Enhancing the atrazine tolerance of Pennisetum americanum (L.) K. Schum by inoculating with indole-3-acetic acid producing strain Pseudomonas chlororaphis PAS18

Transcriptome analysis of Pennisetum americanum × Pennisetum purpureum and Pennisetum americanum leaves in response to high-phosphorus stress

Excessive phosphorus (P) levels can disrupt nutrient balance in plants, adversely affecting growth. The molecular responses of Pennisetum species to high phosphorus stress remain poorly understood. This study examined two Pennisetum species, Pennisetum americanum × Pennisetum purpureum and Pennisetum americanum, under varying P concentrations (200, 600 and 1000 µmol·L- 1 KH2PO4) to elucidate transcriptomic alterations under high-P conditions. Our findings revealed that P. americanum exhibited stronger adaption to high-P stress compared to P. americanum× P. purpureum. Both species showed an increase in plant height and leaf P content under elevated P levels, with P. americanum demonstrating greater height and higher P content than P. americanum× P. purpureum. Transcriptomic analysis identified significant up- and down-regulation of key genes (e.g. SAUR, GH3, AHP, PIF4, PYL, GST, GPX, GSR, CAT, SOD1, CHS, ANR, P5CS and PsbO) involved in plant hormone signal transduction, glutathione metabolism, peroxisomes, flavonoid biosynthesis, amino acid biosynthesis and photosynthesis pathways. Compared with P. americanum× P. purpureum, P. americanum has more key genes in the KEGG pathway, and some genes have higher expression levels. These results contribute valuable insights into the molecular mechanisms governing high-P stress in Pennisetum species and offer implications for broader plant stress research.

Synergistic mitigation of atrazine-induced oxidative stress on soybeans in black soil using biochar and Paenarthrobacter sp. AT5

Atrazine, a widely used herbicide in modern agriculture, can lead to soil contamination and adverse effects on specific crops. To address this, we investigated the efficacy of biochar loaded with Paenarthrobacter sp. AT5 (an atrazine-degrading bacterial strain) in mitigating atrazine's impact on soybeans in black soil. Bacterially loaded biochar (BBC) significantly enhanced atrazine removal rates in both unplanted and planted soil systems. Moreover, BBC application improved soybean biomass, photosynthetic pigments, and antioxidant systems while mitigating alterations in metabolite pathways induced by atrazine exposure. These findings demonstrate the effectiveness of BBC in reducing atrazine-induced oxidative stress on soybeans in black soil, highlighting its potential for sustainable agriculture.

Metabolic insights into how multifunctional microbial consortium enhances atrazine removal and phosphorus uptake at low temperature

Agricultural soils in the black soil region of northeast China often face negative stress due to low temperatures, pesticide contamination, and inadequate nutrient supply. In this study, a new cold-tolerant strain of Peribacillus simplex C1 (C1) was selectively isolated from atrazine contaminated soil. The artificially constructed microbial consortium (CPD) [C1, phosphorus-solubilizing bacterium Enterobacter sp. P1, and atrazine-degrading bacterium Acinetobacter lwoffii DNS32] demonstrated the most effective performance in enhancing atrazine degradation and phosphorus-solubilizing capacity when the initial inoculation ratio of 5:1:2 at 15 °C. CPD enhanced energy-related metabolic pathways and increased choline production to regulate bacterial adaptation to temperature decrease. Additionally, the strains could selectively utilize carbon sources (low molecular weight organic acids) or nitrogen sources (some metabolites of atrazine) provided by each other to enhance growth. Furthermore, strain C1 enhanced membrane fluidity through increased expression of the unsaturated fatty acids. Pot experiments demonstrated that CPD assisted soybean seedlings in resisting dual stresses of low temperature and atrazine contamination by inducing the expression of genes related to photosynthesis, membrane permeability, phosphorus response, and cold tolerance.

