The Hidden World within Plants: Ecological and Evolutionary Considerations for Defining Functioning of Microbial Endophytes

Bacillus velezensis BE2 controls wheat and barley diseases by direct antagonism and induced systemic resistance

Wheat and barley rank among the main crops cultivated on a global scale, providing the essential nutritional foundation for both humans and animals. Nevertheless, these crops are vulnerable to several fungal diseases, such as Septoria tritici blotch and net blotch, which significantly reduce yields by adversely affecting leaves and grain quality. To mitigate the effect of these diseases, chemical fungicides have proven to be genuinely effective; however, they impose a serious environmental burden. Currently, biocontrol agents have attracted attention as a sustainable alternative to fungicides, offering an eco-friendly option. The study aimed to assess the efficacy of Bacillus velezensis BE2 in reducing disease symptoms caused by Zymoseptoria tritici and Pyrenophora teres. This bacterium exhibited significant antagonistic effects in vitro by suppressing fungal development when pathogens and the beneficial strain were in direct confrontation. These findings were subsequently confirmed through microscopic analysis, which illustrated the strain's capacity to inhibit spore germination and mycelial growth in both pathogens. Additionally, the study analysed the cell-free supernatant of the bacterium using UPLC-MS (ultra-performance liquid chromatography-mass spectrometry). The results revealed that strain BE2 produces, among other metabolites, different families of cyclic lipopeptides that may be involved in biocontrol. Furthermore, the beneficial effects of strain BE2 in planta were assessed by quantifying the fungal DNA content directly at the leaf level after bacterization, using two different application methods (foliar and drenching). The results indicated that applying the beneficial bacterium at the root level significantly reduced pathogens pressure. Finally, gene expression analysis of different markers showed that BE2 application induced a priming effect within the first hours after infection. KEY POINTS: • BE2 managed Z. tritici and P. teres by direct antagonism and induced systemic resistance. • Strain BE2 produced seven metabolite families, including three cyclic lipopeptides. • Application of strain BE2 at the root level triggered plant defense mechanisms.

Are plant traits drivers of endophytic communities in seasonally flooded tropical forests?

PREMISE

In the Amazon basin, seasonally flooded (SF) forests offer varying water constraints, providing an excellent way to investigate the role of habitat selection on microbial communities within plants. However, variations in the microbial community among host plants cannot solely be attributed to environmental factors, and how plant traits contribute to microbial assemblages remains an open question.

METHODS

We described leaf- and root-associated microbial communities using ITS2 and 16 S high-throughput sequencing and investigated the stochastic-deterministic balance shaping these community assemblies using two null models. Plant ecophysiological functioning was evaluated by focusing on 10 leaf and root traits in 72 seedlings, belonging to seven tropical SF tree species in French Guiana. We then analyzed how root and leaf traits drove the assembly of endophytic communities.

RESULTS

While both stochastic and deterministic processes governed the endophyte assembly in the leaves and roots, stochasticity prevailed. Discrepancies were found between fungi and bacteria, highlighting that these microorganisms have distinct ecological strategies within plants. Traits, especially leaf traits, host species and spatial predictors better explained diversity than composition, but they were modest predictors overall.

CONCLUSIONS

This study widens our knowledge about tree species in SF forests, a habitat sensitive to climate change, through the combined analyses of their associated microbial communities with functional traits. We emphasize the need to investigate other plant traits to better disentangle the drivers of the relationship between seedlings and their associated microbiomes, ultimately enhancing their adaptive capacities to climate change.

Endophyte mediated biocontrol mechanisms of phytopathogens in agriculture

The global human population is growing and demand for food is increasing. Global agriculture faces numerous challenges, including excessive application of synthetic pesticides, emergence of herbicide-and pesticide-resistant pathogenic microbes, and more frequent natural disasters associated with global warming. Searches for valuable endophytes have increased, with the aim of making agriculture more sustainable and environmentally friendly. Endophytic microbes are known to have a variety of beneficial effects on plants. They can effectively transfer nutrients from the soil into plants, promote plant growth and development, increase disease resistance, increase stress tolerance, prevent herbivore feeding, reduce the virulence of pathogens, and inhibit the growth of rival plant species. Endophytic microbes can considerably minimize the need for agrochemicals, such as fertilizers, fungicides, bactericides, insecticides, and herbicides in the cultivation of crop plants. This review summarizes current knowledge on the roles of endophytes focusing on their mechanisms of disease control against phytopathogens through the secretion of antimicrobial substances and volatile organic compounds, and the induction of systemic resistance in plants. Additionally, the beneficial roles of these endophytes and their metabolites in the control of postharvest diseases in plants have been summarized.

Inhibitory activity of bacterial lipopeptides against Fusarium oxysporum f.sp. Strigae

This study investigated the influence of bacterial cyclic lipopeptides (LP; surfactins, iturins, fengycins) on microbial interactions. The objective was to investigate whether the presence of bacteria inhibits fungal growth and whether this inhibition is due to the release of bacterial metabolites, particularly LP. Selected endophytic bacterial strains with known plant-growth promoting potential were cultured in the presence of Fusarium oxysporum f.sp. strigae (Fos), which was applied as model fungal organism. The extracellular metabolome of tested bacteria, with a focus on LP, was characterized, and the inhibitory effect of bacterial LP on fungal growth was investigated. The results showed that Bacillus velezensis GB03 and FZB42, as well as B. subtilis BSn5 exhibited the strongest antagonism against Fos. Paraburkholderia phytofirmans PsJN, on the other hand, tended to have a slight, though non-significant growth promotion effect. Crude LP from strains GB03 and FZB42 had the strongest inhibitory effect on Fos, with a significant inhibition of spore germination and damage of the hyphal structure. Liquid chromatography tandem mass spectrometry revealed the production of several variants of iturin, fengycin, and surfactin LP families from strains GB03, FZB42, and BSn5, with varying intensity. Using plate cultures, bacillomycin D fractions were detected in higher abundance in strains GB03, FZB42, and BSn5 in the presence of Fos. Additionally, the presence of Fos in dual plate culture triggered an increase in bacillomycin D production from the Bacillus strains. The study demonstrated the potent antagonistic effect of certain Bacillus strains (i.e., GB03, FZB42, BSn5) on Fos development. Our findings emphasize the crucial role of microbial interactions in shaping the co-existence of microbial assemblages.

Comparative genomic analysis of strain Priestia megaterium B1 reveals conserved potential for adaptation to endophytism and plant growth promotion

In our study, we aimed to explore the genomic and phenotypic traits of Priestia megaterium strain B1, which was isolated from root material of healthy apple plants, to adapt to the endophytic lifestyle and promote plant growth. We identified putative genes encoding proteins involved in chemotaxis, flagella biosynthesis, biofilm formation, secretory systems, detoxification, transporters, and transcription regulation. Furthermore, B1 exhibited both swarming and swimming motilities, along with biofilm formation. Both genomic and physiological analyses revealed the potential of B1 to promote plant growth through the production of indole-3-acetic acid and siderophores, as well as the solubilization of phosphate and zinc. To deduce potential genomic features associated with endophytism across members of P. megaterium strains, we conducted a comparative genomic analysis involving 27 and 31 genomes of strains recovered from plant and soil habitats, respectively, in addition to our strain B1. Our results indicated a closed pan genome and comparable genome size of strains from both habitats, suggesting a facultative host association and adaptive lifestyle to both habitats. Additionally, we performed a sparse Partial Least Squares Discriminant Analysis to infer the most discriminative functional features of the two habitats based on Pfam annotation. Despite the distinctive clustering of both groups, functional enrichment analysis revealed no significant enrichment of any Pfam domain in both habitats. Furthermore, when assessing genetic elements related to adaptation to endophytism in each individual strain, we observed their widespread presence among strains from both habitats. Moreover, all members displayed potential genetic elements for promoting plant growth.IMPORTANCEBoth genomic and phenotypic analyses yielded valuable insights into the capacity of P. megaterium B1 to adapt to the plant niche and enhance its growth. The comparative genomic analysis revealed that P. megaterium members, whether derived from soil or plant sources, possess the essential genetic machinery for interacting with plants and enhancing their growth. The conservation of these traits across various strains of this species extends its potential application as a bio-stimulant in diverse environments. This significance also applies to strain B1, particularly regarding its application to enhance the growth of plants facing apple replant disease conditions.

Analysis of differential effects of host plants on the gut microbes of Rhoptroceros cyatheae

As an indispensable part of insects, intestinal symbiotic bacteria play a vital role in the growth and development of insects and their adaptability. Rhoptroceros cyatheae, the main pest of the relict plant Alsophila spinulosa, poses a serious threat to the development of the A. spinulosa population. In the present study, 16S rDNA and internal transcribed spacer high-throughput sequencing techniques were used to analyze the structure of intestinal microbes and the diversity of the insect feeding on two different plants, as well as the similarities between the intestinal microorganisms of R. cyatheae. The dominant bacteria of leaf endophytes were also compared based on the sequencing data. The results showed that Proteobacteria, Firmicutes, and Actinobacteria were the dominant phyla of intestinal bacteria, and Ascomycota was the dominant phylum of intestinal fungi. Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Methylobacterium-Methylorubrum, and Enterococcus were the dominant genera in the intestine of R. cyatheae feeding on two plants, and the relative abundance was significantly different between the two groups. Candida was the common dominant genus of intestinal fungi in the two groups, and no significant difference was observed in its abundance between the two groups. This showed that compared with the intestinal fungi of R. cyatheae, the abundance of the intestinal bacteria was greatly affected by food. The common core microbiota between the microorganisms in A. spinulosa leaves and the insect gut indicated the presence of a microbial exchange between the two. The network correlation diagram showed that the gut microbes of R. cyatheae feeding on Gymnosphaera metteniana were more closely related to each other, which could help the host to better cope with the adverse external environment. This study provides a theoretical basis for the adaptation mechanism of R. cyatheae and a new direction for the effective prevention and control of R. cyatheae.

