The global responses of Mycobacterium tuberculosis to physiological levels of copper

Conditional protein splicing of the Mycobacterium tuberculosis RecA intein in its native host

The recA gene, encoding Recombinase A (RecA) is one of three Mycobacterium tuberculosis (Mtb) genes encoding an in-frame intervening protein sequence (intein) that must splice out of precursor host protein to produce functional protein. Ongoing debate about whether inteins function solely as selfish genetic elements or benefit their host cells requires understanding of interplay between inteins and their hosts. We measured environmental effects on native RecA intein splicing within Mtb using a combination of western blots and promoter reporter assays. RecA splicing was stimulated in bacteria exposed to DNA damaging agents or by treatment with copper in hypoxic, but not normoxic, conditions. Spliced RecA was processed by the Mtb proteasome, while free intein was degraded efficiently by other unknown mechanisms. Unspliced precursor protein was not observed within Mtb despite its accumulation during ectopic expression of Mtb recA within E. coli. Surprisingly, Mtb produced free N-extein in some conditions, and ectopic expression of Mtb N-extein activated LexA in E. coli. These results demonstrate that the bacterial environment greatly impacts RecA splicing in Mtb, underscoring the importance of studying intein splicing in native host environments and raising the exciting possibility of intein splicing as a novel regulatory mechanism in Mtb.

The role of transcriptional regulators in metal ion homeostasis of Mycobacterium tuberculosis

Metal ions are essential trace elements for all living organisms and play critical catalytic, structural, and allosteric roles in many enzymes and transcription factors. Mycobacterium tuberculosis (MTB), as an intracellular pathogen, is usually found in host macrophages, where the bacterium can survive and replicate. One of the reasons why Tuberculosis (TB) is so difficult to eradicate is the continuous adaptation of its pathogen. It is capable of adapting to a wide range of harsh environmental stresses, including metal ion toxicity in the host macrophages. Altering the concentration of metal ions is the common host strategy to limit MTB replication and persistence. This review mainly focuses on transcriptional regulatory proteins in MTB that are involved in the regulation of metal ions such as iron, copper and zinc. The aim is to offer novel insights and strategies for screening targets for TB treatment, as well as for the development and design of new therapeutic interventions.

Aldehyde accumulation in Mycobacterium tuberculosis with defective proteasomal degradation results in copper sensitivity

Mycobacterium tuberculosis is a major human pathogen and the causative agent of tuberculosis disease. M. tuberculosis is able to persist in the face of host-derived antimicrobial molecules nitric oxide (NO) and copper (Cu). However, M. tuberculosis with defective proteasome activity is highly sensitive to NO and Cu, making the proteasome an attractive target for drug development. Previous work linked NO susceptibility with the accumulation of para-hydroxybenzaldehyde (pHBA) in M. tuberculosis mutants with defective proteasomal degradation. In this study, we found that pHBA accumulation was also responsible for Cu sensitivity in these strains. We showed that exogenous addition of pHBA to wild-type M. tuberculosis cultures sensitized bacteria to Cu to a degree similar to that of a proteasomal degradation mutant. We determined that pHBA reduced the production and function of critical Cu resistance proteins of the regulated in copper repressor (RicR) regulon. Furthermore, we extended these Cu-sensitizing effects to an aldehyde that M. tuberculosis may face within the macrophage. Collectively, this study is the first to mechanistically propose how aldehydes can render M. tuberculosis susceptible to an existing host defense and could support a broader role for aldehydes in controlling M. tuberculosis infections. IMPORTANCE M. tuberculosis is a leading cause of death by a single infectious agent, causing 1.5 million deaths annually. An effective vaccine for M. tuberculosis infections is currently lacking, and prior infection does not typically provide robust immunity to subsequent infections. Nonetheless, immunocompetent humans can control M. tuberculosis infections for decades. For these reasons, a clear understanding of how mammalian immunity inhibits mycobacterial growth is warranted. In this study, we show aldehydes can increase M. tuberculosis susceptibility to copper, an established antibacterial metal used by immune cells to control M. tuberculosis and other microbes. Given that activated macrophages produce increased amounts of aldehydes during infection, we propose host-derived aldehydes may help control bacterial infections, making aldehydes a previously unappreciated antimicrobial defense.

The Rip1 intramembrane protease contributes to iron and zinc homeostasis in Mycobacterium tuberculosis

Mycobacterium tuberculosis is exposed to a variety of stresses during a chronic infection, as the immune system simultaneously produces bactericidal compounds and starves the pathogen of essential nutrients. The intramembrane protease, Rip1, plays an important role in the adaptation to these stresses, at least partially by the cleavage of membrane-bound transcriptional regulators. Although Rip1 is known to be critical for surviving copper intoxication and nitric oxide exposure, these stresses do not fully account for the regulatory protein's essentiality during infection. In this work, we demonstrate that Rip1 is also necessary for growth in low-iron and low-zinc conditions, similar to those imposed by the immune system. Using a newly generated library of sigma factor mutants, we show that the known regulatory target of Rip1, SigL, shares this defect. Transcriptional profiling under iron-limiting conditions supported the coordinated activity of Rip1 and SigL and demonstrated that the loss of these proteins produces an exaggerated iron starvation response. These observations demonstrate that Rip1 coordinates several aspects of metal homeostasis and suggest that a Rip1- and SigL-dependent pathway is necessary to thrive in the iron-deficient environments encountered during infection. IMPORTANCE Metal homeostasis represents a critical point of interaction between the mammalian immune system and potential pathogens. While the host attempts to intoxicate microbes with high concentrations of copper or starve the invader of iron and zinc, successful pathogens have acquired mechanisms to overcome these defenses. Our work identifies a regulatory pathway consisting of the Rip1 intramembrane protease and the sigma factor, SigL, that is essential for the important human pathogen, Mycobacterium tuberculosis, to grow in low-iron or low-zinc conditions such as those encountered during infection. In conjunction with Rip1's known role in resisting copper toxicity, our work implicates this protein as a critical integration point that coordinates the multiple metal homeostatic systems required for this pathogen to survive in host tissue.

