Metal Resistance Determinants Research Articles

MEGARes 2.0: a database for classification of antimicrobial drug, biocide and metal resistance determinants in metagenomic sequence data.

Antimicrobial resistance (AMR) is a threat to global public health and the identification of genetic determinants of AMR is a critical component to epidemiological investigations. High-throughput sequencing (HTS) provides opportunities for investigation of AMR across all microbial genomes in a sample (i.e. the metagenome). Previously, we presented MEGARes, a hand-curated AMR database and annotation structure developed to facilitate the analysis of AMR within metagenomic samples (i.e. the resistome). Along with MEGARes, we released AmrPlusPlus, a bioinformatics pipeline that interfaces with MEGARes to identify and quantify AMR gene accessions contained within a metagenomic sequence dataset. Here, we present MEGARes 2.0 (https://megares.meglab.org), which incorporates previously published resistance sequences for antimicrobial drugs, while also expanding to include published sequences for metal and biocide resistance determinants. In MEGARes 2.0, the nodes of the acyclic hierarchical ontology include four antimicrobial compound types, 57 classes, 220 mechanisms of resistance, and 1,345 gene groups that classify the 7,868 accessions. In addition, we present an updated version of AmrPlusPlus (AMR ++ version 2.0), which improves accuracy of classifications, as well as expanding scalability and usability.

Sulfobacillus thermotolerans: new insights into resistance and metabolic capacities of acidophilic chemolithotrophs

The first complete genome of the biotechnologically important species Sulfobacillus thermotolerans has been sequenced. Its 3 317 203-bp chromosome contains an 83 269-bp plasmid-like region, which carries heavy metal resistance determinants and the rusticyanin gene. Plasmid-mediated metal resistance is unusual for acidophilic chemolithotrophs. Moreover, most of their plasmids are cryptic and do not contribute to the phenotype of the host cells. A polyphosphate-based mechanism of metal resistance, which has been previously unknown in the genus Sulfobacillus or other Gram-positive chemolithotrophs, potentially operates in two Sulfobacillus species. The methylcitrate cycle typical for pathogens and identified in the genus Sulfobacillus for the first time can fulfill the energy and/or protective function in S. thermotolerans Kr1 and two other Sulfobacillus species, which have incomplete glyoxylate cycles. It is notable that the TCA cycle, disrupted in all Sulfobacillus isolates under optimal growth conditions, proved to be complete in the cells enduring temperature stress. An efficient antioxidant defense system gives S. thermotolerans another competitive advantage in the microbial communities inhabiting acidic metal-rich environments. The genomic comparisons revealed 80 unique genes in the strain Kr1, including those involved in lactose/galactose catabolism. The results provide new insights into metabolism and resistance mechanisms in the Sulfobacillus genus and other acidophiles.

Isolation and Molecular Identification of Virulence, Antimicrobial and Heavy Metal Resistance Genes in Livestock-Associated Methicillin-Resistant Staphylococcus aureus.

Staphylococcus aureus is one of the most important pathogens of humans and animals. Livestock production contributes a significant proportion to the South African Gross Domestic Product. Consequently, the aim of this study was to determine for the first time the prevalence, virulence, antibiotic and heavy metal resistance in livestock-associated S. aureus isolated from South African livestock production systems. Microbial phenotypic methods were used to detect the presence of antibiotic and heavy metal resistance. Furthermore, molecular DNA based methods were used to genetically determine virulence as well as antibiotic and heavy metal resistance determinants. Polymerase chain reaction (PCR) confirmed 217 out of 403 (53.8%) isolates to be S. aureus. Kirby-Bauer disc diffusion method was conducted to evaluate antibiotic resistance and 90.8% of S. aureus isolates were found to be resistant to at least three antibiotics, and therefore, classified as multidrug resistant. Of the antibiotics tested, 98% of the isolates demonstrated resistance towards penicillin G. High resistance was shown against different heavy metals, with 90% (196/217), 88% (192/217), 86% (188/217) and 84% (183/217) of the isolates resistant to 1500 µg/mL concentration of Cadmium (Cd), Zinc (Zn), Lead (Pb) and Copper (Cu) respectively. A total of 10 antimicrobial resistance and virulence genetic determinants were screened for all livestock associated S. aureus isolates. Methicillin-resistant S. aureus (MRSA) isolates were identified, by the presence of mecC, in 27% of the isolates with a significant relationship (p < 0.001)) with the host animal. This is the first report of mecC positive LA-MRSA in South Africa and the African continent. The gene for tetracycline resistance (tetK) was the most frequently detected of the screened genes with an overall prevalence of 35% and the highest prevalence percentage was observed for goats (56.76%) followed by avian species (chicken, duck and wild birds) (42.5%). Virulence-associated genes were observed across all animal host species. The study reports the presence of luks/pv, a gene encoding the PVL toxin previously described to be a marker for community acquired-MRSA, suggesting the crossing of species between human and livestock. The high prevalence of S. aureus from the livestock indicates a major food security and healthcare threat. This threat is further compounded by the virulence of the pathogen, which causes numerous clinical manifestations. The phenomenon of co-selection is observed in this study as isolates exhibited resistance to both antibiotics and heavy metals. Further, all the screened antibiotic and heavy metal resistance genes did not correspond with the phenotypic resistance.

