Monitoring the stress resistance of Pennisetum purpureum in Pb (II) contaminated soil bioaugmented with Enterobacter cloacae as defence strategy

Metal-tolerant morganella morganii isolates can potentially mediate nickel stress tolerance in Arabidopsis by upregulating antioxidative enzyme activities

Plant growth-promoting rhizobacteria (PGPRs) have been utilized to immobilize heavy metals, limiting their translocation in metal contaminated settings. However, studies on the mechanisms and interactions that elucidate how PGPRs mediate Nickel (Ni) tolerance in plants are rare. Thus, in this study we investigated how two pre-characterized heavy metal tolerant isolates of Morganella morganii (ABT9 and ABT3) improve Ni stress tolerance in Arabidopsis while enhancing its growth and yield. Arabidopsis seedlings were grown for five weeks in control/Ni contaminated (control, 1.5 mM and 2.5 mM) potted soil, in the presence or absence of PGPRs. Plant growth characteristics, quantum yield, and antioxidative enzymatic activities were analyzed to assess the influence of PGPRs on plant physiology. Oxidative stress tolerance was quantified by measuring MDA accumulation in Arabidopsis plants. As expected, Ni stress substantially reduced plant growth (shoot and root fresh weight by 53.25% and 58.77%, dry weight by 49.80% and 57.41% and length by 47.16% and 64.63% over control), chlorophyll content and quantum yield (by 40.21% and 54.37% over control). It also increased MDA content by 84.28% at higher (2.5 mM) Ni concentrations. In contrast, inoculation with M. morganii led to significant improvements in leaf chlorophyll, quantum yield, and Arabidopsis biomass production. The mitigation of adverse effects of Ni stress on biomass observed in M. morganii-inoculated plants was attributed to the enhancement of antioxidative enzyme activities compared to Ni-treated plants. This upregulation of the antioxidative defense mechanism mitigated Ni-induced oxidative stress, leading to improved performance of the photosynthetic machinery, which, in turn, enhanced chlorophyll content and quantum yield. Understanding the underlying mechanisms of these tolerance-inducing processes will help to complete the picture of PGPRs-mediated defense signaling. Thus, it suggests that M. morganii PGPRs candidate can potentially be utilized for plant growth promotion by reducing oxidative stress via upregulating antioxidant defense systems in Ni-contaminated soils and reducing Ni metal uptake.

Toxicity assessment of heavy metal (Pb) and its bioremediation by potential bacterial isolates

Lead (Pb) is a non-essential metal with high toxicity, is persistent, is not biodegradable, and has no known biological function. It is responsible for severe health and environmental issues that need appropriate remediation. Therefore, microbes have thrived in a lead-contaminated environment without exhibiting any negative impacts. The present study aimed to examine the toxic effects of lead on animals and the isolation, identification, and characterization of lead-resistant bacterial strains and their biodegradation potential. After oral administration of lead for 4 weeks, mice showed an elevated level of leukocytes and a decrease in TEC, Hb, PCV, MCV, MCH, and MCHC levels. However, a decline in body weight and inflammation and oxidative stress was observed in liver tissues. To remediate toxic heavy metal, lead-resistant bacterial strains were isolated, among which Enterobacter exhibited maximum degradation potential at high lead concentrations. It was identified by molecular basis and after 16S rRNA sequencing, and 99% resemblance was observed with Enterobacter cloacae. FT-IR analysis of the bacteria illustrated the presence of functional groups, including hydroxyl, carboxyl group, sulfide, and amino groups, on the bacterial cell surface involved in the adsorption of lead. Moreover, electron microscopy (SEM) revealed the morphological and physiochemical changes in the bacterial cell after biosorption, indicating the interaction of Cu ions with functional groups. To summarize, the findings show the highly toxic effects of lead on animals and humans and its effective biodegradation by the bacterial strains in the lead-contaminated environment. This biological strategy can be an ideal alternative to remediate heavy metals from contaminated sites to clean up the environment.

A new paradigm in the bioremoval of lead, nickel, and cadmium using a cocktail of biosystems: a metagenomic approach

