In vitro investigation to explore the toxicity of different groups of pesticides for an agronomically important rhizosphere isolate Azotobacter vinelandii

Short-term responses of identified soil beneficial-bacteria to the insecticide fipronil: toxicological impacts

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 µg 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 (log10 CFU mL-1) and growth of A. salinestris was completely inhibited at 150 µg 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 µgmL-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.

Isolation and assessment of the beneficial effect of exopolysaccharide-producing PGPR in Triticum aestivum (L.) plants grown under NaCl and Cd -stressed conditions

Exopolysaccharide (EPS)-producing beneficial bacteria play a multifaceted role in improving plant growth and adaptive responses against different stressors. In this study, we isolated 25 bacterial strains from pea nodules and were further studied for their sodium chloride (NaCl) and cadmium (Cd) stress tolerance. Based on our results, Rhizobium fabae SR-22 (NCBI Accession number: MG063739.1) showed better tolerance toward salinity and Cd stress and produced a wide range of plant growth-promoting compounds. However, the amount of EPS varies during NaCl and Cd stress. It was important to note that NaCl and Cd beyond the tolerant level, affected the morphology and cellular viability of R. fabae. Interestingly, plant growth-promoting (PGP) substances (indole-3-acetic acid, ammonia, siderophore, and ACC deaminase) released by R. fabae were increased with increasing NaCl concentrations. In contrast, PGP substances were greatly decreased by increasing Cd dosages. Further, the beneficial effect of EPS-producing R. fabae in Triticum aestivum grown in soil treated with different levels of NaCl and Cd was assessed. Inoculation of R. fabae in wheat seedlings grown under higher NaCl and Cd concentrations showed improved growth compared to non-inoculated plants. R. fabae exhibited maximum effect in wheat plants grown under 2% NaCl and increased seed germination (8%), root length (13%), vigor indices (19%), root biomass (20%), chlorophyll-a (31%), total chlorophyll (27%) and carotenoid content. Additionally, R. fabae increased Cd and NaCl tolerance in wheat seedlings and improved their antioxidative responses. Conclusively, this work demonstrated that EPS-producing R. fabae showed a promising role in mitigating salinity and Cd-stress in wheat possibly by reducing salt and HM stress-induced abrasions and growth promotion via inorganic phosphate solubilization, and increased nutrient absorption. In the future, R. fabae equipped with these distinguishing characteristics may be used as effective bio-inoculants/bio-formulations in agriculture to address salinity and HM stress issues.

Comparative evaluation of biodegradation of chlorpyrifos by various bacterial strains: Kinetics and pathway elucidation

The present study focused on the isolation and identification of CP and TCP bacteria degrading bacteria from the rhizospheric zone of aromatic grasses i.e. palmarosa (Cymbopogon martinii (Roxb. Wats), lemongrass (Cymbopogon flexuosus) and vetiver (Chrysopogon zizaniodes (L.) Nash.). So that these isolates alone or in combination with the vegetation of aromatic grasses will be used to clean up CP-contaminated soils. The study also explored enzymatic activities, CO2 release, dechlorination potential, and degradation pathways of bacterial strains. A total of 53 CP-tolerant bacteria were isolated on their physical characteristics and their ability to degrade CP. The ten highly CP-tolerant isolates were Pseudomonas aeruginosa Pa608, three strains of Pseudomonas hibiscicola R4-721 from different rhizosphere, Enterococcus lectis PP2a, Pseudomonas monteilii NBFPALD_RAS131, Enterobacter cloacae L3, Stenotrophomonas maltophilia PEG-390, Escherichia coli ABRL132, and Escherichia coli O104:H4 strain FWSEC0009. The CO2 emission and phosphatase activities of the isolates varied from 3.1 to 8.6 μmol mL-1 and 12.3 to 31 μmol PNP h-1, respectively in the CP medium. The degradation kinetics of CP by these isolates followed a one-phase decay model with a dissipation rate ranging from 0.048 to 0.41 d-1 and a half-life of 1.7-14.3 days. The growth data fitted in the SGompertz equation showed a growth rate (K) of 0.21 ± 0.28 to 0.91 ± 0.33 d-1. The P. monteilii strain had a faster growth rate while E. coli ABRL132 had slower growth among the isolates. The rate of TCP accumulation calculated by the SGompertz equation was 0.21 ± 0.02 to 1.18 ± 0.19 d-1. The Pseudomonas monteilii showed a lower accumulation rate of TCP. Among these, four highly effective isolates were Pseudomonas aeruginosa Pa608, Pseudomonas monteilii NBFPALD_RAS131, Stenotrophomonas maltophilia PEG-390, and Pseudomonas hibiscicola R4-721. Illustrations of the degradation pathways indicated that the difference in metabolic pathways of each isolate was associated with their growth rate, phosphatase, dehydrogenase, oxidase, and dechlorination activities.

The halotolerant exopolysaccharide-producing Rhizobium azibense increases the salt tolerance mechanism in Phaseolus vulgaris (L.) by improving growth, ion homeostasis, and antioxidant defensive enzymes

Globally, agricultural productivity is facing a serious problem due to soil salinity which often causes osmotic, ionic, and redox imbalances in plants. Applying halotolerant rhizobacterial inoculants having multifarious growth-regulating traits is thought to be an effective and advantageous approach to overcome salinity stress. Here, salt-tolerant (tolerating 300 mM NaCl), exopolysaccharide (EPS) producing Rhizobium azibense SR-26 (accession no. MG063740) was assessed for salt alleviation potential by inoculating Phaseolus vulgaris (L.) plants raised under varying NaCl regimes. The metabolically active cells of strain SR-26 produced a significant amount of phytohormones (indole-3-acetic acid, gibberellic acid, and cytokinin), ACC deaminase, ammonia, and siderophore under salt stress. Increasing NaCl concentration variably affected the EPS produced by SR-26. The P-solubilization activity of the SR-26 strain was positively impacted by NaCl, as demonstrated by OD shift in NaCl-treated/untreated NBRIP medium. The detrimental effect of NaCl on plants was lowered by inoculation of halotolerant strain SR-26. Following soil inoculation, R. azibense significantly (p ≤ 0.05) enhanced seed germination (10%), root (19%) shoot (23%) biomass, leaf area (18%), total chlorophyll (21%), and carotenoid content (32%) of P. vulgaris raised in soil added with 40 mM NaCl concentration. Furthermore, strain SR-26 modulated the relative leaf water content (RLWC), proline, total soluble protein (TSP), and sugar (TSS) of salt-exposed plants. Moreover, R. azibense inoculation lowered the concentrations of oxidative stress biomarkers; MDA (29%), H2O2 content (24%), electrolyte leakage (31%), membrane stability (36%) and Na+ ion uptake (28%) when applied to 40 mM NaCl-treated plants. Further, R. azibense increases the salt tolerance mechanism of P. vulgaris by upregulating the antioxidant defensive responses. Summarily, it is reasonable to propose that EPS-synthesizing halotolerant R. azibense SR-26 should be applied as the most cost-effective option for increasing the yields of legume crops specifically P. vulgaris in salinity-challenged soil systems.