Linking Copper-Associated Signal Transduction Systems with Their Environment in Marine Bacteria

Copper is an essential trace element for living cells. However, copper can be potentially toxic for bacterial cells when it is present in excess amounts due to its redox potential. Due to its biocidal properties, copper is prevalent in marine systems due to its use in antifouling paints and as an algaecide. Thus, marine bacteria must possess means of sensing and responding to both high copper levels and those in which it is present at only typical trace metal levels. Bacteria harbor diverse regulatory mechanisms that respond to intracellular and extracellular copper and maintain copper homeostasis in cells. This review presents an overview of the copper-associated signal transduction systems in marine bacteria, including the copper efflux systems, detoxification, and chaperone mechanisms. We performed a comparative genomics study of the copper-regulatory signal transduction system on marine bacteria to examine the influence of the environment on the presence, abundance, and diversity of copper-associated signal transduction systems across representative phyla. Comparative analyses were performed among species isolated from sources, including seawater, sediment, biofilm, and marine pathogens. Overall, we observed many putative homologs of copper-associated signal transduction systems from various copper systems across marine bacteria. While the distribution of the regulatory components is mainly influenced by phylogeny, our analyses identified several intriguing trends: (1) Bacteria isolated from sediment and biofilm displayed an increased number of homolog hits to copper-associated signal transduction systems than those from seawater. (2) A large variability exists for hits to the putative alternate σ factor CorE hits across marine bacteria. (3) Species isolated from seawater and marine pathogens harbored fewer CorE homologs than those isolated from the sediment and biofilm.

Metal manipulators and regulators in human pathogens: A comprehensive review on microbial redox copper metalloenzymes "multicopper oxidases and superoxide dismutases"

The chemistry of metal ions with human pathogens is essential for their survival, energy generation, redox signaling, and niche dominance. To regulate and manipulate the metal ions, various enzymes and metal chelators are present in pathogenic bacteria. Metalloenzymes incorporate transition metal such as iron, zinc, cobalt, and copper in their reaction centers to perform essential metabolic functions; however, iron and copper have gained more importance. Multicopper oxidases have the ability to perform redox reaction on phenolic substrates with the help of copper ions. They have been reported from Enterobacteriaceae, namely Salmonella enterica, Escherichia coli, and Yersinia enterocolitica, but their role in virulence is still poorly understood. Similarly, superoxide dismutases participate in reducing oxidative stress and allow the survival of pathogens. Their role in virulence and survival is well established in Salmonella typhimurium and Mycobacterium tuberculosis. Further, to ensure survival against stress, like metal starvation or metal toxicity, redox metalloenzymes and metal transportation systems of pathogens actively participate in metal homeostasis. Recently, the omics and protein structure biology studies have helped to predict new targets for regulation the colonization potential of the pathogenic strains. The current review is focused on the major roles of redox metalloenzymes, especially MCOs and SODs of human pathogenic bacteria.

Evidence of Homeostatic Regulation in Mycobacterium avium Subspecies paratuberculosis as an Adaptive Response to Copper Stress

Background: Bacteria are capable of responding to various stressors, something which has been essential for their adaptation, evolution, and colonization of a wide range of environments. Of the many stressors affecting bacteria, we can highlight heavy metals, and amongst these, copper stands out for its great antibacterial capacity. Using Mycobacterium tuberculosis (Mtb) as a model, the action of proteins involved in copper homeostasis has been put forward as an explanation for the tolerance or adaptive response of this mycobacteria to the toxic action of copper. Therefore, the aim of this study was to confirm the presence and evaluate the expression of genes involved in copper homeostasis at the transcriptional level after challenging Mycobacterium avium subsp. paratuberculoisis (MAP) with copper ions. Methodology: Buffer inoculated with MAP was treated with two stressors, the presence of copper homeostasis genes was confirmed by bioinformatics and genomic analysis, and the response of these genes to the stressors was evaluated by gene expression analysis, using qPCR and the comparative ΔΔCt method. Results: Through bioinformatics and genomic analysis, we found that copper homeostasis genes were present in the MAP genome and were overexpressed when treated with copper ions, which was not the case with H2O2 treatment. Conclusion: These results suggest that genes in MAP that code for proteins involved in copper homeostasis trigger an adaptive response to copper ions.

A New Benzothiazolthiazolidine Derivative, 11726172, Is Active In Vitro, In Vivo, and against Nonreplicating Cells of Mycobacterium tuberculosis

Tuberculosis (TB) still poses a global menace as one of the deadliest infectious diseases. A quarter of the human population is indeed latently infected with Mycobacterium tuberculosis. People with latent infection have a 5 to 10% lifetime risk of becoming ill with TB, representing a reservoir for TB active infection. This is a worrisome problem to overcome in the case of relapse; unfortunately, few drugs are effective against nonreplicating M. tuberculosis cells. Novel strategies to combat TB, including its latent form, are urgently needed. In response to the lack of new effective drugs and after screening about 500 original chemical molecules, we selected a compound, 11726172, that is endowed with potent antitubercular activity against M. tuberculosis both in vitro and in vivo and importantly also against dormant nonculturable bacilli. We also investigated the mechanism of action of 11726172 by applying a multidisciplinary approach, including transcriptomic, labeled metabolomic, biochemical, and microbiological procedures. Our results represent an important step forward in the development of a new antitubercular compound with a novel mechanism of action active against latent bacilli. IMPORTANCE The discontinuation of TB services due to COVID-19 causes concern about a future resurgence of TB, also considering that latent infection affects a high number of people worldwide. To combat this situation, the identification of antitubercular compounds targeting Mycobacterium tuberculosis through novel mechanisms of action is necessary. These compounds should be active against not only replicating bacteria cells but also nonreplicating cells to limit the reservoir of latently infected people on which the bacterium can rely to spread after reactivation.

Diisonitrile Lipopeptides Mediate Resistance to Copper Starvation in Pathogenic Mycobacteria

Bacterial pathogens and their hosts engage in intense competition for critical nutrients during infection, including metals such as iron, copper, and zinc. Some metals are limited by the host, and some are deployed by the host as antimicrobials. To counter metal limitation, pathogens deploy high-affinity metal acquisition systems, best exemplified by siderophores to acquire iron. Although pathogen strategies to resist the toxic effects of high Cu have been elucidated, the role of Cu starvation and the existence of Cu acquisition systems are less well characterized. In this study, we examined the role of diisonitrile chalkophores of pathogenic mycobacteria, synthesized by the enzymes encoded by the virulence-associated nrp gene cluster, in metal acquisition. nrp gene cluster expression is strongly induced by starvation or chelation of Cu but not starvation of Zn or excess Cu. Mycobacterium tuberculosis and Mycobacterium marinum strains lacking the nrp-encoded nonribosomal peptide sythetase, the fadD10 adenylate-forming enzyme, or the uncharacterized upstream gene ppe1 are all sensitized to Cu, but not Zn, starvation. This low Cu sensitivity is rescued by genetic complementation or by provision of a synthetic diisonitrile chalkophore. These data demonstrate that diisonitrile lipopeptides in mycobacteria are chalkophores that facilitate survival under Cu-limiting conditions and suggest that Cu starvation is a relevant stress for M. tuberculosis in the host.