Metataxonomic analysis of endophytic bacteria of blackberry (Rubus ulmifolius Schott) across tissues and environmental conditions

(1) Background: Endophytic bacteria represent an important component of plant wellness. They have been widely studied for their involvement in plant development and enhancement of stress tolerance. In this work, the endophytic communities of roots, stems, and leaves of blackberry (Rubus ulmifolius Schott) were studied in three different niches: natural, riverside, and human-impacted niches. (2) Results: The microbiome composition revealed that Sphingomonadaceae was the most abundant family in all samples, accounting for 9.4-45.8%. In contrast, other families seem to be linked to a specific tissue or niche. Families Microbacteriaceae and Hymenobacteraceae increased their presence in stem and leaf samples, while Burkholderiaceae abundance was important in riverside samples. Alpha and beta diversity analyses showed that root samples were the most diverse, and they gathered together in the same cluster, apart from the rest of the samples. (3) Conclusions: The analysis of the microbiome of R. ulmifolius plants revealed that the composition was essentially the same in different niches; the differences were primarily influenced by plant tissue factors with a core genome dominated by Sphingomonadaceae. Additionally, it was observed that R. ulmifolius can select its own microbiome, and this remains constant in all tissues evaluated regardless the niche of sampling.

Distinct fungal communities affecting opposite galanthamine accumulation patterns in two Lycoris species

Lycoris radiata is the main source of galanthamine, a clinical drug used in Alzheimer's disease; however, the galanthamine content in L. radiata is low. Lycoris aurea is another Lycoris species with high galanthamine content. Fungal endophytes can enhance plant secondary metabolite accumulation; thus, we compared the fungal communities in these two Lycoris species to identify certain fungal taxa in L. aurea capable of enhancing galanthamine accumulation. Several fungal endophytes, which were enriched in, exclusively isolated from L. aurea, or showed significant correlations with galanthamine, were demonstrated to enhance the accumulation of only galanthamine but no other Amaryllidaceae alkaloids (AAs) in L. radiata. These fungal endophytes mainly upregulated the downstream genes in the biosynthesis pathways of AAs in L. radiata, suggesting that they may allocate more precursors for galanthamine biosynthesis. This study demonstrated that fungal endophytes from L. aurea with higher galanthamine content can specifically enhance the accumulation of this medicinal alkaloid in other Lycoris species, thereby increasing the galanthamine source and reducing galanthamine separation and purification costs. This study broadens our understanding of the complex interactions between plant secondary metabolites and fungal endophytes.

Invisible Inhabitants of Plants and a Sustainable Planet: Diversity of Bacterial Endophytes and their Potential in Sustainable Agriculture

Uncontrolled usage of chemical fertilizers, climate change due to global warming, and the ever-increasing demand for food have necessitated sustainable agricultural practices. Removal of ever-increasing environmental pollutants, treatment of life-threatening diseases, and control of drug-resistant pathogens are also the need of the present time to maintain the health and hygiene of nature, as well as human beings. Research on plant-microbe interactions is paving the way to ameliorate all these sustainably. Diverse bacterial endophytes inhabiting the internal tissues of different parts of the plants promote the growth and development of their hosts by different mechanisms, such as through nutrient acquisition, phytohormone production and modulation, protection from biotic or abiotic challenges, assisting in flowering and root development, etc. Notwithstanding, efficient exploitation of endophytes in human welfare is hindered due to scarce knowledge of the molecular aspects of their interactions, community dynamics, in-planta activities, and their actual functional potential. Modern "-omics-based" technologies and genetic manipulation tools have empowered scientists to explore the diversity, dynamics, roles, and functional potential of endophytes, ultimately empowering humans to better use them in sustainable agricultural practices, especially in future harsh environmental conditions. In this review, we have discussed the diversity of bacterial endophytes, factors (biotic as well as abiotic) affecting their diversity, and their various plant growth-promoting activities. Recent developments and technological advancements for future research, such as "-omics-based" technologies, genetic engineering, genome editing, and genome engineering tools, targeting optimal utilization of the endophytes in sustainable agricultural practices, or other purposes, have also been discussed.

Global insights into endophytic bacterial communities of terrestrial plants: Exploring the potential applications of endophytic microbiota in sustainable agriculture

Endophytic microorganisms are indispensable symbionts during plant growth and development and often serve functions such as growth promotion and stress resistance in plants. Therefore, an increasing number of researchers have applied endophytes for multifaceted phytoremediation (e.g., organic pollutants and heavy metals) in recent years. With the availability of next-generation sequencing technologies, an increasing number of studies have shifted the focus from culturable bacteria to total communities. However, information on the composition, structure, and function of bacterial endophytic communities is still not widely synthesized. To explore the general patterns of variation in bacterial communities between plant niches, we reanalyzed data from 1499 samples in 30 individual studies from different continents and provided comprehensive insights. A group of bacterial genera were commonly found in most plant roots and shoots. Our analysis revealed distinct variations in the diversity, composition, structure, and function of endophytic bacterial communities between plant roots and shoots. These variations underscore the sophisticated mechanisms by which plants engage with their endophytic microbiota, optimizing these interactions to bolster growth, health, and resilience against stress. Highlighting the strategic role of endophytic bacteria in promoting sustainable agricultural practices and environmental stewardship, our study not only offers global insights into the endophytic bacterial communities of terrestrial plants but also underscores the untapped potential of these communities as invaluable resources for future research.

Growth enhancement and changes in bacterial microbiome of cucumber plants exhibited by biopriming with some native bacteria

This study investigated the impact of a mixture of six endophytic bacterial strains isolated from cucumber plants on the growth and microbiome diversity of six cucumber traditional varieties and hybrids. Six bacterial species were isolated and identified by 16 s rRNA sequencing. All the bacteria showed plant growth promoting traits. Bacillus tequilensis showed 80 % inhibition of the mycelia growth of Fusarium oxysporum f.sp. cucumarinum (Foc). Mixed culture of all the bacteria was prepared and applied back to the varieties and hybrids of cucumber plants through seed soaking. Plant growth characteristics indicated that the treated plants showed increased plant growth in terms of plant height, number of leaves, vine length, male:female flower ratio, number of fruits and fruit length. Bacteria treated plants of hybrid HiVeg Chitra recorded 19 cm increase in vine length compared to control plants. The matataxonomic analysis of leaf samples by Illumina sequencing highlighted a diverse bacterial community shift in treated plants, with significant increases in genera like Bacillus and Staphylococcus. The core microbiome analysis identified key genera such as Bacillus, Staphylococcus, Sphingomonas, Methylobacterium, etc that could be pivotal in plant growth promotion. Bacillus and Staphylococcus showed increased abundance in treated varieties, correlating with the observed in plant growth parameters thus indicating their role in growth promotion of cucumber plants. Endophytic bacterial species identified from cucumber plants when re-applied by seed soaking, they promote the plant growth by modulating the microbiome. The bacterial species identified in the study could be potential candidates as microbial bioinputs for cucumber cultivation.

Comparative analysis of the microbiomes of strawberry wild species Fragaria nilgerrensis and cultivated variety Akihime using amplicon-based next-generation sequencing

Fragaria nilgerrensis is a wild strawberry species widely distributed in southwest China and has strong ecological adaptability. Akihime (F. × ananassa Duch. cv. Akihime) is one of the main cultivated strawberry varieties in China and is prone to infection with a variety of diseases. In this study, high-throughput sequencing was used to analyze and compare the soil and root microbiomes of F. nilgerrensis and Akihime. Results indicate that the wild species F. nilgerrensis showed higher microbial diversity in nonrhizosphere soil and rhizosphere soil and possessed a more complex microbial network structure compared with the cultivated variety Akihime. Genera such as Bradyrhizobium and Anaeromyxobacter, which are associated with nitrogen fixation and ammonification, and Conexibacter, which is associated with ecological toxicity resistance, exhibited higher relative abundances in the rhizosphere and nonrhizosphere soil samples of F. nilgerrensis compared with those of Akihime. Meanwhile, the ammonia-oxidizing archaea Candidatus Nitrososphaera and Candidatus Nitrocosmicus showed the opposite tendencies. We also found that the relative abundances of potential pathogenic genera and biocontrol bacteria in the Akihime samples were higher than those in the F. nilgerrensis samples. The relative abundances of Blastococcus, Nocardioides, Solirubrobacter, and Gemmatimonas, which are related to pesticide degradation, and genus Variovorax, which is associated with root growth regulation, were also significantly higher in the Akihime samples than in the F. nilgerrensis samples. Moreover, the root endophytic microbiomes of both strawberry species, especially the wild F. nilgerrensis, were mainly composed of potential biocontrol and beneficial bacteria, making them important sources for the isolation of these bacteria. This study is the first to compare the differences in nonrhizosphere and rhizosphere soils and root endogenous microorganisms between wild and cultivated strawberries. The findings have great value for the research of microbiomes, disease control, and germplasm innovation of strawberry.

Recent progress in the role of seed endophytic bacteria as plant growth-promoting microorganisms and biocontrol agents

The importance of microorganisms residing within the host plant for their growth and health is increasingly acknowledged, yet the significance of microbes associated with seeds, particularly seed endophytic bacteria, remains underestimated. Seeds harbor a wide range of bacteria that can boost the growth and resilience of their host plants against environmental challenges. These endophytic associations also offer advantages for germination and seedling establishment, as seed endophytic bacteria are present during the initial stages of plant growth and development. Furthermore, plants can selectively choose bacteria possessing beneficial traits, which are subsequently transmitted through seeds to confer benefits to future generations. Interestingly, even with the ongoing discovery of endophytes in seeds through high-throughput sequencing methods, certain endophytes remain challenging to isolate and culture from seeds, despite their high abundance. These challenges pose difficulties in studying seed endophytes, making many of their effects on plants unclear. In this article, a framework for understanding the assembly and function of seed endophytes, including their sources and colonization processes was outlined in detail and available research on bacterial endophytes discovered within the seeds of various plant species has also been explored. Thus, this current review aims to provide valuable insights into the mechanism of underlying seed endophytic bacteria-host plant interactions and offers significant recommendations for utilizing the seed endophytic bacteria in sustainable agriculture as plant growth promoters and enhancers of environmental stress tolerance.