Preparation and Immobilization Mechanism on a Novel Composite Carrier PDA-CF/PUF to Improve Cells Immobilization and Xylitol Production

The preparation of a novel composite carrier of polydopamine-modified carbon fiber/polyurethane foam (PDA-CF/PUF) was proposed to improve cell immobilization and the fermentation of xylitol, which is an important food sweetener and multifunctional food additive. Candida tropicalis was immobilized on the composite carrier by adsorption and covalent binding. The properties and immobilization mechanism of the composite carrier and its effect on immobilized cells were investigated. It showed that the modification of PDA enhanced the loading of CF on the PUF surface and the adhesion of cells on the composite carrier surface. Also, the biocompatibility of carriers to cells was improved. In addition, the introduction of PDA increased the active groups on the surface of the carrier, enhanced the hydrophilicity, promoted the cells immobilization, and increased the xylitol yield. It was also found that expression of the related gene XYL1 in cells was significantly increased after the immobilization of the PDA-CF/PUF composite carrier during the fermentation. The PDA-CF/PUF was an immobilized carrier with the excellent biocompatibility and immobilization performance, which has great development potential in the industrial production of xylitol.

Pesticide-tolerant microbial consortia: Potential candidates for remediation/clean-up of pesticide-contaminated agricultural soil

Reclamation of pesticide-polluted lands has long been a difficult endeavour. The use of synthetic pesticides could not be restricted due to rising agricultural demand. Pesticide toxicity has become a pressing agronomic problem due to its adverse impact on agroecosystems, agricultural output, and consequently food security and safety. Among different techniques used for the reclamation of pesticide-polluted sites, microbial bioremediation is an eco-friendly approach, which focuses on the application of resilient plant growth promoting rhizobacteria (PGPR) that may transform or degrade chemical pesticides to innocuous forms. Such pesticide-resilient PGPR has demonstrated favourable effects on soil-plant systems, even in pesticide-contaminated environments, by degrading pesticides, providing macro-and micronutrients, and secreting active but variable secondary metabolites like-phytohormones, siderophores, ACC deaminase, etc. This review critically aims to advance mechanistic understanding related to the reduction of phytotoxicity of pesticides via the use of microbe-mediated remediation techniques leading to crop optimization in pesticide-stressed soils. The literature surveyed and data presented herein are extremely useful, offering agronomists-and crop protectionists microbes-assisted remedial strategies for affordably enhancing crop productivity in pesticide-stressed soils.

Assessing phytotoxicity and cyto-genotoxicity of two insecticides using a battery of in-vitro biological assays

Intensive use of chemical pesticides in agriculture poses environmental risks and may have negative impacts on agricultural productivity. The potential phytotoxicity of two chemical pesticides, chlorpyrifos (CPS) and fensulfothion (FSN), were evaluated using Cicer arietinum and Allium cepa as model crops. Different concentrations (0-100 μgmL-1) of both CPS and FSN decreased germination and biological attributes of C. arietinum. High pesticide doses significantly (p ≤ 0.05) caused membrane damage by producing thiobarbituric acid reactive substances (TBARS) and increasing proline (Pro) content. Pesticides elevated ROS levels and substantially increased the superoxide anions and H2O2 concentrations, thus aggravating cell injury. Plants exposed to high pesticide dosages displayed significantly higher antioxidant levels to combat pesticide-induced oxidative stress. Ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) increased by 48%, 93%, 71%, 52% and 94%, respectively, in C. arietinum roots exposed to 100 µgFSNmL-1. Under CLSM, pesticide-exposed C. arietinum and 2',7'-dichlorodihydrofluorescein diacetate (2'7'-DCF) and 3,3'-diaminobenzidine stained roots exhibited increased ROS production in a concentration-dependent manner. Additionally, enhanced Rhodamine 123 (Rhd 123) and Evan's blue fluorescence in roots, as well as changes in mitochondrial membrane potential (ΔΨm) and cellular apoptosis, were both associated with high pesticide dose. Allium cepa chromosomal aberration (CAs) assay showed a clear reduction in mitotic index (MI) and numerous chromosomal anomalies in root meristematic cells. Additionally, a-dose-dependent increase in DNA damage in root meristematic cells of A. cepa and conversion of the super-coiled form of DNA to open circular in pBR322 plasmid revealed the genotoxic potential of pesticides. The application of CPS and FSN suggests phytotoxic and cyto-genotoxic effects that emphasize the importance of careful monitoring of current pesticide level in soil before application and addition at optimal levels to soil-plant system. It is appropriate to prepare both target-specific and slow-release agrochemical formulations for crop protection with concurrent safeguarding of agroecosystems.

The effects of herbicide application on two soil phosphate solubilizing bacteria: Pantoea agglomerans and Serratia rubidaea

The application of synthetic pesticides is one of the fastest acting tools at farmers' disposal to prevent and mitigate the threats posed by plant pests in agriculture. However, the effects of these above-ground applications of pesticides are known to be detrimental to some belowground, non-target soil biota. At present, the effects many pesticides have on key functional microbial groups associated with phosphate (P) solubilization in the soil are still largely unknown. The purpose of this study was to compare the effects of two herbicides, glyphosate, and paraquat, on phosphate solubilizing bacteria (PSB) with and without pH adjustment (after herbicide addition) since pH is a major indicator of P solubilization. In our assay, two PSB strains (Pantoea agglomerans and Serratia rubidaea) were chosen to assess their ability to solubilize tricalcium phosphate (TCP) by using the vanadate-molybdate method (to measure the amount of P solubilized) in the presence of glyphosate (5.4 g/L and 10.8 g/L) or paraquat (2 g/L and 4 g/L) separately. To assess the effect of PSB treated by the herbicides, a growth experiment using PSB inoculated wheat seedlings was performed under greenhouse conditions (25 °C, light 16 h/8 h dark). After four weeks, wheat above-ground growth parameters were measured. Our results showed that even under recommended doses of glyphosate (5.4 g/L) and paraquat (2 g/L), a decrease in P solubilization activity was observed in P. agglomerans and S. rubidaea. Whilst paraquat affected TCP solubilization more than glyphosate with and without pH adjustment, there was a significant decrease (p < 0.05) in TCP solubilization, up to 39% and 93% in the presence of glyphosate and paraquat, respectively, for S. rubidaea, and up to 45% and 95% in the presence of glyphosate and paraquat, respectively, for P. agglomerans. The effect of the herbicides on the PSB had the same results as in the greenhouse test on wheat seedling growth, confirming that these herbicides have both above and belowground negative effects, despite being used at recommended doses.

Phytogenically Synthesized Zinc Oxide Nanoparticles (ZnO-NPs) Potentially Inhibit the Bacterial Pathogens: In Vitro Studies

The usefulness of nanoparticles (NPs) in biological applications, such as nanomedicine, is becoming more widely acknowledged. Zinc oxide nanoparticles (ZnO-NPs) are a type of metal oxide nanoparticle with an extensive use in biomedicine. Here, ZnO-NPs were synthesized using Cassia siamea (L.) leaf extract and characterized using state-of-the-art techniques; UV-vis spectroscopy, XRD, FTIR, and SEM. At sub-minimum inhibitory concentration (MIC) levels, the ability of ZnO@Cs-NPs to suppress quorum-mediated virulence factors and biofilm formation against clinical MDR isolates (Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum MCC-2290) was tested. The ½MIC of ZnO@Cs-NPs reduced violacein production by C. violaceum. Furthermore, ZnO@Cs-NPs sub-MIC significantly inhibited virulence factors such aspyoverdin, pyocyanin, elastase, exoprotease, rhamnolipid, and the swimming motility of P. aeruginosa PAO1 by 76.9, 49.0, 71.1, 53.3, 89.5, and 60%, respectively. Moreover, ZnO@Cs-NPs also showed wide anti-biofilm efficacy, inhibiting a maximum of 67 and 56% biofilms in P. aeruginosa and C. violaceum, respectively. In addition, ZnO@Cs-NPs suppressed extra polymeric substances (EPS) produced by isolates. Additionally, under confocal microscopy, propidium iodide-stained cells of P. aeruginosa and C. violaceum show ZnO@Cs-NP-induced impairment in membrane permeability, revealing strong anti-bacterial efficacy. This research demonstrates that newly synthesized ZnO@Cs-NPs demonstrate a strong efficacy against clinical isolates. In a nutshell, ZnO@Cs-NPs can be used as an alternative therapeutic agent for managing pathogenic infections.

