Midgut microbiota diversity of potato tuber moth associated with potato tissue consumed

Background

The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is a worldwide pest that feeds on both the leaves and tubers of potato plants. PTM larvae can digest leaves, or tubers, resulting in serious damage to potato plants in the field and potato tubers in storage. To understand how midgut bacterial diversity is influenced by the consumption of these two tissue types, the symbiotic bacteria in the potato-feeding PTM midgut and the endophytic bacteria of potato tissues were analyzed.

Results

At the genus level, the bacterial community composition in the PTM midgut was influenced by the tissues consumed, owing to their different nutrient contents. Escherichia_Shigella and Enterobacter were the most dominant genera in the midgut of leaf-feeding and tuber-feeding PTMs, respectively. Interestingly, even though only present in low abundance in leaves and tubers, Escherichia_Shigella were dominantly distributed only in the midgut of leaf-feeding PTMs, indicating that specific accumulation of these genera have occurred by feeding on leaves. Moreover, Enterobacter, the most dominant genus in the midgut of tuber-feeding PTMs, was undetectable in all potato tissues, indicating it is gut-specific origin and tuber feeding-specific accumulation. Both Escherichia_Shigella and Enterobacter abundances were positively correlated with the dominant contents of potato leaves and tubers, respectively.

Conclusions

Enrichment of specific PTM midgut bacterial communities was related to different nutrient levels in different tissues consumed by the insect, which in turn influenced host utilization. We provide evidence that a portion of the intestinal microbes of PTMs may be derived from potato endophytic bacteria and improve the understanding of the relationship between potato endophytic bacteria and the gut microbiota of PTMs, which may offer support for integrated management of this worldwide pest.

Bioinformatics analysis of endophytic bacteria related to berberine in the Chinese medicinal plant Coptis teeta Wall

Endophytic microorganisms absorb nutrients and prevent pathogen damage, supporting healthy plant growth. However, the relationship between endophytic bacteria and berberine synthesis in the medicinal plant Coptis teeta Wall. remains unclear. Herein, we explored the community composition of endophytic bacteria related to berberine in roots, stems, and leaves of wild-type and cultivated C. teeta. Endophytic bacterial communities were analyzed by 16S rRNA sequencing, and berberine content in roots was analyzed by high-performance liquid chromatography. Proteobacteria, Actinobacteria, and Bacteroidetes were the major phyla, and Mycobacterium, Salmonella, Nocardioides, Burkholderia-Paraburkholderia, and Rhizobium were the dominant genera in root, stem, and leaf tissues. Root berberine content was positively correlated with total N, total P, total K, and available K in rhizosphere soil. In addition, root berberine content was positively correlated with Microbacterium and norank_f_7B-8, whereas soil total K was positively correlated with Microbacterium and Burkholderia-Paraburkholderia in roots. Our results demonstrated a clear correlation between dominant endophytic bacteria and berberine synthesis in C. teeta. The findings are useful for the promotion of berberine production in C. teeta via manipulation of endophytic bacteria.

Nicotiana tabacum seed endophytic communities share a common core structure and genotype-specific signatures in diverging cultivars

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A common core microbiome was found in seeds of diverging N. tabacum cultivars.

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Enterobacteriaceae accounted for the predominant fraction of this core microbiome.

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Cultivars from the same breeding line shared the highest number of bacterial taxa.

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Seed-endophytic communities were extended by distinct taxa in each cultivar.

Seed endophytes of crop plants have recently received increased attention due to their implications in plant health and the potential to be included in agro-biotechnological applications. While previous studies indicated that plants from the Solanaceae family harbor a highly diverse seed microbiome, genotype-specific effects on the community composition and structure remained largely unexplored. The present study revealed Enterobacteriaceae-dominated seed-endophytic communities in four Nicotiana tabacum L. cultivars originating from Brazil, China, and the USA. When the dissimilarity of bacterial communities was assessed, none of the cultivars showed significant differences in microbial community composition. Various unusual endophyte signatures were represented by Spirochaetaceae family members and the genera Mycobacterium, Clostridium, and Staphylococcus. The bacterial fraction shared by all cultivars was dominated by members of the phyla Proteobacteria and Firmicutes. In total, 29 OTUs were present in all investigated cultivars and accounted for 65.5% of the combined core microbiome reads. Cultivars from the same breeding line were shown to share a higher number of common OTUs than more distant lines. Moreover, the Chinese cultivar Yunyan 87 contained the highest number (33 taxa) of unique signatures. Our results indicate that a distinct proportion of the seed microbiome of N. tabacum remained unaffected by breeding approaches of the last century, while a substantial proportion co-diverged with the plant genotype. Moreover, they provide the basis to identify plant-specific endophytes that could be addressed for upcoming biotechnological approaches in agriculture.