Copper microenvironments in the human body define patterns of copper adaptation in pathogenic bacteria

Copper is an essential micronutrient for most organisms that is required as a cofactor for crucial copper-dependent enzymes encoded by both prokaryotes and eukaryotes. Evidence accumulated over several decades has shown that copper plays important roles in the function of the mammalian immune system. Copper accumulates at sites of infection, including the gastrointestinal and respiratory tracts and in blood and urine, and its antibacterial toxicity is directly leveraged by phagocytic cells to kill pathogens. Copper-deficient animals are more susceptible to infection, whereas those fed copper-rich diets are more resistant. As a result, copper resistance genes are important virulence factors for bacterial pathogens, enabling them to detoxify the copper insult while maintaining copper supply to their essential cuproenzymes. Here, we describe the accumulated evidence for the varied roles of copper in the mammalian response to infections, demonstrating that this metal has numerous direct and indirect effects on immune function. We further illustrate the multifaceted response of pathogenic bacteria to the elevated copper concentrations that they experience when invading the host, describing both conserved and species-specific adaptations to copper toxicity. Together, these observations demonstrate the roles of copper at the host–pathogen interface and illustrate why bacterial copper detoxification systems can be viable targets for the future development of novel antibiotic drug development programs.

Copper is required by both animals and bacteria in small quantities as a micronutrient. During infection, the mammalian immune system increases the local concentration of copper, which gives rise to copper toxicity in the pathogen. In turn, bacterial pathogens possess specialized systems to resist this copper toxicity. Copper also plays important, indirect roles in the function of the immune system. In this review, we explain the diverse roles of copper in the human body with a focus on its functions within the immune system. We also describe how bacterial pathogens respond to the copper toxicity that they experience within the host during infection, illustrating both conserved copper homeostasis and detoxification systems in bacteria and species-specific adaptations that have been shown to be important to pathogenicity. The key role of copper at the host–pathogen interface and the essential requirement for pathogenic bacteria to resist copper toxicity makes the protein components that confer resistance on pathogens potential targets for future development of novel antibiotic drugs.

The TbD1 Locus Mediates a Hypoxia-Induced Copper Response in Mycobacterium bovis

The Mycobacterium tuberculosis complex (MTBC) contains the causative agents of tuberculosis (TB) in mammals. The archetypal members of the MTBC, Mycobacterium tuberculosis and Mycobacterium bovis, cause human tuberculosis and bovine tuberculosis, respectively. Although M. tuberculosis and M. bovis share over 99.9% genome identity, they show distinct host adaptation for humans and animals; hence, while the molecular basis of host adaptation is encoded in their genomes, the mechanistic basis of host tropism is still unclear. Exploration of the in vitro phenotypic consequences of known genetic difference between M. bovis and M. tuberculosis offers one route to explore genotype–phenotype links that may play a role in host adaptation. The TbD1 (“Mycobacterium tuberculosis deletion 1 region”) locus encompasses the mmpS6 and mmpL6 genes. TbD1 is absent in M. tuberculosis “modern” lineages (Lineages 2, 3, and 4) but present in “ancestral” M. tuberculosis (Lineages 1 and 7), Mycobacterium africanum lineages (Lineages 5 and 6), newly identified M. tuberculosis lineages (Lineages 8 and 9), and animal adapted strains, such as M. bovis. The function of TbD1 has previously been investigated in M. tuberculosis, where conflicting data has emerged on the role of TbD1 in sensitivity to oxidative stress, while the underlying mechanistic basis of such a phenotype is unclear. In this study, we aimed to shed further light on the role of the TbD1 locus by exploring its function in M. bovis. Toward this, we constructed an M. bovis TbD1 knockout (ΔTbD1) strain and conducted comparative transcriptomics to define global gene expression profiles of M. bovis wild-type (WT) and the ΔTbD1 strains under in vitro culture conditions (rolling and standing cultures). This analysis revealed differential induction of a hypoxia-driven copper response in WT and ΔTbD1 strains. In vitro phenotypic assays demonstrated that the deletion of TbD1 sensitized M. bovis to H2O2 and hypoxia-specific copper toxicity. Our study provides new information on the function of the TbD1 locus in M. bovis and its role in stress responses in the MTBC.

Commonalities of Mycobacterium tuberculosis Transcriptomes in Response to Defined Persisting Macrophage Stresses

As the goal of a bacterium is to become bacteria, evolution has imposed continued selections for gene expression. The intracellular pathogen Mycobacterium tuberculosis, the causative agent of tuberculosis, has adopted a fine-tuned response to survive its host's methods to aggressively eradicate invaders. The development of microarrays and later RNA sequencing has led to a better understanding of biological processes controlling the relationship between host and pathogens. In this study, RNA-seq was performed to detail the transcriptomes of M. tuberculosis grown in various conditions related to stresses endured by M. tuberculosis during host infection and to delineate a general stress response incurring during persisting macrophage stresses. M. tuberculosis was subjected to long-term growth, nutrient starvation, hypoxic and acidic environments. The commonalities between these stresses point to M. tuberculosis maneuvering to exploit propionate metabolism for lipid synthesis or to withstand propionate toxicity whilst in the intracellular environment. While nearly all stresses led to a general shutdown of most biological processes, up-regulation of pathways involved in the synthesis of amino acids, cofactors, and lipids were observed only in hypoxic M. tuberculosis. This data reveals genes and gene cohorts that are specifically or exclusively induced during all of these persisting stresses. Such knowledge could be used to design novel drug targets or to define possible M. tuberculosis vulnerabilities for vaccine development. Furthermore, the disruption of specific functions from this gene set will enhance our understanding of the evolutionary forces that have caused the tubercle bacillus to be a highly successful pathogen.

An improved statistical method to identify chemical-genetic interactions by exploiting concentration-dependence

Chemical-genetics (C-G) experiments can be used to identify interactions between inhibitory compounds and bacterial genes, potentially revealing the targets of drugs, or other functionally interacting genes and pathways. C-G experiments involve constructing a library of hypomorphic strains with essential genes that can be knocked-down, treating it with an inhibitory compound, and using high-throughput sequencing to quantify changes in relative abundance of individual mutants. The hypothesis is that, if the target of a drug or other genes in the same pathway are present in the library, such genes will display an excessive fitness defect due to the synergy between the dual stresses of protein depletion and antibiotic exposure. While assays at a single drug concentration are susceptible to noise and can yield false-positive interactions, improved detection can be achieved by requiring that the synergy between gene and drug be concentration-dependent. We present a novel statistical method based on Linear Mixed Models, called CGA-LMM, for analyzing C-G data. The approach is designed to capture the dependence of the abundance of each gene in the hypomorph library on increasing concentrations of drug through slope coefficients. To determine which genes represent candidate interactions, CGA-LMM uses a conservative population-based approach in which genes with negative slopes are considered significant only if they are outliers with respect to the rest of the population (assuming that most genes in the library do not interact with a given inhibitor). We applied the method to analyze 3 independent hypomorph libraries of M. tuberculosis for interactions with antibiotics with anti-tubercular activity, and we identify known target genes or expected interactions for 7 out of 9 drugs where relevant interacting genes are known.

