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The use of beneficial microorganisms to enhance phosphate fertilizer use efficiency and solubilize residual phosphorus (P) is a promising strategy to improve soil P availability for plants. This study tested the hypothesis that inoculation with arbuscular mycorrhizal fungi, either alone or in combination with Bacillus subtilis , enhances maize growth and optimizes nutrient availability, particularly phosphorus. The experiment was conducted under greenhouse conditions with four replications, following an 8 × 3 factorial design. Treatments included individual inoculations with Bacillus subtilis (IPACC26), Rhizophagus clarus (RJN102A), Claroideoglomus etunicatum (SCT101A), and a commercial inoculant of Rhizophagus intraradices (Rootella BR ULTRA), as well as three co-inoculations (IPACC26 combined with each fungus) and a non-inoculated control. These treatments were combined with three levels of phosphate fertilization (0, 50, and 100% of the recommended P level). Mycorrhizal colonization improved root architecture and increased photosynthetic pigments and uptake of P and other nutrients, resulting in greater plant growth and biomass production. The most pronounced effects were observed in plants inoculated with R. clarus and C. etunicatum , either alone or in combination with B. subtilis , at the 0 and 50% P levels. At 0% P, inoculated plants accumulated significantly more biomass, with root and shoot dry mass up to 3,000% and 680% higher, respectively, than those of uninoculated plants; this effect was associated with a 1,700% increase in shoot P accumulation compared to the control. These findings highlight the potential of these inoculants as biofertilizers for more sustainable and efficient phosphorus management in maize cultivation.

Background Plant microbiota has received increasing attention in recent years. In particular, the microbiota associated with cereals is being extensively studied to identify bacterial strains that can promote plant health and growth. Barley is the fourth most important cereal worldwide in terms of agricultural production. Intensive barley agriculture requires the use of chemical fertilizers to compensate for nutrient deficiencies in soils and limit pathogen development. The isolation and use of bacteria that can enhance the bioavailability of soil nutrients and inhibit the development of plant pathogens could ultimately limit the use of these chemicals. In this study, we have isolated from a barley microbiota three bacterial strains belonging to the genus Streptomyces. These strains were characterized and named GPA1, GPAT2, and GPN2. Results These three closely related isolates were from the same bacterial genus Streptomyces . Based on a phylogenetic analysis, the strains GPAT2 and GPN2 were classified as Streptomyces murinus , while GPA1 was identified as a new species. All strains showed antagonistic activity against two microorganisms that inhibit barley germination: Pseudomonas sp. MRN1 and Fusarium sp. CK. In addition, these strains exhibited different effects on the growth of barley cultivated under hydroponic and axenic conditions. In fact, GPN2 appeared to have no effect whereas the inoculation of barley seedlings with GPAT2 and GPA1 resulted in a reduction and an increase in root length after two weeks of growth, respectively. GPA1 had various Plant Growth-Promoting (PGP) abilities, including phosphate and zinc solubilization and siderophore production. A metabolite profiling of the GPA1 bacterial culture also showed its production and excretion of indole-3-acetic acid (IAA). Conclusion In this study, we have characterized three closely related bacteria, which display different effects on barley seedlings growth. These results revealed that the type of interactions of Streptomyces with barley is strain-dependent, suggesting that these interactions may arise from specific molecular mechanisms acquired through coevolutionary processes.

Wheat is the main staple food in the world, so it is the backbone of food security. Drought not only affects growth and development but also ultimately has a severe impact on the overall productivity of crop plants. Some bacteria are capable of producing exopolysaccharides (EPS) as a survival mechanism, along with other metabolites, which help them survive in stressful conditions. The present study was conducted with the aim of inducing drought stress tolerance in wheat through EPS-producing plant growth-promoting rhizobacteria (PGPR). In this regard, a series of laboratory bioassays were conducted with the aim to isolating, characterizing, and screening the EPS-producing PGPR capable of improving wheat growth under limited water conditions. Thirty rhizobacterial strains (LEW1–LEW30) were isolated from the rhizosphere of wheat. Ten isolates with EPS-producing ability were quantitatively tested for EPS production and IAA production ability. Four of the most efficient EPS-producing strains (LEW3, LEW9, LEW16, and LEW28) were evaluated for their drought tolerance ability along with quantitative production of EPS and IAA under polyethylene glycol (PEG-6000)-induced drought stress. The jar experiment was conducted under gnotobiotic conditions to examine the drought-tolerant wheat genotypes, and two wheat varieties (Johar-16, and Gold-16) were selected for further experiments. The selected varieties were inoculated with EPS-producing rhizobacterial strains and grown under control conditions at different stress levels (0, 2, 4, and 6% PEG-6000). The strain LEW16 showed better results for improving root morphology and seedling growth in both varieties. The maximum increase in germination, growth parameters, percentage, root diameter, root surface area, and root colonization was recorded in Johar-16 by inoculating LEW16 at 6% PEG-6000. Plant growth-promoting traits were tested on the top-performing strains (LEW3, LEW9, and LEW16). Through 16S rRNA sequencing, these strains were identified as Chryseobacterium sp. (LEW3), Acinetobacter sp. (LEW9), and Klebsiella sp. (LEW16), and they showed positive results for phosphorous and zinc solubilization as well as hydrogen cyanide (HCN) production. The partial sequencing results were submitted to the National Center for Biotechnology Information (NCBI) under the accession numbers MW829776, MW829777, and MW829778. These strains are recommended for their evaluation as potential bioinoculants for inducing drought stress tolerance in wheat.