A systematic review of the toxic effects of a nanopesticide on non-target organisms: Estimation of protective concentrations using a species sensitivity distribution (SSD) approach - The case of atrazine

Nanopesticides, such as nanoencapsulated atrazine (nATZ), have been studied and developed as eco-friendly alternatives to control weeds in fields, requiring lower doses. This review contains a historical and systematic literature review about the toxicity of nATZ to non-target species. In addition, the study establishes protective concentrations for non-target organisms through a species sensitivity distribution (SSD) approach. Through the systematic search, we identified 3197 publications. Of these, 14 studies addressed "(nano)atrazine's toxicity to non-target organisms". Chronological and geographic data on the publication of articles, characterization of nATZ (type of nanocarrier, size, polydispersity index, zeta potential), experimental design (test species, exposure time, measurements, methodology, tested concentrations), and toxic effects are summarized and discussed. The data indicate that cell and algal models do not show sensitivity to nATZ, while many terrestrial and aquatic invertebrates, aquatic vertebrates, microorganisms, and plants have high sensitivity to nAZT. The SSD results indicated that D. similis is the most sensitive species to nATZ, followed by C. elegans, E. crypticus, and P. subcapitata. However, the limitations in terms of the number of species and endpoints available to elaborate the SSD reflect gaps in knowledge of the effects of nATZ on different ecosystems.

Elucidating molecular characterization of chlorpyrifos and profenofos degrading distinct bacterial strains for enhancing seed germination potential of Gossypium arboreum L

Chlorpyrifos (CP) and profenofos (PF) are organophosphate pesticides (OPs) widely used in agriculture and are noxious to both fauna and flora. The presented work was designed to attenuate the toxicity of both pesticides in the growth parameters of a cotton crop by applying plant growth-promoting rhizobacteria (PGPR), namely Pseudomonas aeruginosa PM36 and Bacillus sp. PM37. The multifarious biological activities of both strains include plant growth-promoting traits, including phosphate solubilization; indole-3-acetic acid (IAA), siderophore, and HCN production; nitrogen fixation; and enzymatic activity such as cellulase, protease, amylase, and catalase. Furthermore, the molecular profiling of multi-stress-responsive genes, including acdS, ituC, czcD, nifH, and sfp, also confirmed the plant growth regulation and abiotic stress tolerance potential of PM36 and PM37. Both strains (PM36 and PM37) revealed 92% and 89% of CP degradation at 50 ppm and 87% and 81% at 150 ppm within 7 days. Simultaneously 94% and 98% PF degradation was observed at 50 ppm and 90% and 92% at 150 ppm within 7 days at 35 °C and pH 7. Biodegradation was analyzed using HPLC and FTIR. The strains exhibited first-order reaction kinetics, indicating their reliance on CP and PF as energy and carbon sources. The presence of opd, mpd, and opdA genes in both strains also supported the CP and PF degradation potential of both strains. Inoculation of strains under normal and OP stress conditions resulted in a significant increase in seed germination, plant biomass, and chlorophyll contents of the cotton seedling. Our findings indicate that the strains PM36 and PM37 have abilities as biodegraders and plant growth promoters, with potential applications in crop sciences and bioremediation studies. These strains could serve as an environmentally friendly, sustainable, and socially acceptable solution to manage OP-contaminated sites.

Bacterial ACC deaminase: Insights into enzymology, biochemistry, genetics, and potential role in amelioration of environmental stress in crop plants

Growth and productivity of crop plants worldwide are often adversely affected by anthropogenic and natural stresses. Both biotic and abiotic stresses may impact future food security and sustainability; global climate change will only exacerbate the threat. Nearly all stresses induce ethylene production in plants, which is detrimental to their growth and survival when present at higher concentrations. Consequently, management of ethylene production in plants is becoming an attractive option for countering the stress hormone and its effect on crop yield and productivity. In plants, ACC (1-aminocyclopropane-1-carboxylate) serves as a precursor for ethylene production. Soil microorganisms and root-associated plant growth promoting rhizobacteria (PGPR) that possess ACC deaminase activity regulate growth and development of plants under harsh environmental conditions by limiting ethylene levels in plants; this enzyme is, therefore, often designated as a "stress modulator." TheACC deaminase enzyme, encoded by the AcdS gene, is tightly controlled and regulated depending upon environmental conditions. Gene regulatory components of AcdS are made up of the LRP protein-coding regulatory gene and other regulatory components that are activated via distinct mechanisms under aerobic and anaerobic conditions. ACC deaminase-positive PGPR strains can intensively promote growth and development of crops being cultivated under abiotic stresses including salt stress, water deficit, waterlogging, temperature extremes, and presence of heavy metals, pesticides and other organic contaminants. Strategies for combating environmental stresses in plants, and improving growth by introducing the acdS gene into crop plants via bacteria, have been investigated. In the recent past, some rapid methods and cutting-edge technologies based on molecular biotechnology and omics approaches involving proteomics, transcriptomics, metagenomics, and next generation sequencing (NGS) have been proposed to reveal the variety and potential of ACC deaminase-producing PGPR that thrive under external stresses. Multiple stress-tolerant ACC deaminase-producing PGPR strains have demonstrated great promise in providing plant resistance/tolerance to various stressors and, therefore, it could be advantageous over other soil/plant microbiome that can flourish under stressed environments.

Impact of carbendazim on cellular growth, defence system and plant growth promoting traits of Priestia megaterium ANCB-12 isolated from sugarcane rhizosphere

Agrochemicals are consistently used in agricultural practices to protect plants from pathogens and ensure high crop production. However, their overconsumption and irregular use cause adverse impacts on soil flora and non-target beneficial microorganisms, ultimately causing a hazard to the ecosystem. Taking this into account, the present study was conducted to determine the high dosage of fungicide (carbendazim: CBZM) effects on the rhizobacteria survival, plant growth promoting trait and reactive oxygen species (ROS) scavenging antioxidant enzyme system. Thus, a multifarious plant growth promoting rhizobacteria (PGPR) isolate, ANCB-12, was obtained from the sugarcane rhizosphere through an enrichment technique. The taxonomic position of the isolated rhizobacteria was confirmed through 16S rRNA gene sequencing analysis as Priestia megaterium ANCB-12 (accession no. ON878101). Results showed that increasing concentrations of fungicide showed adverse effects on rhizobacterial cell growth and survival. In addition, cell visualization under a confocal laser scanning microscope (CLSM) revealed more oxidative stress damage in the form of ROS generation and cell membrane permeability. Furthermore, the increasing dose of CBZM gradually decreased the plant growth promoting activities of the rhizobacteria ANCB-12. For example, CBZM at a maximum 3,000 μg/ml concentration decreases the indole acetic acid (IAA) production by 91.6%, ACC deaminase by 92.3%, and siderophore production by 94.1%, respectively. Similarly, higher dose of fungicide enhanced the ROS toxicity by significantly (p < 0.05) modulating the stress-related antioxidant enzymatic biomarkers in P. megaterium ANCB-12. At a maximum 3,000 μg/ml CBZM concentration, the activity of superoxide dismutase (SOD) declined by 82.3%, catalase (CAT) by 61.4%, glutathione peroxidase (GPX) by 76.1%, and glutathione reductase (GR) by 84.8%, respectively. The results of this study showed that higher doses of the fungicide carbendazim are toxic to the cells of plant-beneficial rhizobacteria. This suggests that a recommended dose of fungicide should be made to lessen its harmful effects.

