MALDI mass spectrometry-based identification of antifungal molecules from endophytic Bacillus strains with biocontrol potential of Lasiodiplodia theobromae, a grapevine trunk pathogen in Peru

Lasiodiplodia theobromae, a grapevine trunk pathogen, is becoming a significant threat to vineyards worldwide. In Peru, it is responsible for Botryosphaeria dieback in many grapevine-growing areas and it has spread rapidly due to its high transmissibility; hence, control measures are urgent. It is known that some endophytic bacteria are strong inhibitors of phytopathogens because they produce a wide range of antimicrobial molecules. However, studies of antimicrobial features from endophytic bacteria are limited to traditional confrontation methods. In this study, a MALDI mass spectrometry-based approach was performed to identify and characterize the antifungal molecules from Bacillus velezensis M1 and Bacillus amyloliquefaciens M2 grapevine endophytic strains. Solid medium antagonism assays were performed confronting B. velezensis M1 - L. theobromae and B. amyloliquefaciens M2 - L. theobromae for antifungal lipopeptides identification. By a MALDI TOF MS it was possible identify mass spectra for fengycin, iturin and surfactin protoned isoforms. Masses spectrums for mycobacillin and mycosubtilin were also identified. Using MALDI Imaging MS we were able to visualize and relate lipopeptides mass spectra of fengycin (1463.9 m/z) and mycobacillin (1529.6 m/z) in the interaction zone during confrontations. The presence of lipopeptides-synthesis genes was confirmed by PCR. Liquid medium antagonism assays were performed for a proteomic analysis during the confrontation of B. velezensis M1 - L. theobromae. Different peptide sequences corresponding to many antifungal proteins and enzymes were identified by MALDI TOF MS/MS. Oxalate decarboxylase bacisubin and flagellin, reported as antifungal proteins, were identified at 99 % identity through peptide mapping. MALDI mass spectrometry-based identification of antifungal molecules would allow the early selection of endophytic bacteria with antifungal features. This omics tool could lead to measures for prevention of grapevine diseases and other economically important crops in Peru.

Diversity analysis of Populus euphratica endophytic bacteria in Tarim River Basin, China

The bacterial diversity in Populus euphratica stem storage liquid samples grown in Shaya County and Yuli County of the Tarim River Basin was investigated. A culture-dependent (dilution spread plate method) and culture-independent method (PCR-RFLP technique) were used to identify the endophytic bacteria community structure and composition in P. euphratica in Tarim River Basin. Sixty-six bacterial strains were isolated from P. euphratica stem storage liquid samples on three agar media. The 16S rDNA gene was amplified and sequenced using bacterial universal primers. Phylogenetic analysis showed that the 66 strains belonged to three phyla (Firmicutes, Actinomycetes, and Gamma-Proteobacteria) and included 16 genera and 29 species. Among them, Pseudomonas (27.27%) and Bacillus (19.69%) were the dominant isolates. CGM-17 was a potentially new species of Pantoea. Restriction fragment length polymorphism of 16S rDNA gene amplified by polymerase chain reaction (PCR-RFLP) revealed 48 operational taxonomic units (OTUs). Phylogenetic analysis indicated that the 48 OTUs belonged to Firmicutes, Actinobacteria, Proteobacteria (α-, β-, γ-subgroup), Bacteroidetes, and Verrucomicrobia. Gamma-Proteobacteria was the dominant group, similarly to the culture-dependent method, accounting for 53% of the entire bacterial clone library. Our results indicate that P. euphratica endophytic bacteria diversity in the Tarim River Basin was rich, and the resources of endophytic bacteria were high. They provide valuable reference data and species resources for screening indigenous and functional strains of endophytic bacteria in P. euphratica.

Bacillus sp. YC7 from intestines of Lasioderma serricorne degrades nicotine due to nicotine dehydrogenase

A large number of nicotine-containing wastes produced during the tobacco manufacturing process are seriously harmful to the environment and human health. The degradation and transformation of nicotine-containing environmental contaminants to harmless substances has become an urgent requirement. Lasioderma serricorne can grow and reproduce in nicotine-rich sources, and their intestinal microbiota show promising potential to degrade and utilize nicotine. The purpose of this study is to screen and identify nicotine-degrading bacteria from the intestines of L. serricorne and explore their degradation characteristics. A dominant strain, YC7, with significant nicotine degradation capabilities was isolated from the intestines of L. serricorne. The strain was identified as Bacillus using a polyphasic approach. The test results showed it can produce multiple enzymes that include β-glucosidase, cellulase, proteases, and amylases. The nicotine-degrading bacteria were functionally annotated using databases. Nicotine dehydrogenase (NDH) was found by combining an activity tracking test and protein mass spectrometry analysis. The YC-7 NDH in the pathway was molecularly docked and functionally verified via the gene knockdown method. The binding ability of nicotine to nicotine-degrading enzymes was investigated using molecular docking. A high-efficiency nicotine-degrading bacteria, YC-7, was isolated and screened from tobacco, and the gene functions related to degradation were verified. This investigation provides a new hypothesis for screening nicotine-degrading bacteria and increases our knowledge of potential nicotine-degrading microbial sources.

