Plant Growth-promoting Bacteria Research Articles

A plant growth-promoting bacterium supports cadmium detoxification of rice by inducing phenylpropanoid and flavonoid biosynthesis

Cadmium (Cd) is easily absorbed by rice and enters the food chain, posing a health risk to humans. Plant growth promoting bacteria (PGPB) can help the plant respond to Cd stress, but the mechanism of PGPB for Cd reduction is unclear. Therefore, this study was conducted and found inoculation with a newly isolated Pseudomonas koreensis promoted the growth of rice and reduced its Cd content. Fluorescent staining using PI and H2O2 probe indicated that PGPB attenuated oxidative damage in rice. Metabolomics revealed that 59 metabolites were upregulated after inoculation, with phenylpropanoids and flavonoids being significantly activated. Spectrophotometry analysis comfirmed the content of flavonoid, lignin, phenol, glutathione, proline and the activities of antioxidant enzymes were higher in the inoculated rice than in the control. Quantitative PCR showed the expression of genes related to phenylpropanoids (OsPAL, OsC4H, Os4CL) and flavonoids (OsCHS, OsCHI) was significantly increased by PGPB, while the genes of heavy metal transporters (OsNRAMP5, OsHMA2, OsIRT1) were significantly decreased. Overall, this study provides an insight into the PGPB-mediated detoxification mechanism in rice under Cd stress and emphasizes the role of phenylpropanoids and flavonoids in the production of low-Cd rice to ensure human health. Environmental ImplicationRice production and human health are affected by cadmium (Cd) in soil. This is the first study to integrate multiple technical approaches (i.e. metabolomics, morphology, physiology and molecular biology) to reveal the detoxification mechanism mediated by plant growth-promoting bacteria (PGPB) in rice in response to Cd. This study novelly revealed that inoculation with PGPB resulted in higher grain yield and lower Cd content by inducing the biosynthesis of phenylpropanoid and flavonoid in rice. This provided a theoretical basis for future practical regulation of Cd accumulation in crops using PGPB and ensured food safety and human health.

From intercropping to monocropping: the effects of Pseudomonas strain to facilitate nutrient efficiency in peanut and soil

As an oilseed crop, the yield and quality of peanuts are severely constrained by nutrient deficiencies, particularly in calcareous soils in northern China. Maize-peanut intercropping is an effective strategy to enhance mineral nutrient efficiency in peanuts via plant-microbe interaction, but the underlying mechanisms remain elusive. Here, we conducted experiments using a Pseudomonas strain (Pse.IP6) with diverse beneficial characteristics, which was isolated from the rhizosphere of intercropped peanuts. Additionally, Pse.IP6 exhibits high phylogenetic similarity with the Amplicon Sequence Variants 48 (ASV48) which belongs to Pseudomonas and is positively correlated with Fe in plants and soil in intercropping. To confirm the plant growth-promoting potential of Pse.IP6 and its role in intercropping advantage, we constructed pot experiments. Results revealed that Pse.IP6 promoted shoot growth and root development, as well significantly enhanced SPAD value, net photosynthetic rate, stomatal conductance, and transpiration rate of peanut leaves. Moreover, the application of Pse.IP6 resulted in a notable accumulation of nitrogen (N), phosphorus (P), and potassium (K) in shoot and active iron (Fe) in leaves, accompanied by an increased K-N ratio. The primary reason for the nutrient promotion is the enhancement of the bioavailability of nitrate, ammonium, P, K, and Fe in the rhizosphere. Collectively, our findings demonstrate that Pse.IP6, enriched in intercropping peanut, is a plant growth-promoting bacteria, represented by transferring the intercropping advantage on nutrients activation to monocropping peanuts. Our results offer insights into plant-rhizobacteria interaction mechanisms and therefore provide a rhizobacteria-based pathway to improve nutrient efficiency and productivity of crops.

Complete genome sequence of Bradyrhizobium lupini LLZ14, a nitrogen-fixing and plant growth-promoting bacterium.

In this study, we present the complete genome of Bradyrhizobium lupini LLZ14, a nodule-forming bacterium isolated from Lupinus luteus root nodules with high plant growth-promoting abilities. This genome contains genes predicted to be involved in plant stress tolerance and growth promotion, including auxin production, phosphatase, and 1-aminocyclopropane-1-carboxylate deaminase.