Endosphere mycobiome in mature rice roots originate from both seedlings and soils

Plant-fungus symbioses have functional relevance during plant growth and development. However, it is still unknown whether the endosphere fungi in mature plants originated from soils or seeds. To elucidate the origination of endosphere fungi in mature rice roots, the fungal communities in surface sterilized roots and shoots of mature rice plants germinated in soils, rhizosphere soils and seedlings germinated under sterile conditions were analyzed by Illumina-based sequencing and compared. Total 62 fungal OTUs shared in the seedlings, shoots and roots, 126 OTUs shared in the rhizosphere soils, shoots and roots. Fungal OTUs coexisted in the four types of samples belonged to genera of Rhizophagus, Trichoderma, Fusarium, Atractiella, Myrmecridium, Sporothrix, Microdochium, Massariosphaeria, and Phialemonium. The principle component analysis (PCA) and NMDS plot suggested that the fungal community structure in rhizosphere soils was different from that in seedlings significantly. Rhizosphere soil, shoot and root contained more similar fungal community. The fungal community in seedling was similar to that in shoot and root of mature plants. The results suggested that endophytic fungal communities in mature rice plants originated from both seedlings and rhizosphere soils, and more fungal taxa originated from rhizosphere soils. Mature rice plants contain mycobiome transmitted vertically from seeds, which suggests that inoculation of endophytic fungi isolated from seedlings might be an effective way to introduce beneficial fungal inoculants into rice plants successfully.

The Populations of Two Differently Medicine-Used Plants of Hedyotis diffusa and Hedyotis corymbosa Shoot-Assembling Rich Bacterial and Fungal Communities with Varied Compositions but Conserved Structures

The plant-colonized microbial communities have closely micro-ecological effects on host plant growth and health. There are many medicinal plants in the genus Hedyotis, but it is yet unclear about the shoot-assembled bacterial and fungal communities (SBFC) of Hedyotis plants. Hence, eight plant populations of Hedyotis diffusa (HD) and H. corymbosa (HC) were evaluated with 16S rRNA gene and ITS sequences, for comparing the types, abundance, or/and potential functions of SBFC at plant species- and population levels. In tested HD- and HC-SBFC, 682 fungal operational taxonomic units and 1,329 bacterial zero-radius operational taxonomic units were identified, with rich species compositions and varied alpha diversities. Notably, the SBFC compositions of HD and HC plant populations were exhibited with partly different types and abundances at phylum and genus levels but without significantly different beta diversities at plant species and population levels. Typically, the SBFC of HD and HC plant populations were presented with abundance-different biomarkers, such as Frankiaceae and Bryobacteraceae, and with similar micro-ecological functions of microbial metabolisms of lipids, terpenoids,and xenobiotics. Taken together, HD- and HC-SBFC possessed with varied rich compositions, conservative taxonomic structures, and similar metabolic functions, but with small-scale type and abundance differences at plant species- and population- levels.

Culture-based diversity of endophytic fungi of three species of Ferula grown in Iran

A total of 1,348 endophytic fungal strains were isolated from Ferula ovina, F. galbaniflua, and F. persica. They included Eurotiales (16 species), Pleosporales (11 species), Botryosphaeriales (1 species), Cladosporiales (2 species), Helotiales (6 species), Hypocreales (31 species), Sordariales (7 species), Glomerellales (2 species), and Polyporales (1 species). F. ovina had the richest species composition of endophytic fungi, and the endophytic fungi were most abundant in their roots compared to shoots. Chao, Margalef, Shannon, Simpson, Berger-Parker, Menhinick, and Camargo indices showed that F. ovina roots had the most endophytic fungal species. The frequency distribution of fungal species isolated from Ferula spp. fell into the log-series model, and F. ovina roots had the highest Fisher alpha. The dominance indices showed that there are no dominant species in the endophytic fungal community isolated from Ferula spp., indicating community stability. Evenness values were 0.69, 0.90, 0.94, and 0.57 for endophytic fungi isolated from F. ovina roots, F. ovina shoots, F. galbaniflua roots, and F. persica roots, respectively, indicating a species distribution that tends toward evenness. The fungal species community isolated from each of F. ovina roots, F. ovina shoots, F. galbaniflua roots, and F. persica roots was a diverse species group originating from a homogeneous habitat. Their distribution followed a log-normal distribution, suggesting that the interactions of numerous independent environmental factors multiplicatively control species abundances. Principal component analysis showed that the highest species diversity and dominance were observed in the endophytic fungal community isolated from F. ovina and F. persica roots, respectively.

Succession of tissue microbial community during oat developmental

Investigating oat tissue microflora during its different developmental stages is necessary for understanding its growth and anti-disease mechanism. In this study, 16S rDNA and ITS (Internally Transcribed Spacer) high-throughput sequencing technology were used to explore the microflora diversity of oat tissue. Twenty-seven samples of leaves, stems, and roots from three developmental stages, namely the seedling stage (SS), jointing stage (JS), and maturity stage (MS), underwent sequencing analysis. The analysis showed that 6480 operational taxonomic units (OTUs) were identified in the examined samples, of which 1698 were fungal and 4782 were bacterial. Furthermore, 126 OTUs were shared by fungi, mainly Ascomycota, Basidiomycota, and Mucoromycota at the phylum level, and 39 OTUs were shared by bacteria, mainly Actinobacteriota and Proteobacteria at the phylum level. The microbial diversity of oat tissue in the three developmental stages showed differences, and the α-diversity of the bacteria and β-diversity of the bacteria and fungi in the roots were higher than those of the stems and leaves. Among the bacteria species, Thiiopseudomonas, Rikenellaceae RC9 gut group, and Brevibacterium were predominant in the leaves, MND1 was predominant in the roots, and Lactobacillus was predominant in the stems. Moreover, Brevibacterium maintained a stable state at all growth stages. In the fungal species, Phomatospora was dominant in the leaves, Kondoa was dominant in the roots, and Pyrenophora was dominant in the stems. All species with a high abundance were related to the growth process of oats and antagonistic bacteria. Furthermore, connection modules were denser in bacterial than in fungal populations. The samples were treated with superoxide dismutase and peroxidase. There were 42 strains associated with SOD (Superoxide dismutase), 60 strains associated with POD (Peroxidase), and 38 strains in total, which much higher than fungi. The network analysis showed that bacteria might have more dense connection modules than fungi, The number of bacterial connections to enzymes were much higher than that of fungi. Furthermore, these results provide a basis for further mechanistic research.

Epiphytic and endophytic bacteria on Camellia oleifera phyllosphere: exploring region and cultivar effect

The epiphytic and endophytic bacteria play an important role in the healthy growth of plants. Both plant species and growth environmental influence the bacterial population diversity, yet it is inconclusive whether it is the former or the latter that has a greater impact. To explore the communities of the epiphytic and endophytic microbes in Camellia oleifera, this study assessed three representative C. oleifera cultivars from three areas in Hunan, China by Illumina high-throughput sequencing. The results showed that the diversity and species richness of endophytic microbial community in leaves were significantly higher than those of microbial community in the epiphytic. The diversity and species richness of epiphytic and endophytic microbes are complex when the same cultivar was grown in different areas. The C. oleifera cultivars grown in Youxian had the highest diversity of epiphytic microbial community, but the lowest abundance, while the cultivars grown in Changsha had the highest diversity and species richness of endophytic microbes in leaves. It was concluded that the dominant phylum mainly included Proteobacteria, Actinobacteriota and Firmicutes through the analysis of the epiphytic and endophytic microbial communities of C. oleifera. The species and relative abundances of epiphytic and endophytic microbial community were extremely different at the genus level. The analysis of NMDS map and PERMANOVA shows that the species richness and diversity of microbial communities in epiphytes are greatly influenced by region. However, the community structure of endophytic microorganisms in leaves is influenced by region and cultivated varieties, but the influence of cultivars is more significant. Molecular ecological network analysis showed that the symbiotic interaction of epiphytic microbial community was more complex.

Antimicrobials from endophytes as novel therapeutics to counter drug-resistant pathogens

The rapid increase in antimicrobial resistance (AMR) projects a "global emergency" and necessitates a need to discover alternative resources for combating drug-resistant pathogens or "superbugs." One of the key themes in "One Health Concept" is based on the fact that the interconnected network of humans, the environment, and animal habitats majorly contribute to the rapid selection and spread of AMR. Moreover, the injudicious and overuse of antibiotics in healthcare, the environment, and associated disciplines, further aggravates the concern. The prevalence and persistence of AMR contribute to the global economic burden and are constantly witnessing an upsurge due to fewer therapeutic options, rising mortality statistics, and expensive healthcare. The present decade has witnessed the extensive exploration and utilization of bio-based resources in harnessing antibiotics of potential efficacies. The discovery and characterization of diverse chemical entities from endophytes as potent antimicrobials define an important yet less-explored area in natural product-mediated drug discovery. Endophytes-produced antimicrobials show potent efficacies in targeting microbial pathogens and synthetic biology (SB) mediated engineering of endophytes for yield enhancement, forms a prospective area of research. In keeping with the urgent requirements for new/novel antibiotics and growing concerns about pathogenic microbes and AMR, this paper comprehensively reviews emerging trends, prospects, and challenges of antimicrobials from endophytes and their effective production via SB. This literature review would serve as the platform for further exploration of novel bioactive entities from biological organisms as "novel therapeutics" to address AMR.

