Effects of organochlorine pesticides on plant growth-promoting traits of phosphate-solubilizing rhizobacterium, Paenibacillus sp. IITISM08

Unboxing PGPR-mediated management of abiotic stress and environmental cleanup: what lies inside?

Abiotic stresses including heavy metal toxicity, drought, salt and temperature extremes disrupt the plant growth and development and lowers crop output. Presence of environmental pollutants further causes plants suffering and restrict their ability to thrive. Overuse of chemical fertilizers to reduce the negative impact of these stresses is deteriorating the environment and induces various secondary stresses to plants. Therefore, an environmentally friendly strategy like utilizing plant growth-promoting rhizobacteria (PGPR) is a promising way to lessen the negative effects of stressors and to boost plant growth in stressful conditions. These are naturally occurring inhabitants of various environments, an essential component of the natural ecosystem and have remarkable abilities to promote plant growth. Furthermore, multifarious role of PGPR has recently been widely exploited to restore natural soil against a range of contaminants and to mitigate abiotic stress. For instance, PGPR may mitigate metal phytotoxicity by boosting metal translocation inside the plant and changing the metal bioavailability in the soil. PGPR have been also reported to mitigate other abiotic stress and to degrade environmental contaminants remarkably. Nevertheless, despite the substantial quantity of information that has been produced in the meantime, there has not been much advancement in either the knowledge of the processes behind the alleged positive benefits or in effective yield improvements by PGPR inoculation. This review focuses on addressing the progress accomplished in understanding various mechanisms behind the protective benefits of PGPR against a variety of abiotic stressors and in environmental cleanups and identifying the cause of the restricted applicability in real-world.

The alleviation of salt stress on rice through increasing photosynthetic capacity, maintaining redox homeostasis and regulating soil enzyme activities by Enterobacter sp. JIV1 assisted with putrescine

The detrimental impact of soil salinization on crop productivity and agricultural economy has garnered significant attention. A rhizosphere bacterium with favorable salt tolerance and plant growth-promoting (PGP) functions was isolated in this work. The bacterium was identified as Enterobacter through 16 S rDNA sequencing analysis and designated as Enterobacter sp. JIV1. Interestingly, the presence of putrescine (Put), which had been shown to contribute in reducing abiotic stress damage to plants, significantly promoted strain JIV1 to generate 1-aminocyclopropane-1-carboxylic (ACC) deaminase, dissolve phosphorus and secrete indole-3-acetic acid (IAA). However, the synergy of plant growth promoting rhizobacteria (PGPR) and Put in improving plant salt resistance has not been extensively studied. In this study, strain JIV1 and exogenous Put effectively mitigated the inhibitory impact of salt stress simulated by 200 mM NaCl on rice (Oryza sativa L.) growth. The chlorophyll accumulation, photosynthetic efficiency and antioxidant capacity of rice were also significantly strengthened. Notably, the combined application of strain JIV1 and Put outperformed individual treatments. Moreover, the co-addition of strain JIV1 and Put increased soil protease and urease activities by 451.97% and 51.70% compared to that of salt treatment group. In general, Put-assisted PGPR JIV1 provides a new perspective on alleviating the salt-induced negative impacts on plants.

Research progress on remediation of organochlorine pesticide contamination in soil

Deteriorated soil pollution has grown into a worldwide environmental concern over the years. Organochlorine pesticide (OCP) residues, featured with ubiquity, persistence and refractoriness, are one of the main pollution sources, causing soil degradation, fertility decline and nutritional imbalance, and severely impacting soil ecology. Furthermore, residual OCPs in soil may enter the human body along with food chain accumulation and pose a serious health threat. To date, many remediation technologies including physicochemical and biological ways for organochlorine pollution have been developed at home and abroad, but none of them is a panacea suitable for all occasions. Rational selection and scientific decision-making are grounded in in-depth knowledge of various restoration techniques. However, soil pollution treatment often encounters the interference of multiple factors (climate, soil properties, cost, restoration efficiency, etc.) in complex environments, and there is still a lack of systematic summary and comparative analysis of different soil OCP removal methods. Thus, to better guide the remediation of contaminated soil, this review summarized the most commonly used strategies for OCP removal, evaluated their merits and limitations and discussed the application scenarios of different methods. It will facilitate the development of efficient, inexpensive and environmentally friendly soil remediation strategies for sustainable agricultural and ecological development.

