Diversity of sugarcane root-associated endophytic Bacillus and their activities in enhancing plant growth

Soil phosphorus transformation and plant uptake driven by phosphate-solubilizing microorganisms

Phosphorus (P) is an important nutrient for plants, and a lack of available P greatly limits plant growth and development. Phosphate-solubilizing microorganisms (PSMs) significantly enhance the ability of plants to absorb and utilize P, which is important for improving plant nutrient turnover and yield. This article summarizes and analyzes how PSMs promote the absorption and utilization of P nutrients by plants from four perspectives: the types and functions of PSMs, phosphate-solubilizing mechanisms, main functional genes, and the impact of complex inoculation of PSMs on plant P acquisition. This article reviews the physiological and molecular mechanisms of phosphorus solubilization and growth promotion by PSMs, with a focus on analyzing the impact of PSMs on soil microbial communities and its interaction with root exudates. In order to better understand the ability of PSMs and their role in soil P transformation and to provide prospects for research on PSMs promoting plant P absorption. PSMs mainly activate insoluble P through the secretion of organic acids, phosphatase production, and mycorrhizal symbiosis, mycorrhizal symbiosis indirectly activates P via carbon exchange. PSMs can secrete organic acids and produce phosphatase, which plays a crucial role in soil P cycling, and related genes are involved in regulating the P-solubilization ability. This article reviews the mechanisms by which microorganisms promote plant uptake of soil P, which is of great significance for a deeper understanding of PSM-mediated soil P cycling, plant P uptake and utilization, and for improving the efficiency of P utilization in agriculture.

Can endophytic microbial compositions in cane roots be shaped by different propagation methods

In practical production, cane stems with buds are generally used as seed for propagation. However, long-terms cane stems only easily lead to some problems such as disease sensitivity, quality loss, etc. Recently, cane seedings, which are produced by tissue culture were used in sugarcane production, but few studies on cane health related to tissue culture seedings. Therefore, to evaluate the immunity and health of sugarcanes growing from different reproduction modes, the endophytic microbial compositions in cane roots between stem and tissue culture seedlings were analyzed using high-throughput techniques. The results showed that the endophytic microbial compositions in cane roots were significant differences between stem and tissue culture seedlings. At the genus level, Pantoea, Bacillus, Streptomyces, Lechevalieria, Pseudomonas, Nocardioides, unclassified_f__Comamonadaceae enriched as the dominant endophytic bacterial genera, and Rhizoctonia, Sarocladium, Scytalidium, Wongia, Fusarium, unclassified_f__Phaeosphaer, unclassified_c__Sordariom, unclassified_f__Stachybot, Poaceascoma, Microdochium, Arnium, Echria, Mycena and Exophiala enriched as the dominant endophytic fungal genera in cane roots growing from the tissue culture seedlings. In contrast, Mycobacterium, Massilia, Ralstonia, unclassified_f__Pseudonocardiacea, norank_f__Micropepsaceae, Leptothrix and Bryobacter were the dominant endophytic bacterial genera, and unclassified_k__Fungi, unclassified_f__Marasmiaceae, Talaromyces, unclassified_c__Sordariomycetes and Trichocladium were the dominant endophytic fungal genera in cane roots growing from stem seedlings. Additionally, the numbers of bacterial and fungal operational taxonomic units (OTUs) in cane roots growing from tissue culture seedlings were significantly higher than those of stem seedlings. It indicates that not only the endophytic microbial compositions in cane roots can be shaped by different propagation methods, but also the stress resistance of sugarcanes can be improved by the tissue culture propagation method.

A Synthetic Microbial Community of Plant Core Microbiome Can Be a Potential Biocontrol Tool

Microbes are accepted as the foremost drivers of the rhizosphere ecology that influences plant health in direct or indirect ways. In recent years, the rapid development of gene sequencing technology has greatly facilitated the study of plant microbiome structure and function, and various plant-associated microbiomes have been categorized. Additionally, there is growing research interest in plant-disease-related microbes, and some specific microflora beneficial to plant health have been identified. This Review discusses the plant-associated microbiome's biological control pathways and functions to modulate plant defense against pathogens. How do plant microbiomes enhance plant resistance? How does the plant core microbiome-associated synthetic microbial community (SynCom) improve plant health? This Review further points out the primary need to develop smart agriculture practices using SynComs against plant diseases. Finally, this Review provides ideas for future opportunities in plant disease control and mining new microbial resources.