Recombination of endophytic bacteria in asexual plant Ligusticum chuanxiong Hort. caused by transplanting

Background

Long-term asexual reproduction can easily lead to the degradation of plant germplasm, serious diseases and insect pests, reduction of production and even catastrophic crop failure. "Mountain Breeding and Dam Cultivation" is the main cultivation mode of Ligusticum chuanxiong Hort., which successfully avoided the germplasm degradation caused by long-term asexual reproduction. The recombination of endophytic fungi of L. chuanxiong caused by off-site transplantation was considered to be an important reason for its germplasm rejuvenation. However, whether bacteria have the same regularity is not yet known.

Methods

In this study, we carried out the experiment of cultivating propagation materials of L. chuanxiong in different regions and transplanting them to the same region. High-throughput sequencing was performed to analyze the bacterial communities in L. chuanxiong and its soil.

Results

The results showed that after transplanting, the plant height, tiller number, fresh weight, etc. of L. chuanxiong in mountainous areas were significantly higher than those in dam areas. At the same time, significant changes had taken place in the endophytic bacteria in reproductive material stem nodes (Lingzi, abbreviated as LZ). The diversity and abundance of bacteria in dam area LZ (YL) are significantly higher than those in mountainous area LZ (ML). The relative abundance of bacteria such as Xanthobacteraceae, Micromonosporaceae, Beijerinkiaceae, Rhodanobacteria, in ML is significantly higher than YL, mainly classified in Proteobateria and Actinobacteriota. In addition, the abundance advantage of Actinobacteriota still exists in MY (underground mature rhizomes obtained by ML). Meanwhile, the bacterial community was different in different area of transplanting. The diversity of bacterial communities in dam soil (YLS) is significantly higher than that in mountain soil (MLS). MLS had more Acidobacteriota than YLS. Comparative analysis showed that 74.38% of bacteria in ML are found in MLS, and 87.91% of bacteria in YL are found in YLS.

Conclusions

We can conclude that the community structure of endophytic bacteria recombined after the transplantation of L. chuanxiong, which was related to the bacterial community in soils. Moreover, after transplanting in mountainous areas, LZ accumulated more potentially beneficial Actinobacteriota, which may be an important reason for promoting the rejuvenation of germplasm in L. chuanxiong. However, this hypothesis requires more specific experiments to verify. This study provided a new idea that off-site transplanting may be a new strategy to restore vegetative plant germplasm resources.

Nutrient removal and biogas upgrade using co-cultivation of Chlorella vulgaris and three different bacteria under various GR24 concentrations by induction with 5-deoxystrigol

Algae symbiosis technology shows great potential in the synchronous treatment of biogas slurry and biogas, which has promising applications. For improving nutrients and CO₂ removal rates, the present work constructed four microalgal systems: Chlorella vulgaris (C. vulgaris) monoculture, C. vulgaris-Bacillus licheniformis (B. licheniformis), C. vulgaris-activated sludge, and C. vulgaris-endophytic bacteria (S395-2) to simultaneously treat biogas as well as biogas slurry under GR24 and 5DS induction. Our results showed that the C. vulgaris-endophytic bacteria (S395-2) showed optimal growth performance along with photosynthetic activity under the introduction of GR24 (10^-9 M). Under optimal conditions, CO₂ removal efficiency form biogas, together with chemical oxygen demand, total phosphorus and total nitrogen removal efficiencies from biogas slurry reached 67.25 ± 6.71%, 81.75 ± 7.93%, 83.19 ± 8.32%, and 85.17 ± 8.26%, respectively. The addition of symbiotic bacteria isolated from microalgae can promote the growth of C. vulgaris, and the exogenous addition of GR24 and 5DS can strengthen the purification performance of the algae symbiosis to achieve the maximum removal of conventional pollutants and CO₂.

Draft Genome Sequence of Enterobacter cloacae S23 a Plant Growth-promoting Passenger Endophytic Bacterium Isolated from Groundnut Nodule Possesses Stress Tolerance Traits

Aim

This study aims to reveal the passenger endophytic bacterium Enterobacter cloacae S23 isolated from groundnut nodules and to underpin the molecular mechanism and genes responsible for abiotic stress tolerance.

Background

A variety of microorganisms that contribute to nodulation and encourage plant development activity in addition to the nodulating Rhizobium. Passenger endophytes (PE) are endophytes that accidentally penetrate the plant without any selective pressure keeping them in the interior tissue of the plant. PE possesses characteristics that encourage plant development and boost output while reducing pathogen infection and improving biotic and abiotic stress tolerance. However, there is a lack of molecular evidence on the passenger endophyte-mediated alleviation of abiotic stresses.

Objective

This study was formulated to reveal the draft genome sequence of Enterobacter cloacae S23, as well as genes and characteristics involved in plant growth promotion and stress tolerance.

