Bacteria, Fungi and Archaea Domains in Rhizospheric Soil and Their Effects in Enhancing Agricultural Productivity

Shotgun metagenomic insights into secondary metabolite biosynthetic gene clusters reveal taxonomic and functional profiles of microbiomes in natural farmland soil

Antibiotic resistance is a worldwide problem that imposes a devastating effect on developing countries and requires immediate interventions. Initially, most of the antibiotic drugs were identified by culturing soil microbes. However, this method is prone to discovering the same antibiotics repeatedly. The present study employed a shotgun metagenomics approach to investigate the taxonomic diversity, functional potential, and biosynthetic capacity of microbiomes from two natural agricultural farmlands located in Bekeka and Welmera Choke Kebelle in Ethiopia for the first time. Analysis of the small subunit rRNA revealed bacterial domain accounting for 83.33% and 87.24% in the two selected natural farmlands. Additionally, the analysis showed the dominance of Proteobacteria representing 27.27% and 28.79% followed by Actinobacteria making up 12.73% and 13.64% of the phyla composition. Furthermore, the analysis revealed the presence of unassigned bacteria in the studied samples. The metagenome functional analysis showed 176,961 and 104, 636 number of protein-coding sequences (pCDS) from the two samples found a match with 172,655 and 102, 275 numbers of InterPro entries, respectively. The Genome ontology annotation suggests the presence of 5517 and 3293 pCDS assigned to the "biosynthesis process". Numerous Kyoto Encyclopedia of Genes and Genomes modules (KEGG modules) involved in the biosynthesis of terpenoids and polyketides were identified. Furthermore, both known and novel Biosynthetic gene clusters, responsible for the production of secondary metabolites, such as polyketide synthases, non-ribosomal peptide synthetase, ribosomally synthesized and post-translationally modified peptides (Ripp), and Terpene, were discovered. Generally, from the results it can be concluded that the microbiomes in the selected sampling sites have a hidden functional potential for the biosynthesis of secondary metabolites. Overall, this study can serve as a strong preliminary step in the long journey of bringing new antibiotics to the market.

Enhancing Agricultural Sustainability Through Rhizomicrobiome: A Review

Sustainable agriculture represents the responsible utilization of natural resources while safeguarding the well-being of the natural environment. It encompasses the objectives of preserving the environment, fostering economic growth, and promoting socioeconomic equality. To achieve sustainable development for humanity, it is imperative to prioritize sustainable agriculture. One significant approach to achieving this transition is the extensive utilization of microbes, which play a crucial role due to the genetic reliance of plants on the beneficial functions provided by symbiotic microbes. This review focuses on the significance of rhizospheric microbial communities, also known as the rhizomicrobiome (RM). It is a complex community of microorganisms that live in the rhizosphere and influence the plant's growth and health. It provides its host plant with various benefits related to plant growth, including biocontrol, biofertilization, phytostimulation, rhizoremediation, stress resistance, and other advantageous properties. Yet, the mechanisms by which the RM contributes to sustainable agriculture remain largely unknown. Investigating this microbial population presents a significant opportunity to advance toward sustainable agriculture. Hence, this study aims to provide an overview of the diversity and applications of RM in sustainable agriculture practices. Lately, there has been growing momentum in various areas related to rhizobiome research and its application in agriculture. This includes rhizosphere engineering, synthetic microbiome application, agent-based modeling of the rhizobiome, and metagenomic studies. So, developing bioformulations of these beneficial microorganisms that support plant growth could serve as a promising solution for future strategies aimed at achieving a new green revolution.

A culture-independent approach, supervised machine learning, and the characterization of the microbial community composition of coastal areas across the Bay of Bengal and the Arabian Sea

BACKGROUND

Coastal areas are subject to various anthropogenic and natural influences. In this study, we investigated and compared the characteristics of two coastal regions, Andhra Pradesh (AP) and Goa (GA), focusing on pollution, anthropogenic activities, and recreational impacts. We explored three main factors influencing the differences between these coastlines: The Bay of Bengal's shallower depth and lower salinity; upwelling phenomena due to the thermocline in the Arabian Sea; and high tides that can cause strong currents that transport pollutants and debris.

RESULTS

The microbial diversity in GA was significantly higher than that in AP, which might be attributed to differences in temperature, soil type, and vegetation cover. 16S rRNA amplicon sequencing and bioinformatics analysis indicated the presence of diverse microbial phyla, including candidate phyla radiation (CPR). Statistical analysis, random forest regression, and supervised machine learning models classification confirm the diversity of the microbiome accurately. Furthermore, we have identified 450 cultures of heterotrophic, biotechnologically important bacteria. Some strains were identified as novel taxa based on 16S rRNA gene sequencing, showing promising potential for further study.

CONCLUSION

Thus, our study provides valuable insights into the microbial diversity and pollution levels of coastal areas in AP and GA. These findings contribute to a better understanding of the impact of anthropogenic activities and climate variations on biology of coastal ecosystems and biodiversity.

Enhancing phytoremediation of cadmium and arsenic in alkaline soil by Miscanthus sinensis: A study on the synergistic effect of endophytic fungi and biochar