Mycobacterium tuberculosis VapC4 toxin engages small ORFs to initiate an integrated oxidative and copper stress response

The Mycobacterium tuberculosis (Mtb) VapBC4 toxin-antitoxin system is essential for the establishment of Mtb infection. Using a multitier, systems-level approach, we uncovered the sequential molecular events triggered by the VapC4 toxin that activate a circumscribed set of critical stress survival pathways which undoubtedly underlie Mtb virulence. VapC4 exclusively inactivated the sole transfer RNA^Cys (tRNA^Cys) through cleavage at a single site within the anticodon sequence. Depletion of the pool of tRNA^Cys led to ribosome stalling at Cys codons within actively translating messenger RNAs. Genome mapping of these Cys-stalled ribosomes unexpectedly uncovered several unannotated Cys-containing open reading frames (ORFs). Four of these are small ORFs (sORFs) encoding Cys-rich proteins of fewer than 50 amino acids that function as Cys-responsive attenuators that engage ribosome stalling at tracts of Cys codons to control translation of downstream genes. Thus, VapC4 mimics a state of Cys starvation, which then activates Cys attenuation at sORFs to globally redirect metabolism toward the synthesis of free Cys. The resulting newly enriched pool of Cys feeds into the synthesis of mycothiol, the glutathione counterpart in this pathogen that is responsible for maintaining cellular redox homeostasis during oxidative stress, as well as into a circumscribed subset of cellular pathways that enable cells to defend against oxidative and copper stresses characteristically endured by Mtb within macrophages. Our ability to pinpoint activation or down-regulation of pathways that collectively align with Mtb virulence-associated stress responses and the nonreplicating persistent state brings to light a direct and vital role for the VapC4 toxin in mediating these critical pathways.

Mycobacterium tuberculosis complex lineage 5 exhibits high levels of within-lineage genomic diversity and differing gene content compared to the type strain H37Rv

Pathogens of the Mycobacterium tuberculosis complex (MTBC) are considered to be monomorphic, with little gene content variation between strains. Nevertheless, several genotypic and phenotypic factors separate strains of the different MTBC lineages (L), especially L5 and L6 (traditionally termed Mycobacterium africanum) strains, from each other. However, this genome variability and gene content, especially of L5 strains, has not been fully explored and may be important for pathobiology and current approaches for genomic analysis of MTBC strains, including transmission studies. By comparing the genomes of 355 L5 clinical strains (including 3 complete genomes and 352 Illumina whole-genome sequenced isolates) to each other and to H37Rv, we identified multiple genes that were differentially present or absent between H37Rv and L5 strains. Additionally, considerable gene content variability was found across L5 strains, including a split in the L5.3 sub-lineage into L5.3.1 and L5.3.2. These gene content differences had a small knock-on effect on transmission cluster estimation, with clustering rates influenced by the selected reference genome, and with potential overestimation of recent transmission when using H37Rv as the reference genome. We conclude that full capture of the gene diversity, especially high-resolution outbreak analysis, requires a variation of the single H37Rv-centric reference genome mapping approach currently used in most whole-genome sequencing data analysis pipelines. Moreover, the high within-lineage gene content variability suggests that the pan-genome of M. tuberculosis is at least several kilobases larger than previously thought, implying that a concatenated or reference-free genome assembly (de novo) approach may be needed for particular questions.

Nutritional immunity: the impact of metals on lung immune cells and the airway microbiome during chronic respiratory disease

Nutritional immunity is the sequestration of bioavailable trace metals such as iron, zinc and copper by the host to limit pathogenicity by invading microorganisms. As one of the most conserved activities of the innate immune system, limiting the availability of free trace metals by cells of the immune system serves not only to conceal these vital nutrients from invading bacteria but also operates to tightly regulate host immune cell responses and function. In the setting of chronic lung disease, the regulation of trace metals by the host is often disrupted, leading to the altered availability of these nutrients to commensal and invading opportunistic pathogenic microbes. Similarly, alterations in the uptake, secretion, turnover and redox activity of these vitally important metals has significant repercussions for immune cell function including the response to and resolution of infection. This review will discuss the intricate role of nutritional immunity in host immune cells of the lung and how changes in this fundamental process as a result of chronic lung disease may alter the airway microbiome, disease progression and the response to infection.

Multi-omic regulatory networks capture downstream effects of kinase inhibition in Mycobacterium tuberculosis

The ability of Mycobacterium tuberculosis (Mtb) to adapt to diverse stresses in its host environment is crucial for pathogenesis. Two essential Mtb serine/threonine protein kinases, PknA and PknB, regulate cell growth in response to environmental stimuli, but little is known about their downstream effects. By combining RNA-Seq data, following treatment with either an inhibitor of both PknA and PknB or an inactive control, with publicly available ChIP-Seq and protein–protein interaction data for transcription factors, we show that the Mtb transcription factor (TF) regulatory network propagates the effects of kinase inhibition and leads to widespread changes in regulatory programs involved in cell wall integrity, stress response, and energy production, among others. We also observe that changes in TF regulatory activity correlate with kinase-specific phosphorylation of those TFs. In addition to characterizing the downstream regulatory effects of PknA/PknB inhibition, this demonstrates the need for regulatory network approaches that can incorporate signal-driven transcription factor modifications.

Cu Homeostasis in Bacteria: The Ins and Outs

Copper (Cu) is an essential trace element for all living organisms and used as cofactor in key enzymes of important biological processes, such as aerobic respiration or superoxide dismutation. However, due to its toxicity, cells have developed elaborate mechanisms for Cu homeostasis, which balance Cu supply for cuproprotein biogenesis with the need to remove excess Cu. This review summarizes our current knowledge on bacterial Cu homeostasis with a focus on Gram-negative bacteria and describes the multiple strategies that bacteria use for uptake, storage and export of Cu. We furthermore describe general mechanistic principles that aid the bacterial response to toxic Cu concentrations and illustrate dedicated Cu relay systems that facilitate Cu delivery for cuproenzyme biogenesis. Progress in understanding how bacteria avoid Cu poisoning while maintaining a certain Cu quota for cell proliferation is of particular importance for microbial pathogens because Cu is utilized by the host immune system for attenuating pathogen survival in host cells.