Ecotoxicological implications of residual pesticides to beneficial soil bacteria: A review

Optimization of crop production in recent times has become essential to fulfil food demands of constantly increasing human populations worldwide. To address this formidable challenge, application of agro-chemicals including synthetic pesticides in intensive farm practices has increased alarmingly. The excessive and indiscriminate application of pesticides to foster food production however, leads to its exorbitant deposition in soils. After accumulation in soils beyond threshold limits, pesticides harmfully affect the abundance, diversity and composition and functions of rhizosphere microbiome. Also, the cost of pesticides and emergence of resistance among insect-pests against pesticides are other reasons that require attention. Due to this, loss in soil nutrient pool cause a substantive reduction in agricultural production which warrant the search for newer environmentally friendly technology for sustainable crop production. Rhizosphere microbes, in this context, play vital roles in detoxifying the polluted environment making soil amenable for cultivation through detoxification of pollutants, rhizoremediation, bioremediation, pesticide degradation, and stress alleviation, leading to yield optimization. The response of soil microorganisms to range of chemical pesticides is variable ranging from unfavourable to the death of beneficial microbes. At cellular and biochemical levels, pesticides destruct the morphology, ultrastructure, viability/cellular permeability, and many biochemical reactions including protein profiles of soil bacteria. Several classes of pesticides also disturb the molecular interaction between crops and their symbionts impeding the overall useful biological processes. The harmful impact of pesticides on soil microbes, however, is poorly researched. In this review, the recent findings related with potential effects of synthetic pesticides on a range of soil microbiota is highlighted. Emphasis is given to find and suggest strategies to minimize the chemical pesticides usage in the real field conditions to preserve the viability of soil beneficial bacteria and soil quality for safe and sustainable crop production even in pesticide contaminated soils.

Stress-Tolerant Endophytic Isolate Priestia aryabhattai BPR-9 Modulates Physio-Biochemical Mechanisms in Wheat (Triticum aestivum L.) for Enhanced Salt Tolerance

In efforts to improve plant productivity and enhance defense mechanisms against biotic and abiotic stresses, endophytic bacteria have been used as an alternative to chemical fertilizers and pesticides. In the current study, 25 endophytic microbes recovered from plant organs of Triticum aestivum L. (wheat) were assessed for biotic (phyto-fungal pathogens) and abiotic (salinity, drought, and heavy metal) stress tolerance. Among the recovered isolates, BPR-9 tolerated maximum salinity (18% NaCl), drought (15% PEG-6000), and heavy metals (µg mL-1): Cd (1200), Cr (1000), Cu (1000), Pb (800), and Hg (30). Based on phenotypic and biochemical characteristics, as well as 16S rDNA gene sequencing, endophytic isolate BPR-9 was recognized as Priestia aryabhattai (accession no. OM743254.1). This isolate was revealed as a powerful multi-stress-tolerant crop growth promoter after extensive in-vitro testing for plant growth-promoting attributes, nutrient (phosphate, P; potassium, K; and zinc, Zn) solubilization efficiency, extracellular enzyme (protease, cellulase, amylase, lipase, and pectinase) synthesis, and potential for antagonistic activity against important fungal pathogens viz. Alternaria solani, Rhizoctonia solani, Fusarium oxysporum, and Ustilaginoidea virens. At elevated salt levels, increases were noted in indole-3-acetic acid; siderophores; P, K, and Zn-solubilization; ACC deaminase; and ammonia synthesized by Priestia aryabhattai. Additionally, under in-vitro plant bioassays, wheat seedlings inoculated with P. aryabhattai experienced superior growth compared to non-inoculated seedlings in high salinity (0-15% NaCl) environment. Under NaCl stress, germination rate, plant length, vigor indices, and leaf pigments of wheat seedlings significantly increased following P. aryabhattai inoculation. Furthermore, at 2%-NaCl, B. aryabhattai greatly and significantly (p ≤ 0.05) decreased relative leaf water content, membrane damage, and electrolyte leakage compared with the non-inoculated control. Catalase, superoxide dismutase, and peroxidase activity increased by 29, 32, and 21%, respectively, in wheat seedlings exposed to 2% NaCl and inoculated with the bacteria. The present findings demonstrate that endophytic P. aryabhattai strains might be used in the future as a multi-stress reducer and crop growth promoter in agronomically important crops including cereals.

Nano-pesticidal potential of Cassia fistula (L.) leaf synthesized silver nanoparticles (Ag@CfL-NPs): Deciphering the phytopathogenic inhibition and growth augmentation in Solanum lycopersicum (L.)

Plant-based synthesis of silver nanoparticles (Ag-NPs) has emerged as a potential alternative to traditional chemical synthesis methods. In this context, the aim of the present study was to synthesize Ag-NPs from Cassia fistula (L.) leaf extract and to evaluate their nano-pesticidal potential against major phyto-pathogens of tomato. From the data, it was found that particle size of spherical C. fistula leaf synthesized (Ag@CfL-NPs) varied from 10 to 20 nm, with the average diameter of 16 nm. Ag@CfL-NPs were validated and characterized by UV-visible spectroscopy (surface resonance peak λ_max = 430 nm), energy dispersive spectrophotometer (EDX), Fourier transform infrared (FTIR), and X-ray diffraction pattern (XRD), and electron microscopy; scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The FTIR spectra verified the participation of various living molecules (aromatic/aliphatic moieties and proteins) in synthesized Ag@CfL-NPs. The anti-phytopathogenic potential of Ag@CfL-NPs was assessed under in vitro conditions. Increasing doses of Ag@CfL-NPs exhibited an inhibitory effect against bacterial pathogen Pseudomonas syringae and 400 μg Ag@CfL-NPs ml^–1 caused a reduction in cellular viability, altered bacterial morphology, and caused cellular death Furthermore, Ag@CfL-NPs reduced exopolysaccharides (EPS) production and biofilm formation by P. syringae Additionally, Ag@CfL-NPs showed pronounced antifungal activity against major fungal pathogens. At 400 μg Ag@CfL-NPs ml^–1, sensitivity of tested fungi followed the order: Fusarium oxysporum (76%) > R. solani (65%) > Sarocladium (39%). Furthermore, 400 μg Ag@CfL-NPs ml^–1 inhibited the egg-hatching and increased larval mortality of Meloidogyne incognita by 82 and 65%, respectively, over control. Moreover, pot studies were performed to assess the efficacy of Ag@CfL-NPs to phyto-pathogens using tomato (Solanum lycopersicum L.) as a model crop. The applied phyto-pathogens suppressed the biological, physiological, and oxidative-stress responsiveness of tomatoes. However, 100 mg Ag@CfL-NPs kg^–1 improved overall performance and dramatically increased the root length, dry biomass, total chlorophyll, carotenoid, peroxidase (POD), and phenylalanine ammonia lyase (PAL) activity over pathogens-challenged tomatoes. This study is anticipated to serve as an essential indication for synthesis of efficient nano-control agents, which would aid in the management of fatal phyto-pathogens causing significant losses to agricultural productivity. Overall, our findings imply that Ag@CfL-NPs as nano-pesticides might be used in green agriculture to manage the diseases and promote plant health in a sustainable way.

