Okra, an economically significant vegetable crop, is highly vulnerable to wilt disease caused by Fusarium oxysporum, leading to substantial yield reductions. This study probed the impact of F. oxysporum infection on morpho-physiological changes in okra plants and examined the efficacy of Priestia filamentosa, Bacillus halotolerans, and Pseudomonas fluorescens in wilt disease alleviation. The three bacteria exhibited biocontrol efficacy by producing antimicrobial metabolites and hydrolytic enzymes, inducing stress-mitigation. F. oxysporum infection caused pronounced wilting symptoms, vascular discoloration, and chlorosis, accompanied by significant reductions in plant height, dry matter accumulation, and photosynthetic pigments compared to uninfected plants. The scanning electron microscopy image revealed significant distortion in bacteria-treated fungal hyphae. The scanning electron and confocal laser scanning microscopy images of roots and leaves displayed extensive cellular damage, characterized by disrupted epidermal layers and compromised vascular tissues. The level of non-enzymatic (proline and malondialdehyde) and enzymatic (antioxidants) stress markers was substantially reduced after inoculation of all bacteria together, indicating alleviation of oxidative stress compared to diseased plants. The bacterial inoculation, in contrast, improved physiological traits, biomass, chlorophyll formation, and modulated oxidative stress responses, leading to wilt disease suppression through lytic enzymes, siderophores, hydrogen cyanide, and ammonia production. These findings underscore the efficacious role of P. filamentosa, B. halotolerans, and P. fluorescens as sustainable biocontrol agents for managing okra wilt disease, offering an eco-friendly alternative to chemical interventions for improved vegetable productivity.

IntroductionPseudomonas aeruginosa is notorious for its multidrug resistance and its involvement in hospital-acquired infections. In this study, 20 bacterial strains isolated from soil samples near the Hindan River in Ghaziabad, India, were investigated for their biochemical and morphological characteristics, with a focus on identifying strains with exceptional drug resistance and pyocyanin production.MethodsThe isolated bacterial strains were subjected to biochemical and morphological analyses to characterize their properties, with a particular emphasis on exopolysaccharide production. Strain GZB16/CEES1, exhibiting remarkable drug resistance and pyocyanin production. Biochemical and molecular analyses, including sequencing of its 16S rRNA gene (accession number LN735036.1), plasmid-curing assays, and estimation of plasmid size, were conducted to elucidate its drug resistance mechanisms and further pyocynin based target the Candida albicans Strain GZB16/CEES1 demonstrated 100% resistance to various antibiotics used in the investigation, with plasmid-curing assays, suggesting plasmid-based resistance gene transmission. The plasmid in GZB16/CEES1 was estimated to be approximately 24 kb in size. The study focused on P. aeruginosa’s pyocyanin production, revealing its association with anticandidal activity. The minimum inhibitory concentration (MIC) of the bacterial extract against Candida albicans was 50 μg/ml, with a slightly lower pyocyanin-based MIC of 38.5 μg/ml. Scanning electron microscopy illustrated direct interactions between P. aeruginosa strains and Candida albicans cells, leading to the destruction of the latter.DiscussionThese findings underscore the potential of P. aeruginosa in understanding microbial interactions and developing strategies to combat fungal infections. The study highlights the importance of investigating bacterial-fungal interactions and the role of pyocyanin in antimicrobial activity. Further research in this area could lead to the development of novel therapeutic approaches for combating multidrug-resistant infections.

Excessive and injudicious application of agrochemicals to optimize crop production has shown detrimental effects on microbial composition and function, soil-plant ecosystems, and human health via food chain. The microbiological strategies (phosphorus solubilization and ammonium production etc.), reduce the chemical dependency and mitigate environmental and human health risks. This study aimed to isolate and characterize plant beneficial bacteria from maize rhizospheres and asses their impact on wheat performance in pot trials. Cultures were characterized by morphological and biochemical assays. From these, two optimal cultures designated BSK1 and PS1, were selected for further investigation into their plant-growth promoting traits. The bacterial strains have ability to produce indole-3-acetic acid (IAA), siderophore, hydrogen cyanogenic and ammonium compounds along with phosphorus solubilization. Meanwhile, BSK1 demonstrated superior production levels of Indole-3-acetic acid (IAA), (203.61±2.08 μg ml-1), phosphate solubilization (15 mm) and siderophores (17 mm). Furthermore, both cultures exhibited positive qualitative traits for hydrogen cyanogenic and ammonium compounds. Later identified by 16S rRNA gene sequencing as B. subtilis (BSK1) and P. fluorescens (PS1). Respectively. Subsequently, in a two-year trial, the co-inoculation of the wheat plants by B. subtilis with P. fluorescens maximally enhanced the whole plant biomass, total chlorophyll content (7.9 mg/g), grain yields (33.5 g/plant), and protein content (96.2 mg/g) at harvest. A heavy bacterial colonization onto the root rhizosphere was revealed under scanning electron microscopy (SEM) image which was significantly dense for mixed cultures of B. subtilis with P. fluorescens. The results suggest that B. subtilis and P. fluorescens expressing multiple plant growth-promoting activity can be used to produce composite bioinoculants for enhancing wheat production while reducing the use of fertilizers.

