Bacillus altitudinis GG-22: A novel plant growth-promoting bacterium with beneficial agronomic properties.

In sustainable agriculture, there is a tendency for an increased use of microbiological preparations, especially plant growth promoting bacteria (PGPB), that can supplement the phenotypic plasticity and adaptability of plants, stimulate their growth and development, increase resistance to stress. The endophytic PGPB could be a promising element of technologies for the improvement of mineral nutrition and promotion of growth and yield of wheat (Triticum spp.). They are transferred to the plant by a horizontal, from the environment (rhizosphere, phyllosphere), or a vertical, from the seeds (from generation to generation), way. The growth-promoting effect of endophytes is mediated by the synthesis and secretion of phytohormones and secondary metabolites as well as their ability to absorb N2, suppress the development of bacterial and/or fungal phytopathogens; improve mineral nutrition. The review elucidates current data on the presence of bacterial endophytes in various organs of wheat plants and their characterization as potential PGPB. Data on the most common genera of bacterial endophytes of wheat (Bacillus, Micrococcus, Staphylococcus, Pseudomonas, Pantoea, Kosakonia, etc.) are presented, and their influence on plants is described, in particular, the effect on the absorption of micronutrients important for plants and humans such as iron (Fe) and zinc (Zn), resistance to stress factors and growth. The varietal differences in the wheat endophytic microbiome are noted. An increased micronutrient absorption and assimilation assisted by the bacterial endophytes are associated with the changes in endogenous auxins and ethylene, the release of organic acids, siderophores, indirect activation of metal transporters, etc. The mechanisms underlying plant growth stimulation are complex due to interactions between a microorganism and the whole plant microbiome and their changes during the plant ontogenesis. The analysis of the published data confirms the need for further studies of the species composition and mechanisms of interaction of endophytic PGPB to develop new strategies for improving mineral nutrition of wheat and trace element biofortification of grain. It is a feasible and promising technology of the future to overcome the problems of hidden hunger and provide quality food products to the world population with available resources and a reduced negative impact on the environment.

Chapter 23 - Plant growth promoting bacteria (PGPB): applications and challenges in bioremediation of metal and metalloid contaminated soils

The effects of drought on growth and seed quality of oilseed crops are of crucial importance in edible oil production due to its pivotal role in sustainable agriculture. Plant growth-promoting bacteria (PGPB) can improve crop yield by promoting plant growth under various environmental conditions. In the present study, the physiological responses, growth, and seed quality of three camelina doubled haploid lines (DH51, DH69, and DH104) were assessed upon their exposure to two irrigation regimes at the presence of Micrococcus yunnanensis during their reproductive phase. The results showed that the investigated parameters of camelina were affected by genotype, irrigation regimes, and PGPB. Drought decreased crop yield as measured by silique length, silique, and seed number and 1000-weight seed. PGPB significantly decreased the adverse effects of stress consistent by increasing the branches per plant and root length. Drought also caused a significant enhancement in the hydrogen peroxide and malondialdehyde contents, but the PGPB-inoculated plants showed lower contents of both compounds. Relative water content significantly reduced in plant grown under stress but inoculation enhanced the potential of water retaining in plants under stress and non-stress conditions. Drought stress and PGPB elevated proline and total soluble carbohydrate content in genotypes. Drought stress had no significant effect on photosynthetic pigments content of genotypes while inoculation apparently moderated negative impact of drought with enhancement of pigments content. The obtained results were responsible for metabolic changes occurring in response to stress. PGPB improved the plant drought-tolerance by enhancing its physiological traits. The fatty acid profile showed some variations among camelina genotypes under drought stress and PGPB inoculation. Upon symbiosis association, an increase was observed in major constituents of polyunsaturated acids, linoleic and linolenic acids, and a significant increase in oleic acid as a main monounsaturated acid. They also altered another major constituent, gadeolic acid, under water deficit stress and/ or with PGPB. Both drought stress and PGPB decreased the poly unsaturated fatty acids/mono unsaturated fatty acids ratio. In general, there was a significant difference among camelina lines in terms of seed yield and quality in response to drought. Also, it strongly suggested that PGPB application can be a positive strategy to mitigate drought stress and increase crop yield.