The Potential Role of Brassica napus Metallothioneins in Salt Stress and Interactions with Plant Growth-Promoting Bacteria

The Potential Role of Brassica napus Metallothioneins in Salt Stress and Interactions with Plant Growth-Promoting Bacteria

Plant Growth-Promoting Effect and Complete Genomic Sequence Analysis of the Beneficial Rhizosphere Streptomyces sp. GD-4 Isolated from Leymus secalinus

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria residing in the rhizosphere and are capable of enhancing plant growth through various mechanisms. Streptomyces sp. GD-4 is a plant growth-promoting bacterium isolated from the rhizosphere soil of Leymus secalinus. To further elucidate the molecular mechanisms underlying the beneficial effects of the strain on plant growth, we evaluated the growth-promoting effects of Streptomyces sp. GD-4 on forage grasses and conducted comprehensive genome mining and comparative genomic analysis of the strain. Strain GD-4 effectively colonized the rhizosphere of three forages and significantly promoted the growth of both plant roots and leaves. Genome sequence functional annotation of GD-4 revealed lots of genes associated with nitrogen, phosphorus, and sulfur metabolism. Additionally, genes potentially involved in plant growth promotion such as indole-3-acetic acid (IAA) biosynthesis, trehalose production, siderophore production, and phosphate solubilization were annotated. Whole-genome analysis revealed that GD-4 may possess molecular mechanisms involved in soil nutrient cycling in rhizosphere soil and plant growth promotion. The bacteria also possess genes associated with adaptability to abiotic stress conditions, further supporting the ability of Streptomyces sp. GD-4 to colonize nutrient-poor soils. These findings provide a foundation for further research into soil remediation technologies in plateau regions.

Non-native PGPB consortium consisting of Pseudomonas sp. G31 and Azotobacter sp. PBC2 promoted winter wheat growth and slightly altered the native bacterial community

Plant growth-promoting bacteria (PGPB) are considered an effective eco-friendly biostimulator. However, relatively few studies have examined how PGPB affect the native bacterial community of major crops. Thus, this study investigates the impact of a PGPB consortium, comprising Pseudomonas sp. G31 and Azotobacter sp. PBC2 (P1A), on the soil bacterial community of wheat under field conditions. As a result of PGPB application, we observed a significant increase in seed yield, as well as in nitrate content (1st and 3rd time points) and available phosphorus (2nd time point) in the rhizosphere compared to control. For the metataxonomic study, Next-Generation Sequencing was performed using the Illumina NovaSeq 6000 system. The consortium used did not have a significant impact on the diversity of native soil bacteria and slightly affected the taxonomic composition of bacteria with no significant changes in bacterial dominants at the phylum and genus level. Nevertheless, 3 weeks after application, P1A increased the relative abundance of Nitrospira which could have influenced the increase in nitrates in the rhizosphere, and also decreased Bdellovibrio. The results indicate that the P1A consortium, due to its ability to promote plant growth without detrimental alternations in the bacterial community of the soil, may be a potential candidate for commercialization.

Characterization, Identification, and Biosafety Evaluation of Multifaceted Traits of Plant Growth-Promoting Endophytes for Ameliorating Productivity of Forage Sorghum.

Endophytes are bacteria that inhabit host plants for most of their life cycle without causing harm. In the study, 15 endophytic bacteria were isolated from 30 forage Sorghum plants and assessed for various plant growth-promoting (PGP) traits, such as phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, ammonia production, siderophore production, gibberellic acid production, Indole-3-acetic acid (IAA) production, and zinc solubilization. One isolate, JJG_Zn, demonstrated multiple PGP activities and was identified as Enterobacter sp. through 16S rRNA sequencing. Considering the concept of 'One health,' a comprehensive biosafety analysis for any plant growth-promoting bacteria (PGP bacteria) is essential, thus, Enterobacter sp. (JJG_Zn), along with two other standard cultures, Burkholderia seminalis and Stenotrophomonas maltophilia, were evaluated for biosafety tests-including sheep blood agar assay, E.coli sensitivity assay, and pathogenicity tests on albino mice. The results indicated that all three PGP bacteria were potentially innocuous and compatible with each other. Furthermore, the field experiments were conducted at Punjab Agricultural University, Regional Research Station, Bathinda, and School of Organic Farming, IFS, Punjab Agricultural University, Ludhiana during Kharif 2022 employing a randomized complete block design (RCBD) with nine treatment combinations. The treatments included liquid bacterial inoculants (LBIs) of Stenotrophomonas maltophilia, Burkholderia seminalis, and Enterobacter sp. (JJG_Zn) applied in combination with 100% and 75% of the recommended dose of fertilizer (RDF), with each treatment replicated thrice. The treatment T9 (75% RDF + dual inoculation with B. seminalis and S. maltophilia) resulted in the highest productivity, showing a 10.23% increase in pooled green fodder yield (GFY) compared to the control. The treatment T8 (75% RDF + Enterobacter sp. (JJG_Zn)) showed a 5.14% increase in productivity over the control. Thus, liquid bacterial inoculants (LBIs) present a promising approach to enhance the productivity of forage Sorghum.