Gluconacetobacter diazotrophicus Changes The Molecular Mechanisms of Root Development in Oryza sativa L. Growing Under Water Stress

Background: Inoculation with Gluconacetobacter diazotrophicus has shown to influence root development in red rice plants, and more recently, the induced systemic tolerance (IST) response to drought was also demonstrated. The goal of this study was to evaluate the inoculation effect of G. diazotrophicus strain Pal5 on the amelioration of drought stress and root development in red rice (Oryza sativa L.). Methods: The experimental treatments consist of red rice plants inoculated with and without strain Pal5 in presence and absence of water restriction. Physiological, biochemical, and molecular analyses of plant roots were carried out, along with measurements of growth and biochemical components. Results: The plants showed a positive response to the bacterial inoculation, with root growth promotion and induction of tolerance to drought. An increase in the root area and higher levels of osmoprotectant solutes were observed in roots. Bacterial inoculation increased the drought tolerance and positively regulated certain root development genes against the water deficit in plants. Conclusion: G. diazotrophicus Pal5 strain inoculation favored red rice plants by promoting various root growth and developmental mechanisms against drought stress, enabling root development and improving biochemical composition.

Mining the roots of various species of the halophyte Suaeda for halotolerant nitrogen-fixing endophytic bacteria with the potential for promoting plant growth

Saline area may tend to be a productive land; however, many of salt-affected soils have nitrogen limitation and depend on plant-associated diazotrophs as their source of 'new' nitrogen. Herein, a total of 316 salinity tolerant nitrogen-fixing endophytic bacteria were isolated from roots of the halophyte Suaeda sp. sampled from 22 different areas of Iran to prepare the collection of nitrogen-fixing bacterial endophytes and evaluate the plant growth-promoting effect of effective isolates on growth of the halophyte Suaeda maritima. All of the identified nitrogen-fixing endophytes were classified to Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes phylum while we did not detect common nitrogen-fixing endophyte of glycophytes like Azospirillum. The genera Pseudomonas and Microbacterium were both encountered in high abundance in all samples, indicating that they might play an advanced role in the micro-ecosystem of the halophyte Suaeda. In addition, the results also showed that not only soil salinity can affect halophyte endophytic composition but also other factors such as geographical location, plant species, and other soil properties may be involved. Interestingly, only Zhihengliuella halotolerans and Brachybacterium sp. belonging to Actinobacteria could grow in semi-solid N-free (NFb) medium supplemented with 6% NaCl and highly enhanced growth of S. maritima in vitro. Overall, this study offers useful new resources for nitrogen-fixing endophytic bacteria which may be utilized to improve approaches for providing bio-fertilizer useful in saline-based agriculture.

Hydrocarbon-degrading genes in root endophytic communities on oil sands reclamation covers

In response to environmental regulations, the Canadian oil sands industry aims to reclaim all disturbed areas to equivalent land capability prior to mining operations. However, tailing sands used in reclamation contain residual hydrocarbons and plants growing in these areas may rely on hydrocarbon-degrading endophytic bacteria to survive. This study assessed the hydrocarbon-degrading potential (genes: CYP153, alkB and nah) of culturable and unculturable endophytic bacteria associated with annual barley (Hordeum vulgare) and sweet clover (Melilotus albus) plants in an oil sands reclamation area. Our results suggest higher CYP153 gene copy numbers in sweet clover when compared to barley. Yet, no significant differences were detected in 16S rRNA, alkB and nah genes. In addition, total hydrocarbons, pH, total soil carbon, organic carbon and total nitrogen play an important role in determining hydrocarbon-degrading potential in these communities. The assessment of culturable hydrocarbon-degrading bacteria revealed 42 isolates (total of 316) that were positive for at least one hydrocarbon-degrading gene. Most of these isolates were positive for alkB, and closely match the database for Pantoea, Pseudomonas and Enterobacter spp. Thus, to improve oil sands reclamation strategies, plant inoculation with select hydrocarbon-degrading endophytes could be used to increase plant tolerance and hydrocarbon degradation in these areas.