Soil properties and organochlorine compounds co-shape the microbial community structure: A case study of an obsolete site

Organochlorine compounds (OCs) such as chlorobenzenes (CB) are persistent organic pollutants that are ubiquitous in soils at organochlorine pesticides (OCP) production sites. Long-term contamination with OCs might alter the soil microbial structure and further affect soil functions. However, the effects of OCs regarding the shaping of microbial community structures in the soils of OCs-contaminated sites remain obscure, especially in the vertical soil profile where pollutants are highly concealed. Hence this paper explored the status and causes of OCs pollution (CB, hexachlorocyclohexane (HCH), and dichlorodiphenyltrichloroethane (DDT)) in an obsolete site, and its combined effects with soil properties (pH, available phosphorus (AP), dissolved organic carbon (DOC), etc) on microbial community structure. The mean total concentration of OCs in the subsoils was up to 996 times higher than that in the topsoils, with CB constituting over 90% of OCs in the subsoil. Historical causes, anthropogenic effects, soil texture, and the nature of OCs contributed to the differences in the spatial distribution of OCs. Redundancy analysis revealed that both the soil properties and OCs were important factors in shaping microbial composition and diversity. Variation partitioning analysis further indicated that soil properties had a greater impact on microbial community structure than OCs. Significant differences in microbial composition between topsoils and subsoils were observed through linear discriminant analysis effect size (LEfSe) analysis, primarily driven by different pollutant conditions. Additionally, co-occurrence network analysis indicated that heavily contaminated subsoils exhibited closer and more intricate bacterial community interactions compared to lightly contaminated topsoils. This work reveals the impact of environmental factors in co-shaping the structure of soil microbial communities. These findings advance our understanding of the intricate interplay among organochlorine pollutants, soil properties, and microbial communities, and provides valuable insights into devising effective management strategies in OCs-contaminated soils.

Cadmium-tolerant Bacillus cereus 2-7 alleviates the phytotoxicity of cadmium exposure in banana plantlets

Bananas are the world's important fruit and staple crop in the developing countries. Cadmium (Cd) contamination in soils results in the decrease of crop yield and food safety. Bioremediation is an environmental-friendly and effective measure using Cd-tolerant plant growth promoting rhizobacteria (PGPR). In our study, a Cd-resistant PGPR Bacillus cereus 2-7 was isolated and identified from a discarded gold mine. It could produce multiple plant growth promoting biomolecules such as siderophores, indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate (ACC)-deaminase and phosphatase. The extracellular accumulation was a main manner of Cd removal. Surplus Cd induced the expression of Cd resistance/transport genes of B. cereus 2-7 to maintain the intracellular Cd homeostasis. The pot experiment showed that Cd contents decreased by 50.31 % in soil, 45.43 % in roots, 56.42 % in stems and 79.69 % in leaves after the strain 2-7 inoculation for 40 d. Bacterial inoculation alleviated the Cd-induced oxidative stress to banana plantlets, supporting by the increase of chlorophyll contents, plant height and total protein contents. The Cd remediation mechanism revealed that B. cereus 2-7 could remodel the rhizosphere bacterial community structure and improve soil enzyme activities to enhance the immobilization of Cd. Our study provides a Cd-bioremediation strategy using Cd-resistant PGPR in tropical and subtropical area.

Plant -microbe assisted emerging contaminants (ECs) removal and carbon cycling

Continuous increase in the level of atmospheric CO₂ and environmental contaminates has aggravated various threats resulting from environmental pollution and climate change. Research into plant -microbe interaction has been a central concern of ecology for over the year. However, despite the clear contribution of plant -microbe to the global carbon cycle, the role of plant -microbe interaction in carbon pools, fluxes and emerging contaminants (ECs) removal are still a poorly understood. The use of plant and microbes in ECs removal and carbon cycling is an attractive strategy because microbes operate as biocatalysts to remove contaminants and plant roots offer a rich niche for their growth and carbon cycling. However, bio-mitigation of CO₂ and removal of ECs is still under research phase because of the CO₂ capture and fixation efficiency is too low for industrial purposes and cutting-edge removal methods have not been created for such emerging contaminants.