Broad-spectrum applications of plant growth-promoting rhizobacteria (PGPR) across diverse crops and intricate planting systems.

Multifunctional plant growth-promoting rhizobacteria (PGPR) have garnered significant attention in agricultural applications; however, a few have applied them in crop rotation or intercropping fields. To identify PGPR with strong colonization ability and broad spectrum benefit, we screened strains from the local tobacco rhizosphere and evaluated their growth-promoting effects across various crops and farming systems. In this study, strain L8, identified as Bacillus thuringiensis, was selected as a multifunctional PGPR capable of producing indole-3-acetic acid (IAA), solubilizing potassium, and mobilizing both organic and inorganic phosphorus. Compared with the control group, the soil treated with strain L8 in tobacco pot experiments showed significantly higher levels of IAA, available potassium, and available phosphorus. Furthermore, tobacco plants inoculated with L8 exhibited significantly improved growth parameters compared with the uninoculated control. The results indicated that compared with the control, strain L8 increased tobacco fresh weight (by 83.18%), plant height (by 29.32%), relative chlorophyll content (by 14.33%), as well as plant phosphorus (by 23.78%) and potassium (by 30.81%). Interestingly, L8 not only enhanced tobacco growth but also improved tobacco root morphology, significantly increasing root length (1.55-fold), root surface area (1.78-fold), and root volume (2.05-fold) compared with the control. These findings provide valuable insights into utilizing plant growth-promoting bacteria for tobacco production. Moreover, the inoculation strain L8 enriched soil organic matter and nutrient content in both wheat (Triticum aestivum)-maize (Zea mays) rotation and peanut (Arachis hypogaea)-maize intercropping systems. Furthermore, within the intricate tillage systems of wheat-corn rotation and peanut-corn intercropping, multifunctional PGPR strain L8 can play a crucial role in crop growth promotion, yield increase, and higher soil nutrient availability.IMPORTANCEThese findings aim to study the application of plant growth-promoting rhizobacteria (PGPR) in diverse crops and complex planting systems, showing their adaptability and effectiveness in various agricultural contexts. The study suggests that this strain improves nutrient utilization in the soil, enhances soil health, and plays a significant role in plant growth through the secretion of substances like auxin (IAA). In parallel, we observed that applying this strain improved the production efficiency of wheat, corn, and peanuts within complex farming systems, indicating that this method holds the potential for enhancing both the yield and quality of various crops.

Diversity, characterization, and biotechnological potential of plant growth-promoting bacteria from Bryophyllum pinnatum (Lam.) (Crassulaceae) roots and rhizosphere soil.

Cultivable microbial communities associated with plants inhabiting extreme environments have great potential in biotechnological applications. However, there is a lack of knowledge about these microorganisms from Bryophyllum pinnatum (which survives in severely barren soil) and their ability to promote plant growth. The present study focused on the isolation, identification, biochemical characterization, and potential applications of root endophytic bacteria and rhizosphere bacteria. A total of 73 bacterial isolates were obtained, with 50 derived from rhizospheric soil and 23 from root tissue. The identified strains were categorized into 16 genera, with Bacillus, Priestia, Pseudarthrobacter, Neobacillus, Mesobacillus, and Arthrobacter being the most species-rich genera. Heat stress experiments indicated that almost half (50.7%) of the selected isolates were tolerant to heat stress. Furthermore, most strains present diverse capabilities for biotechnological applications, including the potential for indole-3-acetic acid (IAA) production, organic phosphorus solubilization, inorganic phosphorus solubilization, and nitrogen fixation. Some isolates (21.92%) exhibited broad-spectrum antagonistic activity against various phytopathogenic fungi, including Fusarium spp. Agar plate assays revealed that the Cellulomonas hominis strain LS43 and Bacillus inaquosorum strain LS77 significantly increased the total fresh weight of Arabidopsis (P < 0.05), yet these strains did not significantly affect the primary root length or the number of leaves. Notably, a subset of the strains tested did not significantly increase the growth of Arabidopsis and, in fact, had inhibitory effects on certain growth parameters. This is the first investigation highlighting the potential of root endophytic bacteria and rhizosphere bacteria in association with B. pinnatum in barren soils. Thus, these isolated strains positively influence plant nutrient uptake, stress resilience, and biocontrol to reduce chemical inputs in conventional agricultural practices, highlighting the importance of their development as biofertilizers for improving the quality of barren soil.