Endophytic fungi (Trichoderma harzianum (TH) and Paecilomyces lilacinus (PL)) showed potential in phytoremediation for soils contaminated with potentially toxic elements (PTEs (Cd and As)). However, their efficiency is limited, which can be enhanced with the assistance of biochar. This study sought to investigate the effects of TH at two application rates (T1: 4.5 g m-2; T2: 9 g m-2), PL at two application rates (P1: 4.5 g m-2; P2: 9 g m-2), in conjunction with biochar (BC) at 750 g m-2 on the phytoremediation of PTEs by Miscanthus sinensis (M. sinensis). The results showed that the integration of endophytic fungi with biochar notably enhanced the accumulation of Cd and As in M. sinensis by 59.60 %-114.38 % and 49.91 %-134.60 %, respectively. The treatments T2BC and P2BC emerged as the most effective. Specifically, the P2BC treatment significantly enhanced the soil quality index (SQI > 0.55) across all examined soil layers, markedly improving the overall soil condition. It was observed that T2BC treatment could elevate the SQI to 0.56 at the 0-15 cm depth. The combined amendment shifted the primary influences on plant PTEs accumulation from fungal diversity and soil nutrients to bacterial diversity and the availability of soil PTEs. Characteristic microorganisms identified under the combined treatments were RB41 and Pezizaceae, indicating an increase in both bacterial and fungal diversity. This combination altered the soil microbial community, influencing key metabolic pathways. The combined application of PL and biochar was superior to the TH and biochar combination for the phytoremediation of M. sinensis. This approach not only enhanced the phytoremediation potential but also positively impacted soil health and microbial community, suggesting that the synergistic use of endophytic fungi and biochar is an effective strategy for improving the condition of alkaline soils contaminated with PTEs.

Promoting sustainable agriculture by exploiting plant growth-promoting rhizobacteria (PGPR) to improve maize and cowpea crops

Maize and cowpea are among the staple foods most consumed by most of the African population, and are of significant importance in food security, crop diversification, biodiversity preservation, and livelihoods. In order to satisfy the growing demand for agricultural products, fertilizers and pesticides have been extensively used to increase yields and protect plants against pathogens. However, the excessive use of these chemicals has harmful consequences on the environment and also on public health. These include soil acidification, loss of biodiversity, groundwater pollution, reduced soil fertility, contamination of crops by heavy metals, etc. Therefore, essential to find alternatives to promote sustainable agriculture and ensure the food and well-being of the people. Among these alternatives, agricultural techniques that offer sustainable, environmentally friendly solutions that reduce or eliminate the excessive use of agricultural inputs are increasingly attracting the attention of researchers. One such alternative is the use of beneficial soil microorganisms such as plant growth-promoting rhizobacteria (PGPR). PGPR provides a variety of ecological services and can play an essential role as crop yield enhancers and biological control agents. They can promote root development in plants, increasing their capacity to absorb water and nutrients from the soil, increase stress tolerance, reduce disease and promote root development. Previous research has highlighted the benefits of using PGPRs to increase agricultural productivity. A thorough understanding of the mechanisms of action of PGPRs and their exploitation as biofertilizers would present a promising prospect for increasing agricultural production, particularly in maize and cowpea, and for ensuring sustainable and prosperous agriculture, while contributing to food security and reducing the impact of chemical fertilizers and pesticides on the environment. Looking ahead, PGPR research should continue to deepen our understanding of these microorganisms and their impact on crops, with a view to constantly improving sustainable agricultural practices. On the other hand, farmers and agricultural industry players need to be made aware of the benefits of PGPRs and encouraged to adopt them to promote sustainable agricultural practices.

Bacterial Community Structure Responds to Soil Management in the Rhizosphere of Vine Grape Vineyards

The microbial communities of the rhizospheres of vineyards have been subject to a considerable body of research, but it is still unclear how the applied soil cultivation methods are able to change the structure, composition, and level of diversity of their communities. Rhizosphere samples were collected from three neighbouring vineyards with the same time of planting and planting material (rootstock: Teleki 5C; Vitis vinifera: Müller Thurgau). Our objective was to examine the diversity occurring in bacterial community structures in vineyards that differ only in the methods of tillage procedure applied, namely intensive (INT), extensive (EXT), and abandoned (AB). For that we took samples from two depths (10-30 cm (shallow = S) and 30-50 cm (deep = D) of the grape rhizosphere in each vineyard and the laboratory and immediately prepared the slices of the roots for DNA-based analysis of the bacterial communities. Bacterial community structure was assessed by means of PCR-DGGE analysis carried out on the v3 region of 16S rRNA gene. Based on the band composition of the DGGE profiles thus obtained, the diversity of the microbial communities was evaluated and determined by the Shannon-Weaver index (H'). Between the AB and EXT vineyards at the S depth, the similarity of the community structure was 55%; however, the similarity of the D samples was more than 80%, while the difference between the INT samples and the other two was also higher than 80%. Based on our results, we can conclude that intensive cultivation strongly affects the structure and diversity of the bacterial community.

Unveiling the significance of rhizosphere: Implications for plant growth, stress response, and sustainable agriculture

In the rhizosphere, the activities within all processes and functions are primarily influenced by plant roots, microorganisms present in the rhizosphere, and the interactions between roots and microorganisms. The rhizosphere, a dynamic zone surrounding the roots, provides an ideal environment for a diverse microbial community, which significantly shapes plant growth and development. Microbial activity in the rhizosphere can promote plant growth by increasing nutrient availability, influencing plant hormonal signaling, and repelling or outcompeting pathogenic microbial strains. Understanding the associations between plant roots and soil microorganisms has the potential to revolutionize crop yields, improve productivity, minimize reliance on chemical fertilizers, and promote sustainable plant growth technologies. The rhizosphere microbiome could play a vital role in the next green revolution and contribute to sustainable and eco-friendly agriculture. However, there are still knowledge gaps concerning plant root-environment interactions, particularly regarding roots and microorganisms. Advances in metabolomics have helped to understand the chemical communication between plants and soil biota, yet challenges persist. This article provides an overview of the latest advancements in comprehending the communication and interplay between plant roots and microbes, which have been shown to impact crucial factors such as plant growth, gene expression, nutrient absorption, pest and disease resistance, and the alleviation of abiotic stress. By improving these aspects, sustainable agriculture practices can be implemented to increase the overall productivity of plant ecosystems.

