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With the increase of antibiotic drug resistance, alternative antibacterial treatment strategies are needed. Copper is a well-known antimicrobial and antiviral agent; however, the underlying molecular mechanisms by which copper causes cell death are not yet fully understood. Copper is well known for its antimicrobial and antiviral properties. Under aerobic conditions, copper toxicity relies in part on the production of reactive oxygen species (ROS), especially in the periplasmic compartment. However, copper is significantly more toxic under anaerobic conditions, in which ROS cannot be produced. This toxicity has been proposed to arise from the inactivation of proteins through mismetallations. Here, using the bacterium Escherichia coli , we discovered that copper treatment under anaerobic conditions leads to a significant increase in protein aggregation. In vitro experiments using E. coli lysates and tightly controlled redox conditions confirmed that treatment with Cu + under anaerobic conditions leads to severe ROS-independent protein aggregation. Proteomic analysis of aggregated proteins revealed an enrichment of cysteine- and histidine-containing proteins in the Cu + -treated samples, suggesting that nonspecific interactions of Cu + with these residues are likely responsible for the observed protein aggregation. In addition, E. coli strains lacking the cytosolic chaperone DnaK or trigger factor are highly sensitive to copper stress. These results reveal that bacteria rely on these chaperone systems to protect themselves against Cu-mediated protein aggregation and further support our finding that Cu toxicity is related to Cu-induced protein aggregation. Overall, our work provides new insights into the mechanism of Cu toxicity and the defense mechanisms that bacteria employ to survive. IMPORTANCE With the increase of antibiotic drug resistance, alternative antibacterial treatment strategies are needed. Copper is a well-known antimicrobial and antiviral agent; however, the underlying molecular mechanisms by which copper causes cell death are not yet fully understood. Herein, we report the finding that Cu + , the physiologically relevant copper species in bacteria, causes widespread protein aggregation. We demonstrate that the molecular chaperones DnaK and trigger factor protect bacteria against Cu-induced cell death, highlighting, for the first time, the central role of these chaperones under Cu + stress. Our studies reveal Cu-induced protein aggregation to be a central mechanism of Cu toxicity, a finding that will serve to guide future mechanistic studies and drug development.

Soil and water contamination from heavy metals and metalloids is one of the most discussed and caused adverse effects on food safety and marketability, crop growth due to phytotoxicity, and environmental health of soil organisms. A hydroponic investigation was executed to evaluate the influence of citric acid (CA) on copper (Cu) phytoextraction potential of jute (Corchorus capsularis L.). Three-weeks-old seedlings of C. capsularis were exposed to different Cu concentrations (0, 50, and 100 μM) with or without the application of CA (2 mM) in a nutrient growth medium. The results revealed that exposure of various levels of Cu by 50 and 100 μM significantly (p < 0.05) reduced plant growth, biomass, chlorophyll contents, gaseous exchange attributes, and damaged ultra-structure of chloroplast in C. capsularis seedlings. Furthermore, Cu toxicity also enhanced the production of malondialdehyde (MDA) which indicated the Cu-induced oxidative damage in the leaves of C. capsularis seedlings. Increasing the level of Cu in the nutrient solution significantly increased Cu uptake by the roots and shoots of C. capsularis seedlings. The application of CA into the nutrient medium significantly alleviated Cu phytotoxicity effects on C. capsularis seedlings as seen by plant growth and biomass, chlorophyll contents, gaseous exchange attributes, and ultra-structure of chloroplast. Moreover, CA supplementation also alleviated Cu-induced oxidative stress by reducing the contents of MDA. In addition, application of CA is helpful in increasing phytoremediation potential of the plant by increasing Cu concentration in the roots and shoots of the plants which is manifested by increasing the values of bioaccumulation (BAF) and translocation factors (TF) also. These observations depicted that application of CA could be a useful approach to assist Cu phytoextraction and stress tolerance against Cu in C. capsularis seedlings grown in Cu contaminated sites.