CtpB is a plasma membrane copper (I) transporting P-type ATPase of Mycobacterium tuberculosis

BACKGROUND

The intracellular concentration of heavy-metal cations, such as copper, nickel, and zinc is pivotal for the mycobacterial response to the hostile environment inside macrophages. To date, copper transport mediated by P-type ATPases across the mycobacterial plasma membrane has not been sufficiently explored.

RESULTS

In this work, the ATPase activity of the putative Mycobacterium tuberculosis P1B-type ATPase CtpB was associated with copper (I) transport from mycobacterial cells. Although CtpB heterologously expressed in M. smegmatis induced tolerance to toxic concentrations of Cu2+ and a metal preference for Cu+, the disruption of ctpB in M. tuberculosis cells did not promote impaired cell growth or heavy-metal accumulation in whole mutant cells in cultures under high doses of copper. In addition, the Cu+ ATPase activity of CtpB embedded in the plasma membrane showed features of high affinity/slow turnover ATPases, with enzymatic parameters KM 0.19 ± 0.04 µM and Vmax 2.29 ± 0.10 nmol/mg min. In contrast, the ctpB gene transcription was activated in cells under culture conditions that mimicked the hostile intraphagosomal environment, such as hypoxia, nitrosative and oxidative stress, but not under high doses of copper.

CONCLUSIONS

The overall results suggest that M. tuberculosis CtpB is associated with Cu+ transport from mycobacterial cells possibly playing a role different from copper detoxification.

Transcriptome Changes of Mycobacterium marinum in the Process of Resuscitation From Hypoxia-Induced Dormancy

Nearly one-third of the world's population is latently infected with Mycobacterium tuberculosis (M. tb), which represents a huge disease reservoir for reactivation and a major obstacle for effective control of tuberculosis. During latent infection, M. tb is thought to enter nonreplicative dormant states by virtue of its response to hypoxia and nutrient-deprived conditions. Knowledge of the genetic programs used to facilitate entry into and exit from the nonreplicative dormant states remains incomplete. In this study, we examined the transcriptional changes of Mycobacterium marinum (M. marinum), a pathogenic mycobacterial species closely related to M. tb, at different stages of resuscitation from hypoxia-induced dormancy. RNA-seq analyses were performed on M. marinum cultures recovered at multiple time points after resuscitation. Differentially expressed genes (DEGs) at each time period were identified and analyzed. Co-expression networks of transcription factors and DEGs in each period were constructed. In addition, we performed a weighted gene co-expression network analysis (WGCNA) on all genes and obtained 12 distinct gene modules. Collectively, these data provided valuable insight into the transcriptome changes of M. marinum upon resuscitation as well as gene module function of the bacteria during active metabolism and growth.

Interplays between copper and Mycobacterium tuberculosis GroEL1

The chaperone GroEL1 enhances copper tolerance during Mycobacterium bovis BCG biofilm formation. The binding of copper ions to the GroEL1 histidine-rich region protects the chaperone from destabilization and increases its ATPase activity.

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.

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.

Pulmonary arterial hypertension and the potential roles of metallothioneins: A focused review

The pathophysiology of pulmonary arterial hypertension (PAH) is underlined by cell proliferation and vasoconstriction of pulmonary arterioles this involves multiple molecular factors or proteins, but it is not clear what the exact roles of these factors/proteins are. In addition, there may be other factors/proteins that have not been identified that contribute to PAH pathophysiology. Therefore, research has focused on investigating novel role players, in order to facilitate a better understanding of how PAH develop. Evidence suggest that mitochondrial regulators are key role players in PAH pathophysiology, but regulators that have not received sufficient attention in PAH are metallothioneins (MTs). In PAH patients, MT expression is elevated compared to healthy individuals, suggesting that MTs may be possible biomarkers. In other disease-models, MTs have been shown to regulate cell proliferation and vasoconstriction, processes that are instrumental in PAH pathophysiology. Due to the involvement of these processes in PAH pathophysiology and the ability of MTs to modulate them, this paper propose that cellular MTs may also play a role in PAH development. This paper suggests that PAH-research should perhaps begin to investigate the involvement of cellular MTs in the development of PAH.

Rv0474 is a copper-responsive transcriptional regulator that negatively regulates expression of RNA polymerase β subunit in Mycobacterium tuberculosis

We characterize Rv0474, a putative transcriptional regulatory protein of Mycobacterium tuberculosis, which is found to function as a copper-responsive transcriptional regulator at toxic levels of copper. It is an autorepressor, but at elevated levels (10-250 μm) of copper ions the repression is relieved resulting in an increase in Rv0474 expression. Copper-bound Rv0474 is recruited to the rpoB promoter leading to its repression resulting in the growth arrest of the bacterium. Mutational analysis showed that the helix-turn-helix and leucine zipper domains of Rv0474 are essential for its binding to Rv0474 and rpoB promoters, respectively. The mechanism of Rv0474-mediated rpoB regulation seems to be operational only in pathogenic mycobacteria that can persist inside the host.

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.

Copper homeostasis networks in the bacterium Pseudomonas aeruginosa

Bacterial copper (Cu⁺) homeostasis enables both precise metallation of diverse cuproproteins and control of variable metal levels. To this end, protein networks mobilize Cu⁺ to cellular targets with remarkable specificity. However, the understanding of these processes is rather fragmented. Here, we use genome-wide transcriptomic analysis by RNA-Seq to characterize the response of Pseudomonas aeruginosa to external 0.5 mm CuSO₄, a condition that did not generate pleiotropic effects. Pre-steady-state (5-min) and steady-state (2-h) Cu⁺ fluxes resulted in distinct transcriptome landscapes. Cells quickly responded to Cu²⁺ stress by slowing down metabolism. This was restored once steady state was reached. Specific Cu⁺ homeostasis genes were strongly regulated in both conditions. Our system-wide analysis revealed induction of three Cu⁺ efflux systems (a P_1B-ATPase, a porin, and a resistance-nodulation-division (RND) system) and of a putative Cu⁺-binding periplasmic chaperone and the unusual presence of two cytoplasmic CopZ proteins. Both CopZ chaperones could bind Cu⁺ with high affinity. Importantly, novel transmembrane transporters probably mediating Cu⁺ influx were among those largely repressed upon Cu⁺ stress. Compartmental Cu⁺ levels appear independently controlled; the cytoplasmic Cu⁺ sensor CueR controls cytoplasmic chaperones and plasma membrane transporters, whereas CopR/S responds to periplasmic Cu⁺ Analysis of ΔcopR and ΔcueR mutant strains revealed a CopR regulon composed of genes involved in periplasmic Cu⁺ homeostasis and its putative DNA recognition sequence. In conclusion, our study establishes a system-wide model of a network of sensors/regulators, soluble chaperones, and influx/efflux transporters that control the Cu⁺ levels in P. aeruginosa compartments.