Effect of Plant Growth-Promoting Bacteria on Antioxidant Status, Acetolactate Synthase Activity, and Growth of Common Wheat and Canola Exposed to Metsulfuron-Methyl

Metsulfuron-methyl, a widely used herbicide, could cause damage to the sensitive plants in crop-rotation systems at extremely low levels in the soil. The potential of plant growth-promoting bacteria (PGPB) for enhancing the resistance of plants against herbicide stress has been discovered recently. Therefore, it is poorly understood how physiological processes occur in plants, while PGPB reduce the phytotoxicity of herbicides for agricultural crops. In greenhouse studies, the effect of strains Pseudomonas protegens DA1.2 and Pseudomonas chlororaphis 4CH on oxidative damage, acetolactate synthase (ALS), enzymatic and non-enzymatic antioxidants in canola (Brassica napus L.), and wheat (Triticum aestivum L.) were investigated under two levels (0.05 and 0.25 mg∙kg-1) of metsulfuron-methyl using spectrophotometric assays. The inoculation of herbicide-exposed wheat with bacteria significantly increased the shoots fresh weight (24-28%), amount of glutathione GSH (60-73%), and flavonoids (5-14%), as well as activity of ascorbate peroxidase (129-140%), superoxide dismutase SOD (35-49%), and ALS (50-57%). Bacterial treatment stimulated the activity of SOD (37-94%), ALS (65-73%), glutathione reductase (19-20%), and the accumulation of GSH (61-261%), flavonoids (17-22%), and shoots weight (27-33%) in herbicide-exposed canola. Simultaneous inoculation prevented lipid peroxidation induced by metsulfuron-methyl in sensitive plants. Based on the findings, it is possible that the protective role of bacterial strains against metsulfuron-metil is linked to antioxidant system activation.

Rhizobacterial Isolates from Prosopis limensis Promote the Growth of Raphanus sativus L. Under Salt Stress

Microbial biotechnology employes techniques that rely based on the natural interactions that occur in ecosystems. Bacteria, including rhizobacteria, play an important role in plant growth, providing agricultural crops with an alternative that can mitigate the negative effects of abiotic stress, such as those caused by saline environments. In this study, bacterial isolates were obtained from soil and roots of Prosopis limensis Bentham from the department of Lambayeque, Peru. This region has high salinity levels, therefore, the collected samples were used to isolate plant growth-promoting rhizobacteria (PGPR), which were identified through morphological, and physical-biochemical characteristics. These salt tolerant bacteria were screened phosphate solubilization, indole acetic acid, deaminase activity and molecular characterization by 16S rDNA sequencing. Eighteen samples from saline soils of the Prosopis limensis plants in the northern coastal desert of San Jose district, Lambayeque, Peru. The bacterial isolates were screened for salt tolerance ranging from 2 to 10%, a total of 78 isolates were found. Isolates 03, 13 and 31 showed maximum salt tolerance at 10%, in vitro ACC production, phosphate solubilization and IAA production. The three isolates were identified by sequencing the amplified 16S rRNA gene and were found to be Pseudomonas sp. 03 (MW604823), Pseudomonas sp. 13 (MW604824) and Bordetella sp. 31 (MW604826). These microorganisms promoted the germination of radish plants and increased the germination rates for treatments T2, T3 and T4 by 129, 124 and 118% respectively. The beneficial effects of salt tolerant PGPR isolates isolated from saline environments can be new species, used to overcome the detrimental effects of salt stress on plants. The biochemical response and inoculation of the three isolates prove the potential of using these strains as a source of products that can be employed for the development of new compounds proving their potential as biofertilizers for saline environments.

Performance of atrazine adsorption behavior and microbial community structure in Mollisol aggregate fraction

