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A wide range of prokaryotes produce and excrete bacteriocins (proteins with antimicrobial activity) to reduce competition from closely related strains. Application of bacteriocins is of great importance in food industries, while little research has been focused on the agricultural potential of bacteriocins. A number of bacteriocin producing bacteria are members of the phytomicrobiome, and some strains are plant growth promoting rhizobacteria (PGPR). Thuricin 17 is a single small peptide with a molecular weight of 3.162 kDa, a subclass IId bacteriocin produced by Bacillus thuringiensis NEB17, isolated from soybean nodules. It is either cidal or static to a wide range of prokaryotes. In this way, it removes key competition from the niche space of the producer organism. B. thuringiensis NEB17 was isolated from soybean root nodules, and thus is a member of the phytomicrobiome. Interestingly, thuricin 17 is not active against a wide range of rhizobial strains involved in symbiotic nitrogen fixation with legumes or against other PGPR. In addition, it stimulates plant growth, particularly in the presence of abiotic stresses. The stresses it assists with include key ones associated with climate change (drought, high temperature, and soil salinity). Hence, in the presence of stress, it increases the size of the overall niche space, within plant roots, for B. thuringiensis NEB17. Through its anti-microbial activity, it could also enhance plant growth via control of specific plant pathogens. None of the isolated bacteriocins have been examined as broadly as thuricin 17 on plant growth promotion. Thus, this review focuses on the effect of thuricin 17 as a microbe to plant signal that assists crop plants in managing stress and making agricultural systems more climate change resilient.

Growing environmental concerns are potentially narrowing global yield capacity of agricultural systems. Climate change is the most significant problem the world is currently facing. To meet global food demand, food production must be doubled by 2050; over exploitation of arable lands using unsustainable techniques might resolve food demand issues, but they have negative environmental effects. Current crop production systems are a major reason for changing global climate through diminishing biodiversity, physical and chemical soil degradation, and water pollution. The over application of fertilizers and pesticides contribute to climate change through greenhouse gas emissions (GHG) and toxic soil depositions. At this crucial time, there is a pressing need to transition to more sustainable crop production practices, ones that concentrate more on promoting sustainable mechanisms, which enable crops to grow well in resource limited and environmentally challenging environments, and also develop crops with greater resource use efficiency that have optimum sustainable yields across a wider array of environmental conditions. The phytomicrobiome is considered as one of the best strategies; a better alternative for sustainable agriculture, and a viable solution to meet the twin challenges of global food security and environmental stability. Use of the phytomicrobiome, due to its sustainable and environmentally friendly mechanisms of plant growth promotion, is becoming more widespread in the agricultural industry. Therefore, in this review, we emphasize the contribution of beneficial phytomicrobiome members, particularly plant growth promoting rhizobacteria (PGPR), as a strategy to sustainable improvement of plant growth and production in the face of climate change. Also, the roles of soil dwelling microbes in stress amelioration, nutrient supply (nitrogen fixation, phosphorus solubilization), and phytohormone production along with the factors that could potentially affect their efficiency have been discussed extensively. Lastly, limitations to expansion and use of biobased techniques, for instance, the perspective of crop producers, indigenous microbial competition and regulatory approval are discussed. This review largely focusses on the importance and need of sustainable and environmentally friendly approaches such as biobased/PGPR-based techniques in our agricultural systems, especially in the context of current climate change conditions, which are almost certain to worsen in near future.