Currently, agricultural land in most nations is threatened by heavy metal contamination, which could affect agricultural practices. This study screens out potential isolates from the consortia of microbiota recovered from the heavy metal-contaminated soil samples. The bacterial isolate was characterized and analyzed for its impending ability to tolerate heavy metals, chromium reduction, biosorption, and plant growth-promoting activities. The 16S rRNA gene sequencing method was used to identify the bacterial isolate. The phylogenetic analysis of accession number HE681416.1 confirmed that the approved isolate had a 99

Constantly increasing global human populations has put agricultural sector under astounding pressure to fulfil food demands growing worldwide. In order to optimize crop production, usage of agrochemicals in intensive agronomic practices have increased alarmingly. The negative impact of excessive application of agrichemicals on food production, human health and environment raises concerns about its long-term field application. Exploration of alternative means of crop protection and optimization, therefore, warrants inexpensive and environmentally friendly strategy. Use of microbes or microbes-based products among many options is one such important strategy that provides solution to the problems. In this regard, many biocontrol measures have been practiced over time, and some of them have shown exceptional potential and success. Realizing the importance of soil microbiota in crop optimization while reducing the chemical inputs, significance of plant beneficial bacteria in the amelioration of biotic stresses especially the phytopathogens employing microbiome management, microbial volatilomes, and nano-bioformulations is discussed. The relationship between the agriculturally useful soil microbiomes and food crops enables the development of microbes-based antagonist strategies for low-cost production of food crops in worrying open field environment.

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.

EDITORIAL article Front. Microbiol., 22 March 2023Sec. Microbe and Virus Interactions with Plants Volume 14 - 2023 | https://doi.org/10.3389/fmicb.2023.1174634

Considering the excessive pesticide pollution in the environment, atrazine (ATZ), butachlor (BCR) and quizalofop-p-ethyl (QUIZ) were selected to assess their toxic effect on Rhodococcus erythropolis PSB-6 (NCBI Accession No. MG028649). MIC values of ATZ, BCR and QUIZ to R. erythropolis were determined to be 100, 200 and 150 mu M, respectively. Biomarker enzymatic assays including LPO, LDH and oxidative stress (CAT) induced by herbicides represented significant (p <= 0.005) toxicity towards strain PSB-6. Herbicide-induced morphological changes viz. aberrant margins; cellular cracking and distortion/damage in R. erythropolis cells were apparent under SEM observation. Furthermore, herbicide-treated and DAPI (4',6-diamidino-2-phenylindole)-stained cells showed concentration-dependent reduction in cellular permeability as revealed under CLSM. Furthermore, herbicides displayed toxicity towards bioactive molecules of PSB-6 in a dose-related manner. Among them, ATZ imparted maximum negative effect, where it reduced the bacterial production of IAA, ACC deaminase and 2, 3-DHBA by 68% (p <= 0.001), 75% (p <= 0.001), and 83% (p <= 0.005), respectively, over control. Additionally, following herbicide exposure, bacterial counts (log(10) CFU mL(-1)) were reduced. Higher concentrations of ATZ and BCR completely reduced the growth patten of strain PSB-6. The current investigation provides an insight into a mechanistic approach of chemical herbicide-induced hazard toward a beneficial soil isolate. Careful monitoring is therefore necessary before agricultural application of pesticides.

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.

