Copper tolerance and virulence in bacteria

Essential Gene Clusters Involved in Copper Tolerance Identified in Acinetobacter baumannii Clinical and Environmental Isolates

Copper is widely used as antimicrobial in agriculture and medicine. Copper tolerance mechanisms of pathogenic bacteria have been proven to be required for both copper tolerance and survival during bacterial infections. Here, we determined both copper-tolerant phenotype and genotype in A. baumannii originated from clinical and environmental samples. Using copper susceptibility testing, copper-tolerant A. baumannii could be found in both clinical and environmental isolates. Genotypic study revealed that representative copper-related genes of the cluster A (cueR), B (pcoAB), and D (oprC) were detected in all isolates, while copRS of cluster C was detected in only copper-tolerant A. baumannii isolates. Moreover, we found that copper-tolerant phenotype was associated with amikacin resistance, while the presence of copRS was statistically associated with bla_NDM-1. We chose the A. baumannii strain AB003 as a representative of copper-tolerant isolate to characterize the effect of copper treatment on external morphology as well as on genes responsible for copper tolerance. The morphological features and survival of A. baumannii AB003 were affected by its exposure to copper, while whole-genome sequencing and analysis showed that it carried fourteen copper-related genes located on four clusters, and cluster C of AB003 was found to be embedded on genomic island G08. Transcriptional analysis of fourteen copper-related genes identified in AB003 revealed that copper treatment induced the expressions of genes of clusters A, B, and D at the micromolar level, while genes of cluster C were over-expressed at the millimolar levels of copper. This study showed that both clinical and environmental A. baumannii isolates have the ability to tolerate copper and carried numerous copper tolerance determinants including intrinsic copper tolerance (clusters A, B, and D) and acquired copper tolerance (cluster C) that could respond to copper toxicity. Our evidence suggests that we need to reconsider the use of copper in hospitals and other medical environments to prevent the selection and spread of copper-tolerant organisms.

Unusual chemistry of Cu(ii) salan complexes: synthesis, characterization and superoxide dismutase activity

Cu(ii)-salan complexes: structural and spectral characterization, solvent assisted ring cleavage and correlation of superoxide dismutase activity with cyclic voltammetry data and steric effects.

Development of Antibacterial Ti-Cux Alloys for Dental Applications: Effects of Ageing for Alloys with Up to 10 wt% Cu

Peri-implantitis, a disease caused by bacteria, affects dental implants in patients. It is widely treated with antibiotics, however, with growing antibiotic resistance new strategies are required. Titanium-copper alloys are prospective antibacterial biomaterials, with the potential to be a remedy against peri-implantitis and antibiotic resistance. The aim of this study was to investigate Ti-Cu_x alloys, exploring how Cu content (up to 10 wt%) and ageing affect the material properties. Electron microscopy, X-ray diffraction, hardness testing, bacteriological culture, and electrochemical testing were employed to characterize the materials. It was found that alloys with above 3 wt% Cu had two phases and ageing increased the volume fraction of Ti₂Cu. An un-aged alloy of 5 wt% Cu showed what could be Ti₃Cu, in addition to the α-Ti phase. The hardness gradually increased with increased Cu additions, while ageing only affected the alloy with 10 wt% Cu (due to changes in microstructure). Ageing resulted in faster passivation of the alloys. After two hours the aged 10 wt% Cu alloy was the only material with an antibacterial effect, while after six hours, bacteria killing occurred in all alloys with above 5 wt% Cu. In conclusion, it was possible to tune the material and antibacterial properties of Ti-Cu_x alloys by changing the Cu concentration and ageing, which makes further optimization towards an antibacterial material promising.

Life in High Salt Concentrations with Changing Environmental Conditions: Insights from Genomic and Phenotypic Analysis of Salinivibrio sp

Life in salt pans with varying chemical compositions require special adaptation strategies at both the physiological and molecular level. The Marakkanam salt pan in South India is characterized with a high fluctuation in salinity (19–490 ppt), Ultravioletradiation, and heavy metal concentrations. Several bacterial species have been isolated and identified in the view of phylogenetic analysis and for the subsequent production of industrially important enzymes. However, limited information exists on the genomic basis of their survival under variable environmental conditions. To this extent, we sequenced the whole genome of the Salinivibrio sp. HTSP, a moderately halophilic bacterium. We analysed the physiological and genomic attributes of Salinivibrio sp. HTSP to elucidate the strategies of adaptation under various abiotic stresses. The genome size is estimated to be 3.39 Mbp with a mean G + C content of 50.6%, including 3150 coding sequences. The genome possessed osmotic stress-related coding sequences, and genes involved in different pathways of DNA repair mechanisms and genes related to the resistance to toxic metals were identified. The periplasmic stress response genes and genes of different oxidative stress mechanisms were also identified. The tolerance capacity of the bacterial isolates to heavy metals, UV-radiation, and salinity was also confirmed through appropriate laboratory experiments under controlled conditions.

Integrated Bioinformatic Analyses and Immune Characterization of New Neisseria gonorrhoeae Vaccine Antigens Expressed during Natural Mucosal Infection

There is an increasingly severe trend of antibiotic-resistant Neisseria gonorrhoeae strains worldwide and new therapeutic strategies are needed against this sexually-transmitted pathogen. Despite the urgency, progress towards a gonococcal vaccine has been slowed by a scarcity of suitable antigens, lack of correlates of protection in humans and limited animal models of infection. N. gonorrhoeae gene expression levels in the natural human host does not reflect expression in vitro, further complicating in vitro-basedvaccine analysis platforms. We designed a novel candidate antigen selection strategy (CASS), based on a reverse vaccinology-like approach coupled with bioinformatics. We utilized the CASS to mine gonococcal proteins expressed during human mucosal infection, reported in our previous studies, and focused on a large pool of hypothetical proteins as an untapped source of potential new antigens. Via two discovery and analysis phases (DAP), we identified 36 targets predicted to be immunogenic, membrane-associated proteins conserved in N. gonorrhoeae and suitable for recombinant expression. Six initial candidates were produced and used to immunize mice. Characterization of the immune responses indicated cross-reactive antibodies and serum bactericidal activity against different N. gonorrhoeae strains. These results support the CASS as a tool for the discovery of new vaccine candidates.

