Pesticides including insecticides are often applied to prevent distortion posed by plant insect pests. However, the application of these chemicals detrimentally affected the non-target organisms including soil biota. Fipronil (FIP), a broad-spectrum insecticide, is extensively used to control pests across the globe. The frequent usage calls for attention regarding risk assessment of undesirable effects on non-target microorganisms. Here, laboratory-based experiments were conducted to assess the effect of FIP on plant-beneficial bacteria (PBB); Rhizobium leguminosarum (Acc. No. PQ578652), Azotobacter salinestris (Acc. No. PQ578649) and Serratia marcescens (Acc. No. PQ578651). PBB synthesized growth regulating substances were negatively affected by increasing fipronil concentrations. For instance, at 100 mu g FIPmL-1, a decrease in indole-3-acetic acid (IAA) synthesis by bacterial strains followed the order: A. salinestris (95.6%) S. marcescens (91.6%) > R. leguminosarum (87%). Also, exposure of bacteria cells to FIP hindered the growth and morphology of PBB observed as distortion, cracking, and aberrant structure under scanning electron microscopy (SEM). Moreover, FIP-treated and propidium iodide (PI)-stained bacterial cells displayed an insecticide dose-dependent increase in cellular permeability as observed under a confocal laser microscope (CLSM). Colony counts (log(10) CFU mL(-1)) and growth of A. salinestris was completely inhibited at 150 mu g FIPmL-1. The surface adhering ability (biofilm formation) of PBB was also disrupted/inhibited in a FIP dose-related manner. The respiration loss due to FIP was coupled with a reduction in population size. Fipronil at 150 mu gmL(-1) decreased cellular respiration in A. salinestris (72%) S. marcescens (53%) and R. leguminosarum (85%). Additionally, biomarker enzymes; lactate dehydrogenase (LDH), lipid peroxidation (LPO), and oxidative stress (catalase; CAT) induced by FIP represented significant (p <= 0.05) toxicity towards PBB strains. Conclusively, fipronil suggests a toxic effect that emphasizes their careful monitoring in soils before application and their optimum addition in the soil-plant system. It is high time to prepare both target-specific and slow-released agrochemical formulation for crop protection with concurrent safeguarding of soils.

Plant-beneficial bacteria (PBB) have emerged as a promising approach for assisting phytoremediation of heavy metal (HM)-contaminated soils. However, their colonization efficiency is often challenged by complex soil environments. In this study, we screened one rhizobacterium (Klebsiella variicola Y38) and one endophytic bacterium (Serratia surfactantfaciens Y15) isolated from HM-contaminated soils and plants for their high resistance to Cd and strong growth-promoting abilities. These strains were encapsulated individually or in combination with alginate and applied with Medicago sativa in Cd-contaminated soil pot experiments. The effectiveness of different bacterial formulations in promoting plant growth and enhancing Cd bioconcentration in M. sativa was evaluated. Results showed that PBB application enhanced plant growth and antioxidant capacity while reducing oxidative damage. Encapsulated formulations outperformed unencapsulated ones, with combined formulations yielding superior results to individual applications. Quantitative PCR indicated enhanced PBB colonization in Cdcontaminated soils with alginate encapsulation, potentially explaining the higher efficacy of alginateencapsulated PBB. Additionally, the bacterial agents modified Cd speciation in soils, resulting in increased Cd bioaccumulation in M. sativa by 217-337 %. The alginate-encapsulated mixed bacterial agent demonstrated optimal effectiveness, increasing the Cd transfer coefficient by 3.2-fold. Structural equation modeling and correlation analysis elucidated that K. variicola Y38 promoted Cd bioaccumulation in M. sativa roots by reducing oxidative damage and enhancing root growth, while S. surfactantfaciens Y15 facilitated Cd translocation to shoots, promoting shoot growth. The combined application of these bacteria leveraged the benefits of both strains. These findings contribute to diversifying strategies for effectively and sustainably remediating Cdcontaminated soils, while laying a foundation for future investigations into bacteria-assisted phytoremediation.

Soybean (Glycine max [L.] Merr.) is an important oilseed crop with a high economic value. However, three damaging soybean diseases, soybean cyst nematode (SCN; Heterodera glycines Ichinohe), Sclerotinia stem rot caused by the fungus Sclerotinia sclerotiorum (Lid.) de Bary, and soybean root rot caused by Fusarium spp., are major constraints to soybean production in the Great Plains. Current disease management options, including resistant or tolerant varieties, fungicides, nematicides, and agricultural practices (crop rotation and tillage), have limited efficacy for these pathogens or have adverse effects on the ecosystem. Microbes with antagonistic activity are a promising option to control soybean diseases with the advantage of being environmentally friendly and sustainable. In this study, 61 bacterial strains isolated from wheat rhizospheres were used to examine their antagonistic abilities against three soybean pathogens. Six bacterial strains significantly inhibited the growth of Fusarium graminearum in the dual-culture assay. These bacterial strains were identified as Chryseobacterium ginsengisoli, C. indologenes, Pseudomonas poae, two Pseudomonas spp., and Delftia acidovorans by 16S rRNA gene sequencing. Moreover, C. ginsengisoli, C. indologenes, and P. poae significantly increased the mortality of SCN second-stage juveniles (J2), and two Pseudomonas spp. inhibited the growth of S. sclerotiorum in vitro. Further growth chamber tests found that C. ginsengisoli and C. indologenes reduced soybean Fusarium root rot disease. C. ginsengisoli and P. poae dramatically decreased SCN egg number on SCN-susceptible soybean 'Williams 82'. Two Pseudomonas spp. protected soybean plants from leaf damage and collapse after being infected by S. sclerotiorum. These bacteria exhibit versatile antagonistic potential. This work lays the foundation for further research on the field control of soybean pathogens.