Prevalence of Antibiotic and Heavy Metal Resistance Determinants and Virulence-Related Genetic Elements in Plasmids of Staphylococcus aureus.

The use of antibiotics on a mass scale, particularly in farming, and their release into the environment has led to a rapid emergence of resistant bacteria. Once emerged, resistance determinants are spread by horizontal gene transfer among strains of the same as well as disparate bacterial species. Their accumulation in free-living as well as livestock and community-associated strains results in the widespread multiple-drug resistance among clinically relevant species posing an increasingly pressing problem in healthcare. One of these clinically relevant species is Staphylococcus aureus, a common cause of hospital and community outbreaks. Among the rich diversity of mobile genetic elements regularly occurring in S. aureus such as phages, pathogenicity islands, and staphylococcal cassette chromosomes, plasmids are the major mean for dissemination of resistance determinants and virulence factors. Unfortunately, a vast number of whole-genome sequencing projects does not aim for complete sequence determination, which results in a disproportionately low number of known complete plasmid sequences. To address this problem we determined complete plasmid sequences derived from 18 poultry S. aureus strains and analyzed the prevalence of antibiotic and heavy metal resistance determinants, genes of virulence factors, as well as genetic elements relevant for their maintenance. Some of the plasmids have been reported before and are being found in clinical isolates of strains typical for humans or human ones of livestock origin. This shows that livestock-associated staphylococci are a significant reservoir of resistance determinants and virulence factors. Nevertheless, nearly half of the plasmids were unknown to date. In this group we found a potentially mobilizable plasmid pPA3 being a unique example of accumulation of resistance determinants and virulence factors likely stabilized by a presence of a toxin–antitoxin system.

Genomic Characterization of Arcobacter butzleri Isolated From Shellfish: Novel Insight Into Antibiotic Resistance and Virulence Determinants.

Arcobacter (A.) butzleri is an emerging pathogenic microorganism, whose taxonomy has been recently suggested to be emended to the Aliarcobacter (Al.) butzleri comb. nov. Despite extensive taxonomic analysis, only few fragmented studies have investigated the occurrence and the prevalence of virulence and antibiotic resistance determinants of this species in strains isolated from shellfish. Herein we report for the first time the whole genome sequencing and genomic characterization of two A. butzleri strains isolated from shellfish, with particular reference to the antibiotic, heavy metals and virulence determinants. This study supported the taxonomic assignment of these strains to the Al. butzleri species, and allowed us to identify antibiotic and metal resistance along with virulence determinants, also additional to those previously reported for the only two A. butzleri strains from different environments genomically characterized. Moreover, both strains showed resistance to β-lactams, vanocomycin, tetracycline and erythromycin and susceptibility to aminoglycosides and ciprofloxacin. Beside enlarging the availability of genomic data to perform comparative studies aimed at correlating phenotypic differences associated with ecological niche and geographic distribution with the genetic diversity of A. butzleri spp., this study reports the endowment of antibiotic and heavy metal resistance and virulence determinants of these shellfish-isolated strains. This leads to hypothesize a relatively high virulence of A. butzleri isolated from shellfish and prompt the need for a wider genomic analysis and for in vitro and in vivo studies of more strains isolated from this and other ecological niches, to unravel the mechanism of pathogenicity of this species, and the potential risk associated to their consumption.

Genetic characterization of an MDR/virulence genomic element carrying two T6SS gene clusters in a clinical Klebsiella pneumoniae isolate of swine origin.