Relationships Between Copper-Related Proteomes and Lifestyles in β Proteobacteria

Copper is an essential transition metal whose redox properties are used for a variety of enzymatic oxido-reductions and in electron transfer chains. It is also toxic to living beings, and therefore its cellular concentration must be strictly controlled. We have performed in silico analyses of the predicted proteomes of more than one hundred species of β proteobacteria to characterize their copper-related proteomes, including cuproproteins, i.e., proteins with active-site copper ions, copper chaperones, and copper-homeostasis systems. Copper-related proteomes represent between 0 and 1.48% of the total proteomes of β proteobacteria. The numbers of cuproproteins are globally proportional to the proteome sizes in all phylogenetic groups and strongly linked to aerobic respiration. In contrast, environmental bacteria have considerably larger proportions of copper-homeostasis systems than the other groups of bacteria, irrespective of their proteome sizes. Evolution toward commensalism, obligate, host-restricted pathogenesis or symbiosis is globally reflected in the loss of copper-homeostasis systems. In endosymbionts, defense systems and copper chaperones have disappeared, whereas residual cuproenzymes are electron transfer proteins for aerobic respiration. Lifestyle is thus a major determinant of the size and composition of the copper-related proteome, and it is particularly reflected in systems involved in copper homeostasis. Analyses of the copper-related proteomes of a number of species belonging to the Burkholderia, Bordetella, and Neisseria genera indicates that commensals are in the process of shedding their copper-homeostasis systems and chaperones to greater extents yet than pathogens.

The metagenomic landscape of xenobiotics biodegradation in mangrove sediments

Metagenomics is a powerful approach to study microorganisms present in any given environment and their potential to maintain and improve ecosystem health without the need of cultivating these microorganisms in the laboratory. In this study, we combined a cultivation-independent metagenomics approach with functional assays to identify the detoxification potential of microbial genes evaluating their potential to contribute to xenobiotics resistance in oil-impacted mangrove sediments. A metagenomic fosmid library containing 12,960 clones from highly contaminated mangrove sediment was used in this study. For assessment of metal resistance, clones were grown in culture medium with increasing concentrations of mercury. The analyses metagenomic library sequences revealed the presence of genes related to heavy metals and antibiotics resistance in the oil-impacted mangrove microbiome. The taxonomic profiling of these sequences suggests that at the genus level, Geobacter was the most abundant genus in our dataset. A functional screening assessment of the metagenomic library successfully detected 24 potential heavy metal tolerant clones, six of which were capable of growing with increased concentrations of mercury. The genetic characterization of selected clones allowed the detection of genes related to detoxification processes, such as chromate transport protein ChrA, haloacid dehalogenase-like hydrolase, lipopolysaccharide transport system, and 3-oxoacyl-[acyl-carrier-protein] reductase. Clones were capable of growing in medium containing increased concentrations of metals and antibiotics, but none manifested strong mercury removal from culture medium characteristic of mercuric reductase activity. These results suggest that resistance to xenobiotic stress varies greatly and that additional studies to elucidate the potential of metal biotransformation need to be carried out with the goal of improving bioremediation application.

The Scs disulfide reductase system cooperates with the metallochaperone CueP in Salmonella copper resistance

The human pathogen Salmonella enterica serovar Typhimurium (S Typhimurium) contains a complex disulfide bond (Dsb) catalytic machinery. This machinery encompasses multiple Dsb thiol-disulfide oxidoreductases that mediate oxidative protein folding and a less-characterized suppressor of copper sensitivity (scs) gene cluster, associated with increased tolerance to copper. To better understand the function of the Salmonella Scs system, here we characterized two of its key components, the membrane protein ScsB and the periplasmic protein ScsC. Our results revealed that these two proteins form a redox pair in which the electron transfer from the periplasmic domain of ScsB (n-ScsB) to ScsC is thermodynamically driven. We also demonstrate that the Scs reducing pathway remains separate from the Dsb oxidizing pathways and thereby avoids futile redox cycles. Additionally, we provide new insight into the molecular mechanism underlying Scs-mediated copper tolerance in Salmonella We show that both ScsB and ScsC can bind toxic copper(I) with femtomolar affinities and transfer it to the periplasmic copper metallochaperone CueP. Our results indicate that the Salmonella Scs machinery has evolved a dual mode of action, capable of transferring reducing power to the oxidizing periplasm and protecting against copper stress by cooperating with the cue regulon, a major copper resistance mechanism in Salmonella. Overall, these findings expand our understanding of the functional diversity of Dsb-like systems, ranging from those mediating oxidative folding of proteins required for infection to those contributing to defense mechanisms against oxidative stress and copper toxicity, critical traits for niche adaptation and survival.

De novo genome assembly and comparative annotation reveals metabolic versatility in cellulolytic bacteria from cropland and forest soils

Cellulose, the most abundant polysaccharide in nature, is a rich source of renewable energy and sustains soil nutrients. Among the microorganisms known to degrade cellulose, bacteria are less studied compared to fungi. In the present work, we have investigated the culturable bacteria actively involved in cellulose degradation in forest and crop field soils. Based on clear zone formation and enzyme activity assay, we identified 7 bacterial strains positive for cellulose degradation. Of these, two most efficient strains (Bacillus cereus strains BHU1 and BHU2) were selected for whole genome sequencing, annotation, and information regarding GC content, number of genes, total subsystems, starch, and cellulose degradation pathways. Average nucleotide identity (ANI) showed more than 90% similarity between both the strains (BHU1 and BHU2) and with B. cereus ATCC 14579. Both the strains have genes and enzyme families like endoglucanase and β-glucosidase as evident from whole genome sequence. Cellulase containing gene families (GH5, GH8, GH1), and many other carbohydrate-degrading enzymes, were present in both the bacterial strains. Taken together, the results suggest that the strains were efficient in cellulose degradation, and can be used for energy generation and production of value-added product.

Random peptide mixtures entrapped within a copper-cuprite matrix: new antimicrobial agent against methicillin-resistant Staphylococcus aureus

The emergence of global antibiotic resistance necessitates the urgent need to develop new and effective antimicrobial agents. Combination of two antimicrobial agents can potentially improve antimicrobial potency and mitigate the development of resistance. Therefore, we have utilized metal molecular doping methodology whereby antimicrobial random peptides mixture (RPMs) are entrapped in a bactericidal copper metal matrix. The copper/RPM composite exhibits greater antimicrobial activity toward methicillin-resistant Staphylococcus aureus (MRSA) than either copper or RPMs alone. Our findings indicate that this bactericidal antimicrobial biomaterial could be utilized to efficiently eradicate antibiotic-resistant pathogenic bacteria for health, agricultural and environmental applications.