Unveiling stress-adapted endophytic bacteria: Characterizing plant growth-promoting traits and assessing cross-inoculation effects on Populus deltoides under abiotic stress

In the face of the formidable environmental challenges precipitated by the ongoing climate change, Plant Growth-Promoting Bacteria (PGPB) are gaining widespread acknowledgement for their potential as biofertilizers, biocontrol agents, and microbial inoculants. However, a knowledge gap pertains to the ability of PGPB to improve stress tolerance in forestry species via cross-inoculation. To address this gap, the current investigation centres on PGPBs, namely, Acinetobacter johnsonii, Cronobacter muytjensii, and Priestia endophytica, selected from the phyllosphere of robust and healthy plants thriving in the face of stress-inducing conditions. These strains were selected based on their demonstrated adaptability to saline, arid, and nitrogen-deficient environments. The utilization of PGPB treatment resulted in an improvement of stomatal conductance (gs) and transpiration rate (E) in poplar plants exposed to both salt and drought stress. It also induced an increase in essential biochemical components such as proline (PRO), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). These reactions were accompanied by a decrease in leaf malonaldehyde (MDA) content and electrolyte leakage (EL). Furthermore, the PGPB treatment demonstrated a notable enhancement in nutrient absorption, particularly nitrogen and carbon, achieved through the solubilization of nutrients. The estimation of canopy temperature via thermal imaging proved to be an efficient method for distinguishing stress reactions in poplar than conventional temperature recording techniques. In summation, the utilization of PGPB especially Cronobacter muytjensii in this study, yielded profound improvements in the stress tolerance of poplar plants, manifesting in reduced membrane lipid peroxidation, enhanced photosynthesis, and bolstered antioxidant capacity within the leaves.

Exploring the antioxidant potential of endophytic fungi: a review on methods for extraction and quantification of total antioxidant capacity (TAC)

Endophytic fungi have emerged as a significant source of natural products with remarkable bioactivities. Recent research has identified numerous antioxidant molecules among the secondary metabolites of endophytic fungi. These organisms, whether unicellular or micro-multicellular, offer the potential for genetic manipulation to enhance the production of these valuable antioxidant compounds, which hold promise for promoting health, vitality, and various biotechnological applications. In this study, we provide a critical review of methods for extracting, purifying, characterizing, and estimating the total antioxidant capacity (TAC) of endophytic fungi metabolites. While many endophytes produce metabolites similar to those found in plants with established symbiotic associations, we also highlight the existence of novel metabolites with potential scientific interest. Additionally, we discuss how advancements in nanotechnology have opened new avenues for exploring nanoformulations of endophytic metabolites in future studies, offering opportunities for diverse biological and industrial applications.

Analysis of markers for forensic plant species identification

While plant species identification in forensics can be useful in cases involving poisonous, psychoactive, or endangered plant species, it can also become quite challenging, especially, when dealing with processed, decaying, colonized or infected material of plant origin. The Animal Plant and Soil Traces expert working group of the European Network of Forensic Science Institutes in their best practice manual has recommended several markers for plant species identification. Current study is a part of implementation of method in a forensic laboratory and its aim is to evaluate four of the recommended markers (ITS, matK, rbcL, and trnH-psbA) for species identification of forensically important plant species including medicinal, poisonous, psychoactive, and other plants. Such parameters as PCR and sequencing success, sequence length, species resolution rate and species cover in GenBank were analysed. Blind testing was performed to evaluate use of the markers for identification of forensically more complicated samples. According to results, a combination of ITS, matK and trnH-psbA is the best choice for plant species identification. The best results with fresh plant material can be achieved with ITS, trnH-psbA, and matK, while ITS and matK are the best choice when working with low quality plant material. rbcL due to its low species discrimination rate can be used only as an indicative marker.

Disease-induced changes in bacterial and fungal communities from plant below- and aboveground compartments

The plant microbes are an integral part of the host and play fundamental roles in plant growth and health. There is evidence indicating that plants have the ability to attract beneficial microorganisms through their roots in order to defend against pathogens. However, the mechanisms of plant microbial community assembly from below- to aboveground compartments under pathogen infection remain unclear. In this study, we investigated the bacterial and fungal communities in bulk soil, rhizosphere soil, root, stem, and leaf of both healthy and infected (Potato virus Y disease, PVY) plants. The results indicated that bacterial and fungal communities showed different recruitment strategies in plant organs. The number and abundance of shared bacterial ASVs between bulk and rhizosphere soils decreased with ascending migration from below- to aboveground compartments, while the number and abundance of fungal ASVs showed no obvious changes. Field type, plant compartments, and PVY infection all affected the diversity and structures of microbial community, with stronger effects observed in the bacterial community than the fungal community. Furthermore, PVY infection, rhizosphere soil pH, and water content (WC) contributed more to the assembly of the bacterial community than the fungal community. The analysis of microbial networks revealed that the bacterial communities were more sensitive to PVY infection than the fungal communities, as evidenced by the lower network stability of the bacterial community, which was characterized by a higher proportion of positive edges. PVY infection further increased the bacterial network stability and decreased the fungal network stability. These findings advance our understanding of how microbes respond to pathogen infections and provide a rationale and theoretical basis for biocontrol technology in promoting sustainable agriculture. KEY POINTS: • Different recruitment strategies between plant bacterial and fungal communities. • Bacterial community was more sensitive to PVY infection than fungal community. • pH and WC drove the microbial community assembly under PVY infection.

The plant endomicrobiome: Structure and strategies to produce stress resilient future crop

Plants have a microbiome, a diverse community of microorganisms, including bacteria, fungi, and viruses, living inside and on their tissues. Versatile endophytic microorganisms inhabited in every plant part without causing disease and develop endophytic microbiome or endo-microbiome. Plant endo-microbiome are drawn by the nutrient rich micro-environment, and in turn some microbes mutualistically endorse and protect plant from adverse environmental stresses. Plant endo-microbiome interact within well-designed host equilibrium containing xylem, phloem, nutrients, phytohormones, metabolites and shift according to environmental and nutritional change. Plant endo-microbiome regulate and respond to environmental variations, pathogens, herbivores by producing stress regulators, organic acids, secondary metabolites, stress hormones as well as unknown substances and signalling molecules. Endomicrobiome efficiently synthesizes multiple bioactive compounds, stress phytohormones with high competence. The technological innovation as next generation genomics biology and high-throughput multiomics techniques stepping stones on the illumination of critical endo-microbiome communities and functional characterization that aid in improving plant physiology, biochemistry and immunity interplay for best crop productivity. This review article contains deeper insight in endomicrobiome related research work in last years, recruitment, niche development, nutrient dynamics, stress removal mechanisms, bioactive services in plant health development, community architecture and communication, and immunity interplay in producing stress resilient future crop.

Current Advances in the Functional Diversity and Mechanisms Underlying Endophyte-Plant Interactions

Plant phenotype is a complex entity largely controlled by the genotype and various environmental factors. Importantly, co-evolution has allowed plants to coexist with the biotic factors in their surroundings. Recently, plant endophytes as an external plant phenotype, forming part of the complex plethora of the plant microbial assemblage, have gained immense attention from plant scientists. Functionally, endophytes impact the plant in many ways, including increasing nutrient availability, enhancing the ability of plants to cope with both abiotic and biotic stress, and enhancing the accumulation of important plant secondary metabolites. The current state of research has been devoted to evaluating the phenotypic impacts of endophytes on host plants, including their direct influence on plant metabolite accumulation and stress response. However, there is a knowledge gap in how genetic factors influence the interaction of endophytes with host plants, pathogens, and other plant microbial communities, eventually controlling the extended microbial plant phenotype. This review will summarize how host genetic factors can impact the abundance and functional diversity of the endophytic microbial community, how endophytes influence host gene expression, and the host-endophyte-pathogen disease triangle. This information will provide novel insights into how breeders could specifically target the plant-endophyte extended phenotype for crop improvement.

Mechanisms for plant growth promotion activated by Trichoderma in natural and managed terrestrial ecosystems

Trichoderma spp. are free-living fungi present in virtually all terrestrial ecosystems. These soil fungi can stimulate plant growth and increase plant nutrient acquisition of macro- and micronutrients and water uptake. Generally, plant growth promotion by Trichoderma is a consequence of the activity of potent fungal signaling metabolites diffused in soil with hormone-like activity, including indolic compounds as indole-3-acetic acid (IAA) produced at concentrations ranging from 14 to 234 μg l-1, and volatile organic compounds such as sesquiterpene isoprenoids (C15), 6-pentyl-2H-pyran-2-one (6-PP) and ethylene (ET) produced at levels from 10 to 120 ng over a period of six days, which in turn, might impact plant endogenous signaling mechanisms orchestrated by plant hormones. Plant growth stimulation occurs without the need of physical contact between both organisms and/or during root colonization. When associated with plants Trichoderma may cause significant biochemical changes in plant content of carbohydrates, amino acids, organic acids and lipids, as detected in Arabidopsis thaliana, maize (Zea mays), tomato (Lycopersicon esculentum) and barley (Hordeum vulgare), which may improve the plant health status during the complete life cycle. Trichoderma-induced plant beneficial effects such as mechanisms of defense and growth are likely to be inherited to the next generations. Depending on the environmental conditions perceived by the fungus during its interaction with plants, Trichoderma can reprogram and/or activate molecular mechanisms commonly modulated by IAA, ET and abscisic acid (ABA) to induce an adaptative physiological response to abiotic stress, including drought, salinity, or environmental pollution. This review, provides a state of the art overview focused on the canonical mechanisms of these beneficial fungi involved in plant growth promotion traits under different environmental scenarios and shows new insights on Trichoderma metabolites from different chemical classes that can modulate specific plant growth aspects. Also, we suggest new research directions on Trichoderma spp. and their secondary metabolites with biological activity on plant growth.