Investigating the endophytic bacterial diversity and community structures in seeds of genetically related maize (Zea mays L.) genotypes

This research aimed to investigate the composition and diversity of endophytic bacterial community in seeds of four hybrid maize and their parental lines, which was used to reveal the potential relationship and association of endophytic bacteria between maize genotypes and their genetic relevance. High-throughput sequencing (HTS) technology showed that a total of 1419 OTUs (46.6%) were parental lines unique and 1052 OTUs (34.5%) were hybrid varieties unique, with only 575 core OTUs revealed in all the samples. Most OTUs belonged to Proteobacteria. Enterobacter (23.2%), Shigella (21.2%), Pseudomonas (15.8%) and Achromobacter (10.1%) were the major genera; the bacterial community composition and diversity of endophytic bacteria were inconsistent among different seed genotypes. Based on principal component analysis (PCA), the results referred that the endophytic composition of hybrid sample showed obvious correlation with their female parental lines, and in 'Jingke968' and 'MC738' with the same female line the endophytic community was more similar than other hybrid samples. This was the first ever use of HTS technology for investigating the endophytic bacterial diversity and community structures in seeds of genetically related maize genotypes, it was shown that, there were core microbes shared among all genotypes of seed samples, and the female parental line was more significant to impact on the composition of their hybrid seeds than male parental line. This study would provide scientific clues for the future research on the vertical transmission of endophytes among maize generations.

Metagenomic study of endophytic bacterial community of sweet potato (Ipomoea batatas) cultivated in different soil and climatic conditions

The aim of this study was to clarify effects of soil and climatic conditions on community structure of sweet potato bacterial endophytes by applying locked nucleic acid oligonucleotide-PCR clamping technique and metagenomic analysis. For this purpose, the soil samples in three locations were transferred each other and sweet potato nursery plants from the same farm were cultivated for ca. 3 months. After removal of plastid, mitochondria and undefined sequences, the averaged numbers of retained sequences and operational taxonomic units per sample were 20,891 and 846, respectively. Proteobacteria (85.0%), Bacteroidetes (6.6%) and Actinobacteria (6.3%) were the three most dominant phyla, accounting for 97.9% of the reads, and γ-Proteobacteria (66.3%) being the most abundant. Top 10 genera represented 81.2% of the overall reads in which Pseudomonas (31.9-45.0%) being the most predominant. The overall endophytic bacterial communities were similar among the samples which indicated that the soil and the climatic conditions did not considerably affect the entire endophytic community. The original endophytic bacterial community might be kept during the cultivation period.

Metagenomic study of endophytic bacterial community of sweet potato (Ipomoea batatas) cultivated in different soil and climatic conditions

The aim of this study was to clarify effects of soil and climatic conditions on community structure of sweet potato bacterial endophytes by applying locked nucleic acid oligonucleotide-PCR clamping technique and metagenomic analysis. For this purpose, the soil samples in three locations were transferred each other and sweet potato nursery plants from the same farm were cultivated for ca. 3 months. After removal of plastid, mitochondria and undefined sequences, the averaged numbers of retained sequences and operational taxonomic units per sample were 20,891 and 846, respectively. Proteobacteria (85.0%), Bacteroidetes (6.6%) and Actinobacteria (6.3%) were the three most dominant phyla, accounting for 97.9% of the reads, and γ-Proteobacteria (66.3%) being the most abundant. Top 10 genera represented 81.2% of the overall reads in which Pseudomonas (31.9-45.0%) being the most predominant. The overall endophytic bacterial communities were similar among the samples which indicated that the soil and the climatic conditions did not considerably affect the entire endophytic community. The original endophytic bacterial community might be kept during the cultivation period.

Soil phenanthrene phytoremediation capacity in bacteria-assisted Spartina densiflora

Polycyclic aromatic hydrocarbons (PAH) have become a threat for the conservation of wetlands worldwide. The halophyte Spartina densiflora has shown to be potentially useful for soil phenanthrene phytoremediation, but no studies on bacteria-assisted hydrocarbon phytoremediation have been carried out with this halophyte. In this work, three phenanthrene-degrading endophytic bacteria were isolated from S. densiflora tissues and used for plant inoculation. Bacterial bioaugmentation treatments slightly improved S. densiflora growth, photosynthetic and fluorescence parameters. But endophyte-inoculated S. densiflora showed lower soil phenanthrene dissipation rates than non-inoculated S. densiflora (30% below) or even bulk soil (23% less). Our work demonstrates that endophytic inoculation on S. densiflora under greenhouse conditions with the selected PAH-degrading strains did not significantly increase inherent phenanthrene soil dissipation capacity of the halophyte. It would therefore be advisable to provide effective follow-up of bacterial colonization, survival and metabolic activity during phenanthrene soil phytoremediation.