Gene expression is influenced due to 'nano' and 'ionic' copper in pre-formed Pseudomonas aeruginosa biofilms

Today, researchers across the globe suggest the use of antimicrobial coatings containing copper nanoparticles (CuNPs) complementing the traditional protocols to prevent hospital-acquired infections (HAIs). Since Pseudomonas aeruginosa is one of the commonest opportunistic pathogens, we assessed the anti-biofilm activity of CuNPs in P. aeruginosa MTCC 3541 and compared it with Cu²⁺ (copper sulphate) since the latter continues to be used as an antimicrobial-of-choice in food industries, agriculture and water treatment. In this study, we synthesized and characterized stable poly-acrylic acid (PAA) coated CuNPs with a size of 66-150 nm and zeta potential -13 mV. Pseudomonas aeruginosa MTCC 3541 biofilms were highly resistant to both CuNPs and Cu²⁺ (minimum biofilm inhibitory concentration, MBIC 300 and >600 μg/mL respectively). Scanning electron microscopy revealed alterations in cell morphology upon treatment with CuNPs. A closer analysis of the biofilm-specific gene expression (qRT-PCR) revealed that CuNPs downregulated the genes involved in biofilm matrix formation, motility, efflux, membrane lipoprotein synthesis and DNA replication. Both, CuNPs and Cu²⁺ up regulated copper resistance and biofilm dispersion genes. Copper did not affect the bacterial communication system as evidenced by downregulation of the negative regulator of quorum sensing. The gene expression analysis reveals multiple cellular targets for CuNPs and ionic Cu. The present study highlights the fact that CuNPs affect the membrane functions adversely damaging the cell surface. In pre-formed biofilms, CuNPs were more toxic and displayed distinct responses attributable due to 'nano' and 'ionic' copper. Our findings thus support the use of CuNPs for curbing HAIs.

Pathotyping the Zoonotic Pathogen Streptococcus suis: Novel Genetic Markers To Differentiate Invasive Disease-Associated Isolates from Non-Disease-Associated Isolates from England and Wales

Streptococcus suis is one of the most important zoonotic bacterial pathogens of pigs, causing significant economic losses to the global swine industry. S. suis is also a very successful colonizer of mucosal surfaces, and commensal strains can be found in almost all pig populations worldwide, making detection of the S. suis species in asymptomatic carrier herds of little practical value in predicting the likelihood of future clinical relevance. The value of future molecular tools for surveillance and preventative health management lies in the detection of strains that genetically have increased potential to cause disease in presently healthy animals. Here we describe the use of genome-wide association studies to identify genetic markers associated with the observed clinical phenotypes (i) invasive disease and (ii) asymptomatic carriage on the palatine tonsils of pigs on UK farms. Subsequently, we designed a multiplex PCR to target three genetic markers that differentiated 115 S. suis isolates into disease-associated and non-disease-associated groups, that performed with a sensitivity of 0.91, a specificity of 0.79, a negative predictive value of 0.91, and a positive predictive value of 0.79 in comparison to observed clinical phenotypes. We describe evaluation of our pathotyping tool, using an out-of-sample collection of 50 previously uncharacterized S. suis isolates, in comparison to existing methods used to characterize and subtype S. suis isolates. In doing so, we show our pathotyping approach to be a competitive method to characterize S. suis isolates recovered from pigs on UK farms and one that can easily be updated to incorporate global strain collections.

CopA Protects Streptococcus suis against Copper Toxicity

Streptococcus suis is a zoonotic pathogen that causes great economic losses to the swine industry and severe threats to public health. A better understanding of its physiology would contribute to the control of its infections. Although copper is an essential micronutrient for life, it is toxic to cells when present in excessive amounts. Herein, we provide evidence that CopA is required for S. suis resistance to copper toxicity. Quantitative PCR analysis showed that copA expression was specifically induced by copper. Growth curve analyses and spot dilution assays showed that the ΔcopA mutant was defective in media supplemented with elevated concentrations of copper. Spot dilution assays also revealed that CopA protected S. suis against the copper-induced bactericidal effect. Using inductively coupled plasma-optical emission spectroscopy, we demonstrated that the role of CopA in copper resistance was mediated by copper efflux. Collectively, our data indicated that CopA protects S. suis against the copper-induced bactericidal effect via copper efflux.

New insights into copper homeostasis in filamentous fungi

Copper is a metal ion that is required as a micronutrient for growth and proliferation. However, copper accumulation generates toxicity by multiple mechanisms, potentially leading to cell death. Due to its toxic nature at high concentrations, different chemical variants of copper have been extensively used as antifungal agents in agriculture and medicine. Most studies on copper homeostasis have been carried out in bacteria, yeast, and mammalian organisms. However, knowledge on filamentous fungi is less well documented. This review summarizes the knowledge gathered in the last few years about copper homeostasis in the filamentous fungi Aspergillus fumigatus and Aspergillus nidulans: The mechanism of action of copper, the uptake and detoxification systems, their regulation at the transcriptional level, and the role of copper homeostasis in fungal pathogenicity are presented.

Metals as phagocyte antimicrobial effectors

Transition metal ions are essential to bacterial pathogens and their hosts alike but are harmful in excess. In an effort to curtail the replication of intracellular bacteria, host phagocytes exploit both the essentiality and toxicity of transition metals. In the paradigmatic description of nutritional immunity, iron and manganese are withheld from phagosomes to starve microbial invaders of these nutrients. Conversely, the destructive properties of copper and zinc appear to be harnessed by phagocytes, where these metals are delivered in excess to phagosomes to intoxicate internalized bacteria. Here, we briefly summarize key players in metal withholding from intracellular pathogens, before focusing on recent findings supporting the function of copper and zinc as phagocyte antimicrobial effectors. The mechanisms of copper and zinc toxicity are explored, along with strategies employed by intracellular bacterial pathogens to avoid killing by these metals.

Plasmids contribute to food processing environment-associated stress survival in three Listeria monocytogenes ST121, ST8, and ST5 strains

Listeria monocytogenes is a food-borne pathogen responsible for the disease listeriosis and is commonly isolated from food and food production facilities. Many L. monocytogenes strains contain plasmids, though the contributions of plasmids to survival in food production environments are unknown. Three L. monocytogenes ST5, ST8, and ST121 strains containing plasmids, which harbor putative stress response genes, were cured of their plasmids. Wildtype (WT) and plasmid-cured strains were exposed to disinfectant, oxidative, heat, acid, or salt stress. After stress exposure, cells were plated for colony forming unit (CFU) counts to determine survivors. L. monocytogenes WT strains exposed to 0.01% (vol/vol) H₂O₂, 1% (vol/vol) lactic acid, and 15% (wt/vol) NaCl, pH 5 showed significantly higher counts of survivors compared to the plasmid-cured strains. The number of survivors for the ST5 WT strain exposed to 10 μg/mL benzalkonium chloride (BC) was significantly higher than in the plasmid-cured strain. The ST8 and ST5 strains were exposed to elevated temperature (50° and 55 °C respectively); only the ST5 WT strain had significantly higher numbers of survivors than the plasmid-cured strains. Our data revealed that L. monocytogenes ST5, ST8, and ST121 plasmids contribute to tolerance against elevated temperature, salinity, acidic environments, oxidative stress and disinfectants.