Phytoremediation of DEHP and heavy metals co-contaminated soil by rice assisted with a PGPR consortium: Insights into the regulation of ion homeostasis, improvement of photosynthesis and enrichment of beneficial bacteria in rhizosphere soil

The coexistence of di (2-ethylhexyl) phthalate (DEHP), Cd, and Zn poses a serious challenge to soil ecosystems. This study aimed to evaluate the phytoremediation potential of rice assisted with a plant growth promoting rhizobacteria (PGPR) consortium for the remediation of DEHP, Cd, and Zn co-contaminated soil. The consortium consisted of four bacterial strains, all of which exhibited Cd-Zn resistance and DEHP degradability. The results showed that the rice assisted by the bacterial consortium dissipated 86.1% DEHP while removing 76.0% Cd²⁺ and 92.2% Zn²⁺ from soil within 30 d. The presence of the PGPR consortium promoted plant growth and improved soil enzymatic activity, which may have helped enhance the removal of DEHP and heavy metals from the soil. Moreover, the application of the consortium modified the bacterial community and increased the relative abundance of bacteria related to DEHP degradation (Sphingomonas, Xanthobacteraceae), heavy metal immobilization (Massilia), and soil nutrient cycling (Nitrospira, Vicinamibacterales), which promoted plant growth and the removal of DEHP and heavy metals from soil. Notably, the DEHP and heavy metal contents in rice decreased substantially during the phytoremediation process. Therefore, the PGPR consortium could be beneficial for enhancing the removal of DEHP and heavy metals from the soil, without inducing the accumulation of these pollutants in rice. In general, this study confirmed that the combined use of rice and the PGPR consortium could remedy DEHP and heavy metal co-contaminated soil economically and ecologically without simultaneously posing risks for rice consumption.

New insights into engineered plant-microbe interactions for pesticide removal

Over the past decades, rapid industrialization along with the overutilization of organic pollutants/pesticides has altered the environmental circumstances. Moreover, various anthropogenic, xenobiotics and natural activities also affected plants, soil, and human health, in both direct and indirect ways. To counter this, several conventional methods are currently practiced, but are uneconomical, noxious, and is yet inefficient for large-scale application. Plant-microbe interactions are mediated naturally in an ecosystem and are practiced in several areas. Plant growth promoting rhizobacteria (PGPR) possess certain attributes affecting plant and soil consequently performing decontamination activity via a direct and indirect mechanism. PGPR also harbors indispensable genes stimulating the mineralization of several organic and inorganic compounds. This makes microbes potential candidates for contributing to sustainably remediating the harmful pesticide contaminants. There is a limited piece of information about the plant-microbe interaction pertaining predict and understand the overall interaction concerning a sustainable environment. Therefore, this review focuses on the plant-microbe interaction in the rhizosphere and inside the plant's tissues, along with the utilization augmenting the crop productivity, reduction in plant stress along with decontamination of pesticides/organic pollutants in soil for sustainable environmental management.

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.

Improvement of the Cd and Zn phytoremediation efficiency of rice (Oryza sativa) through the inoculation of a metal-resistant PGPR strain