Relevance of plant growth-promoting bacteria in reducing the severity of tomato wilt caused by Fusarium oxysporum f. sp. lycopersici by altering metabolites and related genes

Among the biotic stresses, wilt disease severely affects tomato quality and productivity globally. The causal organism of this disease is Fusarium oxysporum f. sp. lycopersici (Fol), which is very well known and has a significant impact on the productivity of other crops as well. Efforts have been made to investigate the effect of plant growth-promoting bacteria (PGPB) on alleviating tomato wilt disease. Four PGPB strains, such as Pseudomonas aeruginosa BHUPSB01 (T1), Pseudomonas putida BHUPSB04 (T2), Paenibacillus polymyxa BHUPSB16 (T3), and Bacillus cereus IESDJP-V4 (T4), were used as inocula to treat Fol-challenged plants. The results revealed that PGPB treatments T1, T2, T3, and T4 were able to decrease the severity of Fusarium wilt in the tomato plants at different levels. Among the treatments, T3 displayed the strongest protective effect, with the lowest disease frequency, which was 15.25%. There were no significant differences observed in parameters such as fruit yield and relative water content in the PGPB-inoculated plants, although T3 and T4 showed minimal electrolyte leakage. Significant changes in chlorophyll fluorescence were also recorded. A lower level of H2O2 and malondialdehyde (MDA) was observed in the T3 and T4 treatments. In addition, proline accumulation was highest in the T3-treated plants. Antioxidative enzyme activities, such as catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), significantly increased in the PGPB-treated plants. Furthermore, the highest phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) activity was reported in the T3 and T4 plants, respectively. The PGPB-treated plants showed elevated expression of the PAL, PPO, PR3, PR2, SOD, CAT, and PO genes. This study’s results reveal that PGPB strains can be utilized as biocontrol agents (BCAs) to enhance tomato resistance against Fusarium wilt.

Cocultivos de microorganismos endófitos: Estrategia para la producción de bioestimulantes y compuestos de valor agregado

Cocultures between algae and bacteria aim to harness the metabolic capabilities of both microorganisms for biotechnological purposes. However, establishing a successful coculture is challenging because of their different nutritional and environmental requirements. This work proposes the establishment of a coculture between the plant growth-promoting bacterium Methylobacterium oryzae and the unicellular green alga Coccomyxa simplex, both endophytes of Vachellia farnesiana, with the aim of using their metabolic capacities to produce value-added compounds. To achieve this, the conditions to obtain a stable alga-bacteria coculture were defined, and the effect of the coculture and the initial nutrient concentration on lipid and pigment production, as well as plant growth stimulation were evaluated. A stable coculture was successfully established enabling the growth of both microorganisms even in the absence of carbon and nitrogen sources. The coculture stimulated lipid production (up to 43%) and pigment production (by 2.5 to 4.8 times). Additionally, the coculture's supernatant improved the growth of radish seedlings, suggesting that the coculture promotes the production of biostimulant compounds with potential to enhance crop yields and reduce the use of chemical fertilizers.

Association Analysis of the Genomic and Functional Characteristics of Halotolerant Glutamicibacter endophyticus J2-5-19 from the Rhizosphere of Suaeda salsa.