Multiresistant Klebsiella pneumoniae isolates rarely cause infections in pigs. The aim of this study was to investigate a multiresistant porcine K. pneumoniae isolate for plasmidic and chromosomal antimicrobial resistance and virulence genes and their genetic environment. K. pneumoniae strain ZYST1 originated from a pig with pneumonia. Antimicrobial susceptibility testing was performed using broth microdilution. Conjugation experiments were conducted using Escherichia coli J53 as the recipient. The complete sequences of the chromosomal DNA and the plasmids were generated by WGS and analysed for the presence of resistance and virulence genes. The MDR K. pneumoniae ST1 strain ZYST1 contained three plasmids belonging to incompatibility groups IncFIIk5-FIB, IncI1 and IncX4, respectively. The IncFIIk5-FIB plasmid carried the resistance genes aadA2, mph(A), sul1 and aph(3')-Ia, and the IncI1 plasmid carried aadA22 and erm(B). No resistance genes were present on the IncX4 plasmid. Plasmids related to the aforementioned three plasmids were also present in other Enterobacteriaceae species from humans, animals and the environment. Bioinformatic analyses identified a chromosomal 904 kb MDR element flanked by two copies of ISKpn26. This element included virulence factors, such as a type VI secretion system (T6SS) and genes for type 1 fimbriae, the toxin-antitoxin system HipA/HipB, antimicrobial resistance genes, such as blaSHV-187, mdtk, catA and the multiple antibiotic resistance operon marRABC, and heavy metal resistance determinants, such as chrB/chrA and tehA/tehB. This study reports a novel 904 kb MDR/virulence genomic element and three important plasmids coexisting in a clinical K. pneumoniae isolate of animal origin.

Response of the biomining Acidithiobacillus ferrooxidans to high cadmium concentrations

Cadmium is a heavy metal present in contaminated soils. It has no biological role but when entering cells generates DNA damage, overexpression of stress response proteins and misfolded proteins, amongst other deleterious effects. Acidithiobacillus ferrooxidans is an acidophilic bacterium resisting high concentrations of heavy metals such as cadmium. This is important for industrial bioleaching processes where Cd+2 concentrations can be 5–100 mM. Cadmium resistance mechanisms in these microorganisms have not been fully characterized. A. ferrooxidans ATCC 53993 contains genes coding for possible metal resistance determinants such as efflux systems: P-type ATPases, RND transporters and cation diffusion facilitators. In addition, it has extra copies of these genes in its exclusive genomic island (GI). Several of these putative genes were characterized in the present report by determining their transcriptional expression profiles and functionality. Moreover, an iTRAQ proteomic analysis was carried out to explore new cadmium resistance determinants in this bacterium. Changes in iron oxidation components, upregulation of transport proteins and variations in ribosomal protein levels were seen. Finally, increased concentrations of exclusive putative cadmium ATPases present in strain ATCC 53993 GI and other non-identified proteins such as Lferr_0210, forming part of a possible operon, could explain its extreme cadmium resistance. SignificanceCadmium is a very toxic heavy metal present in mining operations and contaminated environments, it can affect all living organisms, including humans. Therefore, it is important to know the resistance mechanisms of bacteria highly resistant to this metal. These microorganisms in turn, can be used to bioremediate more efficiently environments highly polluted with metals. The results obtained suggest A. ferrooxidans strain ATCC 53993 can be an efficient bacterium to remove cadmium, copper and other metals from contaminated sites.

Genomic Islands Confer Heavy Metal Resistance in Mucilaginibacter kameinonensis and Mucilaginibacter rubeus Isolated from a Gold/Copper Mine.

Heavy metals (HMs) are compounds that can be hazardous and impair growth of living organisms. Bacteria have evolved the capability not only to cope with heavy metals but also to detoxify polluted environments. Three heavy metal-resistant strains of Mucilaginibacer rubeus and one of Mucilaginibacter kameinonensis were isolated from the gold/copper Zijin mining site, Longyan, Fujian, China. These strains were shown to exhibit high resistance to heavy metals with minimal inhibitory concentration reaching up to 3.5 mM Cu(II), 21 mM Zn(II), 1.2 mM Cd(II), and 10.0 mM As(III). Genomes of the four strains were sequenced by Illumina. Sequence analyses revealed the presence of a high abundance of heavy metal resistance (HMR) determinants. One of the strain, M. rubeus P2, carried genes encoding 6 putative PIB-1-ATPase, 5 putative PIB-3-ATPase, 4 putative Zn(II)/Cd(II) PIB-4 type ATPase, and 16 putative resistance-nodulation-division (RND)-type metal transporter systems. Moreover, the four genomes contained a high abundance of genes coding for putative metal binding chaperones. Analysis of the close vicinity of these HMR determinants uncovered the presence of clusters of genes potentially associated with mobile genetic elements. These loci included genes coding for tyrosine recombinases (integrases) and subunits of mating pore (type 4 secretion system), respectively allowing integration/excision and conjugative transfer of numerous genomic islands. Further in silico analyses revealed that their genetic organization and gene products resemble the Bacteroides integrative and conjugative element CTnDOT. These results highlight the pivotal role of genomic islands in the acquisition and dissemination of adaptive traits, allowing for rapid adaption of bacteria and colonization of hostile environments.