Exposure to unfavorable conditions is becoming more frequent for plants due to climate change, posing a threat to global food security. Stressful temperature, as a major environmental factor, adversely affects plant growth and development, and consequently agricultural production. Hence, development of sustainable approaches to assist plants in dealing with environmental challenges is of great importance. Compatible plant-microbe interactions and signal molecules produced within these interactions, such as bacteriocins, could be promising approaches to managing the impacts of abiotic stresses on crops. Although the use of bacteriocins in food preservation is widespread, only a small number of studies have examined their potential in agriculture. Therefore, we studied the effect of three concentrations of Thuricin17 (Th17), a plant growth-promoting rhizobacterial signal molecule produced by Bacillus thuringiensis , on germination and vegetative growth of canola ( Brassica napus L.) under stressful temperatures. Canola responded positively to treatment with the bacterial signal molecule under stressful temperatures. Treatment with 10 -9 M Th17 (Thu2) was found to significantly enhance germination rate, seed vigor index, radical and shoot length and seedling fresh weight under low temperature, and this treatment reduced germination time which would be an asset for higher latitude, short growing season climates. Likewise, Thu2 was able to alleviate the adverse effects of high temperature on germination and seed vigor. Regarding vegetative growth, interestingly, moderate high temperature with the assistance of the compound caused more growth and development than the control conditions. Conversely, low temperature negatively affected plant growth, and Th17 did not help overcome this effect. Specifically, the application of 10 -9 (Thu2) and 10 -11 M (Thu3) Th17 had a stimulatory effect on height, leaf area and biomass accumulation under above-optimal conditions, which could be attributed to modifications of below-ground structures, including root length, root surface, root volume and root diameter, as well as photosynthetic rate. However, no significant effects were observed under optimal conditions for almost all measured variables. Therefore, the signal compound tends to have a stimulatory impact at stressful temperatures but not under optimal conditions. Hence, supplementation with Th17 would have the potential as a plant growth promoter under stressed circumstances.

Background Bacillin 20 1 has been shown to act as a biostimulant, it enhances seed germination and increases the biomass of soybean and canola plants. However, the mechanisms underlying these benefits, and their impacts on the plant-associated microbiome, remain unquantified. In this study, we investigated the causal effects of bacillin 20 on the bacterial communities associated with canola. Results We conducted a field study with three different concentrations of bacillin 20 as seed treatment and foliar spray on canola cultivar InVigor L233P followed by a randomized complete block design in clay loam and sandy loam soils and investigated how bacillin 20 influences the structure and richness of bacterial communities across biotypes, including those in root tissues and rhizosphere soil. Our findings revealed that rhizosphere soil bacterial communities clustered closely in the studied clay loam soil. Bacterial alpha diversity did not respond significantly to bacillin 20 treatments, however, Rhizobiales bacteria become most abundant in the rhizosphere soil. Also, four bacteria- Rosemicrobium sp., Sphingomonas sp. and two unclassified Planctomycetes were identified as indicator species in the microbial communities from both clay-loam and sandy-loam soils. We analysed causal relationships between the effects of bacillin 20 and experimentally controlled factors affecting bacterial communities, such as those associated with root tissue, soil and treatment (bacillin 20) types. Some bacterial taxa—ASV55 ( Candidatus Xiphinematobacter ) were negatively affected by bacillin 20 foliar treatment, and ASV73 (unidentified Tepidisphaerales) by seed treatment. Conclusion Overall, our study revealed key explanatory variables influencing the effect of bacillin 20 on the bacterial communities associated with canola roots and rhizosphere soil. Although soil type (clay versus sandy loam) did not directly affect the bacterial communities, we found that bacillin 20 affected the canola root system associated microbiota. This shifts in the associated bacteria could be influenced by developmental stages, not by the treatment of bacillin 20 alone.

Under natural conditions, plants are always associated with a well-orchestrated community of microbes—the phytomicrobiome. The nature and degree of microbial effect on the plant host can be positive, neutral, or negative, and depends largely on the environment. The phytomicrobiome is integral for plant growth and function; microbes play a key role in plant nutrient acquisition, biotic and abiotic stress management, physiology regulation through microbe-to-plant signals, and growth regulation via the production of phytohormones. Relationships between the plant and phytomicrobiome members vary in intimacy, ranging from casual associations between roots and the rhizosphere microbial community, to endophytes that live between plant cells, to the endosymbiosis of microbes by the plant cell resulting in mitochondria and chloroplasts. If we consider these key organelles to also be members of the phytomicrobiome, how do we distinguish between the two? If we accept the mitochondria and chloroplasts as both members of the phytomicrobiome and the plant (entrained microbes), the influence of microbes on the evolution of plants becomes so profound that without microbes, the concept of the “plant” is not viable. This paper argues that the holobiont concept should take greater precedence in the plant sciences when referring to a host and its associated microbial community. The inclusivity of this concept accounts for the ambiguous nature of the entrained microbes and the wide range of functions played by the phytomicrobiome in plant holobiont homeostasis.