Halotolerant plant growth-promoting bacteria (HT-PGPB) have attracted considerable attention for their significant potential in mitigating salt stress in crops. However, the current exploration and development of HT-PGPB remain insufficient to meet the increasing demands of agriculture. In this study, an HT-PGPB isolated from coastal saline-alkali soil in the Yellow River Delta was identified as Glutamicibacter endophyticus J2-5-19. The strain was capable of growing in media with up to 13% NaCl and producing proteases, siderophores, and the plant hormone IAA. Under 4‱ salt stress, inoculation with strain J2-5-19 significantly increased the wheat seed germination rate from 37.5% to 95%, enhanced the dry weight of maize seedlings by 41.92%, and notably improved the development of maize root systems. Moreover, this work presented the first whole-genome of Glutamicibacter endophyticus, revealing that G. endophyticus J2-5-19 resisted salt stress by expelling sodium ions and taking up potassium ions through Na+/H+ antiporters and potassium uptake proteins, while also accumulating compatible solutes such as betaine, proline, and trehalose. Additionally, the genome contained multiple key plant growth-promoting genes, including those involved in IAA biosynthesis, siderophore production, and GABA synthesis. The findings provide a theoretical foundation and microbial resources for the development of specialized microbial inoculants for saline-alkali soils.

Effectiveness of salt priming and plant growth-promoting bacteria in mitigating salt-induced photosynthetic damage in melon.

Seed priming and plant growth-promoting bacteria (PGPB) may alleviate salt stress effects. We exposed a salt-sensitive variety of melon to salinity following seed priming with NaCl and inoculation with Bacillus. Given the sensitivity of photosystem II (PSII) to salt stress, we utilized dark- and light-adapted chlorophyll fluorescence alongside analysis of leaf stomatal conductance of water vapour (Gsw). Priming increased total seed germination by 15.5% under salt-stress. NaCl priming with Bacillus inoculation (PB) increased total leaf area (LA) by 45% under control and 15% under stress. Under the control condition, priming (P) reduced membrane permeability (RMP) by 36% and PB by 55%, while under stress Bacillus (BS) reduced RMP by 10%. Although Bacillus inoculation (B) and priming (P) treatments did not show significant effects on some PSII efficiency parameters (FV/FM, ABS/RC, PIABS, FM), the BS treatment induced a significantly higher quantum efficiency of PSII (ΦPSII) and increased Gsw by 159% in the final week of the experiment. The BS treatment reduced electron transport rate per reaction center (ETO/RC) by 10% in comparison to the salt treatment, which showed less reaction centre damage. Bacillus inoculation and seed priming treatment under the stressed condition (PBS) induced an increase in electron transport rate of 40%. Salt stress started to show significant effects on PSII after 12 days, and adversely impacted all morphological and photosynthetic parameters after 22 days. Salt priming and PGPB mitigated the negative impacts of salt stress and may serve as effective tools in future-proofing saline agriculture.

Exploring the plant-growth promoting bacterium Herbaspirillum seropedicae as catalyst of microbiome remodeling and metabolic changes in wheat plants.

Inoculation with the PGPB Herbaspirillum seropedicae shapes both the structure and putative functions of the wheat microbiome and causes changes in the levels of various plant metabolites described to be involved in plant growth and health. Plant growth promoting bacteria (PGPB) can establish metabolic imprints in their hosts, contributing to the improvement of plant health in different ways. However, while PGPB imprints on plant metabolism have been extensively characterized, much less is known regarding those affecting plant indigenous microbiomes, and hence it remains unknown whether both processes occur simultaneously. In this study, both 16S amplicon and ITS sequencing analyses were carried out to study both the structural as well as the putative functional changes in the seed-borne endophytic microbiome of wheat plants inoculated with the PGPB Herbaspirillum seropedicae strain RAM10. Concomitantly, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analyses were used to investigate the alterations in the root metabolome of PGPB-inoculated plants. PGPB inoculation led to marked differences in the composition of the root microbiome, accompanied by the differential enrichment of microorganisms with putative roles in both plant energy and nitrogen metabolism. In addition, metabolome analyses showed that the levels of 16 metabolites belonging to the phenylpropanoid, terpenoid, and unsaturated fatty acid families were significantly altered in PGPB-inoculated plants. These findings shed light on the interplay between PGPB, the plant and its associated microbiome, indicating that PGPB can act as the driving force mediating long-lasting changes in both the plant metabolome and the plant microbiome.

Bioprospecting of a Native Plant Growth-Promoting Bacterium Bacillus cereus B6 for Enhancing Uranium Accumulation by Sudan Grass (Sorghum sudanense (Piper) Stapf).