The Combined Effect of Cold and Copper Stresses on the Proliferation and Transcriptional Response of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen that can cause severe disease in susceptible humans. This microorganism has the ability to adapt to hostile environmental conditions such as the low temperatures used by the food industry for controlling microorganisms. Bacteria are able to adjust their transcriptional response to adapt to stressful conditions in order to maintain cell homeostasis. Understanding the transcriptional response of L. monocytogenes to stressing conditions could be relevant to develop new strategies to control the pathogen. A possible alternative for controlling microorganisms in the food industry could be to use copper as an antimicrobial agent. The present study characterized three L. monocytogenes strains (List2-2, Apa13-2, and Al152-2A) adapted to low temperature and challenged with different copper concentrations. Similar MIC-Cu values were observed among studied strains, but growth kinetic parameters revealed that strain List2-2 was the least affected by the presence of copper at 8°C. This strain was selected for a global transcriptional response study after a 1 h exposition to 0.5 mM of CuSO4 × 5H2O at 8 and 37°C. The results showed that L. monocytogenes apparently decreases its metabolism in response to copper, and this reduction is greater at 8°C than at 37°C. The most affected metabolic pathways were carbohydrates, lipids and nucleotides synthesis. Finally, 15 genes were selected to evaluate the conservation of the transcriptional response in the other two strains. Results indicated that only genes related to copper homeostasis showed a high degree of conservation between the strains studied, suggesting that a low number of genes is implicated in the response to copper stress in L. monocytogenes. These results contribute to the understanding of the molecular mechanisms used by bacteria to overcome a combination of stresses. This study concluded that the application of copper in low concentrations in cold environments may help to control foodborne pathogens as L. monocytogenes in the industry.

The interplay of the metallosensor CueR with two distinct CopZ chaperones defines copper homeostasis in Pseudomonas aeruginosa

Copper homeostasis in pathogenic bacteria is critical for cuproprotein assembly and virulence. However, in vivo biochemical analyses of these processes are challenging, which has prevented defining and quantifying the homeostatic interplay between Cu⁺-sensing transcriptional regulators, chaperones, and sequestering molecules. The cytoplasm of Pseudomonas aeruginosa contains a Cu⁺-sensing transcriptional regulator, CueR, and two homologous metal chaperones, CopZ1 and CopZ2, forming a unique system for studying Cu⁺ homeostasis. We found here that both chaperones exchange Cu⁺, albeit at a slow rate, reaching equilibrium after 3 h, a time much longer than P. aeruginosa duplication time. Therefore, they appeared as two separate cellular Cu⁺ pools. Although both chaperones transferred Cu⁺ to CueR in vitro, experiments in vivo indicated that CopZ1 metallates CueR, eliciting the translation of Cu⁺ efflux transporters involved in metal tolerance. Although this observation was consistent with the relative Cu⁺ affinities of the three proteins (CopZ1 < CueR < CopZ2), in vitro and in silico analyses also indicated a stronger interaction between CopZ1 and CueR that was independent of Cu⁺ In contrast, CopZ2 function was defined by its distinctly high abundance during Cu²⁺ stress. Under resting conditions, CopZ2 remained largely in its apo form. Metal stress quickly induced CopZ2 expression, and its holo form predominated, reaching levels commensurate with the cytoplasmic Cu⁺ levels. In summary, these results show that CopZ1 acts as chaperone delivering Cu⁺ to the CueR sensor, whereas CopZ2 functions as a fast-response Cu⁺-sequestering storage protein. We propose that equivalent proteins likely play similar roles in most bacterial systems.

Genetically encoded RNA-based sensors for intracellular imaging of silver ions

Silver has been widely used for disinfection. The cellular accumulation of silver ions (Ag+) is critical in these antibacterial effects. The direct cellular measurement of Ag+ is useful for the study of disinfection mechanisms. Herein, we reported a novel genetically encoded RNA-based sensor to image Ag+ in live bacterial cells. The sensor is designed by introducing a cytosine-Ag+-cytosine metallo base pair into a fluorogenic RNA aptamer, Broccoli. The binding of Ag+ induces the folding of Broccoli and activates a fluorescence signal. This sensor can be genetically encoded to measure the cellular flux and antibacterial effect of Ag+.

The role of metal ions in the virulence and viability of bacterial pathogens

Metal ions fulfil a plethora of essential roles within bacterial pathogens. In addition to acting as necessary cofactors for cellular proteins, making them indispensable for both protein structure and function, they also fulfil roles in signalling and regulation of virulence. Consequently, the maintenance of cellular metal ion homeostasis is crucial for bacterial viability and pathogenicity. It is therefore unsurprising that components of the immune response target and exploit both the essentiality of metal ions and their potential toxicity toward invading bacteria. This review provides a brief overview of the transition metal ions iron, manganese, copper and zinc during infection. These essential metal ions are discussed in the context of host modulation of bioavailability, bacterial acquisition and efflux, metal-regulated virulence factor expression and the molecular mechanisms that contribute to loss of viability and/or virulence during host-imposed metal stress.

Measuring Intracellular Metal Concentration via ICP-MS Following Copper Exposure

This chapter describes protocols for measuring fluctuation in intracellular metal concentration of A. baumannii isolates in response to copper exposure using inductively coupled plasma mass spectrometry (ICP-MS).

Handling of nutrient copper in the bacterial envelope

The insertion of copper into bacterial cuproenzymesin vivodoes not always require a copper-binding metallochaperone – why?

Metabolomic and proteomic changes induced by growth inhibitory concentrations of copper in the biofilm-forming marine bacteriumPseudoalteromonas lipolytica

Copper exposure inP. lipolyticaTC8 revealed changes in cell membrane lipid composition and in copper cell homeostasis protein regulation.

Testing Metal Sensitivity of A. baumannii Strains: Survival in Copper-Supplemented Liquid Media and on Copper-Containing Surfaces

This chapter describes protocols for determining A. baumannii isolates' overall levels of sensitivity to heavy metals; copper is used as a model heavy metal. Measurements of the ability of strains to grow in the presence of various concentrations of copper in liquid media and on copper-containing surfaces are described.

Comparative genomics and metagenomics of the metallomes

Recent achievements and advances in comparative genomic and metagenomic analyses of trace metals were reviewed and discussed.