Plant growth-promoting microorganisms (PGPMs) and the specific compounds they produce have the capacity to mitigate the adverse effects of stressors on plants. An example in this regard is Thuricin 17 (Th17), a signal molecule produced by Bacillus thuringiensis NEB17 ( Bt NEB17), a plant growth-promoting rhizobacterium. In this study, we aimed to determine the efficacy of Th17 in mitigating drought and the combination of drought and heat stress in canola [ Brassica napus (L.)] . Two of the best Th17 concentrations, 10 −9 (Th1) M and 10 −11 (Th2) M, were used either as seed treatment plus root drenching or foliar spray. Leaf area and biomass accumulation was increased by both application methods of Th1 under moderate and severe drought stress, whereas more promising results were seen from Th2-treated plants under the combination of stressors. Additionally, root length, root surface, and root volume were increased by 21%, 22%, and 23%, respectively, for plants grown from Th1 seed treatment plus root drenching compared to controls under severe drought conditions. Moreover, SOD, POD, and CAT contents were increased by spraying Th1 and Th2 under individual stresses and the combination of heat and drought, respectively. Accordingly, increases in physiological variables were observed for sprayed plants, which also had higher antioxidant contents. These results indicated that plant responses to the compound varied with concentration of Th17 and plant growth conditions. Specifically, when plants were grown under an individual stress condition, either drought or heat, the higher level of Th17 was more effective, whereas the lower dose demonstrated higher positive impacts under the combination of heat and drought. Regarding application method, both seed treatment plus root drenching and foliar spray had the ability to assist plants in alleviating stresses through growth stimulatory mechanisms. Therefore, Th17 has potential to become an environmentally friendly biostimulant, particularly under stressful environmental conditions.

Terrestrial plants evolution occurred in the presence of microbes, the phytomicrobiome. The rhizosphere microbial community is the most abundant and diverse subset of the phytomicrobiome and can include both beneficial and parasitic/pathogenic microbes. Prokaryotes of the phytomicrobiome have evolved relationships with plants that range from non-dependent interactions to dependent endosymbionts. The most extreme endosymbiotic examples are the chloroplasts and mitochondria, which have become organelles and integral parts of the plant, leading to some similarity in DNA sequence between plant tissues and cyanobacteria, the prokaryotic symbiont of ancestral plants. Microbes were associated with the precursors of land plants, green algae, and helped algae transition from aquatic to terrestrial environments. In the terrestrial setting the phytomicrobiome contributes to plant growth and development by (1) establishing symbiotic relationships between plant growth-promoting microbes, including rhizobacteria and mycorrhizal fungi, (2) conferring biotic stress resistance by producing antibiotic compounds, and (3) secreting microbe-to-plant signal compounds, such as phytohormones or their analogues, that regulate aspects of plant physiology, including stress resistance. As plants have evolved, they recruited microbes to assist in the adaptation to available growing environments. Microbes serve themselves by promoting plant growth, which in turn provides microbes with nutrition (root exudates, a source of reduced carbon) and a desirable habitat (the rhizosphere or within plant tissues). The outcome of this coevolution is the diverse and metabolically rich microbial community that now exists in the rhizosphere of terrestrial plants. The holobiont, the unit made up of the phytomicrobiome and the plant host, results from this wide range of coevolved relationships. We are just beginning to appreciate the many ways in which this complex and subtle coevolution acts in agricultural systems.