Nitrogen-fixing bacteria and Oxalis - evidence for a vertically inherited bacterial symbiosis

BACKGROUND

Plant-endophyte symbioses often revolve around nitrogen metabolism, and involve varying degrees of intimacy. Although evidence for vertical inheritance of nitrogen-fixing endophytic bacteria is increasing, it is confined mostly to crop plants, and to date no such system has been reported for geophytes.

METHODS

Bacterial endophytes associated with Oxalis, the most species-rich geophytic genus form the Cape Flora in southern Africa was studied. Culturable endophytes were isolated from surface-sterilized vegetative and reproductive plant organs for six host species at three locations. Colonies of microbes on various artificial media were morphotyped, enumerated and identified using sequence data. Filter exclusion experiments were conducted to determine if endophytes were vertically transmitted to seeds, determine if mucilage plays a role to actively attract microbes from the soil and to assess microbial richness isolated from the mucilage of Oxalis seedlings. Fluorescent microscopy was implemented in order to visualize endophytic bacteria in cryo-sectioned seeds.

RESULTS

Evidence for a novel, vertically transmitted symbiosis was reported. Communities of nitrogen-fixing and plant growth-promoting Bacillus endophytes were found to associate with selected Oxalis hosts from nitrogen-deficient environments of the Cape. Bacillus endophytes were ubiquitous and diverse across species and plant bodies, and were prominent in seeds. Three common nitrogen-fixing Bacillus have known oxalotrophic properties and appear to be housed inside specialised cavities (containing oxalates) within the plant body and seeds.

CONCLUSIONS

The discovery of vertical transmission and potential benefits to both host and endophyte suggest a particularly tight mutualism in the Oxalis-endophyte system. This discovery suggests unexpected ways in which geophytes might avoid nitrogen deficiency, and suggest that such symbioses are more common than previously expected.

Draft genome analysis of the endophyte, Bacillus toyonensis COPE52, a blueberry (Vaccinium spp. var. Biloxi) growth-promoting bacterium

In this work, we report an analysis of the draft genome of the blueberry (Vaccinium spp. var. Biloxi) growth-promoting endophyte Bacillus toyonensis, strain COPE52. The genome of COPE52 consists of a single 5,806,513 bp replicon, with a 35.1% G + C content. Strain COPE52 was strongly affiliated to B. toyonensis species, based on species delimitation cut-off values established for average nucleotide identity (> 95-96%), genome-to genome distance calculator (> 70%) and phylogenomic analysis. The RAST genomic annotation of the COPE52 strain revealed a total of 5979 total genes, including 5631 protein-coding genes, 11 rRNA genes, 5 ncRNAs, 81 tRNA genes, and 251 pseudogenes. To further validate the in silico analysis results, experiments were carried out to detect the production of indoleacetic acid, protease activity, and the emission of volatiles like acetoin, 2,3-butanediol and dimethyl disulphide as potential plant growth-promoting mechanisms. COPE52 also showed antifungal action against the grey mould phytopathogen, Botrytis cinerea, during in vitro bioassays. In addition, inoculation with strain COPE52 promoted growth biomass and chlorophyll content in blueberry plants (Vaccinium spp. var. Biloxi) under greenhouse conditions. To our knowledge, this is the first study showing genomic and experimental evidence of B. toyonensis as plant growth-promoting bacteria (PGPB).

Phenotypic and genotypic characterization of endophytic bacteria associated with transgenic and non-transgenic soybean plants

Endophytic bacteria isolated from non-transgenic and transgenic Roundup Ready® glyphosate-resistant (GR) soybean plants were investigated to analyze the correspondence between phenotypic and genotypic characteristics and to determine whether or not the strains could be grouped based on the source of isolation in transgenic or non-transgenic plants, respectively. Most of the strains recovered from GR plants have shown the ability for plant growth promotion (PGP) by means of IAA production and inorganic phosphate solubilization, and 100% of the strains showed great motility (swarm or swim); in addition, 90% of the strains were able to metabolize the majority of carbon sources tested. GR soybean fields showed higher endophytes abundance than non-transgenic; however, analyzing the phylogenetic trees constructed using the partial 16SrRNA gene sequences, higher diversity was observed in non-transgenic soybean fields. Overall the majority of isolated endophytes could utilize multiple patterns of carbon sources and express resistance to antibiotics, while isolates varied widely in the PGP ability. The greater pattern and frequency of utilization of carbon sources and frequency and intensity of antibiotic resistance compared with PGP ability within the soybean endophytes community suggest that carbon sources metabolism and antibiotic resistance confer a greater relative fitness benefit than PGP ability. In conclusion, cluster analysis of the phenotypes and 16SrRNA gene sequences reveals lack of correspondence between the pattern of bacterial isolates and the transgenic character of plants, and the heterogeneity of clustering suggested that various adaptive processes, such as stress response, could have contributed to generate phenotypic variability to enhance endophytes overall fitness.