Endophytic bacteria inhabit plant tissues such as roots, stems, leaves, fruits, and seeds and can multiply inside plant tissue without damaging them. This study involves the isolation, characterization, metabolic profiling, and effect of endophytic bacteria isolated from the roots of Scots pine ( Pinus sylvestris ), on the growth of sunflower. In the current study, fifteen isolates of endophytic bacteria were obtained from the roots of Scots pine, and their molecular characterization was performed using 16 s rRNA ribotyping. The molecular characterization revealed that the strains belonged to Bacillus spp., Pseudomonas spp., Micrococcus sp., Serratia sp., Enterobacter sp., Pantoea sp., Staphylococcus sp., and Microbacterium sp. Among the isolated strains, 9 strains showed positive results for ammonium production, 12 strains for calcium solubilization, 11 strains for magnesium solubilization, 5 strains for zinc solubilization, 12 strains for phosphate solubilization, 8 strains for potassium solubilization, 10 strains for indole acetic acid (IAA) production, 9 strains for siderophore, and 6 strains for hydrogen cyanide (HCN) production. The greenhouse experiment results demonstrated that all isolated endophytic bacteria improved the shoot length, dry weight, and chlorophyll content of sunflower, whereas a significant increase was observed by PS-3 ( Bacillus cereus ), PS-6 ( Serratia marcescens ), and PS-8 ( Pseudomonas putida ). Besides, the concentration of nitrogen, phosphorus, and potassium were also measured in sunflower shoots, and results asserted that bacterial inoculation increased the bioavailability of these essential nutrients to plants compared to uninoculated control. Thus, these endophytic bacteria could be used as an encouraging option to improve plant growth and performance.

Endophytic insect pathogenic fungi have a multifunctional lifestyle; in addition to its well-known function as biocontrol agents, it may also help plants respond to other biotic and abiotic stresses, such as iron (Fe) deficiency. This study explores M. brunneum EAMa 01/58-Su strain attributes for Fe acquisition. Firstly, direct attributes include siderophore exudation (in vitro assay) and Fe content in shoots and in the substrate (in vivo assay) were evaluated for three strains of Beauveria bassiana and Metarhizium bruneum. The M. brunneum EAMa 01/58-Su strain showed a great ability to exudate iron siderophores (58.4% surface siderophores exudation) and provided higher Fe content in both dry matter and substrate compared to the control and was therefore selected for further research to unravel the possible induction of Fe deficiency responses, Ferric Reductase Activity (FRA), and relative expression of Fe acquisition genes by qRT-PCR in melon and cucumber plants.. In addition, root priming by M. brunneum EAMa 01/58-Su strain elicited Fe deficiency responses at transcriptional level. Our results show an early up-regulation (24, 48 or 72 h post inoculation) of the Fe acquisition genes FRO1, FRO2, IRT1, HA1, and FIT as well as the FRA. These results highlight the mechanisms involved in the Fe acquisition as mediated by IPF M. brunneum EAMa 01/58-Su strain.

Various microorganisms colonize plant tissues either through epiphytic (surface), endophytic (inside), or rhizospheric association. The diverse phyllosphere microbiomes interact with plant host either through mutualism, commensalism, and/or pathogenesis, and affect the functioning of various biological processes in plants. Among these microbes, beneficial phyllospheric microorganisms have been demonstrated to positively affect plant growth through multiple mechanisms including enhanced availability of nutrients through nitrogen fixation; solubilization of phosphorous, potassium, and zinc; and production of siderophores and growth-promoting hormones. The indirect mode of plant growth stimulation includes inhibition of pathogens by antagonistic phyllospheric microbes, production of ACC deaminase enzyme, exopolysaccharide secretion, and mitigation of abiotic stresses. Application of beneficial phyllospheric microorganisms as biofertilizers and biocontrol agents has been found to suppress plant diseases and resulted in promotion of plant biomass and development, and increases in crop yield in majority of field trials. In addition, these microbes have been demonstrated to preserve soil fertility and microbial biodiversity along with reduced use of chemical fertilizers and pesticides. However, knowledge on the molecular responses modulated in host plants due to application of phyllospheric microbes is still incomplete. This article provides an up-to-date overview on the prevalence and diversity of the phyllospheric microbes, their growth-promoting traits, and different mechanisms of action employed to increase plant health and crop yield after foliar spray or soil inoculation. Furthermore, bioengineering of phyllospheric microbes is discussed to enhance their biological functioning with a better ability to benefit crop plants, and resulting in improved food production to feed the world’s ever-increasing population through an eco-friendly and sustainable approach.