The control of intracellular metal availability is fundamental to bacterial physiology. In the case of copper (Cu), it has been established that rising intracellular Cu levels eventually fill the metal-sensing site of the endogenous Cu-sensing transcriptional regulator, which in turn induces transcription of a copper export pump. This response caps intracellular Cu availability below a well-defined threshold and prevents Cu toxicity. Glutathione, abundant in many bacteria, is known to bind Cu and has long been assumed to contribute to bacterial Cu handling. However, there is some ambiguity since neither its biosynthesis nor uptake is Cu-regulated. Furthermore, there is little experimental support for this physiological role of glutathione beyond measuring growth of glutathione-deficient mutants in the presence of Cu. Our work with group A Streptococcus provides new evidence that glutathione increases the threshold of intracellular Cu availability that can be tolerated by bacteria and thus advances fundamental understanding of bacterial Cu handling. Copper (Cu) is an essential metal for bacterial physiology but in excess it is bacteriotoxic. To limit Cu levels in the cytoplasm, most bacteria possess a transcriptionally responsive system for Cu export. In the Gram-positive human pathogen Streptococcus pyogenes (group A Streptococcus [GAS]), this system is encoded by the copYAZ operon. This study demonstrates that although the site of GAS infection represents a Cu-rich environment, inactivation of the copA Cu efflux gene does not reduce virulence in a mouse model of invasive disease. In vitro , Cu treatment leads to multiple observable phenotypes, including defects in growth and viability, decreased fermentation, inhibition of glyceraldehyde-3-phosphate dehydrogenase (GapA) activity, and misregulation of metal homeostasis, likely as a consequence of mismetalation of noncognate metal-binding sites by Cu. Surprisingly, the onset of these effects is delayed by ∼4 h even though expression of copZ is upregulated immediately upon exposure to Cu. Further biochemical investigations show that the onset of all phenotypes coincides with depletion of intracellular glutathione (GSH). Supplementation with extracellular GSH replenishes the intracellular pool of this thiol and suppresses all the observable effects of Cu treatment. These results indicate that GSH buffers excess intracellular Cu when the transcriptionally responsive Cu export system is overwhelmed. Thus, while the copYAZ operon is responsible for Cu homeostasis , GSH has a role in Cu tolerance and allows bacteria to maintain metabolism even in the presence of an excess of this metal ion. IMPORTANCE The control of intracellular metal availability is fundamental to bacterial physiology. In the case of copper (Cu), it has been established that rising intracellular Cu levels eventually fill the metal-sensing site of the endogenous Cu-sensing transcriptional regulator, which in turn induces transcription of a copper export pump. This response caps intracellular Cu availability below a well-defined threshold and prevents Cu toxicity. Glutathione, abundant in many bacteria, is known to bind Cu and has long been assumed to contribute to bacterial Cu handling. However, there is some ambiguity since neither its biosynthesis nor uptake is Cu-regulated. Furthermore, there is little experimental support for this physiological role of glutathione beyond measuring growth of glutathione-deficient mutants in the presence of Cu. Our work with group A Streptococcus provides new evidence that glutathione increases the threshold of intracellular Cu availability that can be tolerated by bacteria and thus advances fundamental understanding of bacterial Cu handling.

The pollution by heavy metals in coastal waters has gradually intensified due to industrial development. In this study, physiological responses of Ulva lactuca , one of the most common green seaweeds with important ecological and economic value in the global intertidal zone, to acute copper stress were investigated. Results showed that an increase in copper ions concentration significantly inhibited photosynthetic activity and inorganic nitrogen utilization by U. lactuca but, increased its respiration. Copper stress limited the activity and gene expression of enzymes related to carbon and nitrogen assimilation of U. lactuca . Under moderate copper stress, U. lactuca had higher soluble carbohydrate and soluble protein contents, whereas under high copper stress, these components decreased sharply. Copper stress increased malonaldehyde content, and relative electrical conductivity in U. lactuca , but changes in antioxidant enzyme activities were not significant and even slightly decreased. Moreover, the contents of 8-hydroxy-deoxyguanosine and polyADP ribose polymerase in U. lactuca increased by high Cu 2+ concentration culture, indicating that oxidative damage caused by high Cu 2+ level involved its DNA damage and interfered with DNA repair in the alga. Copper stress seemed to be more damaging to the carbon assimilation process of U. lactuca , resulting in weakened resistance to copper stress and lower growth rate. This reflected the threat of coastal high copper stress to intertidal biodiversity. This provided ecological reference for the assessment of offshore heavy metal pollution represented by copper.