Metagenomic Insights and Genomic Analysis of Phosphogypsum and Its Associated Plant Endophytic Microbiomes Reveals Valuable Actors for Waste Bioremediation

The phosphogypsum (PG) endogenous bacterial community and endophytic bacterial communities of four plants growing in phosphogypsum-contaminated sites, Suaeda fruticosa (SF), Suaeda mollis (SM), Mesembryanthmum nodiflorum (MN) and Arthrocnemum indicum (AI) were investigated by amplicon sequencing. Results highlight a more diverse community of phosphogypsum than plants associated endophytic communities. Additionally, the bacterial culturable communities of phosphogypsum and associated plant endophytes were isolated and their plant-growth promotion capabilities, bioremediation potential and stress tolerance studied. Most of plant endophytes were endowed with plant growth-promoting (PGP) activities and phosphogypsum communities and associated plants endophytes proved highly resistant to salt, metal and antibiotic stress. They also proved very active in bioremediation of phosphogypsum and other organic and inorganic environmental pollutants. Genome sequencing of five members of the phosphogypsum endogenous community showed that they belong to the recently described species Bacillus albus (BA). Genome mining of BA allowed the description of pollutant degradation and stress tolerance mechanisms. Prevalence of this tool box in the core, accessory and unique genome allowed to conclude that accessory and unique genomes are critical for the dynamics of strain acquisition of bioremediation abilities. Additionally, secondary metabolites (SM) active in bioremediation such as petrobactin have been characterized. Taken together, our results reveal hidden untapped valuable bacterial actors for waste remediation.

Whole genome sequencing and identification of host-interactive genes in the rice endophytic Leifsonia sp. ku-ls

Leifsonia sp. ku-ls is an endophytic bacterial strain colonizing in high numbers the stem and leaf of the high-yielding and widely grown indica rice cultivar RP Bio-226. Whole genome sequencing of this strain using Illumina Hiseq-2500 system resulted in generation of 10,103,994 paired-end reads of 150 nucleotides length. De novo assembly of the reads with A5MySeq resulted in 51 scaffolds. Kmer analysis with KAT estimated the genome size as 3.83 Mbp with 70% GC content. Annotation of the genome resulted in identification of 3930 protein-coding genes, 45 tRNA genes, and 3 rRNA genes. Detailed analysis of the genes predicted resulted in identification of host beneficial genes which include genes associated with hormone production, nitrogen metabolism, and stress response. There is an elaborate defense against oxidative stress present in this bacterium which also can mitigate plant oxidative stress resulting from disease/abiotic stress. Comparison of this endophytic bacterial genome with non-endophytic Leifsonia sp. showed presence of additional genes, increase in copy number of some of the genes and regulators. Many genes with eukaryotic-like domains have also been identified in this bacterium.

Biogenic AgNPs synthesized via endophytic bacteria and its biological applications

In this present study, the endophytic bacteria were isolated from the drought-tolerant ornamental plant Pennisetum setaceum. The biomass of endophytic bacteria was utilized for the biogenic synthesis of silver nanoparticles (AgNPs). The synthesis of AgNPs was confirmed by UV-Visible and FTIR spectroscopy followed by SEM analysis. The antibacterial studies were performed through MIC, MBC, and biofilm assays. Efficacy of AgNPs against the human breast cancer (MCF-7) cells was also tested, and the IC₅₀ was determined by MTT assay. In our study, we have observed that the synthesized AgNPs exhibited a dose-dependent cytotoxicity (1-100 μg/mL) against MCF-7 cells and morphological alterations of the cells were also visualized and the IC₅₀ was observed at 50 μg/mL. The treatment of synthesized AgNPs altered the expression of apoptotic proteins including Bax, Bcl-2, and inflammatory marker COX-2 in MCF-7 cells. To the best of our knowledge, this is the first report that demonstrates the AgNPs from endophytic bacteria isolated from the plant Pennisetum setaceum can induce apoptosis in human breast cancer MCF-7 cells. Our results suggest that AgNPs used in this study can be utilized to control human pathogens and can also be utilized to induce apoptosis in breast cancer cells.