In plant biology, metabolomics is often used to quantitatively assess small molecules, metabolites, and their intermediates in plants. Metabolomics has frequently been applied to detect metabolic alterations in plants exposed to various biotic and abiotic stresses, including pesticides. The widespread use of pesticides and agrochemicals in intensive crop production systems is a serious threat to the functionality and sustainability of agroecosystems. Pesticide accumulation in soil may disrupt soil–plant relationships, thereby posing a pollution risk to agricultural output. Application of metabolomic techniques in the assessment of the biological consequences of pesticides at the molecular level has emerged as a crucial technique in exposome investigations. State-of-the-art metabolomic approaches such as GC–MS, LC–MS/MS UHPLC, UPLC–IMS–QToF, GC/EI/MS, MALDI-TOF MS, and 1H-HR-MAS NMR, etc., investigating the harmful effects of agricultural pesticides have been reviewed. This updated review seeks to outline the key uses of metabolomics related to the evaluation of the toxicological impacts of pesticides on agronomically important crops in exposome assays as well as bench-scale studies. Overall, this review describes the potential uses of metabolomics as a method for evaluating the safety of agricultural chemicals for regulatory applications. Additionally, the most recent developments in metabolomic tools applied to pesticide toxicology and also the difficulties in utilizing this approach are discussed.

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 mu g mL(-1)) tolerance to all tested agrochemicals. Likewise, among all Azotobacter isolates (n = 15), AZ12 showed maximum (1766 mu g mL(-1)) while AZ7 had lowest (950 mu g mL(-1)) tolerance ability to all tested agrochemicals. Moreover, among phosphate solubilizing bacterial isolates, maximum (1970 mu g mL(-1)) and minimum (1308 mu g 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.

Indiscriminate discharge of heavy metals/metalloids from different sources into the sustainable agro-ecosystem is a major global concern for food security and human health. Arsenic (As), categorized as group one human carcinogen is a quintessential toxic metalloid that alters the microbial compositions and functions, induce physiological and metabolic changes in plants and contaminate surface/ground water. The management of arsenic toxicity, therefore, becomes imminent. Acknowledging the arsenic threat, the study was aimed at identifying arsenic resistant bacteria and evaluating its arsenic removal/detoxification potential. Of the total 118 bacterial isolates recovered from arsenic rich environment, the bacterial strain RSC3 demonstrating highest As tolerance was identified as Enterobacter cloacae by 16S rRNA gene sequence analysis. Enterobacter cloacae tolerated high concentration (6000 ppm) of As and exhibited 0.55 h(-1) of specific growth rate as calculated from growth kinetics data. Strain RSC3 also displayed varying level of resistance to other heavy metals and many antibacterial drugs in plate bioassay. The bacterial strain RSC3 possessed gene (arsC) which causes transformation of arsenate to arsenite. The arsenate uptake and efflux of the bacterial cells was revealed by high throughput techniques such as AAS, SEM/TEM and EDX. The simultaneous As reducing ability, and multi metal/multi-antibiotics resistance potentials of E. cloacae provides a promising option in the microbes based remediation of As contaminated environments.

Among various crop damaging factors, biotic stresses primarily contribute to the limitation of the growth and development of plants, which leads to huge yield losses. Globally, about 25% crop yield is lost due to diseases and insect infestation. The production and consumption of vegetables is growing worldwide due to its nutritional value in human dietary systems. The vegetables are attacked by different soil borne pathogens which compromise yield and quality. To prevent such devastating effects, pesticides are applied in high throughput vegetable cultivation practices. However, the excessive and imprudent application of pesticides negatively affects the microbial diversity and soil biological activity. This in turn, detrimentally affects the yield and quality of vegetables. Eco-friendly sustainable agricultural practices that employ low cost microbial formulations can play pivotal roles in the management of biotic stresses. The use of plant beneficial bacteria to increase vegetable production may restrict pesticides application and also prevent the emergence of resistance of pathogens against toxic chemicals. Considering these, an attempt is made herein to highlight the impact of biotic stresses especially bacterial and fungal pathogens on some of the popularly grown vegetables. This review provides information about the active biomolecules associated with disease suppression and significance of plant beneficial bacteria in the amelioration of lethal vegetable diseases. The interplay between the soil beneficial microbes and vegetables will facilitate the development of bacteria-based antagonist strategies for inexpensive production of vegetables in stressful open field conditions.

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.