Lead (Pb), nickel (Ni), and cadmium (Cd) are known for its harmful effects on the environment. Microbial community related to soil plays a pivotal role in configuring several properties of the ecosystem. Thus, remediation of such heavy metals using multiple biosystems had shown excellent bioremoval potential. The current study demonstrates the integrated approach of Chrysopogon zizanioides in combination with earthworm Eisenia fetida augmented with VITMSJ3 potent strain for the uptake of metals like Pb, Ni, and Cd from the contaminated soil. For the uptake of heavy metals, Pb, Ni, and Cd with the concentrations of 50, 100, and 150 mg kg^-1 were supplemented in pots with plants and earthworms. C. zizanioides was used for bioremoval due to their massive fibrous root system which can absorb heavy metals. A substantial increase of 70-80% Pb, Ni, and Cd was found for VITMSJ3 augmented setup. A total of 12 earthworms were introduced in each setup and were tested for the toxicity and damages in the various internal structures. Reduction in malondialdehyde (MDA) content was observed in the earthworms with VITMSJ3 strain proving less toxicity and damages. Metagenomic analysis of the soil associated bacterial diversity was assessed by amplifying the V3V4 region of the 16S rRNA gene and the annotations were studied. Firmicutes were found to be the predominant genus with 56.65% abundance in the bioaugmented soil R (60) proving the detoxification of metals in the bioaugmented soil. Our study proved that a synergistic effect of plant and earthworm in association with potent bacterial strain had higher uptake of Pb, Ni, and Cd. Metagenomic analysis revealed the changes in microbial abundance in the soil before and after treatment.

Ecological adaptation of earthworms for coping with plant polyphenols, heavy metals, and microplastics in the soil: A review

In recent years, soil pollution by massive accumulation of heavy metals (HMs), microplastics, and refractory hydrocarbon chemicals has become an emerging and global concern, drawing worldwide attention. These pollutants influence soil diversity by hindering the reproduction, abundance, thereby affecting aboveground productivity. The scientific community has recently emphasized the contribution of earthworms to heavy metal accumulation, microplastic degradation, and the decomposition of organic matter in the soil, which helps maintain the soil structure. This review paper aimed to compile scientific facts on how earthworms cope with the effect of HMs, microplastics, and plant polyphenols so that vermiremediation could be widely applied for well-being of the soil ecosystem by environmentalists. Earthworms have special surface-active metabolites in their guts called drilodefensins that help them defend themselves against the oxidative action of plant polyphenols. They also combat the effects of toxic microplastics, and other oxidative compounds by elevating the antioxidant activities of their enzymes and converting them into harmless compounds or useful nutrients. Moreover, earthworms also act as biofilters, bioindicators, bioaccumulators, and transformers of oxidative polyphenols, microplastics, toxic HMs, and other pollutant hydrocarbons. Microorganisms (fungi and bacteria) in earthworms' gut of also assist in the fixation, accumulation, and transformation of these toxicants to prevent their effects. As a potential organism for application in ecotoxicology, it is recommended to propagate earthworms in agricultural fields; isolate, and culture enormously in industry, and inoculate earthworms in the polluted soil, thereby abate toxicity and minimizing the health effect caused by these pollutants as well enhance the productivity of crops.

Understanding the fundamentals of microbial remediation with emphasize on metabolomics

The post-genomic tool metabolomics is a great advancement in science and technology which acquires novel strategies and pathways to analyze various biological compounds. Metabolomics aids in retrieving the qualitative and quantitative data from the various biological system. The current review is focused on the application of metabolomics in bioremediation and helps to focus on the xenobiotic compounds which are discharged into the environment and have long term impact. The microbial based biodegradation can be effectively used along with the combination of metabolomic approach for a better understanding of the breakdown of certain recalcitrant. Additionally, this review also discusses the candidate gene approach which helps to comprehend the functional analysis of microbial genes in response to different contaminants. Therefore, this review intends to discuss the metabolomics in bioremediation by studying the complete set of metabolites involved during the process of degradation and their interaction with the environment.

Phytotoxicity of tris-(1-chloro-2-propyl) phosphate in soil and its uptake and accumulation by pakchoi (Brassica chinensis L. cv. SuZhou)

This study investigated physiological and biochemical changes in pakchoi at different growth stages (25 and 50 d) under different tris-(1-chloro-2-propyl) phosphate (TCIPP) treatments (10, 100, 500, and 1000 μg kg^-1). The uptake and accumulation of TCIPP by pakchoi and variation of TCIPP speciation in soil were also determined. TCIPP decreased the length and fresh weight of pakchoi root compared with those in blank controls, and this effect was significant when the concentration of TCIPP was higher than 100 μg kg^-1. The fresh weight of pakchoi stems and leaves, the chlorophyll content, and the activities of superoxide dismutase, peroxidase, and catalase in the leaves first increased and then decreased with increasing TCIPP concentration. The inflection point of the variation in these indices was 100 μg kg^-1 TCIPP in soil. The contents of proline and malondialdehyde increased continuously with increasing TCIPP concentration. The uptake of TCIPP by pakchoi increased linearly with increasing TCIPP concentration, and the highest TCIPP concentrations in the roots, stems, and leaves were 275.9, 80.0, and 2126.3 μg kg^-1, respectively. TCIPP was easily transferred from the roots to leaves of pakchoi, with translocation factor of up to 12.6. The content of bioavailable TCIPP in soil was high, accounting for 46.5%. Planting pakchoi could significantly reduce the content of bioavailable TCIPP, with removal rate of 39.9%-54.1%. After 50 d of planting pakchoi, the removal rate of TCIPP in soil (10.4%-18.6%) was significantly higher than that in the control without plant, but the contribution of phytoextraction was small, accounting for 2.62%-26.6%.