Diversity of cultivable endophytic bacteria in mulberry and their potential for antimicrobial and plant growth-promoting activities

Endophytic bacteria-based biocontrol is regarded as a potential plant disease management strategy. Present study analyzed the diversity of mulberry endophytic bacteria basing on a culture-dependent approach and further evaluated their antimicrobial and plant growth-promoting (PGP) activities. A total of 608 cultivable endophytic bacteria, belonging to 4 phyla and 36 genera, were isolated from four mulberry cultivars having different resistance to sclerotiniosis in three seasons. Taxonomic compositional analysis results showed that Proteobacteria, Firmicutes, and Actinobacteria were the three dominant bacterial phyla in all communities, with the representative genera Pantoea, Bacillus, Pseudomonas, Curtobacterium, and Sphingomonas. Diversity analysis results indicated that the diversity of winter community was higher than that of spring or autumn, and higher diversities were detected in the resistant cultivar communities compared with the susceptible cultivar. Antagonism assays results showed that 33 isolates exhibited strong and stable activity against three phytopathogens which are Sclerotinia sclerotiorum, Botrytis cinerea, and Colletotrichum gloeosporioide. Eight endophytic bacteria were selected out from 33 antagonists based on the evaluation of antagonistic and PGP activities. Furthermore, pot experiment results revealed that all the 8 tested endophytes stimulated the growth of mulberry seedlings at different levels, and Bacillus sp. CW16-5 exhibited the highest promotion capacity, which the shoot length and the root fresh weight were increased by 83.37% and 217.70%, respectively. Altogether, present study revealed that mulberry harbors a large amount of diverse cultivable endophytic bacteria and they also serve as novel sources of beneficial bacteria and bioactive metabolites.

Drought tolerance improvement in plants: an endophytic bacterial approach

Climate change is a crucial issue among the serious emerging problems which got a global attention in the last few decades. With the climate change, worldwide crop production has been seriously affected by drought stress. In this regard, various technologies including traditional breeding and genetic engineering are used to cope with drought stress. However, the interactions between plants and endophytic bacteria emerged as an interesting era of knowledge that can be used for novel agriculture practices. Endophytic bacteria which survive within plant tissues are among the most appropriate technologies improving plant growth and yield under drought conditions. These endophytic bacteria live within plant tissues and release various phytochemicals that assist plant to withstand in harsh environmental conditions, i.e., drought stress. Their plant growth-promoting characteristics include nitrogen fixation, phosphate solubilization, mineral uptake, and the production of siderophore, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and various phytohormones. These plant growth promoting characteristics of endophytic bacteria improve root length and density, which lead to the enhance drought tolerance. In addition, plant-endophytic bacteria assist plant to withstand against drought stress by producing drought-tolerant substances, for instance, abscisic acid, indole-3-acetic acid, ACC deaminase, and various volatile compounds. Indirectly, endophytic bacteria also improve osmotic adjustment, relative water content, and antioxidant activity of inoculated plants. Altogether, these bacterial-mediated drought tolerance and plant growth-promoting processes continue even under severe drought conditions which lead to enhanced plant growth promotion and yield. The present review highlights a natural and environment-friendly strategy in the form of drought-tolerant and plant growth-promoting endophytic bacteria to improve drought tolerance in plants.

Identification of endophytic bacteria in medicinal plants and their antifungal activities against food spoilage fungi

Endophytes are fungi or bacteria living in the intracellular parts of the plants. In this study, 12 medicinal plants were examined for the presence of endophytic bacteria. Antifungal activities of the isolates were determined against Aspergillus flavus PTCC 5006, Penicillium citrinum PTCC 5304, Aspergillus fumigatus PTCC 5006, Fusarium oxysporum MTCC 284, and Rhizopus stolonifer. In order to determine the metabolites characteristics of these isolates, catalase and proteolytic enzyme treatments were assessed. Moreover, approximate molecular weights of the antifungal substance were measured by fractionation method and the volatile compounds were determined by using GC-mass spectroscopy. Finally, 16s rRNA gene sequencing confirmed the strain of the bacteria. Twenty-one endophytic bacteria, out of a total of 82 isolates, showed antifungal activities against all five spoilage fungi. The results of the PCR assay revealed two species: Bacillus pumilus and B. safensis. Proteolytic enzyme activities and the fractionation of the supernatants proved that more than one compound was responsible for the antifungal activities. This compound could be proteins, peptides, and other low-molecular compounds, such as Butanal, 3-methyl-, Propene, 2-butene, 2-heptanone, 6-methyl-5-methylene-, and 6-oxabicyclo[3.1.0] hexane, which all were identified in the headspace of the GC-mass spectroscopy.

