Production and utilisation of nanoscale materials like metal, metal oxide-based nanoparticles, carbon or organic nanoparticles, and quantum dots in various fields have increased globally in recent decades (Abbas et al., 2020, Santaella and Plancot, 2020). Among these nanomaterials, metal and metal oxide nanoparticles are extensively used in biomedicine and environmental application due to their distinct optical, chemical, mechanical, electrical and magnetic properties (Chen et al., 2017; Mahawar and Prasanna, 2018).
Silver nanoparticles, including various silver-based nanomaterials, are promising antimicrobial agents against pathogenic microorganisms. This unique property finds application in developing wound dressing, food packaging, antimicrobial coating agents in paints, and medical devices. Most significantly, the application of silver nanoparticles in wastewater treatment is highly appreciated (Chavan and Nadanathangam, 2019; Namasivayam et al., 2020). Combined with silver nanoparticles, zinc oxide (ZnO) based nanomaterials also exhibit certain unique properties, mainly antimicrobial and UV blocking or protective, which find application in food packaging, paints, sun screams, electronics, catalysis and catalysis cosmetics (Parashar et al., 2020).
Due to their promising application, these nanoparticles' production, utilisation and release have significantly increased in recent decades, which is known to cause awareness of undesirable or non-target effects (Khan et al., 2022). Recent research on releasing nanoparticles and their interactions with the diverse biotic and abiotic components of the environment or ecosystem, mainly soil and aquatic, revealed the non-target effect. Toxic effect of silver and zinc oxide nanoparticles on the plant growth promoting nitrogen fixing, phosphate solubilising, biofilm formers that associated with Indian agriculture soil (Chavan et al., 2021), titanium di oxide nanoparticles on soil bacterial,fungal, actinomycetes (Anitha Kumari and Thangam, 2022), silver nanoparticles on the sunflower rhizosphere nitrogen fixing bacteria (Rezayatmand and Doudi, 2018), nano zeolite on various soil beneficial microorganism (Sivashankari et al., 2021), ZnO, TiO2 nanoparticles on soil beneficial microorganism and their secondary metabolites (Haris and Ahmad, 2017), iron oxide magnetic nanoparticles on the soil bacterial community (He et al., 2011), copper nanoparticles on the soil bacteria (Sharma and Gupta, 2020), metallic nanoparticles on microbial population of diverse types of soil like silver - Colman et al. (2013), copper oxide, iron oxide on red sandy loam, rendzina soil (Ben-Moshe et al., 2013), titanium di oxide nanoparticles on wheat, soil microorganisms, various metal oxide nanoparticles on garden soil bacteriome (Egboluche et al., 2022) revealed the non-target effect of nanoparticles on soil biological components mainly microbes.
There is various mechanism by which the nanomaterials, mainly nanoparticles (metal-based), enter into the ecosystem and interacts with the various biotic and abiotic components of an ecosystem (Ameen et al., 2021). A huge volume of nanoparticles is released into the environment as the industries are the major source of nanoparticle manufacturers like silver and titanium dioxide. Some nanoparticles are a component of health care, and cosmetics products like silver and zinc oxide were discharged into the environment, including landfills, known to cause diverse effects (Abbas et al., 2020). Released nanoparticles, mainly silver and zinc oxide from such sources, are translocated and interacts with plant and microorganisms associated with diverse ecosystems like soil and aquatic system. These nanoparticles elicit physiological stress in the biotic components by inducing reactive oxygen species (ROS) generation, oxidative stress, membrane disruption, protein unfolding, and inflammation (Bharani and Namasivayam, 2017).
Uptake of nanoparticles by the microbial cells, mainly E. coli, Pseudomonas, and Bacillus, associated with soil or water led to the generation of reactive oxygens species, which causes various physiological effects like membrane permeability changes, leakage of intracellular components that leads to cell death (Khan et al., 2022). Similarly, plant cells uptake the nanoparticles, mainly silver and zinc oxide, from the oxidised and aggregated sources, which are known to cause redox imbalance. This redox imbalance leads to physiological alterations like membrane damage, leakage of intracellular components and cell death. The toxicity of nanoparticles in plant cells is heavily influenced by factors like size, shape and chemical composition, which are translocated to the plant system via xylem tissue (Rajput et al., 2018b). Nanoparticles thus entered trigger physiological alteration as described above.
The impact of nanomaterials on plants (phytotoxic effect) has been studied widely (Rastogi et al., 2017). Zinc oxide nanoparticles on Vigna mungo (Pavani et al., 2018), Hordeum vulgare (Azarin et al., 2022), silver nanoparticles on Borage (Seifsahandi and Sorooshzadeh, 2013), Zinc oxide-titanium dioxide nanoparticles on red bean (Jahan et al., 2018), biogenic silver, copper, gold on black-eyed peas (Sharma and Gupta, 2020), copper nanoparticles on mung beans (Jahagirdar et al., 2019), lettuce (Lactuca sativa) and alfalfa (Medicago sativa (Hong et al., 2015), nickel oxide nanoparticles on aquatic plant Lemna gibba (Oukarroum et al., 2015), silver nanoparticles on Arabidopsis thaliana (Ke et al., 2020), lettuce (Sergimar et al., 2020), silica nanoparticles on pear seedlings (Zarafshar et al., 2015), aluminium and nickel oxide nanoparticles on Nigella arvensis (Chahardoli et al., 2020), aluminium oxide nanoparticles on Triticum aestivum (Yanlk and Vardar, 2015), copper nanoparticles on cucumber (Mosa et al., 2018), soybean (Mirakhorli et al., 2021) have revealed the potential impact of nanomaterials on the plants.