Method

The data were submitted to PATRIC and the TORMES-1.0 Unicyclker tools were used to conduct a complete genome study of Enterobacter cloacae S23. The TORMES-1.0 platform was used to process the reads. RAST tool kit (RASTtk) was used to annotate the S23 sequence. The plant growth-promoting traits such as indole acetic acid production, siderophore secretion, production of extracellular polysaccharides, biofilm formation, phosphate solubilization, and accumulation of osmolytes were examined under normal, 7% NaCl and 30% polyethylene glycol amended conditions to determine their ability to withstand salt and moisture stressed conditions, respectively.

Result

We report the size of Enterobacter cloacae S23 is 4.82Mb which contains 4511 protein-coding sequences, 71 transfer RNA genes, and 3 ribosomal RNA with a G+C content of DNA is 55.10%. Functional analysis revealed that most of the genes are involved in the metabolism of amino acids, cofactors, vitamins, stress response, nutrient solubilization (kdp, pho, pst), biofilm formation (pga) IAA production (trp), siderophore production (luc, fhu, fep, ent, ybd), defense, and virulence. The result revealed that E. cloacae S23 exhibited multiple plant growth-promoting traits under abiotic stress conditions.

Conclusion

Our research suggested that the discovery of anticipated genes and metabolic pathways might characterise this bacterium as an environmentally friendly bioresource to support groundnut growth through several mechanisms of action under multi-stresses.

Endophytic Bacillus sp. AP10 harboured in Arabis paniculata mediates plant growth promotion and manganese detoxification

Phytoremediation of heavy metal-polluted soils assisted by plant-associated endophytes, is a suitable method for plant growth and manganese (Mn) removal in contaminated soils. This investigation was conducted to evaluate the Mn-resistant endophytic resources of the Mn hyperaccumulator Arabis paniculata and their functions in the phytoremediation of Mn²⁺ toxicity. This study isolated an endophytic bacterium with high Mn resistance and indole-3-acetic acid (IAA) production form A. paniculata and identified it as Bacillus sp. AP10 using 16 S rRNA gene sequencing analysis. The effects of Bacillus sp. AP10 on the alleviation of Mn²⁺ toxicity in Arabidopsis thaliana seedlings and the molecular mechanisms were further investigated using biochemical tests and RNA-seq analysis. Under Mn²⁺ stress, Bacillus sp. AP10 increased the biomass, chlorophyll content and the translocation factor (TF) values of Mn in the aerial parts, while decreased the malondialdehyde (MDA) content of A. thaliana seedlings compared with that of control plants. The differentially expressed genes (DEGs) and enrichment analysis showed that Bacillus sp. AP10 could significantly increase the expression of key genes involved in cell-wall loosening, which may improve plant growth under Mn stress. Superoxide dismutase (SOD)-encoding genes were detected as DEGs after AP10 treatment. Moreover, AP10 regulated the expression of genes responsible for phenylpropanoid pathway, which may promote antioxidant flavonoids accumulation for reactive oxygen species (ROS) scavenging to improve Mn tolerance. The activation of ATP-binding cassette (ABC) transporter gene expression especially ABCB1 after AP10 stimulation, explained the elevation of metal ion binding or transport related to enhanced Mn accumulation in plants. Futhermore, AP10 might alleviate Mn toxicity through enhancing abscisic acid (ABA) responsive gene expression and ABA biosynthesis. These findings provide new insights into the functions and regulatory mechanism of Bacillus sp. AP10 in promoting plant growth, and tolerance, improving Mn accumulation and alleviating Mn²⁺ toxicity in plants. The application of Bacillus sp. AP10 as potential phytoremediators may be a promising strategy in Mn²⁺ contaminated fields. AVAILABILITY OF DATA AND MATERIALS: The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Degradation of 8:2 fluorotelomer carboxylic acid (8:2 FTCA) by plants and their co-existing microorganisms

8:2 fluorotelomer carboxylic acid (8:2 FTCA), an important precursor of perfluorocarboxylic acids (PFCAs), is widely detected in environment and biotas. Hydroponic exposures were conducted to investigate the accumulation and metabolism of 8:2 FTCA in wheat (Triticum aestivum L.) and pumpkin (Cucurbita maxima L.). Endophytic and rhizospheric microorganisms co-existing with the plants were isolated to investigate their contributions to degrade 8:2 FTCA. Wheat and pumpkin roots could take up 8:2 FTCA efficiently with the root concentration factor (RCF) as 5.78 and 8.93, respectively. 8:2 FTCA could be biotransformed to 8:2 fluorotelomer unsaturated carboxylic acid (8:2 FTUCA), 7:3 fluorotelomer carboxylic acid (7:3 FTCA), and seven PFCAs with 2-8 carbon chain length in plant roots and shoots. Cytochromes P450 (CYP450) and glutathione-S-transferase (GST) activities in plants were significantly increased, while flavin-dependent monooxygenases (FMOs) activities were not changed, suggesting that CYP 450 and GST were involved in the transformation of 8:2 FTCA in plant tissues. Twelve 8:2 FTCA-degrading endophytic (8 strains) and rhizospheric (4 strains) bacterial strains were isolated from root interior, shoot interior and rhizosphere of plants, respectively. These bacteria were identified as Klebsiella sp. based on the morphology and 16S rDNA sequence, and they could biodegrade 8:2 FTCA to intermediates and stable PFCAs.