Supplementation with plant growth promoting rhizobacteria (PGPR) alleviates cadmium toxicity in Solanum lycopersicum by modulating the expression of secondary metabolites

The current study evaluated the synergistic role of Plant growth promoting rhizobacteria (PGPR), Pseudomonas aeruginosa and Burkholderia gladioli on different physiological, biochemical and molecular activities of 10-days old Solanum lycopersicum seedlings under Cd stress. Cd toxicity altered the levels of phenolic compounds (total phenols (30.2%), flavonoids (92.7%), anthocyanin (59.5%), polyphenols (368.7%)), osmolytes (total osmolytes (10.3%), total carbohydrates (94%), reducing sugars (64.5%), trehalose (112.5%), glycine betaine (59%), proline (54.8%), and free amino acids (63%)), and organic acids in S. lycopersicum seedlings. Inoculation of P. aeruginosa and B. gladioli alleviated Cd-induced toxicity, which was manifested through enhanced phenolic compound levels and osmolytes. Additionally, the levels of low molecular weight organic acids (fumaric acid, malic acid, succinic acid, and citric acid) were also elevated. The expression of genes encoding enzymes for phenols and organic acid metabolism were also studied to be modulated that included CHS (chalcone synthase; 138.4%), PAL (phenylalanine ammonia lyase; 206.7%), CS (citrate synthase; 61.3%), SUCLG1 (succinyl Co-A ligase; 33.6%), SDH (succinate dehydrogenase; 23.2%), FH (fumarate hydratase; 12.4%), and MS (malate synthase; 41.2%) and found to be upregulated in seedlings inoculated independently with P. aeruginosa and B. gladioli. The results provide insights into the role of micro-organisms in alleviating Cd-induced physiological damage by altering levels of different metabolites.

Metal resistant PGPR lowered Cd uptake and expression of metal transporter genes with improved growth and photosynthetic pigments in Lycopersicon esculentum under metal toxicity

Plant growth promoting rhizobacteria (PGPRs) are very effective in immobilization of heavy metals and reducing their translocation in plants via precipitation, complex formation and adsorption. The present study was therefore designed to understand the role of Pseudomonas aeruginosa and Burkholderia gladioli in mitigation of Cd stress (0.4 mM) in 10-days old L. esculentum seedlings. The present work investigated growth characteristics, photosynthetic pigments, metal tolerance index, metal uptake and the contents of metal chelating compounds (protein bound and non-protein bound thiols, total thiols) in microbes inoculated Cd treated L. esculentum seedlings. The gene expression profiling of different metal transporters was conducted in order to investigate the quantitative analysis. Our results revealed Cd generated toxicity in seedlings in terms of reduced growth (root length, shoot length and fresh weight) and photosynthetic pigments (chlorophyll, carotenoid and xanthophyll) which enhanced upon inoculations of P. aeruginosa and B. gladioli. Further, the metal uptake along with levels of protein and non-protein bound thiols was also enhanced in Cd-treated seedlings. Gene expression studies suggested enhanced expression in the metal transporter genes which were further declined in the microbe supplemented seedlings. Therefore, micro-organisms possess growth promoting traits that enable them to reduce metal toxicity in plants.

Metal resistant PGPR lowered Cd uptake and expression of metal transporter genes with improved growth and photosynthetic pigments in Lycopersicon esculentum under metal toxicity

Plant growth promoting rhizobacteria (PGPRs) are very effective in immobilization of heavy metals and reducing their translocation in plants via precipitation, complex formation and adsorption. The present study was therefore designed to understand the role of Pseudomonas aeruginosa and Burkholderia gladioli in mitigation of Cd stress (0.4 mM) in 10-days old L. esculentum seedlings. The present work investigated growth characteristics, photosynthetic pigments, metal tolerance index, metal uptake and the contents of metal chelating compounds (protein bound and non-protein bound thiols, total thiols) in microbes inoculated Cd treated L. esculentum seedlings. The gene expression profiling of different metal transporters was conducted in order to investigate the quantitative analysis. Our results revealed Cd generated toxicity in seedlings in terms of reduced growth (root length, shoot length and fresh weight) and photosynthetic pigments (chlorophyll, carotenoid and xanthophyll) which enhanced upon inoculations of P. aeruginosa and B. gladioli. Further, the metal uptake along with levels of protein and non-protein bound thiols was also enhanced in Cd-treated seedlings. Gene expression studies suggested enhanced expression in the metal transporter genes which were further declined in the microbe supplemented seedlings. Therefore, micro-organisms possess growth promoting traits that enable them to reduce metal toxicity in plants.