance under multiple adversities. Thus, the present review highlights critical roles of endophytic Burkholderia spp., their colonization, alleviation of biotic and abiotic stresses, biotechnological applications and genomic insights.

In vitro Screening of Sunflower Associated Endophytic Bacteria With Plant Growth-Promoting Traits

Harnessing endophytic microbes as bioinoculants promises to solve agricultural problems and improve crop yield. Out of fifty endophytic bacteria of sunflowers, 20 were selected based on plant growth-promoting. These plant growth-promoting bacteria were identified as Bacillus, Pseudomonas, and Stenotrophomonas. The qualitative screening showed bacterial ability to produce hydrogen cyanide, ammonia, siderophore, indole-3-acetic acid (IAA), exopolysaccharide, and solubilize phosphate. The high quantity of siderophore produced by B. cereus T4S was 87.73%. No significant difference was observed in the Bacillus sp. CAL14 (33.83%), S. indicatrix BOVIS40 (32.81%), S. maltophilia JVB5 (32.20%), S. maltophilia PK60 (33.48%), B. subtilis VS52 (33.43%), and P. saponiphilia J4R (33.24%), exhibiting high phosphate-solubilizing potential. S. indicatrix BOVIS40, B. thuringiensis SFL02, B. cereus SFR35, B. cereus BLBS20, and B. albus TSN29 showed high potential for the screened enzymes. Varied IAA production was recorded under optimized conditions. The medium amended with yeast extract yielded high IAA production of 46.43 μg/ml by S. indicatrix BOVIS40. Optimum IAA production of 23.36 and 20.72 μg/ml at 5% sucrose and 3% glucose by S. maltophilia JVB5 and B. cereus T4S were recorded. At pH 7, maximum IAA production of 25.36 μg/ml was obtained by S. indicatrix BOVIS40. All the isolates exhibited high IAA production at temperatures 25, 30, and 37°C. The in vitro seed inoculation enhanced sunflower seedlings compared to the control. Therefore, exploration of copious endophytic bacteria as bioinoculants can best be promising to boost sunflower cultivation.

Induction of Resistance of Antagonistic Bacterium Burkholderia contaminans to Postharvest Botrytis cinerea in Rosa vinifera

In order to study the problem that grapes are vulnerable to microbial infection and decay during storage, a method based on antagonistic Burkholderia contaminans against postharvest Botrytis cinerea of Rosa vinifera was proposed in this paper. The method tested the resistance induction mechanism of Botrytis cinerea after harvest and determined the fruit decay rate treated by antagonistic Burkholderia contaminans. The results showed that the antagonistic bacterium B-1 had bacteriostatic effect on many common pathogens of fruits and vegetables to a certain extent, and the bacteriostatic range was wide. Among them, the inhibition rate of Fusarium moniliforme was 75.5% and that of Botrytis cinerea was 51.2%. After testing, it can be found that antagonistic bacteria have an inhibitory effect on pathogenic fungi and have an effect on phenylpropane metabolic pathway, reactive oxygen species metabolic pathway, and the activities of other resistance-related enzymes. Through comparison, it can be found that the antagonistic Burkholderia contaminans has a strong antibacterial mechanism against Botrytis cinerea of rose grape after harvest. The fruit treated with antagonistic B Burkholderia B-1 has significantly reduced the decay rate and increased the activity of antibacterial active protein.

Strategies to Enhance the Use of Endophytes as Bioinoculants in Agriculture

The findings on the strategies employed by endophytic microbes have provided salient information to the researchers on the need to maximally explore them as bio-input in agricultural biotechnology. Biotic and abiotic factors are known to influence microbial recruitments from external plant environments into plant tissues. Endophytic microbes exhibit mutualism or antagonism association with host plants. The beneficial types contribute to plant growth and soil health, directly or indirectly. Strategies to enhance the use of endophytic microbes are desirable in modern agriculture, such that these microbes can be applied individually or combined as bioinoculants with bioprospecting in crop breeding systems. Scant information is available on the strategies for shaping the endophytic microbiome; hence, the need to unravel microbial strategies for yield enhancement and pathogen suppressiveness have become imperative. Therefore, this review focuses on the endophytic microbiome, mechanisms, factors influencing endophyte recruitment, and strategies for possible exploration as bioinoculants.

Biological Control Activity of Plant Growth Promoting Rhizobacteria Burkholderia contaminans AY001 against Tomato Fusarium Wilt and Bacterial Speck Diseases

Simple Summary

Burkholderia contaminans belongs to B. cepacia complex (Bcc), those of which are found in various environmental conditions. In this study, a novel strain AY001 of B. contaminans (AY001) was identified from the rhizosphere soil sample. AY001 showed (i) various plant growth-promoting rhizobacteria (PGPR)-related traits, (ii) antagonistic activity against different plant pathogenic fungi, (iii) suppressive activity against tomato Fusarium wilt disease, (iv) induced systemic acquired resistance (ISR)-triggering activity, and (v) production of various antimicrobial and plant immune-inducing secondary metabolites. These results suggest that AY001 is, indeed, a successful PGPR, and it can be practically used in tomato cultivation to alleviate biotic and abiotic stresses. However, further safety studies on the use of AY001 will be needed to ensure its safe use in the Agricultural system.

Abstract

Plant growth promoting rhizobacteria (PGPR) is not only enhancing plant growth, but also inducing resistance against a broad range of pathogens, thus providing effective strategies to substitute chemical products. In this study, Burkholderia contaminans AY001 (AY001) is isolated based on its broad-spectrum antifungal activity. AY001 not only inhibited fungal pathogen growth in dual culture and culture filtrate assays, but also showed various PGPR traits, such as nitrogen fixation, phosphate solubilization, extracellular protease production, zinc solubilization and indole-3-acetic acid (IAA) biosynthesis activities. Indeed, AY001 treatment significantly enhanced growth of tomato plants and enhanced resistance against two distinct pathogens, F. oxysporum f.sp. lycopersici and Pseudomonas syringae pv. tomato. Real-time qPCR analyses revealed that AY001 treatment induced jasmonic acid/ethylene-dependent defense-related gene expression, suggesting its Induced Systemic Resistance (ISR)-eliciting activity. Gas chromatography–mass spectrometry (GC-MS) analysis of culture filtrate of AY001 revealed production of antimicrobial compounds, including di(2-ethylhexyl) phthalate and pyrrolo [1,2-a]pyrazine-1,4-dione, hexahydro-3-(phenylmethyl). Taken together, our newly isolated AY001 showed promising PGPR and ISR activities in tomato plants, suggesting its potential use as a biofertilizer and biocontrol agent.