Co-Inoculation of Non-Symbiotic Bacteria Bacillus and Paraburkholderia Can Improve the Soybean Yield, Nutrient Uptake, and Soil Parameters

Due to its nutritional value and oil, soybean (Glycine max L.) became an economic crop in India and worldwide. The current study investigated the effect of forest-associated plant growth-promoting rhizobacteria (PGPR) on soybean yield and grain nutrient content. Five potential bacteria were used in this study based on their PGPR traits. The pot assay result with two crops (soybean and chickpea) confirmed the growth promotion activity of the two strains (Bacillus subtilis MpS15 and Paraburkholderia sabiae NvS21). The result showed significant (p < 0.05) enhancement in plant length and biomass with the seed treatment with strains (MpS15 and NvS21) compared to the control. Later both biocompatible potential strains were used in field experiments as individuals and consortia. Seed treatment of consortia significantly improves the nodulation and photosynthetic content more than individual treatments and control. Compared to the control, the co-inoculation of MpS15 and NvS21 increased soybean grain, straw yield, and grain NPK contents. Interestingly, soil parameters (organic carbon, available NPK) showed a strong correlation (p < 0.05) with plant parameters and nutrient uptake. Overall, our study provides strong relationships between soil parameters, microbial inoculum as consortia, and soybean performance, and these strains may be utilized as bioinoculant in future.

Genotyping-driven diversity assessment of biocontrol potent Bacillus spp. strain collection as a potential method for the development of strain-specific biomarkers

Bacillus species are among the most researched and frequently applied biocontrol agents. To estimate their potential as environmentally friendly microbial-based products, reliable and rapid plant colonization monitoring methods are essential. We evaluated repetitive element-based (rep) and Random Amplified Polymorphic DNA (RAPD) PCR (Polymerase Chain Reaction) genotyping in a diversity assessment of 251 strains from bulk soil, straw, and manure samples across Serbia, highlighting their discriminative force and the presence of unique bands. RAPD 272, OPG 5, and (GTG)₅ primers were most potent in revealing the high diversity of a sizable environmental Bacillus spp. collection. RAPD 272 also amplified a unique band for a proven biocontrol strain, opening the possibility of Sequence Characterized Amplified Region (SCAR) marker design. That will enable colonization studies using the SCAR marker for its specific detection. This study provides a guide for primer selection for diversity and monitoring studies of environmental Bacillus spp. isolates.

Bacillus benefits the competitive growth of Ambrosia artemisiifolia by increasing available nutrient levels

Bacillus can help plants to acquire nutrients either directly or indirectly. However, the role of Bacillus community on the competitive growth of invasive Ambrosia artemisiifolia is poorly understood. Native Setaria viridis is often found in areas that have been invaded by A. artemisiifolia. We sought to determine whether the quantitative and/or qualitative differences in the Bacillus community present on the invasive A. artemisiifolia and native S.viridis provide a competitive advantage to the invasive over native species. A field experiment was established to imitate the invasion of A. artemisiifolia. The 16S rRNA gene was commercially sequenced to identify the bacilli isolated from the rhizosphere soil of field-grown A. artemisiifolia and S. viridis. The Bacillus communities in their rhizosphere were compared, and their effects on the competitive growth of A. artemisiifolia and S. viridis were tested in the pot experiments. Bacillus in the rhizosphere soil of A. artemisiifolia significantly enhanced its intra-specific competitive ability. The relative abundance of B. megaterium in the rhizosphere soil of A. artemisiifolia was significantly higher than that of S. viridis. Inoculation with B. megaterium that was isolated from the rhizosphere soil of both A. artemisiifolia and S. viridis significantly enhanced the relative competitiveness of A. artemisiifolia and inhibited that of S. viridis. The higher abundance of B. megaterium in the rhizosphere of A. artemisiifolia creates higher levels of available nutrients than that in the native S. viridis, which enhance the competitive growth of A. artemisiifolia. The result helps to discover the mechanism of Bacillus community in the invasion of A. artemisiifolia.