This review highlights the benefits of mutualistic plant–microbe interactions in enhancing the resilience of emergent crops and underlies the potential of these crops as valuable resources for exploring novel plant growth-promoting bacteria (PGPB). Emergent crops such as quinoa, amaranth, millet, lupins, hemp and desert truffles exhibit physiological and ecological traits that make them suitable for stress-prone environments. PGPB offer sustainable solutions to mitigate abiotic stress by improving nutrient availability, modulating phytohormone levels, enhancing root development and inducing systemic resistance. While their benefits have been extensively documented in model crops under controlled conditions, their application in emergent crops remains underexplored. This review examines current knowledge on the individual and combined roles of these crops and microbes, highlighting specific examples where PGPB have improved plant performance, yield and stress tolerance. Microbial inoculants show potential not only to boost productivity but also to reduce agrochemical inputs, contributing to sustainability. The review also discusses the need for tailored microbial formulations and effective field application strategies to bridge the gap between experimental research and real-world agricultural practices. Identifying key knowledge gaps, it emphasizes the importance of further research on strain specificity, crop-microbe interactions and multi-strain consortia for scalable and climate-smart agriculture. Ultimately, harnessing the synergisms between PGPB with emergent crops could convert marginal lands into productive, climate-smart farms, increasing food security in the face of environmental challenges posed by global climate change.

The application of plant growth-promoting bacteria (PGPB) is vital for sustainable agriculture with continuous world population growth and an increase in soil salinity. Salinity is one of the severe abiotic stresses which lessens the productivity of agricultural lands. Plant growth-promoting bacteria are key players in solving this problem and can mitigate salinity stress. The highest of reported halotolerant Plant growth-promoting bacteria belonged to Firmicutes (approximately 50%), Proteobacteria (40%), and Actinobacteria (10%), respectively. The most dominant genera of halotolerant plant growth-promoting bacteria are Bacillus and Pseudomonas. Currently, the identification of new plant growth-promoting bacteria with special beneficial properties is increasingly needed. Moreover, for the effective use of plant growth-promoting bacteria in agriculture, the unknown molecular aspects of their function and interaction with plants must be defined. Omics and meta-omics studies can unreveal these unknown genes and pathways. However, more accurate omics studies need a detailed understanding of so far known molecular mechanisms of plant stress protection by plant growth-promoting bacteria. In this review, the molecular basis of salinity stress mitigation by plant growth-promoting bacteria is presented, the identified genes in the genomes of 20 halotolerant plant growth-promoting bacteria are assessed, and the prevalence of their involved genes is highlighted. The genes related to the synthesis of indole acetic acid (IAA) (70%), siderophores (60%), osmoprotectants (80%), chaperons (40%), 1-aminocyclopropane-1-carboxylate (ACC) deaminase (50%), and antioxidants (50%), phosphate solubilization (60%), and ion homeostasis (80%) were the most common detected genes in the genomes of evaluated halotolerant plant growth-promoting and salinity stress-alleviating bacteria. The most prevalent genes can be applied as candidates for designing molecular markers for screening of new halotolerant plant growth-promoting bacteria.

Optimistic contributions of plant growth-promoting bacteria for sustainable agriculture and climate stress alleviation

Combined ability of chromium (Cr) tolerant plant growth promoting bacteria (PGPB) and salicylic acid (SA) in attenuation of chromium stress in maize plants

This present study identifies endophytic bacteria from Linum usitatissimum with multidimensional plant growth-promoting attributes, positioning them as ecological engineers for sustainable agriculture. Plant growth-promoting bacteria (PGPB) are present in symbiotic associations with plants or rhizosphere. These microbes enhance crop productivity and resilience under different environmental conditions. Endophytes are a type of PGPB that inhabit inside plant tissues and contribute to plant growth by phytohormone production, phosphate solubilisation, zinc solubilisation, siderophore production, ammonia production, nitrogen fixation, stress tolerance, and biocontrol mechanisms. Twelve bacterial strains were isolated from Linum usitatissimum exhibiting plant growth-promoting attributes such as ammonia and indole-3-acetic acid (IAA) production, siderophore synthesis, phosphate solubilisation, and extracellular enzyme synthesis. The isolated endophytes were also assessed for different enzymatic activities such as; cellulase, pectinase, xylanase, amylase, and gelatinase, which contribute to development of a symbiotic relationship and are crucial for the degradation of plant cell wall components The most efficient endophytes identified in the present study were Pseudomonas sp. strain JL-1 (ESL1) and Staphylococcus sciuri (ESL2), both of which displayed strong plant growth-promoting potential. ESL1 and ESL2 demonstrated promising plant growth-promoting characteristics and cellulase, pectinase, xylanase, amylase, and gelatinase, activity. ESL2 (Staphylococcus sciuri) enhanced nutrient cycling (phosphate solubilisation: 196–209 µg/ml; siderophores: 68–71%) and stress tolerance (IAA: 11–12 µg/ml), reducing reliance on synthetic inputs. By integrating flax microbiomes into agro-ecosystems, we demonstrate a scalable approach to reconcile crop productivity with soil biodiversity conservation. These results demonstrate the potentiality of these endophytic microbes in sustainable agriculture, environmental management, and microbial biotechnology. Further studies on their metabolic pathways may expand their applications in bioremediation and plant-microbe interactions.