Proteogenomic Analysis of Epibacterium Mobile BBCC367, a Relevant Marine Bacterium Isolated From the South Pacific Ocean

Epibacterium mobile BBCC367 is a marine bacterium that is common in coastal areas. It belongs to the Roseobacter clade, a widespread group in pelagic marine ecosystems. Species of the Roseobacter clade are regularly used as models to understand the evolution and physiological adaptability of generalist bacteria. E. mobile BBCC367 comprises two chromosomes and two plasmids. We used gel-free shotgun proteomics to assess its protein expression under 16 different conditions, including stress factors such as elevated temperature, nutrient limitation, high metal concentration, and UVB exposure. Comparison of the different conditions allowed us not only to retrieve almost 70% of the predicted proteins, but also to define three main protein assemblages: 584 essential core proteins, 2,144 facultative accessory proteins and 355 specific unique proteins. While the core proteome mainly exhibited proteins involved in essential functions to sustain life such as DNA, amino acids, carbohydrates, cofactors, vitamins and lipids metabolisms, the accessory and unique proteomes revealed a more specific adaptation with the expression of stress-related proteins, such as DNA repair proteins (accessory proteome), transcription regulators and a significant predominance of transporters (unique proteome). Our study provides insights into how E. mobile BBCC367 adapts to environmental changes and copes with diverse stresses.

Insight Into the Diversity and Possible Role of Plasmids in the Adaptation of Psychrotolerant and Metalotolerant Arthrobacter spp. to Extreme Antarctic Environments

Arthrobacter spp. are coryneform Gram-positive aerobic bacteria, belonging to the class Actinobacteria. Representatives of this genus have mainly been isolated from soil, mud, sludge or sewage, and are usually mesophiles. In recent years, the presence of Arthrobacter spp. was also confirmed in various extreme, including permanently cold, environments. In this study, 36 psychrotolerant and metalotolerant Arthrobacter strains isolated from petroleum-contaminated soil from the King George Island (Antarctica), were screened for the presence of plasmids. The identified replicons were thoroughly characterized in order to assess their diversity and role in the adaptation of Arthrobacter spp. to harsh Antarctic conditions. The screening process identified 11 different plasmids, ranging in size from 8.4 to 90.6 kb. A thorough genomic analysis of these replicons detected the presence of numerous genes encoding proteins that potentially perform roles in adaptive processes such as (i) protection against ultraviolet (UV) radiation, (ii) resistance to heavy metals, (iii) transport and metabolism of organic compounds, (iv) sulfur metabolism, and (v) protection against exogenous DNA. Moreover, 10 of the plasmids carry genetic modules enabling conjugal transfer, which may facilitate their spread among bacteria in Antarctic soil. In addition, transposable elements were identified within the analyzed plasmids. Some of these elements carry passenger genes, which suggests that these replicons may be actively changing, and novel genetic modules of adaptive value could be acquired by transposition events. A comparative genomic analysis of plasmids identified in this study and other available Arthrobacter plasmids was performed. This showed only limited similarities between plasmids of Antarctic Arthrobacter strains and replicons of other, mostly mesophilic, isolates. This indicates that the plasmids identified in this study are novel and unique replicons. In addition, a thorough meta-analysis of 247 plasmids of psychrotolerant bacteria was performed, revealing the important role of these replicons in the adaptation of their hosts to extreme environments.

Comparative copper toxicity impact and enzymatic cascade effect on Biosorption Activated Media and woodchips for nutrient removal in stormwater treatment

Copper, a commonly occurring heavy metal in stormwater runoff, was tested for its inhibitory effects on key nitrogen cycle bacteria in Biosorption Activated Media (BAM) and woodchip. The information in this paper is used to show that copper can enhance the denitrification process through enzyme cascade reactions since nitrous reductase is the enzyme responsible for the last step of denitrification and is largely dependent on copper as its cofactor. However, media characteristics are critical for assessing multi-enzymatic cascade reactions from the microbial ecology point of view. Moreover, both media showed significant copper removal through various mechanisms at 30 cm depth. The bioactivity evaluation indicates that other bacteria (fermentative bacteria, etc.) can be largely depressed with the presence of copper, hence the biofilm structure would be more vulnerable under shearing effects, which may result in holistic depression on the microbial community.

An important role for periplasmic storage in Pseudomonas aeruginosa copper homeostasis revealed by a combined experimental and computational modeling study

Biological systems require precise copper homeostasis enabling metallation of cuproproteins while preventing metal toxicity. In bacteria, sensing, transport, and storage molecules act in coordination to fulfill these roles. However, there is not yet a kinetic schema explaining the system integration. Here, we report a model emerging from experimental and computational approaches that describes the dynamics of copper distribution in Pseudomonas aeruginosa. Based on copper uptake experiments, a minimal kinetic model describes well the copper distribution in the wild-type bacteria but is unable to explain the behavior of the mutant strain lacking CopA1, a key Cu+ efflux ATPase. The model was expanded through an iterative hypothesis-driven approach, arriving to a mechanism that considers the induction of compartmental pools and the parallel function of CopA and Cus efflux systems. Model simulations support the presence of a periplasmic copper storage with a crucial role under dyshomeostasis conditions in P. aeruginosa. Importantly, the model predicts not only the interplay of periplasmic and cytoplasmic pools but also the existence of a threshold in the concentration of external copper beyond which cells lose their ability to control copper levels.

Copper signalling: causes and consequences

Copper-containing enzymes perform fundamental functions by activating dioxygen (O2) and therefore allowing chemical energy-transfer for aerobic metabolism. The copper-dependence of O2 transport, metabolism and production of signalling molecules are supported by molecular systems that regulate and preserve tightly-bound static and weakly-bound dynamic cellular copper pools. Disruption of the reducing intracellular environment, characterized by glutathione shortage and ambient Cu(II) abundance drives oxidative stress and interferes with the bidirectional, copper-dependent communication between neurons and astrocytes, eventually leading to various brain disease forms. A deeper understanding of of the regulatory effects of copper on neuro-glia coupling via polyamine metabolism may reveal novel copper signalling functions and new directions for therapeutic intervention in brain disorders associated with aberrant copper metabolism.