Copper and Antibiotics: Discovery, Modes of Action, and Opportunities for Medicinal Applications

Copper is a ubiquitous element in the environment as well as living organisms, with its redox capabilities and complexation potential making it indispensable for many cellular functions. However, these same properties can be highly detrimental to prokaryotes and eukaryotes when not properly controlled, damaging many biomolecules including DNA, lipids, and proteins. To restrict free copper concentrations, all bacteria have developed mechanisms of resistance, sequestering and effluxing labile copper to minimize its deleterious effects. This weakness is actively exploited by phagocytes, which utilize a copper burst to destroy pathogens. Though administration of free copper is an unreasonable therapeutic antimicrobial itself, due to insufficient selectivity between host and pathogen, small-molecule ligands may provide an opportunity for therapeutic mimicry of the immune system. By modulating cellular entry, complex stability, resistance evasion, and target selectivity, ligand/metal coordination complexes can synergistically result in high levels of antibacterial activity. Several established therapeutic drugs, such as disulfiram and pyrithione, display remarkable copper-dependent inhibitory activity. These findings have led to development of new drug discovery techniques, using copper ions as the focal point. High-throughput screens for copper-dependent inhibitors against Mycobacterium tuberculosis and Staphylococcus aureus uncovered several new compounds, including a new class of inhibitors, the NNSNs. In this review, we highlight the microbial biology of copper, its antibacterial activities, and mechanisms to discover new inhibitors that synergize with copper.

Essentiality of mmpL3 and impact of its silencing on Mycobacterium tuberculosis gene expression

MmpL3 is an inner membrane transporter of Mycobacterium tuberculosis responsible for the export of trehalose momomycolate, a precursor of the mycobacterial outer membrane component trehalose dimycolate (TDM), as well as mycolic acids bound to arabinogalactan. MmpL3 represents an emerging target for tuberculosis therapy. In this paper, we describe the construction and characterization of an mmpL3 knockdown strain of M. tuberculosis. Downregulation of mmpL3 led to a stop in bacterial division and rapid cell death, preceded by the accumulation of TDM precursors. MmpL3 was also shown to be essential for growth in monocyte-derived human macrophages. Using RNA-seq we also found that MmpL3 depletion caused up-regulation of 47 genes and down-regulation of 23 genes (at least 3-fold change and false discovery rate ≤1%). Several genes related to osmoprotection and metal homeostasis were induced, while several genes related to energy production and mycolic acids biosynthesis were repressed suggesting that inability to synthesize a correct outer membrane leads to changes in cellular permeability and a metabolic downshift.

Bacterial Proteasomes: Mechanistic and Functional Insights

Regulated proteolysis is essential for the normal physiology of all organisms. While all eukaryotes and archaea use proteasomes for protein degradation, only certain orders of bacteria have proteasomes, whose functions are likely as diverse as the species that use them. In this review, we discuss the most recent developments in the understanding of how proteins are targeted to proteasomes for degradation, including ATP-dependent and -independent mechanisms, and the roles of proteasome-dependent degradation in protein quality control and the regulation of cellular physiology. Furthermore, we explore newly established functions of proteasome system accessory factors that function independently of proteolysis.

Genetic-and-Epigenetic Interspecies Networks for Cross-Talk Mechanisms in Human Macrophages and Dendritic Cells during MTB Infection

Tuberculosis is caused by Mycobacterium tuberculosis (Mtb) infection. Mtb is one of the oldest human pathogens, and evolves mechanisms implied in human evolution. The lungs are the first organ exposed to aerosol-transmitted Mtb during gaseous exchange. Therefore, the guards of the immune system in the lungs, such as macrophages (Mϕs) and dendritic cells (DCs), are the most important defense against Mtb infection. There have been several studies discussing the functions of Mϕs and DCs during Mtb infection, but the genome-wide pathways and networks are still incomplete. Furthermore, the immune response induced by Mϕs and DCs varies. Therefore, we analyzed the cross-talk genome-wide genetic-and-epigenetic interspecies networks (GWGEINs) between Mϕs vs. Mtb and DCs vs. Mtb to determine the varying mechanisms of both the host and pathogen as it relates to Mϕs and DCs during early Mtb infection. First, we performed database mining to construct candidate cross-talk GWGEIN between human cells and Mtb. Then we constructed dynamic models to characterize the molecular mechanisms, including intraspecies gene/microRNA (miRNA) regulation networks (GRNs), intraspecies protein-protein interaction networks (PPINs), and the interspecies PPIN of the cross-talk GWGEIN. We applied a system identification method and a system order detection scheme to dynamic models to identify the real cross-talk GWGEINs using the microarray data of Mϕs, DCs and Mtb. After identifying the real cross-talk GWGEINs, the principal network projection (PNP) method was employed to construct host-pathogen core networks (HPCNs) between Mϕs vs. Mtb and DCs vs. Mtb during infection process. Thus, we investigated the underlying cross-talk mechanisms between the host and the pathogen to determine how the pathogen counteracts host defense mechanisms in Mϕs and DCs during Mtb H37Rv early infection. Based on our findings, we propose Rv1675c as a potential drug target because of its important defensive role in Mϕs. Furthermore, the membrane essential proteins v1098c, and Rv1696 (or cytoplasm for Rv0667), in Mtb could also be potential drug targets because of their important roles in Mtb survival in both cell types. We also propose the drugs Lopinavir, TMC207, ATSM, and GTSM as potential therapeutic treatments for Mtb infection since they target the above potential drug targets.