Phytoremediation technology is viewed as a potential solution for addressing soil uranium contamination. Sudan grass (Sorghum sudanense (Piper) Stapf.), noted for its robust root structure and resilience to heavy metals, has garnered significant attention. This paper investigates a strain of uranium-tolerant bacterium, B6, obtained from the inter-root environment of native plants in soil contaminated with uranium tailings. The bacterium was identified as Bacillus cereus. Genomic analyses and assessment of uranium tolerance-promoting properties showed that strain B6 not only exhibited high uranium tolerance, but also possessed beneficial properties such as phosphorus solubilization and iron-producing carriers. In this study, we used strain B6 as an inoculant in combination with Sudan grass for germination and potting experiments. The findings demonstrated that Bacillus cereus B6 could substantially mitigate the adverse effects of uranium stress on Sudan grass, boost the plant's antioxidant response, significantly increase the root length and dry biomass of Sudan grass, and facilitate the accumulation of uranium in the roots, as well as its translocation to the aboveground portions. The study showed that PGPB strain B6 can significantly enhance the effect of plant accumulation of uranium and increase the potential of Sudan grass to become a uranium-rich plant, which provides an important scientific basis and application prospect for the use of microbial-assisted Sudan grass remediation technology to treat uranium-contaminated soil.

Plant Growth-promoting Bacteria Alleviate the Toxic Effects of Soil Microplastics and Heavy Metal Complex Pollution in Hybrid pennisetum

The coexistence of microplastics and heavy metals in soil can lead to more intricate environmental effects. While plant growth-promoting bacteria have been widely recognized for enhancing the remediation of heavy metal-contaminated soils, little research has been conducted to investigate whether they can alleviate the stress of microplastic-heavy metal composite contamination on plants. We investigated the effects of isolated and screened plant growth-promoting bacteria on the growth and cadmium （Cd） accumulation of Hybrid pennisetum under the composite pollution of Cd and polypropylene （PP） with different particle sizes （6.5 and 830 μm） in pot experiments and analyzed their effects on the composition of rhizosphere bacterial communities using high-throughput sequencing. Seven strains of bacteria were isolated and screened from soil contaminated with heavy metal-microplastic composites, identified as Enterobacter and Bacillus spp. All exhibited plant growth-promoting characteristics, including IAA production, siderophores, phosphorus solubilization, and potassium solubilization. Inoculation of plant growth-promoting bacteria increased the length and dry weight of H. pennisetum, effectively alleviating the stress caused by PP+Cd compound pollution. Plant growth-promoting bacteria increased soil available potassium and available phosphorus content, mitigating the decrease in soil mineral nutrients caused by PP+Cd composite pollution. PP+Cd compound pollution and plant growth-promoting bacterial inoculation affected the composition of the rhizosphere bacterial community of H. pennisetum, influencing dominant populations such as Proteobacteria, Firmicutes, and Actinobacteria. This study observed that the isolated and screened plant growth-promoting bacteria can effectively alleviate the plastic-heavy metal complex pollution caused by H. pennisetum. This provides a theoretical basis and data support for the remediation of microplastic heavy metal complex-contaminated soil biological pollution.

Effects of combined inoculation of arbuscular mycorrhizal fungi and plant growth-promoting rhizosphere bacteria on seedling growth and rhizosphere microecology.

The effects of rhizosphere microorganisms on plant growth and the associated mechanisms are a focus of current research, but the effects of exogenous combined inoculation with arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) on seedling growth and the associated rhizosphere microecological mechanisms have been little reported. In this study, a greenhouse pot experiment was used to study the effects of single or double inoculation with AM fungi (Funneliformis mosseae) and two PGPR (Bacillus sp., Pseudomonas sp.) on the growth of tobacco seedlings, together with high-throughput sequencing technology to reveal associated rhizosphere microecological mechanisms. All inoculation treatments significantly increased the aboveground dry weight; root dry weight; seedling nitrogen, phosphorus, and potassium uptake; plant height; stem thickness; maximum leaf area; chlorophyll content; total root length, surface area, and volume; and average root diameter. The highest values for these indices were observed in the combined treatment of F. mosseae and Pseudomonas sp. SG29 (A_SG29). Furthermore, the A_SG29 treatment yielded the highest diversity indexes and largest percentages of significantly enriched bacterial taxa, and significantly promoted the colonization of AMF in tobacco roots and Pseudomonas in rhizosphere soil. Differential metabolic-pathway predictions using PICRUSt2 showed that the A_SG29 treatment significantly increased the metabolic pathway richness of tobacco rhizosphere microorganisms, and significantly up-regulated some metabolic pathways that may benefit plant growth. Co-inoculation with F. mosseae and Pseudomonas sp. SG29 promoted tobacco-seedling growth by significantly improving rhizosphere microbial communities' structure and function. In summary, the combined inoculation of AMF and SG29 promotes tobacco seedling growth, optimizes the rhizosphere microbial community's structure and function, and serves as a sustainable microbial co-cultivation method for tobacco seedling production.