Metapangenomics of wild and cultivated banana microbiome reveals a plethora of host-associated protective functions

BACKGROUND

Microbiomes are critical to plants, promoting growth, elevating stress tolerance, and expanding the plant's metabolic repertoire with novel defense pathways. However, generally microbiomes within plant tissues, which intimately interact with their hosts, remain poorly characterized. These endospheres have become a focus in banana (Musa spp.)-an important plant for study of microbiome-based disease protection. Banana is important to global food security, while also being critically threatened by pandemic diseases. Domestication and clonal propagation are thought to have depleted protective microbiomes, whereas wild relatives may hold promise for new microbiome-based biological controls. The goal was to compare metapangenomes enriched from 7 Musa genotypes, including wild and cultivated varieties grown in sympatry, to assess the host associations with root and leaf endosphere functional profiles.

RESULTS

Density gradients successfully generated culture-free microbial enrichment, dominated by bacteria, with all together 24,325 species or strains distinguished, and 1.7 million metagenomic scaffolds harboring 559,108 predicted gene clusters. About 20% of sequence reads did not match any taxon databases and ~ 62% of gene clusters could not be annotated to function. Most taxa and gene clusters were unshared between Musa genotypes. Root and corm tissues had significantly richer endosphere communities that were significantly different from leaf communities. Agrobacterium and Rhizobium were the most abundant in all samples while Chitinophagia and Actinomycetia were more abundant in roots and Flavobacteria in leaves. At the bacterial strain level, there were > 2000 taxa unique to each of M. acuminata (AAA genotype) and M. balbisiana (B-genotype), with the latter 'wild' relatives having richer taxa and functions. Gene ontology functional enrichment showed core beneficial functions aligned with those of other plants but also many specialized prospective beneficial functions not reported previously. Some gene clusters with plant-protective functions showed signatures of phylosymbiosis, suggesting long-standing associations or heritable microbiomes in Musa.

CONCLUSIONS

Metapangenomics revealed key taxa and protective functions that appeared to be driven by genotype, perhaps contributing to host resistance differences. The recovery of rich novel taxa and gene clusters provides a baseline dataset for future experiments in planta or in vivo bacterization or engineering of wild host endophytes.

Analysis of endophytic bacterial flora of mulberry cultivars susceptible and resistant to bacterial wilt using metagenomic sequencing and culture-dependent approach

Endophytes have a wide range of potential in maintaining plant health and sustainable agricultural environmental conditions. In this study, we analysed the diversity of endophytic bacteria in four mulberry cultivars with different resistance capacity against bacterial wilt using metagenomic sequencing and culture-dependent approaches. We further assessed the role of 11 shared genera in the control of bacterial wilt of mulberry. The results of the present study showed that Actinobacteria, Firmicutes, and Proteobacteria were the three dominant phyla in all communities, with the representative genera Acinetobacter and Pseudomonas. The diversity analysis showed that the communities of the highly and moderately resistant varieties were more diverse compared to those of the weakly resistant and susceptible varieties. The control tests of mulberry bacterial wilt showed that Pantoea, Atlantibacter, Stenotrophomonas, and Acinetobacter were effective, with a control rate of over 80%. Microbacterium and Kosakonia were moderately effective, with a control rate between 50 and 80%. At the same time, Escherichia, Lysinibacillus, Pseudomonas, and Rhizobium were found to be less effective, with a control rate of less than 40%. In conclusion, this study provides a reasonable experimental reference data for the control of bacterial wilt of mulberry.

Research progress of volatile organic compounds produced by plant endophytic bacteria in control of postharvest diseases of fruits and vegetables

Pathogen infestation results in significant losses of fruits and vegetables during handling, transportation, and storage. The use of synthetic fungicides has been a common measure for controlling plant pathogens. However, their excessive use of chemicals has led to increased environmental pollution, leaving large amounts of chemicals in agricultural products, posing a threat to human and animal health. There is now an increasing amount of research activities to explore safer and more innovative ways to control plant pathogens. In this regard, endophytic bacteria contribute significantly. Endophytic bacteria are ubiquitous in the internal tissues of plants without causing damage or disease to the host. Due to their high volatility and difficulties in residue in fruits and vegetables, volatile organic chemicals (VOCs) produced by endophytic bacteria have received a lot of attention in recent years. VOCs are a potential biofumigant for the effective control of postharvest fruits and vegetables diseases. This review focuses mainly on the recent progress in using endophytic bacteria VOCs to control post-harvest fruits and vegetables disease. This review provides a brief overview of the concept, characteristics, and summarises the types, application effect, and control mechanisms of endophytic bacterial VOCs. The research area that is being developed has great application value in agriculture and living practice.