Environmental Concentrations of Copper, Alone or in Mixture With Arsenic, Can Impact River Sediment Microbial Community Structure and Functions

In many aquatic ecosystems, sediments are an essential compartment, which supports high levels of specific and functional biodiversity thus contributing to ecological functioning. Sediments are exposed to inputs from ground or surface waters and from surrounding watershed that can lead to the accumulation of toxic and persistent contaminants potentially harmful for benthic sediment-living communities, including microbial assemblages. As benthic microbial communities play crucial roles in ecological processes such as organic matter recycling and biomass production, we performed a 21-day laboratory channel experiment to assess the structural and functional impact of metals on natural microbial communities chronically exposed to sediments spiked with copper (Cu) and/or arsenic (As) alone or mixed at environmentally relevant concentrations (40 mg kg-1 for each metal). Heterotrophic microbial community responses to metals were evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exoenzymatic, metabolic and functional genes analyses). Exposure to Cu had rapid marked effects on the structure and most of the functions of the exposed communities. Exposure to As had almost undetectable effects, possibly due to both lack of As bioavailability or toxicity toward the exposed communities. However, when the two metals were combined, certain functional responses suggested a possible interaction between Cu and As toxicity on heterotrophic communities. We also observed temporal dynamics in the functional response of sediment communities to chronic Cu exposure, alone or in mixture, with some functions being resilient and others being impacted throughout the experiment or only after several weeks of exposure. Taken together, these findings reveal that metal contamination of sediment could impact both the genetic structure and the functional potential of chronically exposed microbial communities. Given their functional role in aquatic ecosystems, it poses an ecological risk as it may impact ecosystem functioning.

Integrative Conjugative Element ICEHs1 Encodes for Antimicrobial Resistance and Metal Tolerance in Histophilus somni

The objectives of this study were to determine antimicrobial resistance and metal tolerance, and identify associated genes and mobile genetic elements in clinical strains of Histophilus somni isolated from feedlot cattle in Alberta during years 2012-2016 (contemporary isolates, n = 63) and years 1980-1990 (historical isolates, n = 31). Comparison of antimicrobial resistance (AMR) showed a significant increase in resistance among contemporary isolates compared to historical isolates (P < 0.001). Tolerance to copper (Cu) and zinc (Zn) concentrations above 1 mM was observed in 68 and 52% of the contemporary isolates, respectively. The tet(H) gene associated with oxytetracycline resistance and multicopper oxidase (mco) and cation efflux (czcD) genes associated with Cu and Zn tolerance were identified. An integrative conjugative element; ICEHs1, was identified in whole genome sequences of strains resistant to oxytetracycline, which had Cu and Zn minimum inhibitory concentrations (MIC) >1 mM. The length of ICEHs1 was 64,932 bp and it contained 83 genes, including tetracycline resistance gene tetH, a multidrug efflux pump gene ebrB, and metal tolerance genes mco, czcD, and acr3. Comparative genomics of ICEs revealed that ICEHs1 shares high homology with previously described ICEs of Histophilus somni, Pasteurella multocida, and Mannheimia haemolytica. The ICEHs1 is an active element capable of intra- and inter-genus transfer as demonstrated by successful transfer to H. somni and P. multocida recipients. All isolates carrying ICEHs1 were resistant to tetracycline, a commonly used antibiotic in feedlots, and had Cu and Zn MIC higher than 1 mM. Since Cu and Zn are routinely used in feedlots, there is the possibility of co-selection of AMR in H. somni due to selection pressure created by Cu and Zn. Based on results of in-vitro conjugation experiments, ICEHs1 mediated transmission of antimicrobial and metal resistance genes is possible between BRD pathogens in the respiratory tract, potentially undermining treatment options available for histophilosis and BRD.

Experimental Warming Differentially Influences the Vulnerability of Phototrophic and Heterotrophic Periphytic Communities to Copper Toxicity

Aquatic ecosystems are generally subjected to multiple perturbations due to simultaneous or successive combinations of various natural and anthropogenic environmental pressures. To better assess and predict the resulting ecological consequences, increasing attention should be given to the accumulation of stresses on freshwater ecosystems and its effects on the vulnerability of aquatic organisms, including microbial communities, which play crucial functional roles. Here we used a microcosm study to assess the influence of an experimental warming on the vulnerability of phototrophic and heterotrophic periphytic communities to acute and chronic copper (Cu) toxicity. Natural periphytic communities were submitted for 4 weeks to three different temperatures (18, 23, and 28°C) in microcosms contaminated (at about 15 μg L^-1) or not with Cu. The vulnerability of both phototrophic and heterotrophic microbial communities to subsequent acute Cu stress was then assessed by measuring their levels of sensitivity to Cu from bioassays targeting phototrophic (photosynthetic activity) and heterotrophic (β-glucosidase and leucine aminopeptidase extracellular enzymatic activities) microbial functions. We postulated that both the increase in temperature and the chronic Cu exposure would modify microbial community structure, thus leading to changes in the capacity of phototrophic and heterotrophic communities to tolerate subsequent acute exposure to Cu. Our results demonstrated that the influence of temperature on the vulnerability of phototrophic and heterotrophic microbial communities to Cu toxicity can vary greatly according to function studied. These findings emphasize the importance of considering different functional compartments and different functional descriptors to better assess the vulnerability of periphyton to multiple stresses and predict the risks induced by multiple stressors for ecosystem balance and functioning.

Copper Influences the Antibacterial Outcomes of a β-Lactamase-Activated Prochelator against Drug-Resistant Bacteria

The unabated rise in bacterial resistance to conventional antibiotics, coupled with collateral damage to normal flora incurred by overuse of broad-spectrum antibiotics, necessitates the development of new antimicrobials targeted against pathogenic organisms. Here, we explore the antibacterial outcomes and mode of action of a prochelator that exploits the production of β-lactamase enzymes by drug-resistant bacteria to convert a nontoxic compound into a metal-binding antimicrobial agent directly within the microenvironment of pathogenic organisms. Compound PcephPT (phenylacetamido-cephem-pyrithione) contains a cephalosporin core linked to 2-mercaptopyridine N-oxide (pyrithione) via one of its metal-chelating atoms, which minimizes its preactivation interaction with metal ions and its cytotoxicity. Spectroscopic and chromatographic assays indicate that PcephPT releases pyrithione in the presence of β-lactamase-producing bacteria. The prochelator shows enhanced antibacterial activity against strains expressing β-lactamases, with bactericidal efficacy improved by the presence of low-micromolar copper in the growth medium. Metal analysis shows that cell-associated copper accumulation by the prochelator is significantly lower than that induced by pyrithione itself, suggesting that the location of pyrithione release influences biological outcomes. Low-micromolar (4-8 μg/mL) minimum inhibitory concentration (MIC) values of PcephPT in ceftriaxone-resistant bacteria compared with median lethal dose (LD50) values greater than 250 μM in mammalian cells suggests favorable selectivity. Further investigation into the mechanisms of prochelators will provide insight for the design of new antibacterial agents that manipulate cellular metallobiology as a strategy against infection.