Plant disease management via biocontrolbiocontrol of phytopathogensphytopathogens is one of the major approaches to the imagination of sustainable agriculture. Besides agrochemicalsagrochemicals, using inoculants of beneficial bacteriabacteria is a common tool to control fungal and bacterial phytopathogens; they are known as biological control agents (BCAs) or biopesticides. This chapter focuses on using PGPBPGPB (plant growth-promoting bacteriaplant growth-promoting bacteriaPGPBplant growth-promoting bacteria) in consortia to control bacterial and fungal pathogens. The most relevant publicationspublications on biocontrol brought by PGPB in consortia are reviewed, casting insight into the core mechanisms used to achieve effective biocontrol and disease management. In this review, the compatibility and diversity of beneficial PGPB strains, their stability in bioformulationsbioformualtions, environmental safety, and association with various plants have been covered with special emphasis on the mechanisms of biocontrol. There is an urgent requirement for optimization and adjustment of effective PGPB in consortia that can help to improve the biocontrol of phytopathogens in the rhizosphererhizosphere and increase crop productivity while safeguarding human health and environmental integrity.

To overcome abiotic stress such as high salinity or drought, plants will synthesise specific metabolites to enhance the tolerance level. These metabolites are used as markers to relate to the potential metabolite pathways to alleviate salinity or drought stress with enhanced tolerance. The application of plant growth-promoting bacteria (PGPB) is of high potential in reducing the symptoms induced under salinity or drought stress. However, limited studies have reported on the potential metabolite markers to represent the relationship between PGPB and plants to alleviate the salinity or drought stress. This review aims to summarise and develop a novel metabolite framework to relate the potential metabolite markers synthesised under salinity or drought stress as induced by PGPB. The metabolite framework is built based on a range of PGPB-induced metabolite markers modulated in different plants for stress alleviation and growth enhancement. From this review, major metabolite markers induced by PGPB under salinity and drought stress were identified as amino acids (ethylene, indole-3-acetic acid, salicylic acid, and proline) and isoprenoid (abscisic acid) in different plants. This framework is vital for constructing the metabolite network to decipher the underlying mechanisms for PGPB to enhance the tolerance of plants under salinity or drought stress in the future.

Interaction of plant growth promoting bacteria with tomato under abiotic stress: A review

Biofortification of plants using Plant Growth-Promoting Bacteria (PGPB) represents a promising strategy in sustainable agriculture. This paper discusses the PGPB action in the context of their impact on phenolic compounds biosynthesis and the prospects for their application in agriculture. So far, no review article has summarized the significance of PGPB in increasing phenolic compounds in plants. PGPB, such as Pseudomonas, Bacillus, and Azospirillum, promote plant growth by producing phytohormones, enhancing nutrient availability, and stimulating the biosynthesis of secondary metabolites through the activation of Induced Systemic Resistance (ISR). The activation of ISR (Induced Systemic Resistance) by PGPB stimulates the phenylpropanoid pathway, which is the primary biosynthetic route for polyphenolic compounds, including phenolic acids and flavonoids, in plants. Studies indicate that PGPB may increase phenolic compounds content from 9% to over 200%, while simultaneously improving antioxidant activity. Through the secretion of phenolic compounds, PGPB also can mitigate abiotic stresses such as drought, salinity and heavy metal contamination. Among the phenolic compounds whose production in various plant parts can be stimulated by PGPB are flavonoids, such as quercetin, procyanidin B1, EGCG, and catechin, and phenolic acids, including caffeic acid, ferulic acid, and chlorogenic acid. Advancements in omics research will enable a more precise investigation of the impact of PGPB, including endophytic bacteria, on the biosynthetic pathways of phenolic compounds. In the future, this will translate into improved efficiency in stimulating the production of these compounds. Nevertheless, even now, the use of PGPB offers a sustainable alternative to genetic engineering, reducing reliance on chemical inputs in agriculture.