Biodegradation of 4-nitroaniline by novel isolate Bacillus sp. strain AVPP64 in the presence of pesticides

In this study, Bacillus sp. strain AVPP64 was isolated from diuron-contaminated soil. It showed 4-nitroaniline (4-NA) degradation, pesticide tolerance, and self-nutrient integration via nitrogen (N)-fixation and phosphate (P)-solubilization. The rate constant (k) and half-life period (t_1/2) of 4-NA degradation in the aqueous medium inoculated with strain AVPP64 were observed to be 0.445 d^-1 and 1.55 d, respectively. Nevertheless, in the presence of chlorpyrifos, profenofos, atrazine and diuron pesticides, strain AVPP64 degraded 4-NA with t_1/2 values of 2.55 d, 2.26 d, 2.31 d and 3.54 d, respectively. The strain AVPP64 fixed 140 μg mL^-1 of N and solubilized 103 μg mL^-1 of P during the presence of 4-NA. In addition, strain AVPP64 produced significant amounts of plant growth-promoting metabolites like indole 3-acetic acid, siderophores, exo-polysaccharides and ammonia. In the presence of 4-NA and various pesticides, strain AVPP64 greatly increased the growth and biomass of Vigna radiata and Crotalaria juncea plants. These results revealed that Bacillus sp. strain AVPP64 can be used as an inoculum for bioremediation of 4-NA contaminated soil and sustainable crop production even when pesticides are present.

Unraveling the potential of pesticide-tolerant Pseudomonas sp. augmenting biological and physiological attributes of Vigna radiata (L.) under pesticide stress

In the agricultural domain, chemical pesticides are repetitively and harshly used to kill harmful pests, but they often pose a serious threat to microbial diversity, soil fertility and agricultural output. To deal with these problems, pesticide-tolerant plant growth promoting (PGP) rhizobacterial strains are often used to combat pesticidal toxicity. Here, Pseudomonas sp. PGR-11 (accession no. OM348534), recovered from a Vigna radiata (L.) rhizosphere, produced various growth regulating (GR) substances, including indole-3-acetic acid (IAA; 82.5 ± 9.2 μg mL^-1), enzyme 1-aminocyclopropane 1-carboxylate (ACC) deaminase (μM α-ketobutyrate mg^-1 protein h^-1), siderophores and ammonia. Strain PGR-11 grew well when cultured in growth medium with added metalaxyl (MTXL; 1200 μg mL^-1), carbendazim (CBZM; 800 μg mL^-1) and tebuconazole (TBZL; 1600 μg mL^-1). Pseudomonas sp. synthesized PGP substances even in the presence of increasing doses of pesticides. The phytotoxicity of the tested pesticides was assessed both in vitro and under pot-house conditions using a Vigna radiata (L.) crop. Increasing concentrations of chemical pesticides negatively impacted the growth, physiological and biochemical features. However, pesticide-tolerant Pseudomonas sp. relieved the toxicity and improved the biological attributes of the plant. Bio-inoculated plants showed significant enhancement in germination attributes, dry biomass, symbiotic features and yield features when compared to un-inoculated ones. Furthermore, with 100 μg metalaxyl kg^-1 soil, strain PGR-11 increased the chl-a, chl-b, total chlorophyll, carotenoids, SPAD index, photosystem efficiency (Fv/Fm), PSII quantum yield (FPSII), photochemical quenching (qP) and non-photochemical quenching (NpQ) content by 12, 19, 16, 27, 34, 41, 26, 29 and 33%, respectively, over un-inoculated but pesticide-treated plants. Additionally, inoculation of Pseudomonas sp. with 100 μg tebuconazole kg^-1 soil caused a significant (p ≤ 0.05) enhancement in transpiration rate (E), stomatal conductance (g _s), photosynthetic rate (P _N), vapor pressure deficit (kPa) and internal CO₂ concentration (C _i) of 19, 26, 23, 28 and 34%, respectively. Conclusively, the power to tolerate abnormally high pesticide concentration, the capacity to produce/secrete PGP substances even in a pesticide-stressed medium and the potential for improving/increasing the growth and physiology of plants by pesticide detoxification makes Pseudomonas sp. PGR-11 a fascinating choice for augmenting the productivity of V. radiata (L.) even in pesticide-stressed soils. The current findings will be helpful for exploring pesticide-tolerant ACC-deaminase-positive microbial strains as gifted entities for the environmental bioremediation of pesticides.

Beijerinckia fluminensis BFC-33, a novel multi-stress-tolerant soil bacterium: Deciphering the stress amelioration, phytopathogenic inhibition and growth promotion in Triticum aestivum (L.)

Environmental challenges like drought, salinity, heavy metals and pesticides directly/indirectly influence the environment and decreased the agricultural output. During its long developmental stages, cereal crops including wheat is exposed to a variety of abiotic/biotic stressors. Certain beneficial soil bacteria that can ameliorate environmental stresses can be exploited as crop growth promoters/enhancers under adverse situations. In this study, Beijerinckia fluminensis BFC-33 (accession no. MT672580) isolated from potato rhizosphere tolerated variousabiotic (drought, salinity, temperature, heavy metals, and fungicides) stresses. Strain BFC-33 demonstrated multifarious plant-growth-promoting (PGP) characteristics, such as the production of indole-3-acetic acid, P-solubilization, ACC deaminase, ammonia, siderophore, HCN, EPS, and extracellular enzymes. The antagonistic potential of BFC-33 against major fungal pathogens was ranked: Alternaria alternata (79.2%)>Rhizoctonia solani (69%)>Fusarium oxysporum (23.5%)>Ustilaginoidea virens (17%). Furthermore, bacterization of wheat seeds witha multi-stress-tolerant strain revealed B. fluminensis as a plant growth enhancer and biocontrol agent. For instance, increase in root length (cm) in BFC-33 inoculated wheat exposed to abiotic and biotic stresses at the seedling stage was ranked: B. fluminensis (24.2)>B. fluminensis + 100μgTBZLmL^-1 (21.3) = B. fluminensis + 2%PEG (21.3)>B. fluminensis + 100 mM NaCl (19.7)>B. fluminensis + 100μgPbmL^-1 (19) = B. fluminensis 100μgMNZBmL^-1 (19)>B. fluminensis + A. alternata (17.4)>B. fluminensis + 100μgCdmL^-1 (17)>B. fluminensis + F. oxysporum (13.4). In addition, increase in carotenoid accumulation (mg g^-1FW) in the foliage of BFC-33 inoculated wheat exposed to fungal infection was ranked: BFC-33 (3.88)>BFC-33+ A. alternata (3.0)>BFC-33+ R. solani (2.78)>BFC-33+ F. oxysporum (2.44). Moreover, BFC-33 inoculation significantly (p ≤ 0.05) reduced stress-induced stressor molecules (proline and TBARS) and electrolyte leakage. Furthermore, B. fluminensis BFC-33 potentially enhanced the defense responses in wheat seedlings by increasing phenylalanine ammonia lyase (PAL), β-1,3 glucanase, and polyphenol oxidase (PPO), which play a significant role in protecting plants from phytopathogens. Even so, by successfully establishing a product with the requisite effects under field settings, selecting multi-stress-tolerant and antagonistic plant growth promoting rhizobacteria (PGPRs) would be helpful to end-users. Future use of native multi-stress-tolerant bacteria as biocontrol agents in conjunction with existing drought, salinity, heavy metal, and pesticide tolerance might contribute to global food security.