Owing to complex pore systems and chemical substances, soil aggregates provide a spatially heterogeneous microenvironment for adsorption capacity and microbial survival. As the widely used pesticide in farmlands, atrazine environmental behavior is not well known at the aggregate scale. In this study, Mollisol soil samples were sieved into four aggregate-size classes: large macroaggregates (>2 mm, LMa), small macroaggregates (1-2 mm, SMa), microaggregates (0.25-1 mm, Mia) and primary particles (<0.25 mm, P). The pore characteristics of each aggregate fraction was visualized by non-invasive X-ray three-dimensional microscopic computed tomography (3D-CT) combined with pore network extraction. The adsorption kinetics of atrazine in each aggregate-size fraction can be described well by a pseudo-second-order kinetic model. The adsorption isothermal process of atrazine can be better fitted by the Langmuir isotherm model than Freundlich isotherm model. There was an obvious linear correlation between the maximum atrazine adsorption capacity and aggregate SOC content as well as TN. In addition, the abundance of bacteria, actinomycetes and anaerobic bacteria in P was totally higher than those in SMa and Mia. Although pH is strongly linked to the bacterial community in the aggregate fraction, aggregate particle size explained 18 % for shaping the microbial community. Therefore, chemical properties and pore characteristics of each soil aggregate fraction both contributed to performance of atrazine adsorption behavior and microbial community.

Nanomaterial Size and Surface Modification Mediate Disease Resistance Activation in Cucumber (Cucumis sativus)

Crop disease represents a serious and increasing threat to global food security. Lanthanum oxide nanomaterials (La₂O₃ NMs) with different sizes (10 and 20 nm) and surface modifications (citrate, polyvinylpyrrolidone [PVP], and poly(ethylene glycol)) were investigated for their control of the fungal pathogen Fusarium oxysporum (Schl.) f. sp cucumerinum Owen on six-week-old cucumber (Cucumis sativus) in soil. Seed treatment and foliar application of the La₂O₃ NMs at 20-200 mg/kg (mg/L) significantly suppressed cucumber wilt (decreased by 12.50-52.11%), although the disease control efficacy was concentration-, size-, and surface modification-dependent. The best pathogen control was achieved by foliar application of 200 mg/L PVP-coated La₂O₃ NMs (10 nm); disease severity was decreased by 67.6%, and fresh shoot biomass was increased by 49.9% as compared with pathogen-infected control. Importantly, disease control efficacy was 1.97- and 3.61-fold greater than that of La₂O₃ bulk particles and a commercial fungicide (Hymexazol), respectively. Additionally, La₂O₃ NMs application enhanced cucumber yield by 350-461%, increased fruit total amino acids by 295-344%, and improved fruit vitamin content by 65-169% as compared with infected controls. Transcriptomic and metabolomic analyses revealed that La₂O₃ NMs: (1) interacted with calmodulin, subsequently activating salicylic acid-dependent systemic acquired resistance; (2) increased the activity and expression of antioxidant and related genes, thereby alleviating pathogen-induced oxidative stress; and (3) directly inhibited in vivo pathogen growth. The findings highlight the significant potential of La₂O₃ NMs for suppressing plant disease in sustainable agriculture.

Exogenous application of Bradyrhizobium japonicum AC20 enhances soybean tolerance to atrazine via regulating rhizosphere soil microbial community and amino acid, carbohydrate metabolism related genes expression

Atrazine is used to control broad-leaved weeds in farmland and has negative impacts on soybean growth. Legume-rhizobium symbiosis plays an important role in regulating abiotic stress tolerance of plants, however, the mechanisms of rhizobia regulate the tolerance of soybean to atrazine based on the biochemical responses of the plant-soil system are limited. In this experiment, Glycine max (L.) Merr. Dongnong 252, planted in 20 mg kg^-1 of atrazine-contaminated soil, was inoculated with Bradyrhizobium japonicum AC20, and the plant growth, rhizosphere soil microbial diversity and the expression of the genes related to soybean carbon and nitrogen metabolism were assessed. The results indicated that strain AC20 inoculation alleviated atrazine-induced growth inhibition via increasing the contents of leghemoglobin and total nitrogen in soybean seedlings. The psbA gene expression level of the soybean seedlings that inoculated strain AC20 was 1.4 times than that of no rhizobium inoculating treatments. Moreover, the inoculated AC20 increased the abundance of Acidobacteria and Actinobacteria in soybean rhizosphere. Transcriptome analysis demonstrated that strain AC20 regulated the genes expression of amino acid metabolism and carbohydrate metabolism of soybean seedlings. Correlation analysis between 16S rRNA and transcriptome showed that strain AC20 reduced Planctomycetes abundance so as to down-regulated the expression of genes Glyma. 13G087800, Glyma. 12G005100 and Glyma.12G098900 involved in starch synthesis pathway of soybean leaves. These results provide available information for the rhizobia application to enhance the atrazine tolerate in soybean seedlings.