A Microbiome Study Reveals Seasonal Variation in Endophytic Bacteria Among different Mulberry Cultivars

Knowledge of seasonal shifts in the bacterial community composition among different mulberry (Morus L.) cultivars will facilitate to develop the biocontrol phytopathogens strategy using endophytic bacteria. The present study investigated the endophytic bacterial communities of four mulberry cultivars that have different resistance to mulberry fruit sclerotiniosis using Illumina-based sequencing of the 16S rRNA gene fragment in spring and autumn. The results indicated that spring samples harbor higher bacterial operational taxonomic units (OTUs), α-diversity, and bacterial community complexity in comparison with autumn samples. The taxonomic composition analysis showed that the majority of endophytes were composed of Proteobacteria (genus level: Methylobaterium) and Actinobacteria in spring, while sequences classified as Proteobacteria (genus level: Pantoea and Pseudomonas) were abundant in autumn. Analysis of β-diversity also revealed endophytic bacteria were divided into two main groups by season. By comparison among different mulberry cultivars, we found that Pantoea, Methylobaterium, and Pseudomonas were the three major bacterial genera in all cultivars, while their relative abundances varied with cultivars and appeared no obvious relationship with resistance level of mulberry fruit sclerotiniosis. The complex correlation of the endophytic communities in susceptible mulberry cultivars was higher than that of the resistant cultivars. Overall, the findings suggested that season plays a key role in determining the mulberry endophytic bacterial communities, followed by host cultivar, and Proteobacteria was the predominant phylum in both seasons and different mulberry cultivars.

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Season played a key role in determining mulberry endophytic bacterial communities.

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Mulberry endophytic bacterial variation was not obviously related with cultivars.

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Mulberry recruited beneficial endophytes as potential biocontrol agents.

Changes in endophytic bacterial communities during different growth stages of cucumber (Cucumis sativus L.)

Endophytic bacterial diversity in plants presents the level of interaction between culturable and non-culturable endophytic bacteria, thereby providing an appropriate insight into the endophytic environment. This study was conducted to determine the trend of culturable and non-culturable endophytic bacteria at two different sites encompassing four consecutive growth stages. For culturable endophytic bacteria, isolation was carried out using the dilution plate technique, and the obtained colonies were compared using PCR-restriction fragment length polymorphism (RFLP). Different RFLP-types were identified to their nearest neighbour using 16S rRNA sequencing. The non-culturable endophytic bacterial diversity was obtained by next generation sequencing. Results suggested a similar trend among the culturable and non-culturable bacteria for observed operational taxonomic units and diversity indices. It is noticeable that the endophytic bacteria inhabiting in stage 1 disappeared, and instead, different endophytic bacteria appeared. Moreover, the temporal persistence of certain culturable and non-culturable bacteria was also observed. In conclusion, the endophytic bacterial diversity in cucumber initially increased with the plant growth and then decreased at a later stage. Furthermore, it was suggested that plants regulate the number and diversity of endophytes throughout the lifecycle of plants.

Endophytic bacteria isolated from Solanum nigrum L., alleviate cadmium (Cd) stress response by their antioxidant potentials, including SOD synthesis by sodA gene

Cadmium (Cd) is a toxic heavy metal and an abiotic stressor to plants; however, inoculation of endophytic bacteria can raise resistance in plants against Cd, as well as improve plant growth. In the present study, two endophytic bacterial strains were isolated from Solanum nigrum, identified as Serratia sp. IU01 and Enterobacter sp. IU02 by 16S DNA sequencing. Both IU01 and IU02 were tolerant up to 9.0 mM of Cd in culture broth and successive increase in Cd concentration from 0 mM to 9.0 mM, led to an increase in the SOD enzyme activity of the isolates. Both strains were capable of indole-3-acetic acid (IAA) synthesis and phosphate solubilization, detected through gas spectrometry-mass chromatography (GC-MS) and Pikovskaya agar medium respectively. Brassica juncea plants stressed with 0-25 mg/kg Cd showed retardation in all growth attributes, however, inoculation of strain IU01 and IU02 significantly promoted the plant growth attributes as compared to control. Moreover, antioxidant enzymes and metabolites against reactive oxygen species (ROS) including polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), alcohol dehydrogenase (ADH), reduced glutathione (GSH), malondialdehyde (MDA), flavonoid and polyphenolic contents were also significantly relieved by inoculation of IU01 and IU02 in plant exposed to different concentration of Cd stress as compared to control plants. Phytohormone production, phosphate solubilization, and/or antioxidative support of IU01 and IU02 might be responsible for growth promotion and Cd resistance in the plant.