Pesticide-induced disturbances of bee gut microbiotas

Social bee gut microbiotas play key roles in host health and performance. Worryingly, a growing body of literature shows that pesticide exposure can disturb these microbiotas. Most studies examine changes in taxonomic composition in Western honey bee (Apis mellifera) gut microbiotas caused by insecticide exposure. Core bee gut microbiota taxa shift in abundance after exposure but are rarely eliminated, with declines in Bifidobacteriales and Lactobacillus near melliventris abundance being the most common shifts. Pesticide concentration, exposure duration, season and concurrent stressors all influence whether and how bee gut microbiotas are disturbed. Also, the mechanism of disturbance-i.e. whether a pesticide directly affects microbial growth or indirectly affects the microbiota by altering host health-likely affects disturbance consistency. Despite growing interest in this topic, important questions remain unanswered. Specifically, metabolic shifts in bee gut microbiotas remain largely uninvestigated, as do effects of pesticide-disturbed gut microbiotas on bee host performance. Furthermore, few bee species have been studied other than A. mellifera, and few herbicides and fungicides have been examined. We call for these knowledge gaps to be addressed so that we may obtain a comprehensive picture of how pesticides alter bee gut microbiotas, and of the functional consequences of these changes.

Tolerance of pesticides and antibiotics among beneficial soil microbes recovered from contaminated rhizosphere of edible crops

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Soil bacterial isolates were recovered from contaminated rhizosphere regions.

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Majority of bacterial isolatesshowed multifarious plant growth promoting (PGP) activities.

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Bacterial isolates exhibited a varied level of pesticide tolerance.

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Sensitivity/resistance pattern among isolates was variable

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Pesticides tolerance and antibiotic resistance among soil isolates were variably correlated

A total of 45 beneficial soil bacterial isolates (15 each of Pseudomonas, Azotobacter and phosphate solubilizing bacteria: PSB) recovered from polluted rhizosphere soils were morphologically and biochemically characterized. Bacterial isolates produced indole-3-acetic acid (IAA), phenolate siderophores; SA (salicylic acid) and 2, 3-dihydroxy benzoic acid (2, 3-DHBA), 1-amino cyclopropane 1-carboxylate (ACC) deaminase, solubilised insoluble phosphate (Pi), secreted exopolysaccharides (EPS) and produced ammonia and cyanogenic compound (HCN). Isolates were tested for their tolerance ability against 12 different agrochemicals (chemical pesticides) and 14 antibiotics. Among Pseudomonas, isolate PS1 showed maximum (2183 µg mL⁻¹) tolerance to all tested agrochemicals. Likewise, among all Azotobacter isolates (n = 15), AZ12 showed maximum (1766 µg mL⁻¹) while AZ7 had lowest (950 µg mL⁻¹) tolerance ability to all tested agrochemicals. Moreover, among phosphate solubilizing bacterial isolates, maximum (1970 µg mL⁻¹) and minimum (1308 µg mL⁻¹) tolerance to agrochemicals was represented by PSB8 and PSB13 isolates, respectively. The antibiotic sensitivity/resistance among isolates varied considerably. As an example, Pseudomonas spp. was susceptible to several antibiotics, and inhibition zone differed between 10 mm (polymyxin B) to 34 mm (nalidixic acid). Also, isolate PS2 showed resistance to erythromycin, ciprofloxacin, methicillin, novobiocin and penicillin. The resistance percentage to multiple antibiotics among Azotobacter isolates varied between 7 and 33%. Among PSB isolates, inhibition zone differed between 10 and 40 mm and maximum and minimum resistance percentage to multiple antibiotics was recorded as 47% and 20%, respectively. The persistence of pesticides in agricultural soil may contribute to an increase in multidrug resistance among soil microorganisms. In conclusion, plant growth promoting (PGP) substances releasing soil microorganisms comprising of inherent/intrinsic properties of pesticides tolerance and antibiotics resistance may provide an attractive, agronomically feasible, and long-term prospective alternative for the augmentation of edible crops. However, in future, more research is needed to uncover the molecular processes behind the development of pesticide tolerance and antibiotic resistance among soil microorganisms.

Growth, respiratory activity and chlorpyrifos biodegradation in cultures of Azotobacter vinelandii ATCC 12837

This study aimed to evaluate the growth, respiratory activity, and biodegradation of chlorpyrifos in cultures of Azotobacter vinelandii ATCC 12837. A strategy based on the modification of culture media and aeration conditions was carried out to increase the cell concentration of A. vinelandii, in order to favor and determine its tolerance to chlorpyrifos and its degradation ability. The culture in shaken flasks, using sucrose as a carbon source, significantly improved the growth compared to media with mannitol. When the strain was cultivated under oxygen-limited (5.5, 11.25 mmol L⁻¹ h⁻¹) and no-oxygen-limited conditions (22 mmol L⁻¹ h⁻¹), the growth parameters were not affected. In cultures in a liquid medium with chlorpyrifos, the bacteria tolerated a high pesticide concentration (500 ppm) and the growth parameters were improved even under conditions with a reduced carbon source (sucrose 2 g L⁻¹). The strain degraded 99.6% of chlorpyrifos at 60 h of cultivation, in co-metabolism with sucrose; notably, A. vinelandii ATCC 12837 reduced by 50% the initial pesticide concentration in only 6 h (DT₅₀).

Effects of agrochemicals on the beneficial plant rhizobacteria in agricultural systems

Conventional agriculture relies heavily on chemical pesticides and fertilizers to control plant pests and diseases and improve production. Nevertheless, the intensive and prolonged use of agrochemicals may have undesirable consequences on the structure, diversity, and activities of soil microbiomes, including the beneficial plant rhizobacteria in agricultural systems. Although literature continues to mount regarding the effects of these chemicals on the beneficial plant rhizobacteria in agricultural systems, our understanding of them is still limited, and a proper account is required. With the renewed efforts and focus on agricultural and environmental sustainability, understanding the effects of different agrochemicals on the beneficial plant rhizobacteria in agricultural systems is both urgent and important to deduce practical solutions towards agricultural sustainability. This review critically evaluates the effects of various agrochemicals on the structure, diversity, and functions of the beneficial plant rhizobacteria in agricultural systems and propounds on the prospects and general solutions that can be considered to realize sustainable agricultural systems. This can be useful in understanding the anthropogenic effects of common and constantly applied agrochemicals on symbiotic systems in agricultural soils and shed light on the need for more environmentally friendly and sustainable agricultural practices.