Complete genome of Sphingomonas paucimobilis ZJSH1, an endophytic bacterium from Dendrobium officinale with stress resistance and growth promotion potential

Sphingomonas paucimobilis ZJSH1 is an endophytic bacterium isolated from the roots of Dendrobium officinale with the ability to promote plant growth. It was found that the genome of strain ZJSH1 had gene fragment rearrangement compared with the genomes of the other four strains of S. paucimobilis, and the genome was integrated with phage genes. Functional analysis showed that the strain contained colonization-related genes, chemotaxis and invasion. A variety of genes encoding active materials, such as hormones (IAA, SA, ABA and zeaxanthin), phosphate cycle, antioxidant enzymes, and polysaccharides were identified which provide the strain with growth promotion and stress-resistant characteristics. Experiments proved that S. paucimobilis ZJSH1 grew well in media containing 80 g/L sodium chloride, 240 g/L polyethylene glycol and 800 μmol/L Cd²⁺, indicating its potential for resistance to stresses of salt, drought and cadmium, respectively. S. paucimobilis ZJSH1 is the only endophytic bacterium of this species that has been reported to promote plant growth. The analysis of its genome is conducive to understanding its growth-promoting mechanism and laying a foundation for the development and utilization of this species in the field of agriculture.

Effect of GR24 concentrations on tetracycline and nutrient removal from biogas slurry by different microalgae-based technologies

A biogas slurry composed of carbon, nitrogen, phosphorus, and antibiotics was generated. Investigations into the nutrient and tetracycline removal performance of four microalgae-based contaminant removal technologies, including Chlorella vulgaris, C. vulgaris co-cultured with endophytic bacteria, C. vulgaris co-cultured with Ganoderma lucidum, and C. vulgaris co-cultured with G. lucidum and endophytic bacteria, were conducted. The algal-bacterial-fungal consortium with 10^-9 M strigolactone (GR24) yielded the maximum growth rate and average daily yield for algae at 0.325 ± 0.03 d^-1 and 0.192 ± 0.02 g L^-1 d^-1, respectively. The highest nutrient/ tetracycline removal efficiencies were 83.28 ± 7.95 % for chemical oxygen demand (COD), 82.62 ± 7.97 % for total nitrogen (TN), 85.15 ± 8.26 % for total phosphorus (TP) and 83.92 ± 7.65 % for tetracycline. Adding an algal-bacterial-fungal consortium with an optimal synthetic analog GR24 concentration is seemingly an encouraging strategy for enhancing pollutant removal by algae, possibly overcoming the challenges of eutrophication and antibiotic pollution.

The effects of influent chemical oxygen demand and strigolactone analog concentration on integral biogas upgrading and pollutants removal from piggery wastewater by different microalgae-based technologies

Microalgae-based technologies are promising strategies for efficient wastewater treatment and biogas upgrading. In this study, three types of microalga-fungi/bacteria symbiotic systems stimulated with the strigolactone analog (GR24) were used to simultaneously remove nutrients from treated piggery wastewater and CO₂ from biogas. The effects of initial concentrations of chemical oxygen demand (COD) and GR24 on nutrient removal and biogas upgrading were investigated. When the initial COD concentration was 1200 mg/L, the Chlorella vulgaris-Ganoderma lucidum-endophytic bacteria co-cultivation systems achieved the best photosynthetic performance and microalgae growth. Moreover, under the appropriate COD concentration (1200 mg/L), the highest nutrient/CO₂ removal efficiencies were obtained. In addition, 10^-9 M GR24 significantly accelerated nutrient/CO₂ removal efficiencies. These findings provide a theoretical basis for scale-up experiments using microalgae-based technologies.

Potential of Miscanthus floridulus associated with endophytic bacterium Bacillus cereus BL4 to remediate cadmium contaminated soil

Phytoremediation assisted by endophytic bacteria is promising to efficiently remediate cadmium (Cd) contaminated soil. Bacillus cereus BL4, isolated from Miscanthus floridulus growing around a pyrite mine, exhibited high Cd tolerance and plant growth-promoting traits and could improve Cd bioavailability in soil. As a result of the pot experiment, after inoculation with strain BL4, the fresh weight, height, and Cd accumulation of Miscanthus floridulus shoots increased by 19.08-32.26 %, 6.02-16.60 %, and 23.67 %-24.88 %, respectively, and roots increased by 49.38-56.41 %, 22.87-33.93 %, and 28.51 %-42.37 %, respectively. Under Cd stress, the chlorophyll content, photosynthetic rate, and root activity of Miscanthus floridulus increased, while the membrane permeability and malonaldehyde (MDA) content significantly decreased after the inoculation of BL4, which indicated the alleviation of the cytotoxicity of Cd. Accordingly, the glutathione (GSH) content increased, and the activities of antioxidant enzymes presented downward trends after BL4 inoculation. Cd bioavailability in soil increased after BL4 inoculation, accompanied by increases in the activities of soil enzymes (invertase, urease, alkaline phosphatase, dehydrogenase, FDA hydrolase, and catalase) as well as the richness and diversity of soil bacteria. Our findings revealed that strain BL4 might strengthen the phytoremediation of Cd by Miscanthus floridulus through its effects on plant physio-biochemistry and soil microecology, which provided a basis for the relative application to Cd-contaminated soil.