The mechanism of Cu tolerance in plants and its control measures are of considerable significance for the remediation of Cu-contaminated soils. Gibberellic acid (GA 3 ) is involved in plant growth and development and in the response to heavy metal stress. In the present study, changes in the biomass, oxidative stress response responses, and photosynthesis of spinach seedlings were examined under Cu stress with exogenous GA 3 applied at concentrations of 0, 3, 5, 10, 20, 40, 60, or 80 mg L −1 . Under Cu stress, the plant Cu concentration and oxidative damage were greater, photosynthetic parameters and biomass declined, and antioxidant enzyme activities and the proline concentration increased. However, spinach growth did not terminate, indicating that spinach seedlings had strong Cu tolerance. When low concentrations of GA 3 (3–5 mg L −1 ) were added to Cu-stressed spinach seedlings, the damage caused by Cu stress to spinach seedlings was reduced, and the Cu tolerance of spinach seedlings was enhanced, which mainly manifested as reduced oxidation damage, an increased proline concentration, elevated antioxidant enzyme activities, decreased Cu concentration in leaves, and increased Cu concentration in roots, increased photosynthetic parameters, and an increased in the total biomass. In contrast, additions of GA 3 at concentrations higher than 40 mg L −1 intensified oxidative damage and decreased the activities of antioxidant enzymes, photosynthetic parameters, and biomass. Additionally, the Cu concentration increased in leaves and decreased Cu concentration in roots, indicating that high concentrations of GA 3 aggravated stress damage and severely influenced physiological functions in spinach seedlings. In summary, the application of 3–5 mg L −1 GA 3 to spinach seedlings in Cu-contaminated soil can be used to reduce Cu toxicity to plants and increase Cu tolerance.

Metabolic changes under stress are often studied in short-term experiments, revealing rapid responses in gene expression, enzyme activity, and the amount of antioxidants. In a long-term experiment, it is possible to identify adaptive changes in both primary and secondary metabolism. In this study, we characterized the physiological state of tobacco plants and assessed the amount and spectrum of phenolic compounds and the lignification of axial organs under excess copper stress in a long-term experiment (40 days). Plants were treated with 100 and 300 μM CuSO4, as well as a control (Knop solution). Copper accumulation, the size and anatomical structure of organs, stress markers, and the activity of antioxidant enzymes were studied. Lignin content was determined with the cysteine-assisted sulfuric method (CASA), and the metabolite profile and phenolic spectrum were determined with UHPLC-MS and thin-layer chromatography (TLC). Cu2+ mainly accumulated in the roots and, to a lesser extent, in the shoots. Copper sulfate (100 μM) slightly stimulated stem and leaf growth. A higher concentration (300 μM) caused oxidative stress; H2O2 content, superoxide dismutase (SOD), and guaiacol peroxidase (GPOX) activity increased in roots, and malondialdehyde (MDA) increased in all organs. The deposition of lignin increased in the roots and stems compared with the control. The content of free phenolics, which could be used as substrates for lignification, declined. The proportions of ferulic, cinnamic, and p-coumaric acids in the hydrolysate of bound phenolics were higher, and they tended toward additional lignification. The metabolic profile changed in both roots and stems at both concentrations, and changed in leaves only at a concentration of 300 μM. Thus, changes in the phenolic spectrum and the enhanced lignification of cell walls in the metaxylem of axial (root and stem) organs in tobacco can be considered important metabolic responses to stress caused by excess CuSO4.

The excessive accumulation of copper (Cu2+) has become a threat to worldwide crop production. Recently, it was revealed that melatonin (MT) could play a crucial role against heavy metal (HM) stresses in plants. However, the underlying mechanism of MT function acted upon by Cu2+ stress (CS) has not been substantiated in tomatoes. In the present work, we produced MT-rich tomato plants by foliar usage of MT, and MT-deficient tomato plants by employing a virus-induced gene silencing methodology and exogenous foliar application of MT synthesis inhibitor para-chlorophenylalanine (pCPA). The obtained results indicate that exogenous MT meaningfully alleviated the dwarf phenotype and impeded the reduction in plant growth caused by excess Cu2+. Furthermore, MT effectively restricted the generation of reactive oxygen species (ROS) and habilitated cellular integrity by triggering antioxidant enzyme activities, especially via CAT and APX, but not SOD and POD. In addition, MT increased nonenzymatic antioxidant activity, including FRAP and the GSH/GSSG and ASA/DHA ratios. MT usage improved the expression of several defense genes (CAT, APX, GR and MDHAR) and MT biosynthesis-related genes (TDC, SNAT and COMT). Taken together, our results preliminarily reveal that MT alleviates Cu2+ toxicity via ROS scavenging, enhancing antioxidant capacity when subjected to excessive Cu2+. These results build a solid foundation for developing new insights to solve problems related to CS.