Heavy Metals Induced Modulations in Growth, Physiology, Cellular Viability, and Biofilm Formation of an Identified Bacterial Isolate

The release of untreated tannery effluents comprising biotoxic heavy metal (HM) compounds into the ecosystem is one of our society's most serious environmental and health issues. After discharge, HM-containing industrial effluents reach agricultural soils and thus negatively affect the soil microbial diversity. Considering these, we assessed the effect of HMs on identified soil beneficial bacteria. Here, the effects of four heavy metals (HMs), viz., chromium (Cr), cadmium (Cd), nickel (Ni), and lead (Pb), on cellular growth, physiology, cell permeability, and biofilm formation of Enterobacter cloacae MC9 (accession no.: MT672587) were evaluated. HMs in a concentration range of 25-200 μg mL-1 were used throughout the study. Among HMs, Cd in general had the maximum detrimental effect on bacterial physiology. With increasing concentrations of HMs, bacterial activities consistently decreased. For instance, 200 μgCr mL-1 concentration greatly and significantly (p ≤ 0.05) reduced the synthesis of indole-3-acetic acid (IAA) by 70% over control. Furthermore, 200 μg mL-1 Cd maximally and significantly (p ≤ 0.05) reduced the synthesis of 2,3-dihydroxybenzoic acid (2,3-DHBA), salicylic acid (SA), 1-aminocyclopropane 1-carboxylate (ACC) deaminase, and extra polymeric substances (EPSs) of E. cloacae MC9 by 80, 81, 77, and 59%, respectively, over control. While assessing the toxic effect of HMs on the P-solubilizing activity of E. cloacae, the toxicity pattern followed the order Cr (mean value = 94.6 μg mL-1) > Cd (mean value = 127.2 μg mL-1) > Pb (mean value = 132.4 μg mL-1) > Ni (mean value = 140.4 μg mL-1). Furthermore, the colony-forming unit (CFU) count (Log10) of strain MC9 was completely inhibited at 150, 175, and 200 μg mL-1 concentrations of Cr and Cd. The confocal laser scanning microscopic (CLSM) analysis of HM-treated bacterial cells showed an increased number of red-colored dead cells as the concentration of HMs increased from 25 to 200 μg mL-1. Likewise, the biofilm formation ability of strain MC9 was maximally (p ≤ 0.05) inhibited at higher concentrations of Cd. In summary, the present investigation undoubtedly suggests that E. cloacae strain MC9 recovered from the HM-contaminated rhizosphere endowed with multiple activities could play an important role in agricultural practices to augment crop productivity in soils contaminated with HMs. Also, there is an urgent need to control the direct discharge of industrial waste into running water to minimize heavy metal pollution. Furthermore, before the application of HMs in agricultural fields, their appropriate field dosages must be carefully monitored.

Biodegradation of 2-ethylhexyl-4-methoxycinnamate in river sediments and its impact on microbial communities

Numerous studies have evaluated the toxicity and endocrine disrupting properties of organic UV filters for aquatic organisms, but little is known about their biodegradation in river sediments and their impact on microorganisms. We have set up the sterile and microbiological systems in the laboratory, adding 2-ethylhexyl-4-methoxycinnamate (EHMC), one of organic UV filters included in the list of high yield chemicals, at concentrations of 2, 20 and 200 μg/L, and characterized the microbial community composition and diversity in sediments. Monitoring of EHMC degradation within 30 days revealed that the half-life in the microbial system (3.49 days) was much shorter than that in the sterile system (7.55 days). Two potential degradation products, 4-mercaptobenzoic acid and 3-methoxyphenol were identified in the microbial system. Furthermore, high-throughput 16s and 18s rRNA gene sequencing showed that Proteobacteria dominated the sediment bacterial assemblages followed by Chloroflexi, Acidobacteria, Bacteroidetes and Nitrospirae; Eukaryota_uncultured fungus dominated the sediment fungal assemblages. Correlation analysis demonstrated that two bacterium genera (Anaerolineaceae_uncultured and Burkholderiaceae_uncultured) were significantly correlated with the biodegradation of EHMC. These results illustrate the biodegradability of EHMC in river sediments and its potential impact on microbial communities, which can provide useful information for eliminating the pollution of organic UV filters in natural river systems and assessing their potential ecological risks.

Mesorhizobium ciceri as biological tool for improving physiological, biochemical and antioxidant state of Cicer aritienum (L.) under fungicide stress

Fungicides among agrochemicals are consistently used in high throughput agricultural practices to protect plants from damaging impact of phytopathogens and hence to optimize crop production. However, the negative impact of fungicides on composition and functions of soil microbiota, plants and via food chain, on human health is a matter of grave concern. Considering such agrochemical threats, the present study was undertaken to know that how fungicide-tolerant symbiotic bacterium, Mesorhizobium ciceri affects the Cicer arietinum crop while growing in kitazin (KITZ) stressed soils under greenhouse conditions. Both in vitro and soil systems, KITZ imparted deleterious impacts on C. arietinum as a function of dose. The three-time more of normal rate of KITZ dose detrimentally but maximally reduced the germination efficiency, vigor index, dry matter production, symbiotic features, leaf pigments and seed attributes of C. arietinum. KITZ-induced morphological alterations in root tips, oxidative damage and cell death in root cells of C. arietinum were visible under scanning electron microscope (SEM). M. ciceri tolerated up to 2400 µg mL-1 of KITZ, synthesized considerable amounts of bioactive molecules including indole-3-acetic-acid (IAA), 1-aminocyclopropane 1-carboxylate (ACC) deaminase, siderophores, exopolysaccharides (EPS), hydrogen cyanide, ammonia, and solubilised inorganic phosphate even in fungicide-stressed media. Following application to soil, M. ciceri improved performance of C. arietinum and enhanced dry biomass production, yield, symbiosis and leaf pigments even in a fungicide-polluted environment. At 96 µg KITZ kg-1 soil, M. ciceri maximally and significantly (p ≤ 0.05) augmented the length of plants by 41%, total dry matter by 18%, carotenoid content by 9%, LHb content by 21%, root N by 9%, shoot P by 11% and pod yield by 15% over control plants. Additionally, the nodule bacterium M. ciceri efficiently colonized the plant rhizosphere/rhizoplane and considerably decreased the levels of stressor molecules (proline and malondialdehyde) and antioxidant defence enzymes viz. ascorbate peroxidise (APX), guaiacol peroxidise (GPX), catalase (CAT) and peroxidises (POD) of C. arietinum plants when inoculated in soil. The symbiotic strain effectively colonized the plant rhizosphere/rhizoplane. Conclusively, the ability to endure higher fungicide concentrations, capacity to secrete plant growth modulators even under fungicide pressure, and inherent features to lower the level of proline and plant defence enzymes makes this M. ciceri as a superb choice for augmenting the safe production of C. arietinum even under fungicide-contaminated soils.

Organochlorine Pesticides Negatively Influenced the Cellular Growth, Morphostructure, Cell Viability, and Biofilm-Formation and Phosphate-Solubilization Activities of Enterobacter cloacae Strain EAM 35

An in vitro study was conducted to assess the impact of organochlorine pesticides (OCPs) on cellular growth, morphology, cell viability, biofilm-formation activity, and growth-regulating substances of a soil bacterium. Phosphate-solubilizing EAM 35 isolated from rhizosphere soil was molecularly identified as Enterobacter cloacae (accession number MT672578.1). Strain EAM 35 tolerated varying levels of OCPs, viz., benzene hexachloride (BHC), chlorpyrifos (CP), dieldrin (DE), and endosulfan (ES). The toxicity of OCPs to strain EAM 35 was displayed in a concentration-dependent manner. Among the OCPs, ES at a concentration of 200 μM showed a higher toxicity, where it maximally reduced the bacterial synthesis of indole-3-acetic acid (IAA), salicylic acid (SA), and 2,3-dihydroxy-benzoic acid (DHBA) by 73% (p ≤ 0.001), 85% (p ≤ 0.005), and 83% (p ≤ 0.001), respectively, over the control. While comparing the toxicity of OCPs to P-solubilizing activity of E. cloacae after 10 days of growth, the toxicity pattern followed the order ES (mean value = 82.6 μg mL^-1) > CP (mean value = 93.2 μg mL^-1) > DE (mean value = 113.6 μg mL^-1) > BHC (mean value = 127 μg mL^-1). Furthermore, OCP-induced surface morphological distortion in E. cloacae EAM 35 was observed as gaps, pits on both cellular facets, and fragmented and disorganized cell structure under a scanning electron microscope (SEM). The membrane-compromised cells increased as the concentrations of OC pesticides increased from 25 to 200 μM. Additionally, microbial counts (log₁₀ CFU/mL) were also affected after pesticide exposure and decreased with increasing concentrations. While assessing the impact of OCPs on inhibition (%) of log₁₀ CFU/mL, 150, 175, and 200 μM concentrations of ES completely reduced the growth of E. cloacae. Similarly, while comparing the toxicity of higher concentrations of OCPs to bacterial growth, sensitivity followed the order ES > DE > CP > BHC. In addition, the biofilm-formation ability of strain EAM 35 was inhibited in a pesticide-dose-dependent manner, and it was statistically (p ≤ 0.05, p ≤ 0.005, and p ≤ 0.001) significant. Conclusively, the present study clearly suggests that before applying pesticides to soil, their recommended dose should carefully be monitored.