Functional analysis of bacterial genes accidentally packaged in rhizospheric phageome of the wild plant species Abutilon fruticosum

The study aimed to reveal the structure and function of phageome existing in soil rhizobiome of Abutilon fruticosum in order to detect accidentally-packaged bacterial genes that encode Carbohydrate-Active enZymes (or CAZymes) and those that confer antibiotic resistance (e.g., antibiotic resistance genes or ARGs). Highly abundant genes were shown to mainly exist in members of the genera Pseudomonas, Streptomyces, Mycobacterium and Rhodococcus. Enriched CAZymes belong to glycoside hydrolase families GH4, GH6, GH12, GH15 and GH43 and mainly function in D-glucose biosynthesis via 10 biochemical passages. Another enriched CAZyme, e.g., alpha-galactosidase, of the GH4 family is responsible for the wealth of different carbohydrate forms in rhizospheric soil sink of A. fruticosum. ARGs of this phageome include the soxR and OleC genes that participate in the "antibiotic efflux pump" resistance mechanism, the parY mutant gene that participates in the "antibiotic target alteration" mechanism and the arr-1, iri, and AAC(3)-Ic genes that participate in the "antibiotic inactivation" mechanism. It is claimed that the genera Streptomyces, which harbors phages with oleC and parY mutant genes, and Pseudomonas, which harbors phages with soxR and AAC(3)-Ic genes, are approaching multidrug resistance via newly disseminating phages. These ARGs inhibit many antibiotics including oleandomycin, tetracycline, rifampin and aminoglycoside. The study highlights the possibility of accidental packaging of these ARGs in soil phageome and the risk of their horizontal transfer to human gut pathogens through the food chain as detrimental impacts of soil phageome of A. fruticosum. The study also emphasizes the beneficial impacts of phageome on soil microbiome and plant interacting in storing carbohydrates in the soil sink for use by the two entities upon carbohydrate deprivation.

Communication between Plants and Rhizosphere Microbiome: Exploring the Root Microbiome for Sustainable Agriculture

Plant roots host numerous microorganisms around and inside their roots, forming a community known as the root microbiome. An increasing bulk of research is underlining the influences root-associated microbial communities can have on plant health and development. However, knowledge on how plant roots and their associated microbes interact to bring about crop growth and yield is limited. Here, we presented (i) the communication strategies between plant roots and root-associated microbes and (ii) the applications of plant root-associated microbes in enhancing plant growth and yield. This review has been divided into three main sections: communications between root microbiome and plant root; the mechanism employed by root-associated microbes; and the chemical communication mechanisms between plants and microbes and their application in plant growth and yield. Understanding how plant root and root-associated microbes communicate is vital in designing ecofriendly strategies for targeted disease suppression and improved plant growth that will help in sustainable agriculture. Ensuring that plants become healthy and productive entails keeping plants under surveillance around the roots to recognize disease-causing microbes and similarly exploit the services of beneficial microorganisms in nutrient acquisition, stress mitigation, and growth promotion.

Functional annotation of rhizospheric phageome of the wild plant species Moringa oleifera

Introduction

The study aims to describe phageome of soil rhizosphere of M.oleifera in terms of the genes encoding CAZymes and other KEGG enzymes.

Methods

Genes of the rhizospheric virome of the wild plant species Moringa oleifera were investigated for their ability to encode useful CAZymes and other KEGG (Kyoto Encyclopedia of Genes and Genomes) enzymes and to resist antibiotic resistance genes (ARGs) in the soil.

Results

Abundance of these genes was higher in the rhizospheric microbiome than in the bulk soil. Detected viral families include the plant viral family Potyviridae as well as the tailed bacteriophages of class Caudoviricetes that are mainly associated with bacterial genera Pseudomonas, Streptomyces and Mycobacterium. Viral CAZymes in this soil mainly belong to glycoside hydrolase (GH) families GH43 and GH23. Some of these CAZymes participate in a KEGG pathway with actions included debranching and degradation of hemicellulose. Other actions include biosynthesizing biopolymer of the bacterial cell wall and the layered cell wall structure of peptidoglycan. Other CAZymes promote plant physiological activities such as cell-cell recognition, embryogenesis and programmed cell death (PCD). Enzymes of other pathways help reduce the level of soil H₂O₂ and participate in the biosynthesis of glycine, malate, isoprenoids, as well as isoprene that protects plant from heat stress. Other enzymes act in promoting both the permeability of bacterial peroxisome membrane and carbon fixation in plants. Some enzymes participate in a balanced supply of dNTPs, successful DNA replication and mismatch repair during bacterial cell division. They also catalyze the release of signal peptides from bacterial membrane prolipoproteins. Phages with the most highly abundant antibiotic resistance genes (ARGs) transduce species of bacterial genera Pseudomonas, Streptomyces, and Mycobacterium. Abundant mechanisms of antibiotic resistance in the rhizosphere include "antibiotic efflux pump" for ARGs soxR, OleC, and MuxB, "antibiotic target alteration" for parY mutant, and "antibiotic inactivation" for arr-1.

Discussion

These ARGs can act synergistically to inhibit several antibiotics including tetracycline, penam, cephalosporin, rifamycins, aminocoumarin, and oleandomycin. The study highlighted the issue of horizontal transfer of ARGs to clinical isolates and human gut microbiome.

Effects of Variation in Tamarix chinensis Plantations on Soil Microbial Community Composition in the Middle Yellow River Floodplain

Floodplains have important ecological and hydrological functions in terrestrial ecosystems, experience severe soil erosion, and are vulnerable to losing soil fertility. Tamarix chinensis Lour. plantation is the main vegetation restoration measure for maintaining soil quality in floodplains. Soil microorganisms are essential for driving biogeochemical cycling processes. However, the effects of sampling location and shrub patch size on soil microbial community composition remain unclear. In this study, we characterized changes in microbial structure, as well as the factors driving them, in inside- and outside-canopy soils of three patch sizes (small, medium, large) of T. chinensis plants in the middle Yellow River floodplain. Compared with the outside-canopy soils, inside-canopy had higher microbial phospholipid fatty acids (PLFAs), including fungi, bacteria, Gram-positive bacteria (GP), Gram-negative bacteria (GN), and arbuscular mycorrhizal fungi. The ratio of fungi to bacteria and GP to GN gradually decreased as shrub patch size increased. Differences between inside-canopy and outside-canopy soils in soil nutrients (organic matter, total nitrogen, and available phosphorus) and soil salt content increased by 59.73%, 40.75%, 34.41%, and 110.08% from small to large shrub patch size. Changes in microbial community composition were mainly driven by variation in soil organic matter, which accounted for 61.90% of the variation in inside-canopy soils. Resource islands could alter microbial community structure, and this effect was stronger when shrub patch size was large. The results indicated that T. chinensis plantations enhanced the soil nutrient contents (organic matter, total nitrogen, and available phosphorus) and elevated soil microbial biomass and changed microbial community composition; T. chinensis plantations might thus provide a suitable approach for restoring degraded floodplain ecosystems.