Cadmium (Cd) and zinc (Zn) in contaminated soil inhibit rice yield and produce toxic effects on human body through rice accumulation. Plant growth promoting rhizobacteria (PGPR) assisted phytoremediation is an effective ecological measure to improve the remediation efficiency of heavy metal contaminated soil. The purpose of this study was to investigate the efficiency of the combination of rice and Cd/Zn-tolerant PGPR strain Bacillus sp. ZC3-2-1 for the remediation of Cd-Zn contaminated soil. Moreover, the effects of inoculations on rhizosphere bacterial communities and ion homeostasis of rice under Cd-Zn exposure will also be explored. The results showed that compared with the treatment without inoculation, ZC3-2-1 decreased the bioavailable Cd and Zn concentrations in soil by 39.3% and 32.0%, respectively, and increase the phytoextraction of Cd²⁺ and Zn²⁺ by rice to 48.2% and 8.0%, respectively. This inoculation process significantly increased the rice biomass, resulting that the contents of Cd²⁺ and Zn²⁺ per biomass unit of rice didn't change significantly. This fact meant that ZC3-2-1 could improve the phytoremediation efficiency of Cd-Zn contaminated soil by promoting the phytoextraction and immobilization of the metal, while might not affect the crop food safety. Besides, through regulation of the Na⁺ and Mg²⁺ concentration in rice, ZC3-2-1 played a positive role in maintaining ion homeostasis which was disrupted by Zn or Cd. Moreover, ZC3-2-1 could modulate the beneficial bacterial communities in rice rhizosphere soil, and then enhanced Cd-Zn immobilization and enzyme activities in soil, leading to the enhancement of rice growth and phytoremediation efficiency. Above all, this study provided novel insights into developing an efficient phytoremediation system and safe production of rice in Cd-Zn contaminated soil with the application of Bacillus sp. ZC3-2-1, as well as advance our understanding of the principles of rhizosphere bacterial community assemble and maintaining ion homeostasis in rice during this phytoremediation process.

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.

Characterizations of novel pesticide-degrading bacterial strains from industrial wastes found in the industrial cities of Pakistan and their biodegradation potential

BACKGROUND

Lack of infrastructure for disposal of effluents in industries leads to severe pollution of natural resources in developing countries. These pollutants accompanied by solid waste are equally hazardous to biological growth. Natural attenuation of these pollutants was evidenced that involved degradation by native microbial communities. The current study encompasses the isolation of pesticide-degrading bacteria from the vicinity of pesticide manufacturing industries.

METHODS

The isolation and identification of biodegrading microbes was done. An enrichment culture technique was used to isolate the selected pesticide-degrading bacteria from industrial waste.

RESULTS

Around 20 different strains were isolated, among which six isolates showed significant pesticide biodegrading activity. After 16S rRNA analysis, two isolated bacteria were identified as Acinetobacter baumannii (5B) and Acidothiobacillus ferroxidans, and the remaining four were identified as different strains of Pseudomonas aeruginosa (1A, 2B, 3C, 4D). Phylogenetic analysis confirmed their evolution from a common ancestor. All strains showed distinctive degradation ability up to 36 hours. The Pseudomonas aeruginosa strains 1A and 4D showed highest degradation percentage of about 80% for DDT, and P. aeruginosa strain 3C showed highest degradation percentage, i.e., 78% for aldrin whilst in the case of malathion, A. baumannii and A. ferroxidans have shown considerable degradation percentages of 53% and 54%, respectively. Overall, the degradation trend showed that all the selected strains can utilize the given pesticides as sole carbon energy sources even at a concentration of 50 mg/mL.

CONCLUSION

This study provided strong evidence for utilizing these strains to remove persistent residual pesticide; thus, it gives potential for soil treatment and restoration.

Potential use of Solanum lycopersicum and plant growth promoting rhizobacterial (PGPR) strains for the phytoremediation of endosulfan stressed soil

This study aimed to assess the role of Solanum lycopersicum and plant growth promoting rhizobacterial (PGPR) strains to remove endosulfan present in the soil. S. lycopersicum was grown in endosulfan amended soil (5, 10, 25, and 50 mg kg^-1) inoculated with PGPR strains for 40, 80, and 120 days. The influence of PGPR inoculation on endosulfan accumulation in plant tissues, endosulfan degradation in soil, and plant growth parameters were evaluated. The oxidative stress tolerance was assessed by determining the malondialdehyde formation in S. lycopersicum planted in endosulfan stressed soil inoculated with PGPR strains. The results showed that uptake of endosulfan followed root > shoot pathway in association with a reduction in endosulfan accumulation in inoculated plants as related to un-inoculated plants. Moreover, inoculation of PGPR strains showed a beneficial influence on the degradation of endosulfan, Bacillus sp. PRB101 showed maximum degradation (89% at 5 mg kg^-1 of soil) of endosulfan at 120 days after sowing. Furthermore, the content of malondialdehyde was lower in inoculated plants as related to un-inoculated plants. Inoculation of PGPR strains efficiently enhanced plant biomass. The findings showed the effectiveness of PGPR strains to increase the decontamination of endosulfan stressed soil and decline endosulfan concentration in the plant tissues.