Various bacterial species are associated with plant roots. However, symbiotic and free-living plant growth-promoting bacteria (PGPB) can only help plants to grow and develop under normal and stressful conditions. Several biochemical and in vitro assays were previously designed to differentiate between the PGPB and other plant-associated bacterial strains. This chapter describes and summarizes some of these assays and proposes a strategy to screen for PGPB. To determine the involvement of the PGPB in abiotic stress tolerance, assays for the ability to produce 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, ammonium, gibberellic acid (GA), indole acetic acid (IAA), and microbial volatile organic compounds (mVOCs) are described in this chapter. Additionally, assays to show the capacity to solubilize micronutrients such as potassium, phosphorus, and zinc by bacteria were also summarized in this chapter. To determine the contribution of the PGPB in biotic stress tolerance in plants, Fe-siderophore, hydrogen cyanide, and antibiotic and antifungal metabolites production assays were described. Moreover, assays to investigate the growth-promotion activities of a bacterium strain on plants, using the gnotobiotic root elongation, in vitro, and pots assays, were explained. Finally, an assay for the localization of endophytic bacterium in plant tissues was also presented in this chapter. Although the assays described in this chapter can give evidence of the nature of the mechanism behind the PGPB actions, other unknown growth-promoting means are yet to decipher, and until then, new methodologies will be developed.

Plant growth-promoting bacteria (PGPB) associated with Coffea arabica L. and Coffea canephora Pierre ex Froehner offer a viable strategy to reduce synthetic inputs and enhance resilience in coffee agroecosystems. This review synthesizes evidence from the past decade on rhizosphere-associated and endophytic taxa, their plant growth-promotion and biocontrol mechanisms and the resulting agronomic outcomes. A compartment-specific core microbiome is reported, in the rhizosphere of both hosts, in which Bacillus and Pseudomonas consistently dominate. Within endophytic communities, Bacillus predominates across tissues (roots, leaves and seeds), whereas accompanying genera are host- and tissue-specific. In C. arabica, endophytes frequently include Pseudomonas in roots and leaves. In C. canephora, root endophytes recurrently include Burkholderia, Kitasatospora and Rahnella, while seed endophytes are enriched for Curtobacterium. Functionally, coffee-associated PGPB solubilize phosphate; fix atmospheric nitrogen via biological nitrogen fixation; produce auxins; synthesize siderophores; and express 1-aminocyclopropane-1-carboxylate deaminase. Indirect benefits include the production of antifungal and nematicidal metabolites, secretion of hydrolytic enzymes and elicitation of induced systemic resistance. Under greenhouse conditions, inoculation with PGPB commonly improves germination, shoot and root biomass, nutrient uptake and tolerance to drought or nutrient limitation. Notable biocontrol activity against fungal phytopathogens and plant-parasitic nematodes has also been documented. Key priorities for translation to practice should include (i) multi-site, multi-season field trials to quantify performance, persistence and economic returns; (ii) strain-resolved omics to link taxa to functions expressed within the plant host; (iii) improved bioformulations compatible with farm management and (iv) rationally designed consortia aligned with production goals and biosafety frameworks.

Plant growth-promoting bacteria (PGPB) afford plants several advantages (i.e., improvement of nutrient acquisition, growth, and development; induction of abiotic and biotic stress tolerance). Numerous PGPB strains have been isolated and studied over the years. However, only a few of them are available on the market, mainly due to the failed bacterial survival within the formulations and after application inside agroecosystems. PGPB strains with these challenging limitations can be used for the formulation of cell-free supernatants (CFSs), broth cultures processed through several mechanical and physical processes for cell removal. In the scientific literature there are diverse reviews and updates on PGPB in agriculture. However, no review deals with CFSs and the CFS metabolites obtainable by PGPB. The main objective of this review is to provide useful information for future research on CFSs as biostimulant and biocontrol agents in sustainable agriculture. Studies on CFS agricultural applications, both for biostimulant and biocontrol applications, have been reviewed, presenting limitations and advantages. Among the 109 articles selected and examined, the Bacillus genus seems to be the most promising due to the numerous articles that support its biostimulant and biocontrol potentialities. The present review underlines that research about this topic needs to be encouraged; evidence so far obtained has demonstrated that PGPB could be a valid source of secondary metabolites useful in sustainable agriculture.