Exploring the potential of endophyte-plant interactions for improving crop sustainable yields in a changing climate

Climate change poses a major threat to global food security, significantly reducing crop yields as cause of abiotic stresses, and for boosting the spread of new and old pathogens and pests. Sustainable crop management as a route to mitigation poses the challenge of recruiting an array of solutions and tools for the new aims. Among these, the deployment of positive interactions between the micro-biotic components of agroecosystems and plants can play a highly significant role, as part of the agro-ecological revolution. Endophytic microorganisms have emerged as a promising solution to tackle this challenge. Among these, Arbuscular Mycorrhizal Fungi (AMF) and endophytic bacteria and fungi have demonstrated their potential to alleviate abiotic stresses such as drought and heat stress, as well as the impacts of biotic stresses. They can enhance crop yields in a sustainable way also by other mechanisms, such as improving the nutrient uptake, or by direct effects on plant physiology. In this review we summarize and update on the main types of endophytes, we highlight several studies that demonstrate their efficacy in improving sustainable yields and explore possible avenues for implementing crop-microbiota interactions. The mechanisms underlying these interactions are highly complex and require a comprehensive understanding. For this reason, omic technologies such as genomics, transcriptomics, proteomics, and metabolomics have been employed to unravel, by a higher level of information, the complex network of interactions between plants and microorganisms. Therefore, we also discuss the various omic approaches and techniques that have been used so far to study plant-endophyte interactions.

Unveiling growth-promoting attributes of peanut root endophyte Micromonospora sp

In this study, 20 endophytic actinobacteria were isolated from different parts of peanut plants growing in cropland with low and high salt in West Bengal, India. The endophytes underwent a rigorous morphological, biochemical, and genetic screening process to evaluate their effectiveness in enhancing plant growth. About 20% of these isolates were identified as potential plant growth-promoting endophytic actinobacteria, which showed high 16S rRNA gene sequence similarity (up to 99-100%) with different species of Micromonospora. Among these isolates, Micromonospora sp. ASENR15 produced the highest levels of indole acetic acid (IAA) and gibberellic acid (GA), while Micromonospora sp. ASENL2, Micromonospora sp. ANENR4, and Micromonospora sp. ASENR12 produced the highest level of siderophore. Among these leaf and root endophytic Micromonospora, strain ANENR4 was tested for its plant growth-promoting attributes. ANENR4 can be transmitted into the roots of a healthy peanut plant, enhances growth, and colonize the roots in abundance, suggesting the potential agricultural significance of the strain. Moreover, the study is the first report of endophytic Micromonospora in peanuts with PGP effects. The outcomes of this study open avenues for further research on harnessing the benefits of this endophytic Micromonospora for optimizing plant growth in agriculture.

Comprehensive genomic analysis of Bacillus subtilis and Bacillus paralicheniformis associated with the pearl millet panicle reveals their antimicrobial potential against important plant pathogens

BACKGROUND

Plant microbiome confers versatile functional roles to enhance survival fitness as well as productivity. In the present study two pearl millet panicle microbiome member species Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36 found to have beneficial traits including plant growth promotion and broad-spectrum antifungal activity towards taxonomically diverse plant pathogens. Understanding the genomes will assist in devising a bioformulation for crop protection while exploiting their beneficial functional roles.

RESULTS

Two potential firmicute species were isolated from pearl millet panicles. Morphological, biochemical, and molecular characterization revealed their identities as Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36. The seed priming assays revealed the ability of both species to enhance plant growth promotion and seedling vigour index. Invitro assays with PBs 12 and PBl 36 showed the antibiosis effect against taxonomically diverse plant pathogens (Magnaporthe grisea; Sclerotium rolfsii; Fusarium solani; Alternaria alternata; Ganoderma sp.) of crops and multipurpose tree species. The whole genome sequence analysis was performed to unveil the genetic potential of these bacteria for plant protection. The complete genomes of PBs 12 and PBl 36 consist of a single circular chromosome with a size of 4.02 and 4.33 Mb and 4,171 and 4,606 genes, with a G + C content of 43.68 and 45.83%, respectively. Comparative Average Nucleotide Identity (ANI) analysis revealed a close similarity of PBs 12 and PBl 36 with other beneficial strains of B. subtilis and B. paralicheniformis and found distant from B. altitudinis, B. amyloliquefaciens, and B. thuringiensis. Functional annotation revealed a majority of pathway classes of PBs 12 (30) and PBl 36 (29) involved in the biosynthesis of secondary metabolites, polyketides, and non-ribosomal peptides, followed by xenobiotic biodegradation and metabolism (21). Furthermore, 14 genomic regions of PBs 12 and 15 of PBl 36 associated with the synthesis of RiPP (Ribosomally synthesized and post-translationally modified peptides), terpenes, cyclic dipeptides (CDPs), type III polyketide synthases (T3PKSs), sactipeptides, lanthipeptides, siderophores, NRPS (Non-Ribosomal Peptide Synthetase), NRP-metallophone, etc. It was discovered that these areas contain between 25,458 and 33,000 secondary metabolite-coding MiBiG clusters which code for a wide range of products, such as antibiotics. The PCR-based screening for the presence of antimicrobial peptide (cyclic lipopeptide) genes in PBs 12 and 36 confirmed their broad-spectrum antifungal potential with the presence of spoVG, bacA, and srfAA AMP genes, which encode antimicrobial compounds such as subtilin, bacylisin, and surfactin.

CONCLUSION

The combined in vitro studies and genome analysis highlighted the antifungal potential of pearl millet panicle-associated Bacillus subtilis PBs12 and Bacillus paralicheniformis PBl36. The genetic ability to synthesize several antimicrobial compounds indicated the industrial value of PBs 12 and PBl 36, which shed light on further studies to establish their action as a biostimulant for crop protection.

Endophytic Alternaria and Fusarium species associated to potato plants (Solanum tuberosum L.) in Iran and their capability to produce regulated and emerging mycotoxins

Endophytic fungi live inside virtually every plant species, without causing any apparent disease or damage to the host. Nevertheless, under particular conditions, mutualistic lifestyle of endophytes may change to pathogenic. In this study, the biodiversity of Alternaria and Fusarium species, the two most abundant endophytic fungi isolated from healthy potato plants in two climatically different regions of Iran, Ardebil in the north-west and Kerman in the south-east, was investigated. Seventy-five Fusarium strains and 83 Alternaria strains were molecularly characterized by multi-locus gene sequencing. Alternaria strains were characterized by the sequences of gpd and caM gene fragments and the phylogenetic tree was resolved in 3 well-separated clades. Seventy-three strains were included in the clade A, referred as Alternaria section, 6 strains were included in clade B, referred as Ulocladioides section, and 4 strains were included in clade C, referred as Infectoriae section. Fusarium strains, identified by sequencing the translation elongation factor 1α (tef1), β-tubulin (tub2) and internal transcribed spacer (ITS) genomic regions, were assigned to 13 species, viz. F. brachygibosum, F. clavum, F. equiseti, F. flocciferum, F. incarnatum, F. nirenbergiae, F. nygamai, F. oxysporum, F. proliferatum, F. redolens, F. sambucinum, F. solani and F. thapsinum. Twenty-six selected strains, representative of F. equiseti, F. nirenbergiae, F. oxysporum, F. nygamai, F. proliferatum, and F. sambucinum, were also tested for production of the mycotoxins deoxynivalenol (DON), nivalenol (NIV), diacetoxyscirpenol (DAS), T-2 toxin (T-2), beauvericin (BEA), enniatins (ENNs), fumonisins (FBs), fusaric acid (FA) and moniliformin (MON). None of the tested strains produced trichothecene toxins (DON, NIV, DAS and T-2). Two out of 2 F. equiseti isolates, 1/6 F. oxysporum, 1/3 F. proliferatum, and 1/9 F. nygamai did not produce any of the tested toxins; the rest of strains produced one or more BEA, ENNs, FBs, FA and MON toxins. The most toxigenic strain, F. nygamai ITEM-19012, produced the highest quantities of FBs (7946, 4693 and 4333 μg/g of B1, B2, and B3 respectively), along with the highest quantities of both BEA (4190 μg/g) and MON (538 μg/g). These findings suggest that contamination of potato tubers with mycotoxins in the field or at post-harvest, due to a change in lifestyle of endophytic microflora, should be carefully considered and furtherly investigated.

Assemblages of rhizospheric and root endospheric mycobiota and their ecological associations with functional traits of rice

The soil-root interface harbors complex fungal communities that play vital roles in the fitness of host plants. However, little is known about the assembly rules and potential functions of rhizospheric and endospheric mycobiota. A greenhouse experiment was conducted to explore the fungal communities inhabiting the rhizosphere and roots of 87 rice cultivars at the tillering stage via amplicon sequencing of the fungal internal transcribed spacer 1 region. The potential relationships between these communities and host plant functional traits were also investigated using Procrustes analysis, generalized additive model fitting, and correlation analysis. The fungal microbiota exhibited greater richness, higher diversity, and lower structural variability in the rhizosphere than in the root endosphere. Compared with the root endosphere, the rhizosphere supported a larger coabundance network, with greater connectivity and stronger cohesion. Null model-based analyses revealed that dispersal limitation was primarily responsible for rhizosphere fungal community assembly, while ecological drift was the dominant process in the root endosphere. The community composition of fungi in the rhizosphere was shown to be more related to plant functional traits, such as the root/whole plant biomass, root:shoot biomass ratio, root/shoot nitrogen (N) content, and root/shoot/whole plant N accumulation, than to that in the root endosphere. Overall, at the early stage of rice growth, diverse and complex rhizospheric fungal communities are shaped by stochastic-based processes and exhibit stronger associations with plant functional traits.