An alkaline protease from Bacillus cereus NJSZ-13 can act as a pathogenicity factor in infection of pinewood nematode

Endophytic bacteria are an important biological control for nematodes. We isolated the nematicidal Bacillus cereus NJSZ-13 from healthy Pinus elliottii trunks. Bioassay experiments showed killing of all tested nematodes by proteins from the NJSZ-13 culture filtrate within 72 h. Degradation of the nematode cuticles was observed, suggesting the action of extracellular bacterial enzymes. The responsible protease was purified by ammonium sulfate precipitation, hydrophobic interaction chromatography, ion-exchange chromatography, and SDS-PAGE. The protease had a molecular weight of 28 kDa and optimal activity at 55 °C and pH 9, indicating an alkaline protease. The study suggests the potential for using this B. cereus NJSZ-13 strain protease to prevent pinewood nematode infection.

Metabolic profile and molecular characterization of endophytic bacteria isolated from Pinus sylvestris L. with growth-promoting effect on sunflower

Endophytic bacteria inhabit plant tissues such as roots, stems, leaves, fruits, and seeds and can multiply inside plant tissue without damaging them. This study involves the isolation, characterization, metabolic profiling, and effect of endophytic bacteria isolated from the roots of Scots pine (Pinus sylvestris), on the growth of sunflower. In the current study, fifteen isolates of endophytic bacteria were obtained from the roots of Scots pine, and their molecular characterization was performed using 16 s rRNA ribotyping. The molecular characterization revealed that the strains belonged to Bacillus spp., Pseudomonas spp., Micrococcus sp., Serratia sp., Enterobacter sp., Pantoea sp., Staphylococcus sp., and Microbacterium sp. Among the isolated strains, 9 strains showed positive results for ammonium production, 12 strains for calcium solubilization, 11 strains for magnesium solubilization, 5 strains for zinc solubilization, 12 strains for phosphate solubilization, 8 strains for potassium solubilization, 10 strains for indole acetic acid (IAA) production, 9 strains for siderophore, and 6 strains for hydrogen cyanide (HCN) production. The greenhouse experiment results demonstrated that all isolated endophytic bacteria improved the shoot length, dry weight, and chlorophyll content of sunflower, whereas a significant increase was observed by PS-3 (Bacillus cereus), PS-6 (Serratia marcescens), and PS-8 (Pseudomonas putida). Besides, the concentration of nitrogen, phosphorus, and potassium were also measured in sunflower shoots, and results asserted that bacterial inoculation increased the bioavailability of these essential nutrients to plants compared to uninoculated control. Thus, these endophytic bacteria could be used as an encouraging option to improve plant growth and performance.

Identification and Evaluation of the Growth Promotion of Endophytic Bacteria on in vitro Potato Plants

<b>Background and Objective:</b> Isolation and investigation of plant growth promoting bacteria on potato plants can provide significant information for the application of beneficial bacteria in potato production. This study aims to isolate and characterize endophytic bacteria isolated from potato roots. In addition, the potential application of endophytes in promoting potato growth under <i>in vitro</i> conditions was also investigated. <b>Materials and Methods:</b> The roots from 15 healthy potato plants were excised and surface sterilized by NaOCl and finally rinsed by sterilized water. The confirmed surface-sterilized roots were then aseptically cut into small fragments and spread onto the isolation media, followed by incubation at 27°C for up to 3 days. Six isolates that showed differences in colony morphology were selected for further investigation. All isolates were screened for IAA production, nitrogen fixation, and phosphate solubilization. <b>Results:</b> Five of the isolates were identified as <i>Bacillus</i> and isolate 30 was identified as <i>Paenibacillus alvei</i>. All isolates exhibited good IAA production. While Iso-27 had no nitrogen fixation activity, Iso-28 showed the highest level of nitrogen fixation activity (3.59 mg L¹), four isolates (Iso-9, Iso-10, Iso-11, Iso-28) could solubilize phosphate, ranging from 49.64 g L¹ to 67.98 mg L¹. After being inoculated with <i>in vitro</i> potato plants, isolates 9, 10, 28, 30, improved the stalk length, root number, fresh mass and dried mass of the potato plants. <b>Conclusion:</b> The four isolates can potentially be applied in <i>in vitro</i> potato culture.

Morphological and molecular characterization of bacterial endophytes from Centella asiatica leaves

BACKGROUND

Endophytes are a rich source of novel, distinct, and applicable compounds of interest in agricultural, medical, cosmetic, and pharmaceutical industries. In this respect, they have been attracting growing interest in the past few years. Endophytes are defined as microorganisms such as bacteria and fungi which have a mutualistic relationship with their host plants without causing any harm to their host. In this study, we isolated and identified bacterial endophytes from Centella asiatica collected in Western Cape, South Africa.