Organic fertilization systems on the vegetative growth and essential oil production of Pelargonium graveolens

The aromatic plant Pelargonium graveolens L. 'Hérit, known as geranium, presents bioactive compounds of high economic interest. Since the secondary metabolism is affected by several factors such as the cultivation conditions, this work aimed to assess the impact of different fertilization systems on geranium vegetative growth and essential oil content and yield. The treatments were: T1) chemical fertilization (N-P-K); T2) no fertilization; T3) biodynamic fertilization; T4) organic fertilization; T5) biodynamic fertilization + plant growth-promoting bacteria (PGPB); T6) organic fertilization + PGPB; and T7) organic compost. The application of Azospirillum brasilense (PGPB) had no significant effect on geranium vegetative growth and essential oil production. Essential oil production was not observed in plants treated with chemical (T1) or biodynamic fertilizers (T3 and T5). Plants treated with organic fertilization (T4 and T6) showed greater agronomic development in addition to essential oil content and yield. Consequently, organic fertilization emerges as a promising approach for cultivating P. graveolens.

A Novel Membrane-Associated Protein Aids Bacterial Colonization of Maize.

The soil environment affected by plant roots and their exudates, termed the rhizosphere, significantly impacts crop health and is an attractive target for engineering desirable agricultural traits. Engineering microbes in the rhizosphere is one approach to improving crop yields that directly minimizes the number of genetic modifications made to plants. Soil microbes have the potential to assist with nutrient acquisition, heat tolerance, and drought response if they can persist in the rhizosphere in the correct numbers. Unfortunately, the mechanisms by which microbes adhere and persist on plant roots are poorly understood, limiting their application. This study examined the membrane proteome shift upon adherence to roots in two bacteria of interest, Klebsiella variicola and Pseudomonas putida. From this surface proteome data, we identified a novel membrane protein from a nonlaboratory isolate of P. putida that increases binding to maize roots using unlabeled proteomics. When this protein was moved from the environmental isolate to a common lab strain (P. putida KT2440), we observed increased binding capabilities of P. putida KT2440 to both abiotic mimic surfaces and maize roots. We observed a similar increased binding capability to maize roots when the protein was heterologously expressed in K. variicola and Stutzerimonas stutzeri. With the discovery of this novel binding protein, we outline a strategy for harnessing natural selection and wild isolates to build more persistent strains of bacteria for field applications and plant growth promotion.

Co-Inoculation of Azospirillum brasilense and Bacillus sp. Enhances Biomass and Photosynthetic Efficiency in Urochloa brizantha

The synergism between plant growth-promoting bacteria species (PGPB) was evaluated regarding the effect of inoculation on productivity and the physiological aspects of Urochloa brizantha. The study included seven experimental groups arranged in a 3 × 2 + 1 factorial design consisting of three inoculants (Azospirillum brasilense, Bacillus sp. isolate EB-40, and Bacillus sp. isolate EB-40 + A. brasilense mixture), two application methods (seed and foliar spray), and controls. The MIX conjugate inoculation significantly increased plant height in all three harvests, with gains of 57%. At 60 and 90 days, MIX increased the number of tillers by 47% and the number of leaves by 61% compared to other treatments in all harvests. MIX also increased shoot dry mass in the second and third harvests, with improvements of 57–60% compared to the control. MIX improved the quantum efficiency of photosystem II and the ratio between variable and maximum chlorophyll fluorescence. Maximum fluorescence (Fm) was 11% higher in MIX-treated plants compared to the control, indicating increased potential photosynthesis. Variable fluorescence (Fv) efficiency improved by 22% for inoculation with A. brasilense and Bacillus sp. Our study reveals that A. brasilense plus the Bacillus sp. isolate EB-40 (MIX) has the potential to improve the resilience and productivity of U. brizantha.