Plants suffer heavily from oxidative stress while exposed to heavy metals that cause damage and alter cellular homeostasis leading to the death of plants. The toxicity of heavy metals is, however, counterbalanced by complex cellular, physiological, biochemical, and molecular mechanisms which together allow plants to grow proficiently even under metal stressed conditions. Among various metal toxicity alleviation strategies, the production of phytocompounds plays a central role in circumventing metal stress. The biosynthesis of phytochemicals including high molecular mass antioxidant enzymes and low molecular compounds like phenolics, proline, salicylic acid, phytochelatins and metallothioneins favor survival and supports the growth of plants during stress. The role of stress-induced phytocompounds in combating metal toxicity is, however, poorly researched. In this mini-review, the abiotic stress tolerance strategies impacted by different enzymatic and non-enzymatic phytochemicals synthesized and secreted by plants exposed to heavy metals are highlighted. The phytochemicals mediated metal removal approaches provide an option for enhancing the growth and development of plants under abiotic stresses.

Heavy metal pollution has increased alarmingly due largely to industrialization, intensive agricultural practices and other anthropogenic activities. Soil heavy metal contamination is the serious threat to the food security worldwide. Due to non-degradative nature, metals persist for a longer period of time in the environment, can be toxic to human health and environments. Acknowledging the toxicity threat, various physical, chemical and biological detoxification strategies such as soil stabilization, soil excavation, soil washing, thermal desorption, chemical extraction and phytoremediation, have been employed in laboratory and under field conditions to treat metal contamination. Such techniques have not completely been successful due to cost, technical complexity, generation of secondary pollutants and conflicting results. Nanotechnology, a rapidly evolving field, has recently been used to remediate hazardous metals. Nanoparticles due to their unique chemical and physical properties are considered important in toxicity alleviation from contaminated environment. The integrated nanoparticles-bioremediation strategies called nano-bioremediation is other promising option that stimulate microbiome functions to remove harmful contaminants from the polluted area. The reported metal removal efficiency of nanobioremediation varies between 12

Traditionally, medicinal plants have long been used as a natural therapy. Plant-derived extracts or phytochemicals have been exploited as food additives and for curing many health-related ailments. The secondary metabolites produced by many plants have become an integral part of human health and have strengthened the value of plant extracts as herbal medicines. To fulfil the demand of health care systems, food and pharmaceutical industries, interest in the cultivation of precious medicinal plants to harvest bio-active compounds has increased considerably worldwide. To achieve maximum biomass and yield, growers generally apply chemical fertilizers which have detrimental impacts on the growth, development and phytoconstituents of such therapeutically important plants. Application of beneficial rhizosphere microbiota is an alternative strategy to enhance the production of valuable medicinal plants under both conventional and stressed conditions due to its low cost, environmentally friendly behaviour and non-destructive impact on fertility of soil, plants and human health. The microbiological approach improves plant growth by various direct and indirect mechanisms involving the abatement of various abiotic stresses. Given the negative impacts of fertilizers and multiple benefits of microbiological resources, the role of plant growth promoting rhizobacteria (PGPR) in the production of biomass and their impact on the quality of bio-active compounds (phytochemicals) and mitigation of abiotic stress to herbal plants have been described in this review. The PGPR based enhancement in the herbal products has potential for use as a low cost phytomedicine which can be used to improve health care systems.

Bioremediation among many cleanup technologies, considered an attractive and affordable remediation technology with no side effects on agroenvironment, is adopted to circumvent polluted soils making ecologically disturbed soils cultivable again. Soil microbes spanning different genera and groups evade the toxicity of various environmental contaminants like heavy metals, pesticides, and hydrocarbons. Biofertilizer organisms, among soil microbiomes, have been used in the management of abiotic and biotic stresses and as a formulation to optimize yields and quality of food crops. The exploitation of soil microbes both as pollution alleviating agents (bioremediation) and as crop stimulants (biofertilizers) has provided solutions to both the challenges of environmental stresses and expensive chemical fertilizers. Considering the impactful role of biofertilizers in soil amelioration and plant growth promotion, the priority of current research has been directed toward finding unexplored microbes with dual features as bioremediating materials and as biofertilizers. Despite the growing interest in biofertilizer-based remediation technology, the full potential of this technology has not yet been realized. Recent developments in bacterial biofertilizer (especially nitrogen and phosphate biofertilizers)-based bioremediation of polluted soils and sustainable crop production are reviewed. Here, the microbial formulations, biofertilizer-based strategies for stress management, and their prospects for sustainable crop production are surveyed and presented. Collectively, the information provided herein is desirable to fully explore the bioremediation potential of bacterial biofertilizers and is likely to generate interest for adoption and application of this microbiological technology for remediation of contaminated soils vis-à-vis crop production under both conventional and stressful conditions to satisfy global “food and feed” demands.