RESULTS

Twenty bacterial endophytes were isolated from Centella asiatica and characterized by using morphological and molecular techniques. Based on molecular traits, the isolates were identified as Pseudomonas sp. strain SGM1, Pseudomonas sp. strain SGM2, Pseudomonas sp. strain SGM3, Pseudomonas sp. strain SGM4, Pseudomonas sp. strain SGM5, Pseudomonas sp. strain SGM6, Pseudomonas sp. strain SGM7, Novosphingobium sp. strain SGM8, Pseudomonas sp. strain SGM9, Pseudomonas sp. strain SGM10, Chryseobacterium sp. strain SGM11, Enterobacter sp. strain SGM12, Enterobacter sp. strain SGM13, Pseudomonas sp. strain SGM14, Enterobacter sp. strain SGM15, Enterobacter sp. strain SGM16, Agrobacterium sp. strain SGM17, Pantoea sp. strain SGM18, Paraburkholderia sp. strain SGM19, and Pseudomonas sp. strain SGM20. Pseudomonas genus was dominant with eleven isolates. Morphological trait results showed that all isolates were gram-negative rod-shaped bacteria.

CONCLUSION

According to our understanding, this study revealed the first twenty endophytic bacteria isolated from Centella asiatica growing in the Western Cape Province, South Africa. Data obtained in the current study will increase the knowledge of the already existing microbial diversity associated with Centella asiatica. Further work is needed to evaluate the antioxidant and antibacterial activities in vitro and assess the growth and medicinal compounds of the identified endophytic bacteria in a laboratory scale bioreactors.

Effects of four endophytic bacteria on cadmium speciation and remediation efficiency of Sedum plumbizincicola in farmland soil

Cadmium (Cd) pollution in farmland soils severely affects agricultural production safety, thereby threatening human health. Sedum plumbizincicola is a Cd and Zn hyperaccumulator commonly used for the phytoremediation of Cd-contaminated soil. This study was aimed to improve the remediation effect of S. plumbizincicola on Cd-contaminated farmland soil and provide a theoretical basis for the enhancement of endophytic bacteria in the repair of Cd-contaminated soil with S. plumbizincicola. Four kinds of endophytic bacteria, namely Buttiauxella, Pedobacter, Aeromonas eucrenophila, and Ralstonia pickettii, were used, and soil culture experiments and pot experiments were conducted to explore the effects of endophytic bacteria on soil Cd speciation and phytoremediation efficiency of Cd-contaminated farmland soils. Under the experimental conditions, after inoculation with endophytic bacteria, the soil pH was effectively reduced, content of weak acid-extracted Cd and oxidizable Cd increased, and content of reducible Cd and residual Cd decreased. Soil Cd activity was increased, and the availability coefficient of soil Cd increased by 1.15 to 6.41 units compared with that of the control (CK₂). Compared with CK₂, the biomass of S. plumbizincicola significantly increased by 23.23-55.12%; Cd content in shoots and roots of S. plumbizincicola increased by 29.63-46.01% and 11.42-84.47%, respectively; and bioconcentration factor was 2.13 to 2.72 times that of CK₂. The Cd removal rate of S. plumbizincicola monocropping was 48.25%. When S. plumbizincicola was planted with inoculating endophytic bacteria, the Cd removal rate in the soil reached 61.18-71.49%, which was significantly higher than that of CK₂ (p < 0.05). The treatment with endophytic bacteria activated soil Cd, promoted the growth of S. plumbizincicola, increased its Cd content, and enhanced the phytoremediation of Cd-contaminated farmland soil. Therefore, endophytic bacteria can be used to improve the remediation efficiency of S. plumbizincicola in Cd-contaminated farmland soils.

Effect of different CO2 concentrations on biogas upgrading and nutrient removal by microalgae-fungi co-culture

Owing to the high carbon dioxide (CO₂)-fixation efficiency, microalgae-based technology has been widely used for biogas purification. The present study explored the effect of CO₂ concentration on biogas purification by an algal-fungal-bacterial symbiotic system. Two algal-fungal-bacterial symbiotic systems were cultivated to purify four simulated biogas samples with different CO₂ concentrations. The results showed that GR24, a synthetic analog of strigolactone, stimulated the growth of the algal-fungal-bacterial symbiotic system. The optimal CO₂ concentration for the purification of the simulated biogas was 45% (V/V), and the optimal symbiotic system was Chlorella vulgaris-Ganoderma lucidum-endophytic bacteria-GR24. The maximum chemical oxygen demand (COD; 82.61 ± 7.73%), total nitrogen (TN; 81.36 ± 7.97%), total phosphorus (TP; 85.69 ± 8.19), and CO₂ (69.23 ± 6.56%) removal efficiencies were detected with the addition of 10^-9 M GR24 to the C. vulgaris-G. lucidum-endophytic bacterial symbiotic system. These findings confirmed the effect of CO₂ concentration on the purification of biogas by the algal-bacterial symbiotic system. The study provides a theoretical basis for further research on the treatment of wastewater and biogas.

Comparative analysis of the endophytic bacteria inhabiting the phyllosphere of aquatic fern Azolla species by high-throughput sequencing

BACKGROUND

Azolla is a small floating fern living in symbiosis with nitrogen-fixing cyanobacteria and provides a variety of important ecosystem benefits. Previous studies have presented that Azolla harbors diverse bacteria that may play a key role in host fitness and productivity. However, the characteristics of endophytic bacteria inhabiting the phyllosphere of different species of Azolla have not yet been fully understood.