Chemical Warfare at the Microorganismal Level: A Closer Look at the Superoxide Dismutase Enzymes of Pathogens

Superoxide anion radical is generated as a natural byproduct of aerobic metabolism but is also produced as part of the oxidative burst of the innate immune response design to kill pathogens. In living systems, superoxide is largely managed through superoxide dismutases (SODs), families of metalloenzymes that use Fe, Mn, Ni, or Cu cofactors to catalyze the disproportionation of superoxide to oxygen and hydrogen peroxide. Given the bursts of superoxide faced by microbial pathogens, it comes as no surprise that SOD enzymes play important roles in microbial survival and virulence. Interestingly, microbial SOD enzymes not only detoxify host superoxide but also may participate in signaling pathways that involve reactive oxygen species derived from the microbe itself, particularly in the case of eukaryotic pathogens. In this Review, we will discuss the chemistry of superoxide radicals and the role of diverse SOD metalloenzymes in bacterial, fungal, and protozoan pathogens. We will highlight the unique features of microbial SOD enzymes that have evolved to accommodate the harsh lifestyle at the host-pathogen interface. Lastly, we will discuss key non-SOD superoxide scavengers that specific pathogens employ for defense against host superoxide.

Genome-wide analysis of the regulation of Cu metabolism in Cryptococcus neoformans

The ability of the human fungal pathogen Cryptococcus neoformans to adapt to variable copper (Cu) environments within the host is key for successful dissemination and colonization. During pulmonary infection, host alveolar macrophages compartmentalize Cu into the phagosome and C. neoformans Cu-detoxifying metallothioneins, MT1 and MT2, are required for survival of the pathogen. In contrast, during brain colonization the C. neoformans Cu+ importers Ctr1 and Ctr4 are required for virulence. Central for the regulation and expression of both the Cu detoxifying MT1/2 and the Cu acquisition Ctr1/4 proteins is the Cu-metalloregulatory transcription factor Cuf1, an established C. neoformans virulence factor. Due to the importance of the distinct C. neoformans Cu homeostasis mechanisms during host colonization and virulence, and to the central role of Cuf1 in regulating Cu homeostasis, we performed a combination of RNA-Seq and ChIP-Seq experiments to identify differentially transcribed genes between conditions of high and low Cu. We demonstrate that the transcriptional regulation exerted by Cuf1 is intrinsically complex and that Cuf1 also functions as a transcriptional repressor. The Cu- and Cuf1-dependent regulon in C. neoformans reveals new adaptive mechanisms for Cu homeostasis in this pathogenic fungus and identifies potential new pathogen-specific targets for therapeutic intervention in fungal infections.

Glutamic acid leaching of synthetic covellite - A model system combining experimental data and geochemical modeling

For Kupferschiefer mining established pyrometallurgical and acidic bioleaching methods face numerous problems. This is due to the finely grained and dispersed distribution of the copper minerals, the complex mineralogy, comparably low copper content, and the possibly high carbonate and organic content in this ore. Leaching at neutral pH seemed worth a try: At neutral pH the abundant carbonates do not need to be dissolved and therewith would not consume excessive amounts of provided acids. Certainly, copper solubility at neutral pH is reduced compared to an acidic environment; however, if copper complexing ligands would be supplied abundantly, copper contents in the mobile phase could easily reach the required economic level. We set up a model system to study the effect of parameters such as pH, microorganisms, microbial metabolites, and organic ligands on covellite leaching to get a better understanding of the processes in copper leaching at pH ≥ 6. With this model system we could show that glutamic acid and the microbial siderophore desferrioxamine B promote covellite dissolution. Both experimental and modeling data showed that pH is an important parameter in covellite dissolution. An increase of pH from 6 to 9 could elevate copper extraction in the presence of glutamic acid by a factor of five. These results have implications for both development of a biotechnological process regarding metal extraction from Kupferschiefer, and for the interaction of bacterial metabolites with the lithosphere and potential mobilization of heavy metals in alkaline environments.

Contact killing and antimicrobial properties of copper

With the emergence of antibiotic resistance, the interest for antimicrobial agents has recently increased again in public health. Copper was recognized in 2008 by the United States Environmental Protection Agency (EPA) as the first metallic antimicrobial agent. This led to many investigations of the various properties of copper as an antibacterial, antifungal and antiviral agent. This review summarizes the latest findings about 'contact killing', the mechanism of action of copper nanoparticles and the different ways micro-organisms develop resistance to copper.

Identification of membrane-associated proteins with pathogenic potential expressed by Corynebacterium pseudotuberculosis grown in animal serum

Objective

Previous works defining antigens that might be used as vaccine targets against Corynebacterium pseudotuberculosis, which is the causative agent of sheep and goat caseous lymphadenitis, have focused on secreted proteins produced in a chemically defined culture media. Considering that such antigens might not reflect the repertoire of proteins expressed during infection conditions, this experiment aimed to investigate the membrane-associated proteins with pathogenic potential expressed by C. pseudotuberculosis grown directly in animal serum.

Results

Its membrane-associated proteins have been extracted using an organic solvent enrichment methodology, followed by LC–MS/MS and bioinformatics analysis for protein identification and classification. The results revealed 22 membrane-associated proteins characterized as potentially pathogenic. An interaction network analysis indicated that the four potentially pathogenic proteins ciuA, fagA, OppA4 and OppCD were biologically connected within two distinct network pathways, which were both associated with the ABC Transporters KEGG pathway. These results suggest that C. pseudotuberculosis pathogenesis might be associated with the transport and uptake of nutrients; other seven identified potentially pathogenic membrane proteins also suggest that pathogenesis might involve events of bacterial resistance and adhesion. The proteins herein reported potentially reflect part of the protein repertoire expressed during real infection conditions and might be tested as vaccine antigens.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3180-5) contains supplementary material, which is available to authorized users.

Multiple signaling systems target a core set of transition metal homeostasis genes using similar binding motifs

Bacterial response to metals can require complex regulation. We report an overlapping regulation for copper and zinc resistance genes in the denitrifying bacterium, Pseudomonas stutzeri RCH2, by three two-component regulatory proteins CopR1, CopR2 and CzcR. We conducted genome-wide evaluations to identify gene targets of two paralogous regulators, CopR1 and CopR2, annotated for copper signaling, and compared the results with the gene targets for CzcR, implicated in zinc signaling. We discovered that the CopRs and CzcR have largely common targets, and crossregulate a core set of P. stutzeri copper and zinc responsive genes. We established that this crossregulation is enabled by a conserved binding motif in the upstream regulatory regions of the target genes. The crossregulation is physiologically relevant as these regulators synergistically and antagonistically target multicopper oxidases, metal efflux and sequestration systems. CopR1 and CopR2 upregulate two cop operons encoding copper tolerance genes, while all three regulators downregulate a putative copper chaperone, Psest_1595. CzcR also upregulated the oprD gene and the CzcIABC Zn²⁺ efflux system, while CopR1 and CopR2 downregulated these genes. Our study suggests that crossregulation of copper and zinc homeostasis can be advantageous, and in P. stutzeri this is enabled by shared binding motifs for multiple response regulators.