Occurrence of diverse Bradyrhizobium spp. in roots and rhizospheres of two commercial Brazilian sugarcane cultivars

The genus Bradyrhizobium harbors many endosymbionts of legumes, but recent research has shown their widespread presence in soils and in non-legumes, notably in roots of sugarcane. This study aimed to investigate the Bradyrhizobium sp. community density in the endosphere and the rhizosphere of two commercial sugarcane cultivars. Samples of the rhizosphere and root endosphere of two Brazilian sugarcane cultivars (RB867515 and IACSP95-5000) were collected, serially diluted, and inoculated on axenic cowpea (Vigna unguiculata) and the induction of nodules was evaluated. Based on the results, a density was estimated of at least 1.6 × 10⁴ rhizobia g root^-1 in rhizosphere samples and up to 105 rhizobia g root ^-1 in endosphere. BOX-PCR profiling of 93 Bradyrhizobium isolates revealed genetic variability, with some dominant (up to 18 representants) and less dominant genotypes. 16S rRNA and ITS sequence analyses confirmed nine phylotypes, six of which pertained to the B. elkanii clade and three to the B. japonicum clade. Five isolates were genetically similar to the recently described species B. sacchari. There was no effect of the factors "plant cultivar" and "root compartment" on Bradyrhizobium sp. community composition and the most abundant genotypes occurred both in rhizosphere and endosphere of both cultivars. Therefore, this study confirms the natural presence of diverse Bradyrhizobium spp. in sugarcane root systems (mainly the rhizosphere) and indicates that certain Bradyrhizobium phylotypes have a special affinity for sugarcane root colonization.

Reducing arsenic in rice grains by leonardite and arsenic-resistant endophytic bacteria

Arsenic contaminated in rice plants can cause many physiological, biochemical and productivity in rice. This also had a negative impact on human health. To decrease arsenic in grains, a combination of leonardite as amendment and arsenic-resistance endophytic bacteria was investigated. The results showed that 1% (w/v) leonardite (91.86 ± 2.04%) had the highest efficiency in adsorbing initial arsenic concentration of 2 mg L^-1, which was higher than bagasse fly ash (16.25 ± 3.97%), rice husk ash (10.36 ± 1.28%), and sawdust fly ash (63.00 ± 5.67%) under the same condition. This was due to the higher aluminium and iron contents of leonardite strongly binding to arsenic anions. Meanwhile, Bacillus pumilus had an ability to decrease arsenic accumulation in rice grains to levels below those achieved by Pseudomonas sp. and Bacillus thuringiensis. This was possibly due to B. pumilus producing higher siderophore. Interestingly, a combination of microbe and leonardite addition could decrease arsenic accumulation in grains to below the permissible limit (0.2 mg As kg^-1 for inorganic arsenic). It could also reduce oxidative stress and showed down-regulation of Lsi1, Lsi2 and OsPT4 at the heading stage, which coincided with low arsenic and high silicon accumulation in roots. Therefore, this result could be used to decrease arsenic accumulation in grains in arsenic-contaminated paddy fields, improved rice plants defense and endured of arsenic stress, and increased rice productivity.

Contribution of Bacillus cereus ERBP in ozone detoxification by Zamioculcas zamiifolia plants: Effect of ascorbate peroxidase, catalase and total flavonoid contents for ozone detoxification

Eighteen plant species were screened for ozone (O₃) removal in a continuous system. Zamioculcas zamiifolia had the highest O₃ removal efficiency. To enhance O₃ removal by Z. zamiifolia, adding a compatible endophytic bacteria, Bacillus cereus ERBP into Z. zamiifolia was studied. After operating under an O₃ continuous system (150-250 ppb) at a flow rate of 0.3 L min^-1 for 80 h, inoculated plants (74%) exhibited higher O₃ removal efficiency than non-inoculated ones (53%). In addition, after O₃ exposure (80 h), the population of B. cereus ERBP in inoculated plants was significantly increased in both shoots approximately 35 folds and leaves 13 folds compared to inoculated plants without O₃ exposure. The results also showed that B. cereus ERBP had the ability to protect Z. zamiifolia against O₃ stress conditions. The increase in B. cereus ERBP populations was attributed to the significant increase in ascorbate peroxidase (APX) and catalase (CAT) activity. In addition, increasing B. cereus ERBP populations led to raise total flavonoid contents which is one of antioxidant compounds. Increasing APX, CAT activities, and total flavonoid contents can enhance O₃ detoxification in plant tissues. The mechanism of B. cereus ERBP for enhancing O₃ phytoremediation was proposed in this study. The results suggested that B. cereus ERBP was a potential tool for alleviating O₃ stress on Z. zamiifolia and enhancing O₃ phytoremediation efficiency.