Microbial population of soils irrigated with industrial wastewater may contain certain exopolysaccharides (EPS) and indole-3-acetic acid (IAA) producing bacterial strains having the ability to tolerate heavy metals along with plant growth–promoting (PGP) traits. As cadmium is one of the most toxic heavy metals for soils, plants, animals, and human beings, the present study was planned to isolate and characterize EPS- and IAA-producing, Cd-tolerant bacterial strains having tolerance against heavy metals along with plant growth–promoting traits. A total of 30 rhizobacterial strains (FN1–FN30) were isolated from rhizosphere soil collected from fields around industrial areas and roadsides irrigated with industrial wastewater. Out of these, eight isolates with the combined ability of IAA production and EPS production were characterized for PGP traits. On the basis of multifarious PGP traits and the results of root colonization assay, three most efficient EPS- and IAA-producing, Cd-tolerant plant growth–promoting strains, i.e., FN13, FN14, and FN16, were selected for multiple metal (Cd, Pb, Ni, and Cu) tolerance test along with quantification of growth, and IAA and EPS production abilities under Cd stress. Increasing levels of Cd stress negatively affected the tested characteristics of these strains, but FN13 showed more stability in growth, IAA production (18.24 μg mL −1 ), and EPS production (148.99 μg mL −1 ) compared to other strains under Cd stress. The morphological and biochemical analysis confirmed FN13 as Gram-positive, rod-shaped bacteria with smooth colonies of yellow appearance. The strain FN13 has strong root colonization (3.36 × 10 6 CFU g −1 ) ability for mustard seedlings and can solubilize Zn and phosphate along with the production of HCN, ammonia, and siderophores. The 16S rRNA sequencing confirmed it as the Bacillus safensis strain FN13. It can be explored as potential phytostabilizing biofertilizer for heavy metal–contaminated soils.

Purpose In sustainable agriculture, microbial allies like purple non-sulfur bacteria (PNSB) are becoming increasingly important. This study investigates the potential of PNSB strains A3-5 and F3-3, highlighting their unique abilities in nutrient solubilization, fixation, and production of plant growth-promoting substances. Methods The study investigates the metabolic capabilities of the strains, including the synthesis of 5-aminolevulinic acid (5-ALA) and indole-3-acetic acid (IAA), nitrogen (N 2 ) fixation, and the solubilization of essential minerals such as phosphorus (P), calcium (Ca), and zinc (Zn), as well as siderophore production. Additionally, the strains’ abilities were tested in hydroponic systems with rice seedlings under normal (pH = 4.70) and acidic (pH = 3.64) conditions to evaluate their potential for promoting plant growth across different pH levels. Results Both the individual strains and their combined culture demonstrated beneficial traits conducive to plant growth. The A3-5 strain exhibited superior performance in Zn solubilization (solubilization index of 2.86), IAA production (159.1 µg/mL), and siderophore production (2.72 cm). Conversely, the F3-3 strain demonstrated a superior ability for N 2 -fixation (9.33 mg/L) and P solubilization capacity (20 mg/L). The mixed culture amalgamated the highest siderophore production (3.09 cm) and 5-ALA production (6.10 µg/mL). Notably, the F3-3 strain of PNSB significantly enhanced both root and shoot growth under normal and acidic conditions, with the most remarkable effect being a 189% surge in fresh shoot weight under acidic conditions. Conclusion F3-3 strain, with its robust performance and plant growth enhancement, is promising for sustainable farming. Despite mixed culture’s higher yield of beneficial compounds, F3-3 holds more practical potential. However, as the study was conducted in a controlled environment, field studies are necessary to confirm these findings and understand the strain’s real-world performance. 

The ability of microorganisms to promote plant growth and mitigate abiotic and biotic stresses makes them an interesting tool for sustainable agriculture. Numerous studies aim to identify new, promising bacteria isolates. Traditional culture-based methods, which focus on selecting microorganisms with plant-growth-promoting traits, such as hormone production, nutrient solubilization, and antifungal properties, are widely used. This study aims to investigate the role of plant-growth-promoting properties in bacteria-mediated stress mitigation and the suitability of traditional culture-based methods as a screening tool for the identification of beneficial bacteria. To this end, we tested three endophytic Bacillus isolates, which have previously been shown to affect tolerance against iron toxicity in lowland rice, (a) for their effect on the resistance against brown spot disease, and (b) for plant-growth-promoting traits using common culture-based methods. Both B. pumilus isolates inhibited fungal growth in vitro and reduced brown spot disease in two of three rice cultivars in planta, although they tested negative for all plant-growth-promoting traits. While B. megaterium was negative for ACC deaminase activity and nutrient solubilization, it exhibited auxin production. Nevertheless, B. megaterium did not suppress brown spot disease in any of the three rice cultivars. This study shows that bacteria do not necessarily have to possess classical plant-growth-promoting properties in order to be beneficial to plants, and it emphasizes the limitation of common culture-based methods in effectively identifying beneficial bacteria. Moreover, our results highlight the significance of the interaction between bacteria and plant cultivars in determining the beneficial effects of Bacillus spp. on plants under biotic or abiotic stresses.