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.

Unlocking the potential of plant growth-promoting rhizobacteria on soil health and the sustainability of agricultural systems

The concept of soil health refers to specific soil properties and the ability to support and sustain crop growth and productivity, while maintaining long-term environmental quality. The key components of healthy soil are high populations of organisms that promote plant growth, such as the plant growth promoting rhizobacteria (PGPR). PGPR plays multiple beneficial and ecological roles in the rhizosphere soil. Among the roles of PGPR in agroecosystems are the nutrient cycling and uptake, inhibition of potential phytopathogens growth, stimulation of plant innate immunity, and direct enhancement of plant growth by producing phytohormones or other metabolites. Other important roles of PGPR are their environmental cleanup capacities (soil bioremediation). In this work, we review recent literature concerning the diverse mechanisms of PGPR in maintaining healthy conditions of agricultural soils, thus reducing (or eliminating) the toxic agrochemicals dependence. In conclusion, this review provides comprehensive knowledge on the current PGPR basic mechanisms and applications as biocontrol agents, plant growth stimulators and soil rhizoremediators, with the final goal of having more agroecological practices for sustainable agriculture.

Global trends in pesticides: A looming threat and viable alternatives

Pesticides are widely used chemical compounds in agriculture to destroy insects, pests and weeds. In modern era, they form an indispensable part of agricultural and health practices. Globally, nearly 3 billion kg of pesticides are used every year with a budget of ~40 billion USD. This extensive usage has increased the crop yield as well as led to significant reduction in harvest losses and thereby, enhanced food availability. On the other hand, indiscriminate usage of these chemicals has led to several environmental implications and caused adverse effects on human health. Epidemiological evidences have revealed the harmful effects of pesticides exposure on various organs including liver, brain, lungs and colon. Recent investigations have shown that pesticides can also lead to fatal consequences such as cancer among individuals. These chemicals enter ecosystem, thus hampering the sensitive environmental equilibrium through bio-accumulation. Due to their non-biodegradable nature, they can persist in nature for years and are regarded as potent biohazard. Worldwide, very few surveillance methods have been considered, which can bring awareness among the individuals, therefore the present review is an attempt to delineate consequences induced by various types of pesticide exposure on the environment. Further, the prospective of biopesticides use could facilitate the increase of crop production without compromising human health.

Influence of plant growth promoting rhizobacterial strains Paenibacillus sp. IITISM08, Bacillus sp. PRB77 and Bacillus sp. PRB101 using Helianthus annuus on degradation of endosulfan from contaminated soil

Endosulfan is a broad spectrum insecticide used in agriculture for protection of various food and non-food crops. It is persistent in nature and hence found in soil, air and water. The potential use of plants and microorganisms for the removal of endosulfan from soil was studied. Helianthus annuus plant was grown in soil spiked with 5, 10, 25 and 50 mg kg^-1 concentrations of endosulfan and inoculated with plant growth promoting rhizobacterial strains Paenibacillus sp. IITISM08, Bacillus sp. PRB77 and Bacillus sp. PRB101 for 40, 80 and 120 days. Potential of plant for endosulfan uptake was evaluated by investigating the endosulfan levels in plant tissues (root and shoot). The results indicated that endosulfan accumulation followed the pattern of root > shoot as well as decrease in uptake of endosulfan in root and shoot of a plant grown in bacterial inoculated soil as compared to un-inoculated soil. Bacterial inoculation had a positive effect on endosulfan degradation. Maximum degradation of 92% at 5 mg kg^-1 of endosulfan in soil was observed on inoculation with PRB101 after 120 days of inoculation. The results showed that plant growth promoting bacteria enhances plant biomass production. Lipid peroxidation was also estimated by determining the malondialdehyde (MDA) production, which is a biomarker of oxidative damage. Decrease in MDA formation by root and leaves of plants grown in the bacteria inoculated plant was also observed. The results suggested the effectiveness of plant growth promoting rhizobacteria to boost accumulation potential, biomass production and enhance remediation of endosulfan contaminated soil.