IMPORTANCE

The assembly processes and functions of root-associated mycobiota are among the most fascinating yet elusive topics in microbial ecology. Our results revealed that stochastic forces (dispersal limitation or ecological drift) act on fungal community assembly in both the rice rhizosphere and root endosphere at the early stage of plant growth. In addition, high covariations between the rhizosphere fungal community compositions and plant functional trait profiles were clearly demonstrated in the present study. This work provides empirical evidence of the root-associated fungal assembly principles and ecological relationships of plant functional traits with rhizospheric and root endospheric mycobiota, thereby potentially providing novel perspectives for enhancing plant performance.

Draft Genome Sequence of Pantoea sp. Strain MHSD4, a Bacterial Endophyte With Bioremediation Potential

Pantoea sp. strain MHSD4 is a bacterial endophyte isolated from the leaves of the medicinal plant Pellaea calomelanos. Here, we report on strain MHSD4 draft whole genome sequence and annotation. The draft genome size of Pantoea sp. strain MHSD4 is 4 647 677 bp with a G+C content of 54.2% and 41 contigs. The National Center for Biotechnology Information Prokaryotic Genome Annotation Pipeline tool predicted a total of 4395 genes inclusive of 4235 protein-coding genes, 87 total RNA genes, 14 non-coding (nc) RNAs and 70 tRNAs, and 73 pseudogenes. Biosynthesis pathways for naphthalene and anthracene degradation were identified. Putative genes involved in bioremediation such as copA, copD, cueO, cueR, glnGm, and trxC were identified. Putative genes involved in copper homeostasis and tolerance were identified which may suggest that Pantoea sp. strain MHSD4 has biotechnological potential for bioremediation of heavy metals.

Isolation of endophytes from Dioscorea nipponica Makino for stimulating diosgenin production and plant growth

KEY MESSAGE

Both bacterial and fungal endophytes exhibited one or more plant growth-promoting (PGP) traits. Among these strains, the Paenibacillus peoriae SYbr421 strain demonstrated the greatest activity in the direct biotransformation of tuber powder from D. nipponica into diosgenin. Endophytes play crucial roles in shaping active metabolites within plants, significantly influencing both the quality and yield of host plants. Dioscorea nipponica Makino accumulates abundant steroidal saponins, which can be hydrolyzed to produce diosgenin. However, our understanding of the associated endophytes and their contributions to plant growth and diosgenin production is limited. The present study aimed to assess the PGP ability and potential of diosgenin biotransformation by endophytes isolates associated with D. nipponica for the efficient improvement of plant growth and development of a clean and effective approach for producing the valuable drug diosgenin. Eighteen bacterial endophytes were classified into six genera through sequencing and phylogenetic analysis of the 16S rDNA gene. Similarly, 12 fungal endophytes were categorized into 5 genera based on sequencing and phylogenetic analysis of the ITS rDNA gene. Pure culture experiments revealed that 30 isolated endophytic strains exhibited one or more PGP traits, such as nitrogen fixation, phosphate solubilization, siderophore synthesis, and IAA production. One strain of endophytic bacteria, P. peoriae SYbr421, effectively directly biotransformed the saponin components in D. nipponica. Moreover, a high yield of diosgenin (3.50%) was obtained at an inoculum size of 4% after 6 days of fermentation. Thus, SYbr421 could be used for a cleaner and more eco-friendly diosgenin production process. In addition, based on the assessment of growth-promoting isolates and seed germination results, the strains SYbr421, SYfr1321, and SYfl221 were selected for greenhouse experiments. The results revealed that the inoculation of these promising isolates significantly increased the plant height and fresh weight of the leaves and roots compared to the control plants. These findings underscore the importance of preparing PGP bioinoculants from selected isolates as an additional option for sustainable diosgenin production.

Biological control potential of worrisome wheat blast disease by the seed endophytic bacilli

Crop production often faces challenges from plant diseases, and biological control emerges as an effective, environmentally friendly, cost-effective, and sustainable alternative to chemical control. Wheat blast disease caused by fungal pathogen Magnaporthe oryzae Triticum (MoT), is a potential catastrophic threat to global food security. This study aimed to identify potential bacterial isolates from rice and wheat seeds with inhibitory effects against MoT. In dual culture and seedling assays, three bacterial isolates (BTS-3, BTS-4, and BTLK6A) demonstrated effective suppression of MoT growth and reduced wheat blast severity when artificially inoculated at the seedling stage. Genome phylogeny identified these isolates as Bacillus subtilis (BTS-3) and B. velezensis (BTS-4 and BTLK6A). Whole-genome analysis revealed the presence of genes responsible for controlling MoT through antimicrobial defense, antioxidant defense, cell wall degradation, and induced systemic resistance (ISR). Taken together, our results suggest that the suppression of wheat blast disease by seed endophytic B. subtilis (BTS-3) and B. velezensis (BTS-4 and BTLK6A) is liked with antibiosis and induced systemic resistance to wheat plants. A further field validation is needed before recommending these endophytic bacteria for biological control of wheat blast.

Epigenetic weapons of plants against fungal pathogens

In the natural environment, plants face constant exposure to biotic stress caused by fungal attacks. The plant's response to various biotic stresses relies heavily on its ability to rapidly adjust the transcriptome. External signals are transmitted to the nucleus, leading to activation of transcription factors that subsequently enhance the expression of specific defense-related genes. Epigenetic mechanisms, including histone modifications and DNA methylation, which are closely linked to chromatin states, regulate gene expression associated with defense against biotic stress. Additionally, chromatin remodelers and non-coding RNA play a significant role in plant defense against stressors. These molecular modifications enable plants to exhibit enhanced resistance and productivity under diverse environmental conditions. Epigenetic mechanisms also contribute to stress-induced environmental epigenetic memory and priming in plants, enabling them to recall past molecular experiences and utilize this stored information for adaptation to new conditions. In the arms race between fungi and plants, a significant aspect is the cross-kingdom RNAi mechanism, whereby sRNAs can traverse organismal boundaries. Fungi utilize sRNA as an effector molecule to silence plant resistance genes, while plants transport sRNA, primarily through extracellular vesicles, to pathogens in order to suppress virulence-related genes. In this review, we summarize contemporary knowledge on epigenetic mechanisms of plant defense against attack by pathogenic fungi. The role of epigenetic mechanisms during plant-fungus symbiotic interactions is also considered.

Identification and distribution of a fungal endosymbiotic Alternaria species (Alternaria section Undifilum sp.) in Astragalus garbancillo tissues

Plants belonging to the genera Astragalus, Oxytropis, Ipomoea, Sida, and Swainsona often contain the toxin swainsonine (SW) produced by an associated fungal symbiont. Consumption of SW-containing plants causes a serious neurological disorder in livestock, which can be fatal. In this study, a fungal endophyte, Alternaria section Undifilum, was identified in Astragalus garbancillo seeds, using polymerase chain reaction (PCR) followed by direct sequencing. In seeds, the SW concentrations were about 4 times higher than in other parts of the plant. Furthermore, microscopic examination demonstrated that the fungus mycelium grows inside the petioles and stems, on the outer surface and inside the mesocarp of the fruit, in the mesotesta and endotesta layers of the seed coat, and inside the endosperm of the seeds. Our results support the notion that the SW-producing fungus is vertically transmitted in the host plant A. garbancillo.

Molecular authentication, metabolite profiling and in silico-in vitro cytotoxicity screening of endophytic Penicillium ramusculum from Withania somnifera for breast cancer therapeutics

In the present study, we isolated a potent endophytic fungus from the roots of Withania somnifera. The endophytic fungal strain was authenticated as Penicillium ramusculum SVWS3 based on morphological and molecular sequencing using four gene data and phylogenetic analyses. In vitro cytotoxicity studies unveiled the remarkable cytotoxic potential of the crude extract derived from P. ramusculum, exhibiting dose-dependent effects on MDA-MB-468 and MCF-7 cells. At a concentration of 100 µg/mL, the crude extract resulted in cell viability of 29.78% for MDA-MB-468 cells and 14.61% for MCF-7 cells. The IC50 values were calculated as 62.83 ± 0.93 µg/mL and 17.23 ± 1.43 µg/mL, respectively for MDA-MB-468 and MCF-7 cells. Caspase activation assay established the underlying mechanism of the crude extract depicting the activation of caspases 3 and 7, indicating the induction of apoptosis in MCF-7 cells. Chemotaxonomic profiling elucidated the ability of P. ramusculum to synthesize a diverse array of bioactive compounds, including Fasoracetam, Tryprostatin B, Odorinol, Thyronine, Brevianamide F, Proglumide, Perlolyrine, Tyrphostin B48, Baptifoline, etc. Molecular docking studies inferred that Baptifoline, Brevianamide F, Odorinol, Perlolyrine, Thyronine, Tryphostin B48, and Tryprostatin B were the lead compounds that could effectively interact with the five selected target receptors of breast cancer, further surpassing the positive controls analyzed. Pharmacokinetic profiling revealed that Baptifoline, Odorinol, and Thyronine depicted an excellent therapeutic profile of druggability. These findings collectively substantiate the anticancer activity of bioactive metabolites synthesized by P. ramusculum SVWS3. Hence, the endophytic P. ramusculum SVWS3 can be an authentic source for developing novel chemotherapeutic drug formulations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03906-3.