The copper transporter (COPT/Ctr) gene family plays a critical part in maintaining the balance of the metal, and many diverse species depend on COPT to move copper (Cu) across the cell membrane. In Arabidopsis thaliana, Oryza sativa, Medicago sativa, Zea mays, Populus trichocarpa, Vitis vinifera, and Solanum lycopersicum, a genome-wide study of the COPT protein family was performed. To understand the major roles of the COPT gene family in Kandelia obovata (Ko), a genome-wide study identified four COPT genes in the Kandelia obovata genome for the first time. The domain and 3D structural variation, phylogenetic tree, chromosomal distributions, gene structure, motif analysis, subcellular localization, cis-regulatory elements, synteny and duplication analysis, and expression profiles in leaves and Cu were all investigated in this research. Structural and sequence investigations show that most KoCOPTs have three transmembrane domains (TMDs). According to phylogenetic research, these KoCOPTs might be divided into two subgroups, just like Populus trichocarpa. KoCOPT gene segmental duplications and positive selection pressure were discovered by universal analysis. According to gene structure and motif analysis, most KoCOPT genes showed consistent exon–intron and motif organization within the same group. In addition, we found five hormones and four stress- and seven light-responsive cis-elements in the KoCOPTs promoters. The expression studies revealed that all four genes changed their expression levels in response to copper (CuCl2) treatments. In summary, our study offers a thorough overview of the Kandelia obovata COPT gene family’s expression pattern and functional diversity, making it easier to characterize each KoCOPT gene’s function in the future.

Vetiveria zizanioides , renowned for its robust stability and exceptional capacity to sequester heavy metals, has garnered widespread application in tailings ecological restoration efforts. Arbuscular mycorrhizal fungi (AMF), which are capable of forming symbiotic relationships with more than 80% of terrestrial plant roots, play a pivotal role in enhancing plant nutrient uptake and bolstering resilience. In this study, we conducted a comprehensive investigation into the physiological and biochemical responses of Vetiveria zizanioides subjected to varying levels of copper stress (with copper concentrations ranging from 0 mg/kg to 400 mg/kg), with or without AMF inoculation. Additionally, we performed nontargeted metabonomic analyses to gain deeper insights into the metabolic changes that occur in vetiver grass under AMF inoculation and copper stress. Our findings revealed that Vetiveria zizanioides inoculated with AMF consistently demonstrated superior growth performance across all copper stress levels compared with noninoculated counterparts. Using nontargeted metabonomic analyses, inoculation with AMF affects the metabolism of phenylalanine and related pathways in vetiver as well as contributing to the promotion of the formation of phytochelatins (PCs) from glutamate, thereby alleviating copper stress. The results highlight the potential of AMF-inoculated Vetiveria zizanioides as a promising bioremediation tool capable of effectively mitigating the adverse effects of heavy metal pollution.

Background Salt Overly Sensitive 1 ( SOS1 ), a plasma membrane Na + /H + exchanger, is essential for plant salt tolerance. Salt damage is a significant abiotic stress that impacts plant species globally. All living organisms require copper (Cu), a necessary micronutrient and a protein cofactor for many biological and physiological processes. High Cu concentrations, however, may result in pollution that inhibits the growth and development of plants. The function and production of mangrove ecosystems are significantly impacted by rising salinity and copper contamination. Results A genome-wide analysis and bioinformatics techniques were used in this study to identify 20 SOS1 genes in the genome of Kandelia obovata . Most of the SOS1 genes were found on the plasma membrane and dispersed over 11 of the 18 chromosomes. Based on phylogenetic analysis, KoSOS1s can be categorized into four groups, similar to Solanum tuberosum . Kandelia obovata's SOS1 gene family expanded due to tandem and segmental duplication. These SOS1 homologs shared similar protein structures, according to the results of the conserved motif analysis. The coding regions of 20 KoSOS1 genes consist of amino acids ranging from 466 to 1221, while the exons include amino acids ranging from 3 to 23. In addition, we found that the 2.0 kb upstream promoter region of the KoSOS1s gene contains several cis-elements associated with phytohormones and stress responses. According to the expression experiments, seven randomly chosen genes experienced up- and down-regulation of their expression levels in response to copper (CuCl 2 ) and salt stressors. Conclusions For the first time, this work systematically identified SOS1 genes in Kandelia obovata . Our investigations also encompassed physicochemical properties, evolution, and expression patterns, thereby furnishing a theoretical framework for subsequent research endeavours aimed at functionally characterizing the Kandelia obovata SOS1 genes throughout the life cycle of plants.