Short-Term Evaluation of the Spatial Distribution of Trophic Groups of Amoebae in the Rhizosphere of Zea mays Inoculated with Rhizophagus intraradices

Primary production in terrestrial ecosystems is sustained by plants, microbiota, and fungi, which are the major organic matter providers in the root zone, setting in motion the soil food webs. Predators like soil amoebae voraciously feed on bacteria, fungi, and microbial eukaryotes releasing the nutrients sequestered in their biomass. Early food web setting up is crucial for seedling nutrition and its further development after establishment. Mycorrhizal fungi are more than phosphorus providers, and we wonder what their role is in structuring the predators' trophic groups in the root zone. We evaluated the effect of Rhizophagus intraradices inoculated in Zea mays (mycorrhizosphere), on the structuration of amoebae trophic groups along vertical and horizontal (3, 6, and 9 cm) soil distribution when compared to un-inoculated plants, after 20 days in microcosms. Amoebae species richness was highest in non-mycorrhizal seedlings in the root zone at 6- to 9-cm depth, and 3 cm away from plants. More bacterial species are needed when plants are devoid of mycorrhiza, and their influence is constrained 3 cm away from roots. Higher diversity of trophic groups was recorded at mycorrhizal seedlings and at the compartment influenced by the mycelium at 6- to 9-cm depth. The highest bacterivorous diversity, higher number of rare species and protozoa-eating amoebae, and the absence of fungivorous group recorded at the mycorrhizosphere of Z. mays, indicate that the community was very different from the non-mycorrhizal plants. We conclude that the arbuscular mycorrhizal fungus exerts significant changes on the community of trophic groups of amoebae.

Current advances and research prospects for agricultural and industrial uses of microbial strains available in world collections

Microorganisms are an important component of the ecosystem and have an enormous impact on human lives. Moreover, microorganisms are considered to have desirable effects on other co-existing species in a variety of habitats, such as agriculture and industries. In this way, they also have enormous environmental applications. Hence, collections of microorganisms with specific traits are a crucial step in developing new technologies to harness the microbial potential. Microbial culture collections (MCCs) are a repository for the preservation of a large variety of microbial species distributed throughout the world. In this context, culture collections (CCs) and microbial biological resource centres (mBRCs) are vital for the safeguarding and circulation of biological resources, as well as for the progress of the life sciences. Ex situ conservation of microorganisms tagged with specific traits in the collections is the crucial step in developing new technologies to harness their potential. Type strains are mainly used in taxonomic study, whereas reference strains are used for agricultural, biotechnological, pharmaceutical research and commercial work. Despite the tremendous potential in microbiological research, little effort has been made in the true sense to harness the potential of conserved microorganisms. This review highlights (1) the importance of available global microbial collections for man and (2) the use of these resources in different research and applications in agriculture, biotechnology, and industry. In addition, an extensive literature survey was carried out on preserved microorganisms from different collection centres using the Web of Science (WoS) and SCOPUS. This review also emphasizes knowledge gaps and future perspectives. Finally, this study provides a critical analysis of the current and future roles of microorganisms available in culture collections for different sustainable agricultural and industrial applications. This work highlights target-specific potential microbial strains that have multiple important metabolic and genetic traits for future research and use.

Functional Diversity of Microbial Communities in the Soybean (Glycine max L.) Rhizosphere from Free State, South Africa

The plant microbiome is involved in enhancing nutrient acquisition, plant growth, stress tolerance, and reducing chemical inputs. The identification of microbial functional diversity offers the chance to evaluate and engineer them for various agricultural processes. Using a shotgun metagenomics technique, this study examined the functional diversity and metabolic potentials of microbial communities in the rhizosphere of soybean genotype link 678. The dominant genera are Geobacter, Nitrobacter, Burkholderia, Candidatus, Bradyrhizobium and Streptomyces. Twenty-one functional categories were present, with fourteen of the functions being dominant in all samples. The dominant functions include carbohydrates, fatty acids, lipids and isoprenoids, amino acids and derivatives, sulfur metabolism, and nitrogen metabolism. A Kruskal–Wallis test was used to test samples’ diversity differences. There was a significant difference in the alpha diversity. ANOSIM was used to analyze the similarities of the samples and there were significant differences between the samples. Phosphorus had the highest contribution of 64.3% and was more prominent among the soil properties that influence the functional diversity of the samples. Given the functional groups reported in this study, soil characteristics impact the functional role of the rhizospheric microbiome of soybean.

Soil pH, Calcium Content and Bacteria as Major Factors Responsible for the Distribution of the Known Fraction of the DNA Bacteriophage Populations in Soils of Luxembourg

Bacteriophages participate in soil life by influencing bacterial community structure and function, biogeochemical cycling and horizontal gene transfer. Despite their great abundance, diversity, and importance in microbial processes, they remain little explored in environmental studies. The influence of abiotic factors on the persistence of bacteriophages is now recognized; however, it has been mainly studied under experimental conditions. This study aimed to determine whether the abiotic factors well-known to influence bacteriophage persistence also control the natural distribution of the known DNA bacteriophage populations. To this end, soil from eight study sites including forests and grasslands located in the Attert River basin (Grand Duchy of Luxembourg) were sampled, covering different soil and land cover characteristics. Shotgun metagenomics, reference-based bioinformatics and statistical analyses allowed characterising the diversity of known DNA bacteriophage and bacterial communities. After combining soil properties with the identified DNA bacteriophage populations, our in-situ study highlighted the influence of pH and calcium cations on the diversity of the known fraction of the soil DNA bacteriophages. More interestingly, significant relationships were established between bacteriophage and bacterial populations. This study provides new insights into the importance of abiotic and biotic factors in the distribution of DNA bacteriophages and the natural ecology of terrestrial bacteriophages.