Impact of Foliar Fungicide Application on the Culturable Fungal Endophyte Community of Soybean Seed in the Midwest United States

The purpose of our study was to determine whether the application of quinone outside inhibitor (QoI) and pyrazole-carboxamide fungicides as a tank mix would impact the endophyte community of soybean seed. Field trials during 2018 in Iowa, South Dakota, and Wisconsin, U.S.A., investigated the impact of a single combination fungicide spray at early pod set in soybeans. The composition of culturable endophytic fungi in mature soybean seed was assessed on three cultivars per state, with maturity groups (MGs) ranging from 1.1 to 4.7. An unusually wet 2018 season delayed harvest, which led to a high level of fungal growth in grain. The survey included 1,080 asymptomatic seeds that were disinfested and individually placed on 5-cm-diameter Petri plates of acidified water agar. The survey yielded 721 fungal isolates belonging to 24 putative species in seven genera; taxa were grouped into genera based on a combination of morphological and molecular evidence. The dominant genera encountered in the survey were Alternaria, Diaporthe, and Fusarium. The study showed that the fungicide treatment reduced the incidence of Fusarium in Wisconsin seed, increased the incidence of Diaporthe in seed from all states, and had no impact on the incidence of Alternaria. This is one of the first attempts to characterize the diversity of seed endophytes in soybean and the first to characterize the impacts of fungicide spraying on these endophyte communities across three states. Our study provides evidence that the impact of a fungicide spray on soybean seed endophyte communities may be influenced by site, weather, and cultivar maturity group.

Lipopolysaccharides of Herbaspirillum species and their relevance for bacterium-host interactions

The lipopolysaccharides of Herbaspirillum lusitanum P6-12T (HlP6-12T) and H. frisingense GSF30T (HfGSF30T) was isolated by phenol-water extraction from bacterial cells and was characterized using chemical analysis and SDS-PAGE. It was shown that these bacteria produce LPSs that differ in their physicochemical properties and macromolecular organization. In this paper, the lipid A structure of the HlP6-12T LPS, was characterized through chemical analyses and matrix-assisted laser desorption ionization (MALDI) mass spectrometry. To prove the effect of the size of micelles on their bioavailability, we examined the activity of both LPSs toward the morphology of wheat seedlings. Analysis of the HlP6-12T and HfGSF30T genomes showed no significant differences between the operons that encode proteins involved in the biosynthesis of the lipids A and core oligosaccharides. The difference may be due to the composition of the O-antigen operon. HfGSF30T has two copies of the rfb operon, with the main one divided into two fragments. In contrast, the HlP6-12T genome contains only a single rfb-containing operon, and the other O-antigen operons are not comparable at all. The integrity of O-antigen-related genes may also affect LPS variability of. Specifically, we have observed a hairpin structure in the middle of the O-antigen glycosyltransferase gene, which led to the division of the gene into two fragments, resulting in incorrect protein synthesis and potential abnormalities in O-antigen production.

Secretory molecules from secretion systems fine-tune the host-beneficial bacteria (PGPRs) interaction

Numerous bacterial species associate with plants through commensal, mutualistic, or parasitic association, affecting host physiology and health. The mechanism for such association is intricate and involves the secretion of multiple biochemical substances through dedicated protein systems called secretion systems SS. Eleven SS pathways deliver protein factors and enzymes in their immediate environment or host cells, as well as in competing microbial cells in a contact-dependent or independent fashion. These SS are instrumental in competition, initiation of infection, colonization, and establishment of association (positive or negative) with host organisms. The role of SS in infection and pathogenesis has been demonstrated for several phytopathogens, including Agrobacterium, Xanthomonas, Ralstonia, and Pseudomonas. Since there is overlap in mechanisms of establishing association with host plants, several studies have investigated the role of SSs in the interaction of plant and beneficial bacteria, including symbiotic rhizobia and plant growth bacteria (PGPB). Therefore, the present review updates the role of different SSs required for the colonization of beneficial bacteria such as rhizobia, Burkholderia, Pseudomonas, Herbaspirillum, etc., on or inside plants, which can lead to a long-term association. Most SS like T3SS, T4SS, T5SS, and T6SS are required for the antagonistic activity needed to prevent competing microbes, including phytopathogens, ameliorate biotic stress in plants, and produce substances for successful colonization. Others are required for chemotaxis, adherence, niche formation, and suppression of immune response to establish mutualistic association with host plants.

Zinc oxide nanoparticles enhance plasmid transfer among growth-promoting endophytes in Arabidopsis thaliana

Nanoparticles (NPs) hold great promise for agricultural applications, yet their potential impact on exogenous gene transfer within plant remains poorly understood. In this study, we utilized the non-conjugative plasmid pCAMBIA1300, harboring the bialaphos resistance (bar) gene expressed in plant and the kanamycin resistance (kanR) gene as selectable marker in bacteria. Our results revealed a significant increase in the transfer of plasmid (via carrier Escherichia coli DH5α), both intra- and inter-species within the endophyte, when Arabidopsis thaliana was exposed to environmentally relevant level of zinc oxide (ZnO) NPs at a concentration of 0.7 μg/mL throughout its lifespan. Intriguingly, the plasmid exhibited selective transfer to growth-promoting endophytes, such as Enterobacter, Serratia, and Achromobacter, with the presence of ZnO NPs expanding the pool of potential recipients. This result is due to the facilitation of an endophytic and mutualistic lifestyle of invasive E. coli DH5α and the enrichment of beneficial bacteria aided by ZnO NPs. The plant's descendant generations did not express the bar gene, and the endophytes carrying the exogenous plasmid did not transmit it to sub sequent generation. This research provides crucial insights for assessing the potential risks associated with gene contamination and ensuring the safe and sustainable use of NPs in agriculture.

Beneficial endophytic fungi improve the yield and quality of Salvia miltiorrhiza by performing different ecological functions

Background

Endophytic fungi can enhance the growth and synthesis of secondary metabolites in medicinal plants. Salvia miltiorrhiza Bunge is frequently employed for treating cardiovascular and cerebrovascular ailments, with the primary bioactive components being salvianolic acid and tanshinone. However, their levels in cultivated S. miltiorrhiza are inferior to that of the wild herbs, so the production of high-quality medicinal herbs is sharply declining. Consequently, the utilization of beneficial endophytic fungi to improve the yield and quality of S. miltiorrhiza holds great significance for the cultivation of medicinal plants.

Methods

In this study, nine non-pathogenic, endophytic fungal strains were introduced into sterile S. miltiorrhiza seedlings and cultivated both in vitro and in situ (the greenhouse). The effects of these strains on the growth indices, C and N metabolism, antioxidant activity, photosynthesis, and content of bioactive ingredients in S. miltiorrhiza were then evaluated.

Results

The results showed that the different genera, species, or strains of endophytic fungi regulated the growth and metabolism of S. miltiorrhiza in unique ways. These endophytic fungi primarily exerted their growth-promoting effects by increasing the net photosynthetic rate, intercellular CO2 concentration, and the activities of sucrose synthase, sucrose phosphate synthase, nitrate reductase, and glutamine synthetase. They also enhanced the adaptability and resistance to environmental stresses by improving the synthesis of osmoregulatory compounds and the activity of antioxidant enzymes. However, their regulatory effects on the growth and development of S. miltiorrhiza were affected by environmental changes. Moreover, the strains that significantly promoted the synthesis and accumulation of phenolic acids inhibited the accumulation of tanshinones components, and vice versa. The endophytic fungal strains Penicillium meloforme DS8, Berkeleyomyces basicola DS10, and Acremonium sclerotigenum DS12 enhanced the bioaccumulation of tanshinones. Fusarium solani DS16 elevated the rosmarinic acid content and yields in S. miltiorrhiza. The strain Penicillium javanicum DS5 improved the contents of dihydrotanshinone, salvianolic acid B, and rosmarinic acid. The strains P. meloforme DS8 and B. basicola DS10 improved resistance.

Conclusion

Various endophytic fungi affected the quality and yield of S. miltiorrhiza by regulating different physiological and metabolic pathways. This study also provides a novel and effective method to maximize the effects of beneficial endophytic fungi by selecting specific strains to design microbial communities based on the different ecological functions of endophytic fungi under varying environments and for specific production goals.

Soil and seed both influence bacterial diversity in the microbiome of the Cannabis sativa seedling endosphere

Introduction

Phytobiomes have a significant impact on plant health. The microbiome of Cannabis sativa is particularly interesting both because of renewed interest in this crop and because it is commercially propagated in two different ways (i.e. clonally and by seed). Angiosperms obtain a founding population of seed-borne endophytes from their seed-bearing parent. This study examines the influence of both seed and soil-derived bacteria on the endospheres of cannabis seedlings of both hemp- and drug-types.

Methods

A multi-factorial metagenomic study was conducted with three cannabis genotypes and two soil sources, which were tested both before and after autoclave sterilization. Seedlings were grown on soil, then rinsed and surface-sterilized, and 16S rDNA amplicons from seedling endophytes were sequenced, taxonomically classified, and used to estimate alpha- and beta-diversity in Qiime2. The statistical significance of differences in seedling microbiomes across treatments was tested, and PiCRUST2 was used to infer the functional relevance of these differences.

Results

Soil was found to have a profound effect on the alpha-diversity, beta-diversity, relative abundance, and functional genes of endophytic bacteria in germinating cannabis seedlings. Additionally, there was a significant effect of cannabis genotype on beta diversity, especially when genotypes were grown in sterilized soil. Gammaproteobacteria and Bacilli were the two most abundant taxa and were found in all genotypes and soil types, including sterilized soil.

Discussion

The results indicated that a component of cannabis seedling endosphere microbiomes is seed-derived and conserved across the environments tested. Functional prediction of seedling endophytes using piCRUST suggested a number of important functions of seed-borne endophytes in cannabis including nutrient and amino acid cycling, hormone regulation, and as precursors to antibiotics. This study suggested both seed and soil play a critical role in shaping the microbiome of germinating cannabis seedlings.