Harnessing Rhizobia to Improve Heavy-Metal Phytoremediation by Legumes.

Rhizobia are bacteria that can form symbiotic associations with plants of the Fabaceae family, during which they reduce atmospheric di-nitrogen to ammonia. The symbiosis between rhizobia and leguminous plants is a fundamental contributor to nitrogen cycling in natural and agricultural ecosystems. Rhizobial microsymbionts are a major reason why legumes can colonize marginal lands and nitrogen-deficient soils. Several leguminous species have been found in metal-contaminated areas, and they often harbor metal-tolerant rhizobia. In recent years, there have been numerous efforts and discoveries related to the genetic determinants of metal resistance by rhizobia, and on the effectiveness of such rhizobia to increase the metal tolerance of host plants. Here, we review the main findings on the metal resistance of rhizobia: the physiological role, evolution, and genetic determinants, and the potential to use native and genetically-manipulated rhizobia as inoculants for legumes in phytoremediation practices.

The AbaR antibiotic resistance islands found in Acinetobacter baumannii global clone 1 - Structure, origin and evolution.

In multiply resistant Acinetobacter baumannii, complex transposons located in the chromosomal comM gene carry antibiotic and heavy metal resistance determinants. For one type, known collectively as AbaR, the ancestral form, AbaR0, entered a member of global clone 1 (GC1) in the mid 1970s and continued to evolve in situ forming many variants. In AbaR0, antibiotic and mercuric ion resistance genes are located between copies of a cadmium-zinc resistance transposon, Tn6018, and this composite transposon is in a class III transposon, Tn6019, carrying arsenate/arsenite resistance genes and five tni transposition genes. The antibiotic resistance genes in the AbaR0 and derived AbaR3 configurations are aphA1b, blaTEM, catA1, sul1, tetA(A), and cassette-associated aacC1 and aadA1 genes. These genes are in a specific arrangement of fragments from well-known transposons, e.g. Tn1, Tn1721, Tn1696 and Tn2670, that arose in an IncM1 plasmid. All known GC1 lineage 1 isolates carry AbaR0 or AbaR3, which arose around 1990, or a variant derived from one of them. Variants arose via deletions caused by one of three internal IS26s, by recombination between duplicate copies of sul1 or Tn6018, or by gene cassette addition or replacement. A few GC2 isolates also carry an AbaR island with different cassette-associated genes, aacA4 and oxa20.

Cupriavidus metallidurans Strains with Different Mobilomes and from Distinct Environments Have Comparable Phenomes.

Cupriavidus metallidurans has been mostly studied because of its resistance to numerous heavy metals and is increasingly being recovered from other environments not typified by metal contamination. They host a large and diverse mobile gene pool, next to their native megaplasmids. Here, we used comparative genomics and global metabolic comparison to assess the impact of the mobilome on growth capabilities, nutrient utilization, and sensitivity to chemicals of type strain CH34 and three isolates (NA1, NA4 and H1130). The latter were isolated from water sources aboard the International Space Station (NA1 and NA4) and from an invasive human infection (H1130). The mobilome was expanded as prophages were predicted in NA4 and H1130, and a genomic island putatively involved in abietane diterpenoids metabolism was identified in H1130. An active CRISPR-Cas system was identified in strain NA4, providing immunity to a plasmid that integrated in CH34 and NA1. No correlation between the mobilome and isolation environment was found. In addition, our comparison indicated that the metal resistance determinants and properties are conserved among these strains and thus maintained in these environments. Furthermore, all strains were highly resistant to a wide variety of chemicals, much broader than metals. Only minor differences were observed in the phenomes (measured by phenotype microarrays), despite the large difference in mobilomes and the variable (shared by two or three strains) and strain-specific genomes.

Heterogeneous and Flexible Transmission of mcr-1 in Hospital-Associated Escherichia coli.