Partners to survive: Hoffmannseggia doellii root-associated microbiome at the Atacama Desert

The discovery and characterization of plant species adapted to extreme environmental conditions have become increasingly important. Hoffmannseggia doellii is a perennial herb endemic to the Chilean Atacama Desert that grows in the western Andes between 2800 and 3600 m above sea level. Its growing habitat is characterized by high radiation and low water and nutrient availability. Under these conditions, H. doellii can grow, reproduce, and develop an edible tuberous root. We characterized the H. doellii soil-associated microbiomes to understand the biotic factors that could influence their surprising ability to survive. We found an increased number of observed species and higher phylogenetic diversity of bacteria and fungi on H. doellii root soils compared with bare soil (BS) along different sites and to soil microbiomes of other plant species. Also, the H. doellii-associated microbiome had a higher incidence of overall positive interactions and fungal within-kingdom interactions than their corresponding BS network. These findings suggest a microbial diversity soil modulation mechanism that may be a characteristic of highly tolerant plants to diverse and extreme environments. Furthermore, since H. doellii is related to important cultivated crops, our results create an opportunity for future studies on climate change adaptation of crop plants.

The application of plant growth-promoting rhizobacteria in Solanum lycopersicum production in the agricultural system: a review

Food safety is a significant challenge worldwide, from plantation to cultivation, especially for perishable products such as tomatoes. New eco-friendly strategies are needed, and beneficial microorganisms might be a sustainable solution. This study demonstrates bacteria activity in the tomato plant rhizosphere. Further, it investigates the rhizobacteria's structure, function, and diversity in soil. Rhizobacteria that promote the growth and development of tomato plants are referred to as plant growth-promoting bacteria (PGPR). They form a series of associations with plants and other organisms in the soil through a mutualistic relationship where both parties benefit from living together. It implies the antagonistic activities of the rhizobacteria to deter pathogens from invading tomato plants through their roots. Some PGPR are regarded as biological control agents that hinder the development of spoilage organisms and can act as an alternative for agricultural chemicals that may be detrimental to the health of humans, animals, and some of the beneficial microbes in the rhizosphere soil. These bacteria also help tomato plants acquire essential nutrients like potassium (K), magnesium (Mg), phosphorus (P), and nitrogen (N). Some rhizobacteria may offer a solution to low tomato production and help tackle food insecurity and farming problems. In this review, an overview of soil-inhabiting rhizobacteria focused on improving the sustainable production of Solanum lycopersicum.

Role of Nodulation-Enhancing Rhizobacteria in the Promotion of Medicago sativa Development in Nutrient-Poor Soils

Legumes are usually used as cover crops to improve soil quality due to the biological nitrogen fixation that occurs due to the interaction of legumes and rhizobia. This symbiosis can be used to recover degraded soils using legumes as pioneer plants. In this work, we screened for bacteria that improve the legume–rhizobia interaction in nutrient-poor soils. Fourteen phosphate solubilizer-strains were isolated, showing at least three out of the five tested plant growth promoting properties. Furthermore, cellulase, protease, pectinase, and chitinase activities were detected in three of the isolated strains. Pseudomonas sp. L1, Chryseobacterium soli L2, and Priestia megaterium L3 were selected to inoculate seeds and plants of Medicago sativa using a nutrient-poor soil as substrate under greenhouse conditions. The effects of the three bacteria individually and in consortium showed more vigorous plants with increased numbers of nodules and a higher nitrogen content than non-inoculated plants. Moreover, bacterial inoculation increased plants’ antioxidant activities and improved their development in nutrient-poor soils, suggesting an important role in the stress mechanisms of plants. In conclusion, the selected strains are nodulation-enhancing rhizobacteria that improve leguminous plants growth and nodulation in nutrient-poor soils and could be used by sustainable agriculture to promote plants’ development in degraded soils.

Endophytic Fungi: An Effective Alternative Source of Plant-Derived Bioactive Compounds for Pharmacological Studies

Plant-associated fungi (endophytic fungi) are a biodiversity-rich group of microorganisms that are normally found asymptomatically within plant tissues or in the intercellular spaces. Endophytic fungi promote the growth of host plants by directly producing secondary metabolites, which enhances the plant's resistance to biotic and abiotic stresses. Additionally, they are capable of biosynthesizing medically important "phytochemicals" that were initially thought to be produced only by the host plant. In this review, we summarized some compounds from endophyte fungi with novel structures and diverse biological activities published between 2011 and 2021, with a focus on the origin of endophytic fungi, the structural and biological activity of the compounds they produce, and special attention paid to the exploration of pharmacological activities and mechanisms of action of certain compounds. This review revealed that endophytic fungi had high potential to be harnessed as an alternative source of secondary metabolites for pharmacological studies.

Bacillus sp. and arbuscular mycorrhizal fungi consortia enhance wheat nutrient and yield in the second-year field trial: Superior performance in comparison with chemical fertilizers

AIMS

The aim of the study is to analyse the effect of microbial consortia for wheat biofortification, growth, yield and soil fertility as part of a 2-year field study and compare it with the use of chemical fertilizers.