Canola (Brassica. napus), one of the main oilseed crops, is widely cultivated worldwide. However, canola crop productivity has declined under stressful conditions due to climate change. Hence, developing sustainable strategies to assist plants in coping with environmental stressors is essential. Plant growth promoting microorganisms (PGPMs) and specific compounds they produce might have the capacity to mitigate the adverse effects of stressful conditions on plants. An example in this context is Thuricin 17 (Th17), a bacteriocin produced by Bacillus thuringiensis NEB17 (BtNEB17), a plant growth promoting rhizobacterium. While bacteriocins are broadly used in food preservation, their potential in agriculture has received little attention. Therefore, we examined the efficacy of Th17 as a plant biostimulant under a range of stressful conditions in both controlled environments and agriculture field conditions.At the first stage, we studied the effect of three concentrations of Th17, including 10⁻⁷, 10⁻⁹ and 10⁻¹¹ M, on germination and vegetive growth under stressful temperatures (chapter 3). The 10⁻⁹ M level significantly enhanced germination rate, seed vigor index, radical and shoot length and seedling fresh weight under low temperature, and this treatment reduced germination time compared to 10⁻⁷ and 10⁻¹¹ M, and controls. During vegetive growth, seed treatment plus root drenching of both 10⁻⁹ and 10⁻¹¹ M had a stimulatory effect on height, leaf area and biomass accumulation under stressed conditions, which could be associated with modifications of root system structure and photosynthetic rate. No significant effects were observed under optimal conditions.In another controlled environment study (chapter 4), the impacts of 10⁻⁹ and 10⁻¹¹ M Th17, either as seed treatment plus root drenching or foliar spray were assessed under PEG-induced drought, heat and combination of heat and drought levels. The 10⁻⁹ M level stimulated growth under induvial stresses while 10⁻¹¹ M seemed more effective once heat and drought occurred simultaneously. Total root length, total root volume and root surface were improved by treating seeds with 10⁻⁹ M followed by root drench under drought conditions. In contrast, foliar spraying of both doses enhanced antioxidant enzyme levels. Additionally, increases in photosynthetic rate were reported from those sprayed plants, which also had higher superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) contents.As the primary goal of this project was to determine whether Th17 can improve canola yields (chapter 5), a two-year (2020 and 2021) field study across two soil types (clay loam and sandy loam) at two seeding dates was conducted in southern Québec, Canada. Concentrations of 10⁻⁹ and 10⁻¹¹ M were applied either as seed treatment or foliar application. Due to specific adverse environmental conditions, there were variations in sowing periods, phenological plant cycles and sampling points, which all led to inconsistency in data sets and Th17 responses across field-trial years. The 10⁻¹¹ M dose caused greater seed yields; however, responses to application methods varied at specific field sites. Foliar spray of 10⁻¹¹ M Th17 increased yields by 26% on clay loam and 21% on sandy loam compared to controls at the first seeding dates in 2020. Conversely, significant results were seen from 10⁻¹¹ M seed-treated plots in 2021; yields were 24% higher than controls on clay loam soil at the first seeding and 23% more on sandy loam soil at the second seeding in 2021.

Understanding how biostimulants modulate plant-associated microbiomes is critical for advancing sustainable agriculture. Here, we investigated the effects of Bacillus-derived bacillin 20 on the root and rhizosphere microbiomes of soybean (Glycine max) using amplicon-based profiling, community ecology, and network analysis. Microbial community assembly was driven primarily by plant compartmentalization, with higher bacterial richness in the rhizosphere and stronger host filtering in root-associated microbiomes. PERMANOVA analysis indicated that compartment explained most of the variation in community structure, whereas bacillin 20 treatment had no statistically significant effect. Despite no meaningful shifts in alpha diversity, bacillin 20 was associated with subtle, non-significant compositional trends in specific taxa across treatments. Indicator species and core microbiome analyses revealed compartment-specific taxa with potential roles in nutrient cycling, stress tolerance, and plant growth promotion. Bacillin 20 was associated with changes in cross-domain microbial co-occurrence patterns, including differences in network connectivity, particularly in the rhizosphere, where several fungal ASVs (e.g., ASV33, ASV5, ASV8, and ASV88) exhibited high centrality. These findings indicate that bacillin 20 is associated with changes in microbial interaction patterns while maintaining overall community diversity. Overall, treatment effects were minor relative to compartment-driven structuring of the microbiome. Together, our results suggest that microbiome-informed approaches, including the use of targeted biostimulants, may contribute to the management of plant-microbe interactions in agricultural systems. Future studies integrating multi-omics approaches will be required to elucidate the underlying mechanisms of these interactions.