Functional interplay between antagonistic bacteria and Rhizoctonia solani in the tomato plant rhizosphere

Microbial interactions with plant roots play an imperial role in tomato plant growth and defense against the Rhizoctonia solani. This study performed a field experiment with two antagonistic bacteria (Pseudomonas and Bacillus) inoculated in healthy and Rhizoctonia solani treated soil in tomato rhizosphere to understand the metabolic pattern and microbial function during plant disease suppression. In the present study, we assessed soil and microbial enzymes, bacterial and fungal cell forming unit (CFU), and carbon utilization profiling through Bio-Eco plates of rhizoplane samples. Antagonist bacteria and pathogen interaction significantly (p < 0.05) influenced the bacterial count, soil enzymes (chitinase and glucanase), and bacterial function (siderophore and chitinase production). These results indicated that these variables had an imperial role in disease suppression during plant development. Furthermore, the metabolic profiling showed that carbon source utilization enhanced under fruit development and ripening stages. These results suggested that carbon sources were essential in plant/pathogen/antagonist interaction. Substrates like β-methyl-D-glucoside, D-mannitol, D-galacturonic acid, N-acetyl-D-glucosamine, and phenylethylamine strongly connect with the suppuration of root rot disease. These carbon sources may help to propagate a healthy microbial community to reduce the pathogen invasion in the plant root system, and these carbon sources can be stimulators of antagonists against pathogens in the future.

Streptomyces can be an excellent plant growth manager

Streptomyces, the most abundant and arguably the most important genus of actinomycetes, is an important source of biologically active compounds such as antibiotics, and extracellular hydrolytic enzymes. Since Streptomyces can have a beneficial symbiotic relationship with plants they can contribute to nutrition, health and fitness of the latter. This review article summarizes recent research contributions on the ability of Streptomyces to promote plant growth and improve plant tolerance to biotic and abiotic stress responses, as well as on the consequences, on plant health, of the enrichment of rhizospheric soils in Streptomyces species. This review summarizes the most recent reports of the contribution of Streptomyces to plant growth, health and fitness and suggests future research directions to promote the use of these bacteria for the development of a cleaner agriculture.

Re-vitalizing of endophytic microbes for soil health management and plant protection

Soil health management and increase crop productivity are challenging issues for researchers and scientists. Many research publications have given multiple technological solutions for improving soil health and crop productivity but main problem is sustainability of those technologies under field condition and different agro-climatic zone. Due to the random industrialization, deforestation, mining and other environmental factor reduce soil fertility and human health. Many alternative options e.g., crop rotation, green manuring, integrated farming, biofertilizer (plant-growth-promoting microorganism, microbial consortium of rhizosphere soils), and vermicomposting are available for adapting and improving the soil heath and crop productivity by farmers. Recent trends of new research dimension for sustainable agriculture, endophytic microbes and its consortium is one of the better alternative for increasing crop productivity, soil health and fertility management. However, current trends are focuses on the endophytic microbes, which are present mostly in all plant species. Endophytic microbes are isolated from plant parts-root, shoot, leaf, flower and seeds which have very potential ability of plant growth promotion and bio-controlling agent for enhancing plant growth and development. Mostly plant endophytes showed multi-dimensional (synergistic, mutualistic, symbiotic etc.) interactions within the host plants. It promotes the plant growth, protects from pathogen, and induces resistance against biotic and abiotic environmental stresses, and improves the soil fertility. Till date, most of the scientific research has been done on assuming that interaction of plant endophytes with the host is similar like the plant-growth-promoting microorganism (PGPM). It would be very interesting to explore the functional properties of plant endophytes to modulate the essential gene expression during biotic and abiotic stresses. Endophytes have the ability to induce the soil fertility by improving soil essential nutrient, enzymatic activity and influence the other physiochemical property. In this study, we have discussed details about functional properties of plant endophytes and their mechanism for enhancing plant productivity and soil health and fertility management under climate-resilient agricultural practices. Our main objective is to promote and explore the beneficial plant endophytes for enhancing sustainable agricultural productivity.