CsoR Is Essential for Maintaining Copper Homeostasis in Mycobacterium tuberculosis

Mycobacterium tuberculosis, a pathogen infecting one third of the world population, faces numerous challenges within the host, including high levels of copper. We have previously shown that M. tuberculosis CsoR is a copper inducible transcriptional regulator. Here we examined the hypothesis that csoR is necessary for maintaining copper homeostasis and surviving under various stress conditions. With an unmarked csoR knockout strain, we were able to characterize the role of csoR in M. tuberculosis as it faced copper and host stress. Growth under high levels of copper demonstrated that M. tuberculosis survives copper stress significantly better in the absence of csoR. Yet under minimal levels of copper, differential expression analysis revealed that the loss of csoR results in a cell wide hypoxia-type stress response with the induction of the DosR regulon. Despite the stress placed on M. tuberculosis by the loss of csoR, survival of the knockout strain was increased compared to wild type during the early chronic stages of mouse infection, suggesting that csoR could play an active role in modulating M. tuberculosis fitness within the host. Overall, analysis of CsoR provided an increased understanding of the M. tuberculosis copper response with implications for other intracellular pathogens harboring CsoR.

Copper homeostasis in Mycobacterium tuberculosis

Copper (Cu) is a trace element essential for the growth and development of almost all organisms, including bacteria. However, Cu overload in most systems is toxic. Studies show Cu accumulates in macrophage phagosomes infected with bacteria, suggesting Cu provides an innate immune mechanism to combat invading pathogens. To counteract the host-supplied Cu, increasing evidence suggests that bacteria have evolved Cu resistance mechanisms to facilitate their pathogenesis. In particular, Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, has evolved multiple pathways to respond to Cu. Here, we summarize what is currently known about Cu homeostasis in Mtb and discuss potential sources of Cu encountered by this and other pathogens in a mammalian host.

The Sculpting of the Mycobacterium tuberculosis Genome by Host Cell-Derived Pressures

Mycobacterium tuberculosis is an incredibly successful pathogen with an extraordinary penetrance of its target host population. The ability to infect many yet cause disease in few is undoubtedly central to this success. This ability relies on sensing and responding to the changing environments encountered during the course of disease in the human host. This chapter discusses these environmental cues and stresses, and explores how the genome of Mtb has evolved under the purifying selections that they exert. In analyzing the response of Mtb to a broad range of intracellular pressures it is clear that, despite genome down-sizing, Mtb has retained an extraordinary flexibility in central carbon metabolism. We believe that it is this metabolic plasticity, more than any of the virulence factors, that is the foundation for Mtb's qualities of endurance.

Localization of Human Copper Transporter 1 in the Eye and its Role in Eales Disease

PURPOSE

Copper (Cu) is an essential trace element; however excess is toxic due to the pro-oxidant activity. Increased intracellular Cu levels in vitreous and monocyte were reported in Eales disease (ED) previously. Copper transporter1 (CTR1) maintains copper homeostasis and hence, we studied the presence of CTR1 in ocular tissues and its role in ED.

METHODS

Real-time PCR, ELISA and Western blot experiments were performed in donor eyeballs tissues and PBMCs isolated from controls and ED. Immunostaining were performed for CTR1 from donor eyeballs and one ED case.

RESULTS

CTR1 protein was expressed in all ocular tissues. PBMCs showed a three-fold increase in CTR1 protein in ED when compared with controls. Retinal sections from ED patients also revealed increased CTR1 protein expression in retinal tissues, compared with control.

CONCLUSIONS

CTR1 was significantly increased in ED when compared with controls, indicating its considerable role in the ED pathology.

Towards understanding the biological function of the unusual chaperonin Cpn60.1 (GroEL1) of Mycobacterium tuberculosis

The 60 kDa heat shock proteins, also known as Cpn60s (GroELs) are components of the essential protein folding machinery of the cell, but are also dominant antigens in many infectious diseases. Although generally essential for cellular survival, in some organisms such as Mycobacterium tuberculosis, one or more paralogous Cpn60s are known to be dispensable. In M. tuberculosis, Cpn60.2 (GroEL2) is essential for cell survival, but the biological role of the non-essential Cpn60.1 (GroEL1) is still elusive. To understand the relevance of Cpn60.1 (GroEL1) in M. tuberculosis physiology, detailed transcriptomic analyses for the wild type H37Rv and cpn60.1 knockout (groEL1-KO) were performed under in vitro stress conditions: stationary phase, cold shock, low aeration, mild cold shock and low pH. Additionally, the survival of the groEL1-KO was assessed in macrophages at multiplicity of infection (MOI) of 1:1 and 1:5. We observed that survival under low aeration was significantly compromised in the groEL1-KO. Further, the gene expression analyses under low aeration showed change in expression of several key virulence factors like two component system PhoP/R and MprA/B, sigma factors SigM and C and adversely affected known hypoxia response regulators Rv0081, Rv0023 and DosR. Our work is therefore suggestive of an important role of Cpn60.1 (GroEL1) for survival under low aeration by affecting the expression of genes known for hypoxia response.

Mycobacteria, metals, and the macrophage

Mycobacterium tuberculosis is a facultative intracellular pathogen that thrives inside host macrophages. A key trait of M. tuberculosis is to exploit and manipulate metal cation trafficking inside infected macrophages to ensure survival and replication inside the phagosome. Here, we describe the recent fascinating discoveries that the mammalian immune system responds to infections with M. tuberculosis by overloading the phagosome with copper and zinc, two metals which are essential nutrients in small quantities but are toxic in excess. M. tuberculosis has developed multi-faceted resistance mechanisms to protect itself from metal toxicity including control of uptake, sequestration inside the cell, oxidation, and efflux. The host response to infections combines this metal poisoning strategy with nutritional immunity mechanisms that deprive M. tuberculosis from metals such as iron and manganese to prevent bacterial replication. Both immune mechanisms rely on the translocation of metal transporter proteins to the phagosomal membrane during the maturation process of the phagosome. This review summarizes these recent findings and discusses how metal-targeted approaches might complement existing TB chemotherapeutic regimens with novel anti-infective therapies.

Mycobacterium tuberculosis and Copper: A Newly Appreciated Defense against an Old Foe?

Several independent studies have recently converged upon the conclusion that the human bacterial pathogen Mycobacterium tuberculosis encounters copper during infections. At least three independently regulated pathways respond to excess copper and are required for the full virulence of M. tuberculosis in animals. In this review, I will discuss the functions of the best-characterized copper-responsive proteins in M. tuberculosis, the potential sources of copper during an infection, and remaining questions about the interface between copper and tuberculosis.