RESULTS

In this study, the 16S ribosomal DNA (rDNA) V5-V7 region of bacteria was determined by Illumina high-throughput sequencing platform to study the diversity and richness of endophytic bacterial communities in the phyllosphere of five Azolla species collected from different countries. A total of 1150 operational taxonomic units (OTUs) were detected for the endophytic bacteria community. According to the α diversity indices, the diversity of bacteria was ordered as Azolla imbricata > A. pinnata > A. filiculoides > A. mexicana > A. caroliniana. The PCoA results displayed that the bacterial communities of A. mexicana and A. caroliniana shared the highest similarity, followed by the similarity between A. pinnata and A. imbricata, and they were significantly distinct from the community of A. filiculoides. The dominant bacteria of Azolla mainly belonged to the phylum of Proteobacteria, followed by Actinobacteria, Chlorobillobacteria, and Firmicutes. In detail, the relative abundance of Proteobacteria in A. imbricata was 52.23%, whereas it was more than 80.00% in the other four species of Azolla. Notably, Herbaspirillum (45.91%, 44.08%) and Methylophilus (29.97%, 37.96%) were the main genera inhabiting A. mexicana and A. caroliniana respectively. Ferrovibrio (18.54%) and Rhizobium (16.68%) were the dominant genera inhabiting A. filiculoides. The group of unidentified genera (41.63%, 44.92%) consisted most of the bacteria in A. imbricata and A. pinnata respectively. Further analysis suggested that the significant different bacteria identified in LDA Effect Size analysis existed Azolla species-specific patterns.

CONCLUSIONS

In summary, all results suggested that the diversity and composition of the endophytic bacterial communities were different in Azolla species.

Chromium toxicity and its remediation by using endophytic bacteria and nanomaterials: A review

Chromium (Cr) is a crucial element for all life forms. Various anthropogenic activities have been responsible for environmental contamination with Cr (VI) in recent years. For this review, articles were collected using electronic databases such as Web of Science, Pubmed, ProQuest, and Google Scholar as per the guidelines of PRISMA-2015, applying the Boolean search methods. Chromium can cause severe health complications in humans and animals and threatens the surrounding environment, with negative impacts on crop yield, development, and quality. Hence, monitoring Cr contamination is essential, and various remediation technologies have emerged in the past 50 years to reduce the amount of Cr in the environment. This review focuses on chromium exposure and the associated environmental health risks. We also reviewed sustainable remediation processes, with emphasis on nanoparticle and endophytic remediation processes.

Isolation and identification of an endophytic bacteria Bacillus sp. K-9 exhibiting biocontrol activity against potato common scab

Potato scab is an important soil-borne disease that can significantly reduce the quality and economic value of potatoes. The purpose of this study was to isolate, screen and identify endophytic bacteria that have antagonistic and control effects on potato scab disease, and to determine the control effect and yield traits of the selected strains on potato scab disease in field conditions. A bacterial strain K-9 was isolated from the junction between scab spot and healthy epidermis of potato tuber. The K-9 strain was identified as Bacillus sp. through morphological, physiological and biochemical characterization, and 16S rDNA and gyrB gene sequence analysis. The diameter of the inhibition zone of strain K-9 against Streptomyces scabies on the YME plate was 3.82 cm. The K-9 strain could inhibit eight types of crop pathogens, with the highest inhibition rate (70.39%) against another soil-borne potato disease (potato black scurf). In the field test, the control effect of K-9 strain against potato scab was not significantly different from that of mixed bacteria or chemical agents, but the disease index and the scab index in the K-9 treatment were significantly lower than in the control. The potato yield in the K-9 treatment was 12.44% higher than the control. In summary, the K-9 strain can prevent not only potato scab, but also increase potato yield. Therefore, the endophytic bacterial K-9 strain may be a potential biological control agent.

Exploring the diversity and potential interactions of bacterial and fungal endophytes associated with different cultivars of olive (Olea europaea) in Brazil

The olive crop has expanded in the southeastern region of South America, particularly in Brazil. Thus, the objectives of this study were to identify the diversity of endophytic microorganisms associated with olive leaves with culture-dependent and culture-independent methods, to explore which factors influence the composition and abundance of this microbial community, to identify the trophic mode of these fungi by FunGuild and, to verify type associations between bacterial and fungal communities. Leaf samples were collected from 93 plants in nine locations in the Brazilian states of São Paulo and Minas Gerais. Leaves were first superficially disinfected before fungal isolation and next-generation metabarcoding sequencing was completed targeting the 16S rRNA regions for bacteria and ITS1 for fungi. In total, 800 isolates were obtained, which were grouped into 191 morphotypes and molecularly identified, resulting in 38 genera, 32 of which were recorded for the first time in cultivated olive trees in Brazil. For the isolated fungi, the most abundant trophic level was pathotrophic and for the culture-independent method was unidentified followed by symbiotrophic. The metabarcoding results revealed that factors such as plant age, altitudinal gradient, and geographic location can influence the microbial community of commercial olive plants, while the specific cultivar did not.