Endophytic bacterium CIMAP-A7 mediated amelioration of atrazine induced phyto-toxicity in Andrographis paniculata

The presence of atrazine, a triazine herbicide, and its residues in agriculture soil poses a serious threat to human health and environment through accumulation in edible plant parts. Hence, the present study focused on atrazine induced stress amelioration of Andrographis paniculata, an important medicinal plant, by a plant growth promoting and atrazine degrading endophytic bacterium CIMAP-A7 inoculation. Atrazine has a non-significant effect at a lower dose while at a higher dose (lower: 25 and higher: 50 mg kg^-1) 22 and 36% decrease in secondary metabolite content and plant dry weight of A. paniculata was recorded, respectively. Endophyte CIMAP-A7 inoculation significantly reduced atrazine soil content, by 78 and 51% at lower and a higher doses respectively, than their respective control treatments. Inoculation of CIMAP-A7 exhibited better plant growth in terms of increased total chlorophyll, carotenoid, protein, and metabolite content with reduced atrazine content under both atrazine contaminated and un-contaminated treatments. Atrazine induced oxidative stress in A. paniculata was also ameliorated by CIMAP-A7 by reducing stress enzymes, proline, and malondialdehyde accumulation under contaminated soil conditions than un-inoculated treatments. Furthermore, the presence of atrazine metabolites deisopropylatrazine (DIA) and desethylatrazine (DEA) strongly suggests a role of CIMAP-A7 in mineralization however, the absence of these metabolites in uninoculated soil and all plant samples were recorded. These findings advocate that the amelioration of atrazine induced stress with no/least pesticide content in plant tissues by plant-endophyte co-interactions would be efficient in the remediation of atrazine contaminated soils and ensure safe crop produce.

Phosphate bacterial solubilization: A key rhizosphere driving force enabling higher P use efficiency and crop productivity

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Phosphate bacteria bio-solubilization significantly increase crop P acquisition and productivity.

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Phosphate solubilizing bacteria increase RP agronomic efficiency as well as P fertilizers efficiency.

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This process can be optimized through a rational bacterial screening to assure efficient PSB are selected.

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Appropriate formulation of PSB is a sustainable approach to enhance P-fertilizers efficiency.

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Development of innovative PSB-Phosphate formulations is likely to sustain crop production.

Background

Increasing crop production to feed a growing population has driven the use of mineral fertilizers to ensure nutrients availability and fertility of agricultural soils. After nitrogen, phosphorus (P) is the second most important nutrient for plant growth and productivity. However, P availability in most agricultural soils is often limited because P strongly binds to soil particles and divalent cations forming insoluble P-complexes. Therefore, there is a constant need to sustainably improve soil P availability. This may include, among other strategies, the application of microbial resources specialized in P cycling, such as phosphate solubilizing bacteria (PSB). This P-mediating bacterial component can improve soil biological fertility and crop production, and should be integrated in well-established formulations to enhance availability and efficiency in use of P. This is of importance to P fertilization, including both organic and mineral P such as rock phosphate (RP) aiming to improve its agronomic efficiency within an integrated crop nutrition system where agronomic profitability of P and PSB can synergistically occur.

Aim of Review

The purpose of this review is to discuss critically the important contribution of PSB to crop P nutrition in concert with P fertilizers, with a specific focus on RP. We also highlight the need for PSB bioformulations being a sustainable approach to enhance P fertilizer use efficiency and crop production.

Key Scientific Concepts of Review

We first recognize the important contribution of PSB to sustain crop production, which requires a rational approach for both screening and evaluation of PSB enabling an accurate assessment of the bacterial effects both alone and in intertwined interaction with plant roots. Furthermore, we propose new research ideas about the development of microbial bioformulations based on PSB with a particular focus on strains exhibiting synergetic effects with RP.