Proteomic Analysis of Drug-Resistant Mycobacteria: Co-Evolution of Copper and INH Resistance

Tuberculosis, caused by the pathogen Mycobacterium tuberculosis, is a worldwide public health threat. Mycobacterium tuberculosis is capable of resisting various stresses in host cells, including high levels of ROS and copper ions. To better understand the resistance mechanisms of mycobacteria to copper, we generated a copper-resistant strain of Mycobacterium smegmatis, mc²155-Cu from the selection of copper sulfate treated-bacteria. The mc²155-Cu strain has a 5-fold higher resistance to copper sulfate and a 2-fold higher resistance to isoniazid (INH) than its parental strain mc²155, respectively. Quantitative proteomics was carried out to find differentially expressed proteins between mc²155 and mc²155-Cu. Among 345 differentially expressed proteins, copper-translocating P-type ATPase was up-regulated, while all other ABC transporters were down-regulated in mc²155-Cu, suggesting copper-translocating P-type ATPase plays a crucial role in copper resistance. Results also indicated that the down-regulation of metabolic enzymes and decreases in cellular NAD, FAD, mycothiol, and glutamine levels in mc²155-Cu were responsible for its slowing growth rate as compared to mc²155. Down-regulation of KatG2 expression in both protein and mRNA levels indicates the co-evolution of copper and INH resistance in copper resistance bacteria, and provides new evidence to understanding of the molecular mechanisms of survival of mycobacteria under stress conditions.

Global transcriptional profiles of the copper responses in the cyanobacterium Synechocystis sp. PCC 6803

Copper is an essential element involved in fundamental processes like respiration and photosynthesis. However, it becomes toxic at high concentration, which has forced organisms to control its cellular concentration. We have recently described a copper resistance system in the cyanobacterium Synechocystis sp. PCC 6803, which is mediated by the two-component system, CopRS, a RND metal transport system, CopBAC and a protein of unknown function, CopM. Here, we report the transcriptional responses to copper additions at non-toxic (0.3 µM) and toxic concentrations (3 µM) in the wild type and in the copper sensitive copR mutant strain. While 0.3 µM copper slightly stimulated metabolism and promoted the exchange between cytochrome c6 and plastocyanin as soluble electron carriers, the addition of 3 µM copper catalyzed the formation of ROS, led to a general stress response and induced expression of Fe-S cluster biogenesis genes. According to this, a double mutant strain copRsufR, which expresses constitutively the sufBCDS operon, tolerated higher copper concentration than the copR mutant strain, suggesting that Fe-S clusters are direct targets of copper toxicity in Synechocystis. In addition we have also demonstrated that InrS, a nickel binding transcriptional repressor that belong to the CsoR family of transcriptional factor, was involved in heavy metal homeostasis, including copper, in Synechocystis. Finally, global gene expression analysis of the copR mutant strain suggested that CopRS only controls the expression of copMRS and copBAC operons in response to copper.

Metal resistance-related genes are differently expressed in response to copper and zinc ion in six Acidithiobacillus ferrooxidans strains

Metal resistance of acidophilic bacteria is very significant during bioleaching of copper ores since high concentration of metal is harmful to the growth of microorganisms. The resistance levels of six Acidithiobacillus ferrooxidans strains to 0.15 M copper and 0.2 M zinc were investigated, and eight metal resistance-related genes (afe-0022, afe-0326, afe-0329, afe-1143, afe-0602, afe-0603, afe-0604, and afe-1788) were sequenced and analyzed. The transcriptional expression levels of eight possible metal tolerance genes in six A. ferrooxidans strains exposed to 0.15 M Cu(2+) and 0.2 M Zn(2+) were determined by real-time quantitative PCR (RT-qPCR), respectively. The copper resistance levels of six A. ferrooxidans strains declined followed by DY26, DX5, DY15, GD-B, GD-0, and YTW. The zinc tolerance levels of six A. ferrooxidans strains exposed to 0.2 M Zn(2+) from high to low were YTW > GD-B > DY26 > GD-0 > DX5 > DY15. Seven metal tolerance-related genes all presented in the genome of six strains, except afe-0604. The metal resistance-related genes showed different transcriptional expression patterns in six A. ferrooxidans strains. The expression of gene afe-0326 and afe-0022 in six A. ferrooxidans strains in response to 0.15 M Cu(2+) showed the same trend with the resistance levels. The expression levels of genes afe-0602, afe-0603, afe-0604, and afe-1788 in six strains response to 0.2 M Zn(2+) did not show a clear correlation between the zinc tolerance levels of six strains. According to the results of RT-qPCR and bioinformatics analysis, the proteins encoded by afe-0022, afe-0326, afe-0329, and afe-1143 were related to Cu(2+) transport of A. ferrooxidans strains.

Mycobacterium tuberculosis P-type ATPases: possible targets for drug or vaccine development

Tuberculosis (TB) has been the biggest killer in the human history; currently, Mycobacterium tuberculosis (Mtb) kills nearly 2 million people each year worldwide. The high prevalence of TB obligates the identification of new therapeutic targets and the development of anti-TB vaccines that can control multidrug resistance and latent TB infections. Membrane proteins have recently been suggested as key targets for bacterial viability. Current studies have shown that mycobacteria P-type ATPases may play critical roles in ion homeostasis and in the response of mycobacteria to toxic substances in the intraphagosomal environment. In this review, we bring together the genomic, transcriptomic, and structural aspects of the P-type ATPases that are relevant during active and latent Mtb infections, which can be useful in determining the potential of these ATPases as drug targets and in uncovering their possible roles in the development of new anti-TB attenuated vaccines.

Metallobiology of Tuberculosis

Transition metals are essential constituents of all living organisms, playing crucial structural and catalytic parts in many enzymes and transcription factors. However, transition metals can also be toxic when present in excess. Their uptake and efflux rates must therefore be carefully controlled by biological systems. In this chapter, we summarize the current knowledge about uptake and efflux systems in Mycobacterium tuberculosis for mainly three of these metals, namely iron, zinc, and copper. We also propose questions for future research in the field of metallobiology of host-pathogen interactions in tuberculosis.

Pathogenic adaptations to host-derived antibacterial copper

Recent findings suggest that both host and pathogen manipulate copper content in infected host niches during infections. In this review, we summarize recent developments that implicate copper resistance as an important determinant of bacterial fitness at the host-pathogen interface. An essential mammalian nutrient, copper cycles between copper (I) (Cu(+)) in its reduced form and copper (II) (Cu(2+)) in its oxidized form under physiologic conditions. Cu(+) is significantly more bactericidal than Cu(2+) due to its ability to freely penetrate bacterial membranes and inactivate intracellular iron-sulfur clusters. Copper ions can also catalyze reactive oxygen species (ROS) generation, which may further contribute to their toxicity. Transporters, chaperones, redox proteins, receptors and transcription factors and even siderophores affect copper accumulation and distribution in both pathogenic microbes and their human hosts. This review will briefly cover evidence for copper as a mammalian antibacterial effector, the possible reasons for this toxicity, and pathogenic resistance mechanisms directed against it.