dsRNA Uptake in Plant Pests and Pathogens: Insights into RNAi-Based Insect and Fungal Control Technology

Efforts to develop more environmentally friendly alternatives to traditional broad-spectrum pesticides in agriculture have recently turned to RNA interference (RNAi) technology. With the built-in, sequence-specific knockdown of gene targets following delivery of double-stranded RNA (dsRNA), RNAi offers the promise of controlling pests and pathogens without adversely affecting non-target species. Significant advances in the efficacy of this technology have been observed in a wide range of species, including many insect pests and fungal pathogens. Two different dsRNA application methods are being developed. First, host induced gene silencing (HIGS) harnesses dsRNA production through the thoughtful and precise engineering of transgenic plants and second, spray induced gene silencing (SIGS) that uses surface applications of a topically applied dsRNA molecule. Regardless of the dsRNA delivery method, one aspect that is critical to the success of RNAi is the ability of the target organism to internalize the dsRNA and take advantage of the host RNAi cellular machinery. The efficiency of dsRNA uptake mechanisms varies across species, and in some uptake is negligible, rendering them effectively resistant to this new generation of control technologies. If RNAi-based methods of control are to be used widely, it is critically important to understand the mechanisms underpinning dsRNA uptake. Understanding dsRNA uptake mechanisms will also provide insight into the design and formulation of dsRNAs for improved delivery and provide clues into the development of potential host resistance to these technologies.

Fungicide-Tolerant Plant Growth-Promoting Rhizobacteria Mitigate Physiological Disruption of White Radish Caused by Fungicides Used in the Field Cultivation

Excessive use of fungicides in agriculture may result in substantial accumulation of active residues in soil, which affect crop health and yield. We investigated the response of Raphanus sativus (white radish) to fungicides in soil and potential beneficial interactions of radish plants with fungicide-tolerant plant growth-promoting rhizobacteria (PGPR). The PGPR were isolated from cabbage and mustard rhizospheres. Morphological and biochemical characteristics measured using standard methods, together with analysis of partial 16S rRNA gene sequences, revealed that fungicide-tolerant PGPR, isolates PS3 and AZ2, were closely related to Pseudomonas spp. These PGPR survived in the presence of high fungicide concentrations i.e., up to 2400 μg mL-1 carbendazim (CBZM) and 3200 μg mL-1 hexaconazole (HEXA). Bacterial isolates produced plant growth stimulants even under fungicide stress, though fungicides induced surface morphological distortion and alteration in membrane permeability of these bacteria, which was proved by a set of microscopic observations. Fungicides considerably affected the germination efficiency, growth, and physiological development of R. sativus, but these effects were relieved when inoculated with PGPR isolates. For instance, CBZM at 1500 mg kg-1 decreased whole dry biomass by 71%, whole plant length by 54%, total chlorophyll by 50%, protein content by 61%, and carotenoid production by 29%. After applying isolate AZ2 for white radish grown in CBZM (10 mg kg-1)-amended soil, it could improve plant growth and development with increased whole plant dry weight (10%), entire plant length (13%) and total chlorophyll content (18%). Similarly, isolate PS3 enhanced plant survival by relieving plant stress with declined biomarkers, i.e., proline (12%), malondialdehyde (3%), ascorbate peroxidase (6.5%), catalase (18%), and glutathione reductase (4%). Application of isolates AZ2 and PS3 could be effective for remediation of fungicide-contaminated soil and for improving the cultivation of radish plants while minimizing inputs of fungicides.

Kitazin-pea interaction: understanding the fungicide induced nodule alteration, cytotoxicity, oxidative damage and toxicity alleviation byRhizobium leguminosarum

Realizing the severity of fungicidal toxicity to legumes and importance of fungicide tolerant rhizobia in legume production, kitazin tolerant (2400 μg mL⁻¹) strain RP1 was recovered from pea nodules and was identified as Rhizobium leguminosarum (accession no. KY940047). R. leguminosarum produced indole acetic acid (80.5 ± 2.5 mL⁻¹), siderophores: salicylic acid (54 ± 7.3 μg mL⁻¹) and 2,3-dihydoxybenzoic acid (31.9 ± 2.7 μg mL⁻¹), α-ketobutyrate (51 ± 3.2 per mg per protein per hour), solubilized insoluble phosphate (29.5 ± 1.8 μg mL⁻¹) and secreted 29.5 + 2.6 μg mL⁻¹ exopolysaccharides, which, however, decreased consistently with gradually increasing kitazin concentrations. Beyond the tolerance level, kitazin caused structural damage and altered membrane integrity of RP1, as revealed under scanning (SEM) and confocal (CLSM) electron microscopy. Phytotoxicity of kitazin to peas was obvious under both in vitro and in vivo conditions. A significant reduction of 23, 68, 57 and 50% in germination, seedling vigor index, plumule length and radicle length was found at 2× kitazin compared to the control. Cellular damage and cytotoxicity induced by kitazin in membrane altered root cells was detected with acridine orange/propidium iodide (AO/PI) and Evans blue dye. A maximum increase of 1.72, 5.2, 9.3 and 1.72, 5.2, 9.3-fold in red and blue fluorescence was quantified at 1×, 2×, and 3× doses of kitazin, respectively. In contrast, application of R. leguminosarum RP1 alleviated toxicity and enhanced the length of plant organs, dry biomass, symbiotic attributes, photosynthetic pigments, nutrient uptake and grain features of peas comparatively uninoculated and fungicide-treated plants. Additionally, strain RP1 expressively reduced the antioxidant enzymes peroxidase, ascorbate peroxidase, guaiacol peroxidase, catalase and malondialdehyde contents by 10, 2.2, 11, 20 and 4% compared to stressed plants raised at 192 μg kg⁻¹ soil. Moreover, a decline of 19, 21 and 20% in proline content extracted from roots, shoots and grains, respectively was recorded for R. leguminosarum inoculated pea plants grown with 96 μg kg⁻¹ kitazin. Also, the SEM and CLSM of roots revealed the bacterial colonization. In conclusion, R. leguminosarum tolerated a higher level of kitazin, secreted plant growth promoting (PGP) bioactive molecules even under fungicide stress and significantly increased the performance of peas while reducing the levels of proline and antioxidant enzymes. So, it can safely be suggested to legume growers that RP1 strain could inexpensively be explored as an efficient biofertilizer for enhancing the production of legumes especially peas while growing even under fungicide (kitazin) enriched soils.

Realizing the severity of fungicidal toxicity to legumes and the importance of fungicide tolerant rhizobia in legume production, kitazin tolerant strain RP1 was recovered from pea nodules and was identified as Rhizobium leguminosarum.