Response strategies of stem/leaves endophyte communities to nano-plastics regulate growth performance of submerged macrophytes

Research on the toxicity effects of nano-plastics on submerged macrophytes has been increasing over the past several years. However, how the endophytic bacteria of submerged macrophytes respond to nano-plastics remains unknown, although they have been widely shown to help terrestrial plants cope with various environmental stressors. Here, a microcosm experiment was performed to unravel the effects of high concentration of nano-plastics (20 mg/L) on three submerged macrophyte (Vallisneria natans, Potamogeton maackianus, Myriophyllum spicatum) and their endophytic bacterial communities. Results indicated that nano-plastics induced antioxidative stress in plants, but significantly reduction in relative growth rate (RGR) only occurred in V. natans (from 0.0034 to -0.0029 day-1), accompanied by change in the stem/leaves endophyte community composition. Further analysis suggested nano-plastics caused a reduction in environmental nutrient availability and the proportion of positive interactions between endophyte communities (43%), resulting in the lowest RGR of V. natans. In contrast, endophytes may help P. maackianus and M. spicatum cope with nano-plastic stress by increasing the proportion of positive correlations among communities (70% and 75%), leaving their RGR unaffected. Collectively, our study elucidates the species-specific response strategies of submerged macrophyte-endophyte to nano-plastics, which helps to reveal the different phytoremediation potential of submerged macrophytes against nano-plastic pollution.

Shared governance in the plant holobiont and implications for one health

The holobiont Holobiont theory is more than 80 years old, while the importance of microbial communities for plant holobionts was already identified by Lorenz Hiltner more than a century ago. Both concepts are strongly supported by results from the new field of microbiome research. Here, we present ecological and genetic features of the plant holobiont that underpin principles of a shared governance between hosts and microbes and summarize the relevance of plant holobionts in the context of global change. Moreover, we uncover knowledge gaps that arise when integrating plant holobionts in the broader perspective of the holobiome as well as one and planetary health concepts. Action is needed to consider interacting holobionts at the holobiome scale, for prediction and control of microbiome function to improve human and environmental health outcomes.

Community ecological succession of endophytic fungi associates with medicinal compound accumulation in Sophora alopecuroides

Endophytic fungi of medicinal plants are symbiotic with the host and play an important role in determining metabolites. To understand the relationship between the accumulation of Sophora alopecuroides' medicinal bioactive compounds and the ecological succession of endophytic fungi, here we collected samples from S. alopecuroides at four developmental stages (adult, flowering, podding, and mature) and different organs (roots, stems, leaves, and seeds) at the mature stage. We then used high-performance liquid chromatography-mass spectrometry and high-throughput sequencing on the internal transcribed spacer region to identify the medicinal compounds and endophytic fungal communities in each sample. The endophytic fungal community characteristics and accumulation of medicinally bioactive compounds of S. alopecuroides varied with the host's developmental stages and organs, with the highest total alkaloids content of 111.9 mg/g at the mature stage. Membership analysis and network connection analysis showed a total of 15 core endophytic fungi in different developmental stages and 16 core endophytic fungi in different organs at the mature stage. The unclassified Ascomycota, Aspergillus, and Alternaria were significantly and positively correlated with the medicinal compounds of S. alopecuroides at the mature stage (r > 0.6 or r < -0.6; P < 0.05). In this study, we identified key endophytic fungal resources that affect the content of medicinally bioactive compounds in S. alopecuroides. This discovery could lay the foundation for enhancing the yield of medicinally bioactive compounds in S. alopecuroides and the development and application of functional endophytic fungi.IMPORTANCESophora alopecuroides is a traditional Chinese herbal medicine. The major medicinal chemicals are considered to be quinolizidine alkaloids. Quinolizidine alkaloids have been widely used for the treatment of tumors, dysentery, and enteritis. Previous studies have found that endophytic fungi in S. alopecuroides can promote the accumulation of host quinolizidine alkaloids. However, the relationship between the accumulation of S. alopecuroides' medicinal bioactive compounds and the ecological succession of endophytic fungi remains unclear. In this study, we screened the key endophytic fungal resources affecting the content of medicinally bioactive compounds and laid the foundation for subsequent research on the mechanism by which endophytic fungi promote the accumulation of medicinally bioactive compounds in S. alopecuroides.

Unraveling two decades of phyllosphere endophytes: tracing research trends and insights through visualized knowledge maps, with emphasis on microbial interactions as emerging frontiers

Phyllosphere endophytes play a critical role in a myriad of biological functions, such as maintaining plant health and overall fitness. They play a determinative role in crop yield and quality by regulating vital processes, such as leaf functionality and longevity, seed mass, apical growth, flowering, and fruit development. This study conducted a comprehensive bibliometric analysis aiming to review the prevailing research trajectories in phyllosphere endophytes and harness both primary areas of interest and emerging challenges. A total of 156 research articles on phyllosphere endophytes, published between 2002 and 2022, were retrieved from the Web of Science Core Collection (WoSCC). A systematic analysis was conducted using CiteSpace to visualize the evolution of publication frequency, the collaboration network, the co-citation network, and keywords co-occurrence. The findings indicated that initially, there were few publications on the topic of phyllosphere endophytes. However, from 2011 onwards, there was a notable increase in the number of publications on phyllosphere endophytes, gaining worldwide attention. Among authors, Arnold, A Elizabeth is widely recognized as a leading author in this research area. In terms of countries, the USA and China hold the highest rankings. As for institutional ranking, the University of Arizona is the most prevalent and leading institute in this particular subject. Collaborative efforts among the authors and institutions tend to be confined to small groups, and a large-scale collaborative network needs to be established. This study identified the influential journals, literature, and hot research topics. These findings also highlight the interconnected nature of key themes, e.g., phyllosphere endophyte research revolves around the four pillars: diversity, fungal endophytes, growth, and endophytic fungi. This study provides an in-depth perspective on phyllosphere endophytes studies, revealing the identification of biodiversity and microbial interaction of phyllosphere endophytes as the principal research frontiers. These analytical findings not only elucidate the recent trajectory of phyllosphere endophyte research but also provide invaluable insights for similar studies and their potential applications on a global scale.

Cellulolytic Aerobic Bacteria Isolated from Agricultural and Forest Soils: An Overview

This review provides insights into cellulolytic bacteria present in global forest and agricultural soils over a period of 11 years. It delves into the study of soil-dwelling cellulolytic bacteria and the enzymes they produce, cellulases, which are crucial in both soil formation and the carbon cycle. Forests and agricultural activities are significant contributors to the production of lignocellulosic biomass. Forest ecosystems, which are key carbon sinks, contain 20-30% cellulose in their leaf litter. Concurrently, the agricultural sector generates approximately 998 million tons of lignocellulosic waste annually. Predominant genera include Bacillus, Pseudomonas, Stenotrophomonas, and Streptomyces in forests and Bacillus, Streptomyces, Pseudomonas, and Arthrobacter in agricultural soils. Selection of cellulolytic bacteria is based on their hydrolysis ability, using artificial cellulose media and dyes like Congo red or iodine for detection. Some studies also measure cellulolytic activity in vitro. Notably, bacterial cellulose hydrolysis capability may not align with their cellulolytic enzyme production. Enzymes such as GH1, GH3, GH5, GH6, GH8, GH9, GH10, GH12, GH26, GH44, GH45, GH48, GH51, GH74, GH124, and GH148 are crucial, particularly GH48 for crystalline cellulose degradation. Conversely, bacteria with GH5 and GH9 often fail to degrade crystalline cellulose. Accurate identification of cellulolytic bacteria necessitates comprehensive genomic analysis, supplemented by additional proteomic and transcriptomic techniques. Cellulases, known for degrading cellulose, are also significant in healthcare, food, textiles, bio-washing, bleaching, paper production, ink removal, and biotechnology, emphasizing the importance of discovering novel cellulolytic strains in soil.

Unveiling the dynamic relationship of viruses and/or symbiotic bacteria with plant resilience in abiotic stress

In the ecosphere, plants interact with environmental biotic and abiotic partners, where unbalanced interactions can induce unfavourable stress conditions. Abiotic factors (temperature, water, and salt) are primarily required for plants healthy survival, and any change in their availability is reflected as a stress signal. In certain cases, the presence of infectious pathogens such as viruses, bacteria, fungi, protozoa, nematodes, and insects can also create stress conditions in plants, leading to the emergence of disease or deficiency symptoms. While these symptoms are often typical of abiotic or biotic stress, however, there are instances where they can intensify under specific conditions. Here, we primarily summarize the viral interactions with plants during abiotic stress to understand how these associations are linked together during viral pathogenesis. Secondly, focus is given to the beneficial effects of root-associated symbiotic bacteria in fulfilling the basic needs of plants during normal as well as abiotic stress conditions. The modulations of plant functional proteins, and their occurrence/cross-talk, with pathogen (virus) and symbiont (bacteria) molecules are also discussed. Furthermore, we have highlighted the biochemical and systematic adaptations that develop in plants due to bacterial symbiosis to encounter stress hallmarks. Lastly, directions are provided towards exploring potential rhizospheric bacteria to maintain plant-microbes ecosystem and manage abiotic stress in plants to achieve better trait health in the horticulture crops.

A comprehensive examination of microbial hazards and risks during indoor soilless leafy green production

Produce grown under controlled environment agriculture (CEA) is often assumed to have a reduced risk of pathogen contamination due to the low chance of exposure to outdoor contaminant factors. However, the 2021 outbreak and numerous recalls of CEA-grown lettuce and microgreens demonstrate the possibility of pathogen introduction during indoor production when there is a failure in the implementation of food safety management systems. Indoor production of commercial leafy greens, such as lettuce and microgreens, is performed across a range of protective structures from primitive household setups to advanced and partially automatized growing systems. Indoor production systems include hydroponic, aquaponic, and aeroponic configurations. Hydroponic systems such as deep water culture and nutrient film technique comprised of various engineering designs represent the main system types used by growers. Depending on the type of leafy green, the soilless substrate, and system selection, risk of microbial contamination will vary during indoor production. In this literature review, science-based pathogen contamination risks and mitigation strategies for indoor production of microgreens and more mature leafy greens are discussed during both pre-harvest and post-harvest stages of production.