METHODS AND RESULTS

A field trial (second year) was conducted with various combinations of plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF) treatments, ranging from a single inoculant to multiple combinations. The microbial consortia used were Bacillus sp. and AMF based on first-year field trial results. The consortia based on native (CP4) and non-native (AHP3) PGPB (Bacillus sp.) and AMF performed better in terms of nutrients content in wheat grain tissue and yield-related traits compared with chemical fertilizer treated and untreated control. Dual treatment of PGPB (CP4+AHP3) combined with AMF resulted in a significant increase in antioxidants. The spatial colonization of AMF in roots indicated that both the isolates CP4 and AHP3 were able to enhance the AMF colonization in root tissue. Furthermore, soil enzymes' activities were higher with the PGPB and AMF combination giving the best results. A positive correlation was recorded between plant growth, grain yield and soil physicochemical parameters.

CONCLUSIONS

Our findings confirm that the combined treatment of CP4 and AHP3 and AMF functions as an effective microbial consortium with excellent application prospects for wheat biofortification, grain yield and soil fertility compared with chemical fertilizers.

SIGNIFICANCE AND IMPACT OF STUDY

The extensive application of chemical fertilizers on low-yielding field sites is a severe concern for cereal crops, especially wheat in the Asian continent. This study serves as a primer for implementing site-specific sustainable agricultural-management practices using a green technology leading to significant gains in agriculture.

High-throughput molecular technologies for unraveling the mystery of soil microbial community: challenges and future prospects

Soil microbial communities play a crucial role in soil fertility, sustainability, and plant health. However, intensive agriculture with increasing chemical inputs and changing environments have influenced native soil microbial communities. Approaches have been developed to study the structure, diversity, and activity of soil microbes to better understand the biology and plant-microbe interactions in soils. Unfortunately, a good understanding of soil microbial community remains a challenge due to the complexity of community composition, interactions of the soil environment, and limitations of technologies, especially related to the functionality of some taxa rarely detected using conventional techniques. Culture-based methods have been shown unable and sometimes are biased for assessing soil microbial communities. To gain further knowledge, culture-independent methods relying on direct analysis of nucleic acids, proteins, and lipids are worth exploring. In recent years, metagenomics, metaproteomics, metatranscriptomics, and proteogenomics have been increasingly used in studying microbial ecology. In this review, we examined the importance of microbial community to soil quality, the mystery of rhizosphere and plant-microbe interactions, and the biodiversity and multi-trophic interactions that influence the soil structure and functionality. The impact of the cropping system and climate change on the soil microbial community was also explored. Importantly, progresses in molecular biology, especially in the development of high-throughput biotechnological tools, were extensively assessed for potential uses to decipher the diversity and dynamics of soil microbial communities, with the highlighted advantages/limitations.

Characterization of plant growth-promoting rhizobacterial isolates associated with food plants in South Africa

The region around the plant root referred to as the rhizosphere, is the zone where various microbial activity occurs. It performs crucial functions such as increasing the uptake of nutrients for plant development and preventing plant against plant pathogens. Keeping in mind the beneficial role performed by rhizospheric microorganisms, rhizobacterial species were isolated from the maize and soybean plant's rhizosphere. The isolated microorganisms were evaluated for their biochemical characteristics, plant growth-promoting potentials, tolerance to different environmental conditions, and their antifungal activity against Fusarium graminearum, a fungal pathogen that infects maize. The rhizobacterial isolates with multiple plant growth-promoting potentials were identified as Bacillus spp (80.77%), Rhodocyclaceae bacterium (3.85%), Enterococcus spp (3.85%). Massilia spp (3.85%. and Pseudomonas (7.69%) species based on their 16S rRNA molecular characterization. The bacterial isolates possessed antifungal activities against Fusarium graminearum, promote maize and soybeans seed under laboratory conditions, and exhibited different levels of tolerance to pH, temperature, salt, and heavy metal. Based on this, the whole genome sequencing of Bacillus sp. OA1, Pseudomonas rhizosphaerea OA2, and Pseudomonas sp. OA3 was performed using Miseq Illumina system to determine the functional genes and secondary metabolites responsible for their plant growth-promoting potential Thus, the result of this research revealed that the selected bacterial isolates possess plant growth-promoting potentials that can make them a potential candidate to be employed as microbial inoculants for protecting plants against phytopathogens, environmental stress and increasing plant growth and productivity.

Biotechnological utilization: the role of Zea mays rhizospheric bacteria in ecosystem sustainability

Maize is an essential cereal crop and the third most essential food crop globally. The extensive dependence on pesticides and chemical fertilizers to control pests and increase crop yield, respectively, has generated an injurious impact on soil and animal health. Plant growth-promoting rhizobacteria (PGPR), which depict a broad array of bacteria inhabiting the root vicinity and root surface, have proven to be a better alternative. These organisms expressly or by implication foster the growth and development of plants by producing and secreting numerous regulatory compounds in the rhizosphere. Some rhizobacteria found to be in association with Zea mays rhizosphere include Bacillus sp., Azotobacter chroococcum, Burkholderia spp., Streptomyces spp., Pseudomonas spp., Paenibacillus spp., and Sphingobium spp. For this review, the mechanism of action of these rhizospheric bacteria was grouped into three, which are bioremediation, biofertilization, and biocontrol. KEY POINTS: • Plant-microbe interaction is vital for ecosystem functioning. • PGPR can produce volatile cues to deter ravaging insects from plants.