Screening of nanomaterials mediated phytotoxic effect can be done by many methods. Among these methods, oxidative stress markers, mainly enzymatic antioxidant measurement, play a vital role in phytotoxicity assessment. Antioxidative system based on enzymes plays a significant role in protecting against reactive oxygen species that cause adverse effects (Shah et al., 2021). Evaluation of enzymatic antioxidants reveals the oxidative stress, mainly catalase (CAT), superoxide dismutase (SOD), and glutathione s transferase (GST) that act specially on the toxic radicals or ions followed by clearance from the cells or tissues and protect from the adverse effects (Siddiq and Husen, 2017). In this present investigation, the enzymatic antioxidants' status as a molecular basis in terms of quantitative measurement of catalase (CAT), superoxide dismutase (SOD), and glutathione S transferase (GST) genes expression was done by qRT-PCR. Measuring the differences in the expression between the control and treatment groups demonstrates the nanotoxic effect.
In this study, the toxic effect of metallic nanoparticles on the persistence and Agro active properties of effective microorganisms (EM) like beneficial mixed microbial culture formulated with various biocompatible Agro-based products. Effective microorganisms (EM) are a group of beneficial mixed microbial cultures that exhibit a wide range of Agro active and environmental applications (Joshi et al., 2019). The beneficial effect of EM in the agriculture and environmental sector has been extensively studied in several parts of the world (Sivasubramanian and Namasivayam, 2014). Impact of EM-like microbial consortium on plant growth promotion effect, including soil conditioning effect (Iriti et al., 2019), multifunctional microbial consortium and their plant growth promotion efficacy combined with bioactive compounds (Tabacchioni et al., 2021). Effective microorganisms-mediated biostabilisation of organic manure (Hidalgo et al., 2022) and biocontrol of plant pathogens associated with various economically important crops using microbial consortium demonstrates the potential applications of EM, like beneficial microbial cultures in agriculture. Bioremediation of various toxic pollutants associated with diverse environmental sources reported by the scientific community also revealed the uniqueness of EM in human welfare.
However, many reports are available on the beneficial impacts of EM, like microbial consortium, the biocompatibility of EM formulation with various engineered materials, mainly nanomaterials, has yet to be studied. With this objective, the present study is aimed to investigate the effect of metal and metal oxide nanoparticles (silver & zinc oxide nanoparticles) on plant growth parameters of green gram plants that are inoculated with EM like a microbial consortium. Associated with plant growth parameters determination, the soil conditioning effect was also studied. Green gram (Vigna radiata), commonly known as mung bean, an important protein-rich seed (25%), is India's third important pulse crop, which contributes around 10% of the total pulses production (Green gram outlook Greengram Outlook Report, 2021. The green gram biomass is an excellent nitrogen source due to its high protein content. (Tripathi et al., 2021). Most phytotoxicity studies have been successfully done with seeds of pulses, mainly green gram, as the model due to the simplicity and reliability: of seed germination, root elongation and seedlings' physiological development. Various distinct characteristics of green gram seeds, like high sensitivity to long-time storage, toxicant chemicals exposure or interaction, can be easily inferred by the notable biochemical or physiological responses (Maji et al., 2020).
In this study, the commercial formulation of EM, like microbial culture, was formulated separately with rice bran, sugar cane syrup, groundnut cake and a combination of rice bran, sugar cane syrup, and groundnut cake. The respective formulation was exposed to nanoparticles-treated soil inoculated with green gram raised under the pot culture technique. Evaluation of the plant growth parameters and soil conditioning effect in the respective treatment group revealed the nanotoxicity described above.
Chemicals, reagents, culture medium
All the chemicals and reagents as analytical grade with high purity were obtained from Sigma. The medium used for microbial culturing was purchased from Hi Media (India).
EM-like microbial mixed culture
A commercial formulation of EM-like microbial mixed beneficial culture used in this study comprised viable cells of Lactobacillus lactis, Streptomyces sp, Candida lipolytica and spore suspension of Aspergillus oryzae in liquid form. Colony morphology on solid medium and inoculum in liquid medium of respective microbial member was shown in Fig. 1. The physical stability of the formulation was checked by measuring the pH, colour change, odour and aggregates or clumps formation. No marked changes
Due to the increased production and utilisation of nanomaterials, it is necessary to study the interaction of these nanomaterials with the ecosystem's various biotic and abiotic components (Huang et al., 2019). Recent ecotoxicological studies revealed the non-target effect of these nanomaterials on diverse biotic components. In this study, the toxic effect of silver and zinc oxide nanoparticles on the EM-like microbial mixed culture mediated soil conditioning and plant growth promotion effect
The success of microbial inoculants primarily depends on formulation techniques that enhance the viability or survival rate of the microbial cells, which in turn enhances the desired agro active properties. Most significantly, these formulating agents form a protective layer that surrounds the cells (encapsulation) and thus protect from the various external adverse formulation of this microbial preparation using biocompatible, eco-friendly and cheap resources has gained more attention in the
Credit author statement
S.Karthick Raja Namasivayam- Conceptualization, conducted research work, manuscript writing, Sharvan Kumar-conducted some parts of the Research work, K. Samrat- Statistical analysis, image processing, Arvind Bharani- Statistical analysis, image processing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
We acknowledge SIST for characterisation studies.
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