Copper-related toxicity in replicating and dormantMycobacterium tuberculosiscaused by 1-hydroxy-5-R-pyridine-2(1H)-thiones

1-Hydroxy-5-R-pyridine-2(1H)-thiones are novel copper-dependentM. tuberculosisinhibitors that provide intracellular accumulation of toxic concentrations of copper.

Influence of temperature in pollution-induced community tolerance approaches used to assess effects of copper on freshwater phototrophic periphyton

By measuring levels of tolerance to toxicants in microbial communities using functional toxicity tests under controlled conditions, pollution-induced community tolerance (PICT) approaches offer an effect-based tool to assess the ecological risk of chemicals in aquatic systems. However, induced tolerance of exposed microbial communities cannot always be attributed solely to the presence of toxicants as various environmental factors, such as temperature, can also be involved. Several PICT studies have been conducted to assess the effects of copper (Cu) on phototrophic periphyton, but little is known about the influence of temperature on the response of these microbial communities to acute and chronic exposure to Cu. Here, we report on a microcosm approach to assess the effects of two contrasting temperatures (18°C and 28°C) on (i) the baseline level of Cu tolerance in non-Cu-exposed phototrophic periphyton (i.e. effect of temperature on tolerance baseline), (ii) Cu tolerance acquisition by phototrophic periphyton in response to a 3-week chronic exposure to Cu at a nominal concentration of 60μgL^-1 (i.e. effect of temperature on PICT selection) and (iii) tolerance measured during short-term toxicity tests (i.e. effect of temperature on PICT detection). The aim was to evaluate how temperature conditions during the different phases of the PICT approaches may modify the causal relationship between chronic Cu exposure and measured Cu tolerance levels. Our results evidence the influence of temperature both on the basal capacity of phototrophic periphyton to tolerate subsequent exposure to Cu (i.e. influence on tolerance baseline) and on its capacity to acquire tolerance following chronic exposure to Cu (i.e. influence on PICT selection). Hence temperature must be considered when using PICT to establish causal links between chronic Cu exposure and effects on phototrophic periphyton.

Cytoplasmic Copper Detoxification in Salmonella Can Contribute to SodC Metalation but Is Dispensable during Systemic Infection

Salmonella enterica serovar Typhimurium is a leading cause of foodborne disease worldwide. Severe infections result from the ability of S Typhimurium to survive within host immune cells, despite being exposed to various host antimicrobial factors. SodCI, a copper-zinc-cofactored superoxide dismutase, is required to defend against phagocytic superoxide. SodCII, an additional periplasmic superoxide dismutase, although produced during infection, does not function in the host. Previous studies suggested that CueP, a periplasmic copper binding protein, facilitates acquisition of copper by SodCII. CopA and GolT, both inner membrane ATPases that pump copper from the cytoplasm to the periplasm, are a source of copper for CueP. Using in vitro SOD assays, we found that SodCI can also utilize CueP to acquire copper. However, both SodCI and SodCII have a significant fraction of activity independent of CueP and cytoplasmic copper export. We utilized a series of mouse competition assays to address the in vivo role of CueP-mediated SodC activation. A copA golT cueP triple mutant was equally as competitive as the wild type, suggesting that sufficient SodCI is active to defend against phagocytic superoxide independent of CueP and cytoplasmic copper export. We also confirmed that a strain containing a modified SodCII, which is capable of complementing a sodCI deletion, was fully virulent in a copA golT cueP background competed against the wild type. These competitions also address the potential impact of cytoplasmic copper toxicity within the phagosome. Our data suggest that Salmonella does not encounter inhibitory concentrations of copper during systemic infection.IMPORTANCESalmonella is a leading cause of gastrointestinal disease worldwide. In severe cases, Salmonella can cause life-threatening systemic infections, particularly in very young children, the elderly, or people who are immunocompromised. To cause disease, Salmonella must survive the hostile environment inside host immune cells, a location in which most bacteria are killed. Our work examines how one particular metal, copper, is acquired by Salmonella to activate a protein important for survival within immune cells. At high levels, copper itself can inhibit Salmonella Using a strain of Salmonella that cannot detoxify intracellular copper, we also addressed the in vivo role of copper as an antimicrobial agent.

Copper-containing mesoporous bioactive glass nanoparticles as multifunctional agent for bone regeneration

The application of mesoporous bioactive glasses (MBGs) containing controllable amount of different ions, with the aim to impart antibacterial activity, as well as stimulation of osteogenesis and angiogenesis, is attracting an increasing interest. In this contribution, in order to endow nano-sized MBG with additional biological functions, the framework of a binary SiO₂-CaO mesoporous glass was modified with different concentrations of copper ions (2 and 5%mol.), through a one-pot ultrasound-assisted sol-gel procedure. The Cu-containing MBG (2%mol.) showed high exposed surface area (550m²g^-1), uniform mesoporous channels (2.6nm), remarkable in vitro bioactive behaviour and sustained release of Cu²⁺ ions. Cu-MBG nanoparticles and their ionic dissolution extracts exhibited antibacterial effect against three different bacteria strains, E. coli, S. aureus, S. epidermidis, and the ability to inhibit and disperse the biofilm produced by S. epidermidis. The obtained results suggest that the developed material, which combines in single multifunctional agent excellent bioactivity and antimicrobial ability, offers promising opportunities for the prevention of infectious diseases and the effective treatment of bone defects.

STATEMENT OF SIGNIFICANCE

In order to endow mesoporous bioactive glass, characterized by excellent bioactive properties, with additional biological functions, Cu-doped mesoporous SiO₂-CaO glass (Cu-MBG) in the form of nanoparticles was prepared by an ultra-sound assisted one pot synthesis. The analysis of the bacterial viability, using different bacterial strains, and the morphological observation of the biofilm produced by the Staphylococcus epidermidis, revealed the antimicrobial effectiveness of the Cu-MBG and the relative ionic extracts against both the bacterial growth and the biofilm formation/dispersion, providing a true alternative to traditional antibiotic systemic therapies. The proposed multifunctional agent represents a promising and versatile platform for bone and soft tissues regeneration.