New insight into the divergent responses of plants to warming in the context of root endophytic bacterial and fungal communities

Plant adaptation under climate changes is critical to the maintenance of terrestrial ecosystem structure and function. Studying the response of the endophytic community to climate warming is a novel way to reveal the mechanism of host environmental adaptability because of the prominent role endophytes play in host nutrient acquisition and stress tolerance. However, host performance was generally neglected in previous relevant research, which limits our understanding of the relationships between the endophytic community and host responses to climate warming. The present study selected two plants with different responses to climate warming. Elymus nutans is more suitable for growing in warm environments at low altitude compared to Kobresia pygmaea. K. pygmaea and E. nutans were sampled along an altitude gradient in the natural grassland of Qinghai-Tibet Plateau, China. Root endophytic bacterial and fungal communities were analyzed using high throughput sequencing. The results revealed that hosts growing in more suitable habitats held higher endophytic fungal diversity. Elevation and host identity significantly affected the composition of the root endophytic bacterial and fungal community. 16S rRNA functional prediction demonstrated that hosts that adapted to lower temperatures recruited endophytic communities with higher abundance of genes related to cold resistance. Hosts that were more suitable for warmer and drier environments recruited endophytes with higher abundance of genes associated with nutrient absorption and oxidation resistance. We associated changes in the endophytic community with hosts adaptability to climate warming and suggested a synchronism of endophytic communities and hosts in environmental adaptation.

Improving rice salt tolerance by precision breeding in a new era

Rice is a premier staple food that constitutes the bulk of the daily diet of the majority of people in Asia. Agricultural productivity must be boosted to support this huge demand for rice. However, production is jeopardized by soil salinity. Advances in whole-genome sequencing, marker-assisted breeding strategies, and targeted mutagenesis have substantially improved the toolbox of today's breeders. Given that salinity has a major influence on rice at both the seedling and reproductive stages, understanding and manipulating this trait will have an enormous impact on sustainable production. This article summarizes recent developments in the understanding of the mechanisms of salt tolerance and how state-of-the-art tools such as RNA guided CRISPR endonuclease technology including targeted mutagenesis or base and prime editing can help in gene discovery and functional analysis as well as in transferring favorable alleles into elite breeding material to speed the breeding of salt-tolerant rice cultivars.

Early ecological succession patterns of bacterial, fungal and plant communities along a chronosequence in a recently deglaciated area of the Italian Alps

In this study, the early ecological succession patterns of Forni Glacier (Ortles-Cevedale group, Italian Alps) forefield along an 18-year long chronosequence (with a temporal resolution of 1 year) has been reported. Bacterial and fungal community structures were inferred by high-throughput sequencing of 16S rRNA gene and ITS, respectively. In addition, the occurrence of both herbaceous and arboreous plants was also recorded at each plot. A significant decrease of alpha-diversity in more recently deglaciated areas was observed for both bacteria and plants. Time since deglaciation and pH affected the structure of both fungal and bacterial communities. Pioneer plants could be a major source of colonization for both bacterial and fungal communities. Consistently, some of the most abundant bacterial taxa and some of those significantly varying with pH along the chronosequence (Polaromonas, Granulicella, Thiobacillus, Acidiferrobacter) are known to be actively involved in rock-weathering processes due to their chemolithotrophic metabolism, thus suggesting that the early phase of the chronosequence could be mainly shaped by the biologically controlled bioavailability of metals and inorganic compounds. Fungal communities were dominated by ascomycetous filamentous fungi and basidiomycetous yeasts. Their role as cold-adapted organic matter decomposers, due to their heterotrophic metabolism, was suggested.

Rhizosphere Microbiome Cooperations: Strategies for Sustainable Crop Production

Interactions between microorganisms and host plants determine the growth and development as well as the health of the host plant. Various microbial groups inhabit the rhizosphere, each with its peculiar function. The survival of each microbial group depends to a large extent on its ability to colonize the plant root and outcompete the native organisms. The role of the rhizospheric microbiome in enhancing plant growth has not been fully maximized. An understanding of the complexities of microbial interactions and factors affecting their assembly in the community is necessary to benefit maximally from the cooperations of various microbial communities for sustainable crop production. In this review, we outline the various organisms associated with the plant rhizosphere with emphasis on their interactions and mechanisms used in plant growth promotion.

Rhizosphere bacterial and fungal communities succession patterns related to growth of poplar fine roots

Understanding the succession patterns of microbial community along root growth provides deep insights into interaction between fine roots and microbes. In the study, we investigated this issue using fine roots from poplar trees and grouped these fine roots into three growth stages: newborn white roots (WR), mature yellow roots (YR) and aging brown roots (BR). Root surface traits were observed under a scanning electron microscopy (SEM). Adhered soils on roots of the three growth stages were grouped into the three soil compartments, correspondingly. The 16S rRNA and ITS1 region were sequenced for bacteria and fungi inhabiting rhizosphere soils, respectively. Phospholipid fatty acid (PLFA) technology was employed to examine the biomass of bacterial and fungal communities. The anatomical traits of fine roots show apparent differences among the WR, YR and BR. Both bacteria and fungi have 25 dominant genera with a relative abundance over 1%, of which, four genera of the bacteria (Bacillus, Burkholderia, Ralstonia and Dyella) differ in abundance among the WR, YR and BR soil compartments and four genera of the fungi (Fusarium, Chaetomium, Penicillium and Scleroderma) differ in abundance among these soil compartments. The operational taxonomic units (OTUs) showed the highest richness in the WR soil compartment for bacteria and in the YR soil compartment for fungi, indicating a different succession pattern between the bacterial and fungal communities. Furthermore, the biomass of bacterial community is larger than the fungal community according to PLFAs, and both decreased along fine root growth. The total carbon (TC) in the soil increases along root growth while the dissolved organic carbon (DOC) decreases. Redundancy analysis (RDA) shows a close correlation between twelve dominant bacteria genera and the total organic carbon (TOC), the readily oxidizable organic carbon (ROC) and DOC and ten dominant fungi genera with the TOC and ROC. In conclusion, our results indicate that fine roots growth has shaped the composition and structure of root associated bacterial and fungal communities.