Effect of endosulfan tolerant bacterial isolates (Delftia lacustris IITISM30 and Klebsiella aerogenes IITISM42) with Helianthus annuus on remediation of endosulfan from contaminated soil

Endosulfan contaminated soil has become an important risk to the environment and human health worldwide. In the present study, endosulfan tolerant bacterial strain Delftia lacustris IITISM30 and Klebsiella aerogenes IITISM42 were isolated from pesticide stressed agricultural soil and tested for plant growth promoting activities. A pot experiment was performed using Helianthus annuus, grown in soil supplemented with endosulfan and inoculated with pure and consortium of bacterial strain IITISM30 and IITISM42. Inoculation increased plant biomass production and endosulfan degradation, maximum degradation (90% at 5 mg kg^-1 of soil) was observed by inoculation with a consortium of bacterial strain IITISM30 and IITISM42. Moreover, there was significantly less endosulfan accumulation was observed in roots and shoots of bacterial inoculated plants as compared to uninoculated plants. Decrease in production of malonialdehyde (MDA) was noticed on inoculation of a bacterial strain. The study demonstrated that inoculation of a consortium of endosulfan tolerant plant growth promoting bacterial isolates could more effectively remediate endosulfan contaminated soils and decrease endosulfan residues in plants, than individual strains. Moreover, it revealed that combined use of H. annuus and endosulfan tolerant bacterial isolates IITISM30 and IITISM42 has great potential for remediating endosulfan contaminated soil.

Cellular destruction, phytohormones and growth modulating enzymes production by Bacillus subtilis strain BC8 impacted by fungicides

In vitro experiments were performed to ascertain the impact of kitazin, hexaconazole, metalaxyl and carbendazim on growth behaviour, enzymatic profile, ultrastructure, cell permeability and bioactive molecules of phosphate-solubilizing bacterium. Strain BC8 isolated from Brassica oleracea rhizosphere was characterized and identified as Bacillus subtilis by 16S rDNA sequencing (Accession no. MG028650) technique. Strain BC8 was unambiguously chosen due to its high tolerance capability to various fungicides and substantial production of plant growth regulators. The biomarker enzymatic assays (lipid peroxidation, lactate dehydrogenase) and oxidative stress (catalase) induced by fungicides exhibited significant (p < 0.05) toxicity of fungicides toward strain BC8. Fungicides caused the cellular/ultrastructural damage and reduced the viability of strain BC8 as clearly revealed under scanning (SEM), high resolution transmission (HR-TEM) and confocal laser scanning (CLSM) microscopy. As the concentration of fungicides increased, a gradual drop in the plant growth promoting traits of B. subtilis strain BC8 was observed. Kitazin at 2400 μg mL^-1, hexaconazole at 1500 μg mL^-1, metalaxyl at 1200 μg mL^-1 and carbendazim at 1200 μg mL^-1decreased the IAA production by 35 (48.3 μg mL^-1), 27 (51.5 μg mL^-1), 39 (43.6 μg mL^-1) and 47% (37.3 μg mL^-1), respectively, over control (71.3 μg mL^-1), while, α-ketobutyrate was declined by 51 (29.6), 56 (26.2), 61 (22.8) and 68 (19)%, respectively, over untreated control (59.9 mg protein^-1 h^-1). Also, with increase in the concentration of fungicides there was a significant decrease in plant nutrient (P); the maximum being (19.6 μg mL^-1) observed at 1500 μg mL^-1 hexaconazole with consequent drop in pH (from pH 6.4 to 4.2). The current findings clearly suggest that despite injury, B. subtilis maintained secreting active biomolecules and this property makes this organism truly indispensable for enhancing crop production under fungicide stressed conditions.