Endophytic Bacillus Bacteria Living in Sugarcane Plant Tissues and Telchin licus licus Larvae (Drury) (Lepidoptera: Castniidae): The Symbiosis That May Open New Paths in the Biological Control

Bacteria of the genus Bacillus can colonize endophytically and benefit several crops including the control of some pest orders. In view of the benefits provided by these microorganisms and in order to find out an efficient biotechnological control for the giant borer, our interest in studying the microorganisms in symbiosis with sugarcane and the giant borer has arisen, since there is no efficient chemical or biological control method for this pest. Therefore, endophytic Bacillus strains were isolated from three sugarcane niches (apoplast fluid, central internode cylinder and roots) and also from the giant borer larvae living inside sugarcane varieties grown in the Northeast region of Brazil. The taxonomical characterization (16S rRNA) of 157 Gram-positive isolates showed that 138 strains belonged to the Bacillus genus. The most representative species were phylogenetically closely related to B. megaterium (11.5%) followed by B. safensis (10.8%), B. cereus (8.9%), B. oleronius (8.9%), B. amyloliquefaciens (7.0%), and B. pacificus (6.4%). BOX-PCR analyses showed very distinct band pattern profiles suggesting a great diversity of Bacillus species within the sugarcane niches and the digestive tract, while the B. cereus group remained very closely clustered in the dendrogram. According to XRE biomarker analysis, eleven strains (FORCN005, 007, 008, 011, 012, 014, 067, 076, 092, 093, and 135) correspond to B. thuringiensis species. Additional studies using conserved genes (glp, gmk, pta, and tpi) indicated that most of these strains were phylogenetically closely related to B. thuringiensis and may be considered different subspecies. In conclusion, this study suggests that the culturable Bacillus species are greatly diversified within the plant niches and showed Bacillus species in the digestive tract of the giant borer for the first time. These results open new perspectives to understand the role and functions played by these microorganisms in symbiosis with this pest and also the possibility of developing an efficient biological control method for the giant borer using strains identified as the B. thuringiensis species.

Acclimatization of Musa spp. seedlings using endophytic Bacillus spp. and Buttiauxella agrestis strains

The association of different species of endophytic bacteria with the rhizosphere of the host plants can stimulate growth, development and acclimatization, offering a greater quantity of seedlings, in addition to reducing the cycle, providing economic return to the producer. The objective of this study was to evaluate the effect of introduction four bacterial isolates through inoculation into the root system in three banana cultivars (Prata Anã, Grande Naine and BRS Princesa) in the acclimatization phase. The evaluated treatments were: control (nutrient broth without bacteria); Bacillus cereus strain 1 (BC1); Bacillus cereus strain 2 (BC2); Bacillus thuringiensis (BT); Buttiauxella agrestis (BA). The morphological characteristics related to the development of the plants (total height and pseudostem diameter) were evaluated throughout the acclimatization period. After 90 days of transplanting and acclimatization, root length, leaf number, dry root weight, pseudostem and leaf, leaf area, internal carbon concentration, stomatal conductance, photosynthesis rate, transpiration rate, leaf temperature and chlorophyll were evaluated. The bacteria showed different results in relation to the studied cultivars. Considering the morphological and physiological characteristics observed in this study, B. thuringiensis for the cultivars Prata Anã and Grande Naine and the B. agrestis for the cultivar BRS Princesa are recommended for the process of acclimatization of banana seedlings, as they stimulated growth of the plant, increasing the dry mass, besides promoting the growth of roots. In this way, they improved the physiological aspects of the plants and reduced the period of acclimatization of the banana.