Pharmacological Potential of Fungal Endophytes Associated with Medicinal Plants: A Review

Endophytic microbes are microorganisms that colonize the intracellular spaces within the plant tissues without exerting any adverse or pathological effects. Currently, the world population is facing devastating chronic diseases that affect humans. The resistance of pathogens to commercial antibiotics is increasing, thus limiting the therapeutic potential and effectiveness of antibiotics. Consequently, the need to search for novel, affordable and nontoxic natural bioactive compounds from endophytic fungi in developing new drugs with multifunction mechanisms to meet human needs is essential. Fungal endophytes produce invaluable bioactive metabolic compounds beneficial to humans with antimicrobial, anticancer, antidiabetic, anti-inflammatory, antitumor properties, etc. Some of these bioactive compounds include pestacin, taxol, camptothecin, ergoflavin, podophyllotoxin, benzopyran, isopestacin, phloroglucinol, tetrahydroxy-1-methylxanthone, salidroside, borneol, dibenzofurane, methyl peniphenone, lipopeptide, peniphenone etc. Despite the aforementioned importance of endophytic fungal metabolites, less information is available on their exploration and pharmacological importance. Therefore, in this review, we shall elucidate the fungal bioactive metabolites from medicinal plants and their pharmacological potential.

Metarhizium: jack of all trades, master of many

The genus Metarhizium and Pochonia chlamydosporia comprise a monophyletic clade of highly abundant globally distributed fungi that can transition between long-term beneficial associations with plants to transitory pathogenic associations with frequently encountered protozoans, nematodes or insects. Some very common 'specialist generalist' species are adapted to particular soil and plant ecologies, but can overpower a wide spectrum of insects with numerous enzymes and toxins that result from extensive gene duplications made possible by loss of meiosis and associated genome defence mechanisms. These species use parasexuality instead of sex to combine beneficial mutations from separate clonal individuals into one genome (Vicar of Bray dynamics). More weakly endophytic species which kill a narrow range of insects retain sexuality to facilitate host-pathogen coevolution (Red Queen dynamics). Metarhizium species can fit into numerous environments because they are very flexible at the genetic, physiological and ecological levels, providing tractable models to address how new mechanisms for econutritional heterogeneity, host switching and virulence are acquired and relate to diverse sexual life histories and speciation. Many new molecules and functions have been discovered that underpin Metarhizium associations, and have furthered our understanding of the crucial ecology of these fungi in multiple habitats.

Plant-archaea relationships: a potential means to improve crop production in arid and semi-arid regions

Crop production in arid and semi-arid regions of the world is limited by several abiotic factors, including water stress, temperature extremes, low soil fertility, high soil pH, low soil water-holding capacity, and low soil organic matter. Moreover, arid and semi-arid areas experience low levels of rainfall with high spatial and temporal variability. Also, the indiscriminate use of chemicals, a practice that characterizes current agricultural practice, promotes crop and soil pollution potentially resulting in serious human health and environmental hazards. A reliable and sustainable alternative to current farming practice is, therefore, a necessity. One such option includes the use of plant growth-promoting microbes that can help to ameliorate some of the adverse effects of these multiple stresses. In this regard, archaea, functional components of the plant microbiome that are found both in the rhizosphere and the endosphere may contribute to the promotion of plant growth. Archaea can survive in extreme habitats such as areas with high temperatures and hypersaline water. No cases of archaea pathogenicity towards plants have been reported. Archaea appear to have the potential to promote plant growth, improve nutrient supply and protect plants against various abiotic stresses. A better understanding of recent developments in archaea functional diversity, plant colonizing ability, and modes of action could facilitate their eventual usage as reliable components of sustainable agricultural systems. The research discussed herein, therefore, addresses the potential role of archaea to improve sustainable crop production in arid and semi-arid areas.

The endosphere microbial communities, a great promise in agriculture

Agricultural food production and sustainability need intensification to address the current global food supply to meet human demand. The continuous human population increase and other anthropogenic activities threaten food security. Agrochemical inputs have long been used in conventional agricultural systems to boost crop productivity, but they are disadvantageous to a safe environment. Towards developing environmentally friendly agriculture, efforts are being directed in exploring biological resources from soil and plant microbes. The survival of the rhizosphere and endosphere microbiota is influenced by biotic and abiotic factors. Plant microbiota live interdependently with the host plants. Endophytes are regarded as colonizer microbes inhabiting and establishing microbial communities within the plant tissue. Their activities are varied and include fixing atmospheric nitrogen, solubilizing phosphate, synthesis of siderophores, secretion of metabolite-like compounds containing active biocontrol agents in the control of phytopathogens, and induced systemic resistance that stimulates plant response to withstand stress. Exploring beneficial endophyte resources in the formulation of bio-inoculants, such as biofertilizers, as an alternative to agrochemicals (fertilizers and pesticides) in developing environmentally friendly agriculture and for incorporation into crop breeding and disease control program is promising. Therefore, in this review, endosphere microbial ecology, associating environmental factors, and their roles that contribute to their effectiveness in promoting plant growth for maximum agricultural crop productivity were highlighted.

Metagenomics methods for the study of plant-associated microbial communities: A review

Plant microbiota have different effects on the plant which can be beneficial or pathogenic. In this study, we concentrated on beneficial microbes associated with plants using endophytic microbes as a case study. Detailed knowledge of the microbial diversity, abundance, composition, functional genes patterns, and metabolic pathways at genome level could assist in understanding the contributions of microbial community towards plant growth and health. Recently, the study of microbial community has improved greatly with the discovery of next-generation sequencing and bioinformatics technologies. Analysis of next generation sequencing data and a proper computational method plays a key role in examining microbial metagenome. This review presents the general metagenomics and computational methods used in processing plant associated metagenomes with concentration on endophytes. This includes 1) introduction of plant-associated microbiota and the factors driving their diversity. 2) plant metagenome focusing on DNA extraction, verification and quality control. 3) metagenomics methods used in community analysis of endophytes focusing on maize plant and, 4) computational methods used in the study of endophytic microbiomes. Limitations and future prospects of metagenomics and computational methods for the analysis of plant-associated metagenome (endophytic metagenome) were also discussed with the aim of fostering its development. We conclude that there is need to adopt advanced genomic features such as k-mers of random size, which do not depend on annotation and can represent other sequence alternatives.