ABSTRACTThe recent emergence of a transferable colistin resistance mechanism, MCR-1, has gained global attention because of its threat to clinical treatment of infections caused by multidrug-resistant Gram-negative bacteria. However, the possible transmission route of mcr-1 among Enterobacteriaceae species in clinical settings is largely unknown. Here, we present a comprehensive genomic analysis of Escherichia coli isolates collected in a hospital in Hangzhou, China. We found that mcr-1-carrying isolates from clinical infections and feces of inpatients and healthy volunteers were genetically diverse and were not closely related phylogenetically, suggesting that clonal expansion is not involved in the spread of mcr-1. The mcr-1 gene was found on either chromosomes or plasmids, but in most of the E. coli isolates, mcr-1 was carried on plasmids. The genetic context of the plasmids showed considerable diversity as evidenced by the different functional insertion sequence (IS) elements, toxin-antitoxin (TA) systems, heavy metal resistance determinants, and Rep proteins of broad-host-range plasmids. Additionally, the genomic analysis revealed nosocomial transmission of mcr-1 and the coexistence of mcr-1 with other genes encoding β-lactamases and fluoroquinolone resistance in the E. coli isolates. These findings indicate that mcr-1 is heterogeneously disseminated in both commensal and pathogenic strains of E. coli, suggest the high flexibility of this gene in its association with diverse genetic backgrounds of the hosts, and provide new insights into the genome epidemiology of mcr-1 among hospital-associated E. coli strains.

Plasmids of Psychrotolerant Polaromonas spp. Isolated From Arctic and Antarctic Glaciers - Diversity and Role in Adaptation to Polar Environments.

Cold-active bacteria of the genus Polaromonas (class Betaproteobacteria) are important components of glacial microbiomes. In this study, extrachromosomal replicons of 26 psychrotolerant Polaromonas strains, isolated from Arctic and Antarctic glaciers, were identified, sequenced, and characterized. The plasmidome of these strains consists of 13 replicons, ranging in size from 3,378 to 101,077 bp. In silico sequence analyses identified the conserved backbones of these plasmids, composed of genes required for plasmid replication, stable maintenance, and conjugal transfer. Host range analysis revealed that all of the identified plasmids are narrow-host-range replicons, only able to replicate in bacteria of closely related genera (Polaromonas and Variovorax) of the Comamonadaceae family. Special attention was paid to the identification of plasmid auxiliary genetic information, which may contribute to the adaptation of bacteria to environmental conditions occurring in glaciers. Detailed analysis revealed the presence of genes encoding proteins potentially involved in (i) protection against reactive oxygen species, ultraviolet radiation, and low temperatures; (ii) transport and metabolism of organic compounds; (iii) transport of metal ions; and (iv) resistance to heavy metals. Some of the plasmids also carry genes required for the molecular assembly of iron–sulfur [Fe-S] clusters. Functional analysis of the predicted heavy metal resistance determinants demonstrated that their activity varies, depending on the host strain. This study provides the first molecular insight into the mobile DNA of Polaromonas spp. inhabiting polar glaciers. It has generated valuable data on the structure and properties of a pool of plasmids and highlighted their role in the biology of psychrotolerant Polaromonas strains and their adaptation to the environmental conditions of Arctic and Antarctic glaciers.

Characterization of a promiscuous cadmium and arsenic resistance mechanism in Thermus thermophilus HB27 and potential application of a novel bioreporter system

BackgroundThe characterization of the molecular determinants of metal resistance has potential biotechnological application in biosensing and bioremediation. In this context, the bacterium Thermus thermophilus HB27 is a metal tolerant thermophile containing a set of genes involved in arsenic resistance which, differently from other microbes, are not organized into a single operon. They encode the proteins: arsenate reductase, TtArsC, arsenic efflux membrane transporter, TtArsX, and transcriptional repressor, TtSmtB.ResultsIn this work we show that the arsenic efflux protein TtArsX and the arsenic responsive transcriptional repressor TtSmtB are required to provide resistance to cadmium. We analyzed the sensitivity to Cd(II) of mutants lacking TtArsX, finding that they are more sensitive to this metal than the wild type strain. In addition, using promoter probe reporter plasmids, we show that the transcription of TtarsX is also stimulated by the presence of Cd(II) in a TtSmtB-dependent way. Actually, a regulatory circuit composed of TtSmtB and a reporter gene expressed from the TtarsX promoter responds to variation in Cd(II), As(III) and As(V) concentrations.ConclusionsOur results demonstrate that the system composed by TtSmtB and TtArsX is responsible for both the arsenic and cadmium resistance in T. thermophilus. The data also support the use of T. thermophilus as a suitable chassis for the design and development of As-Cd biosensors.

Resistance to Metals Used in Agricultural Production.

Metals and metalloids have been used alongside antibiotics in livestock production for a long time. The potential and acute negative impact on the environment and human health of these livestock feed supplements has prompted lawmakers to ban or discourage the use of some or all of these supplements. This article provides an overview of current use in the European Union and the United States, detected metal resistance determinants, and the proteins and mechanisms responsible for conferring copper and zinc resistance in bacteria. A detailed description of the most common copper and zinc metal resistance determinants is given to illustrate not only the potential danger of coselecting antibiotic resistance genes but also the potential to generate bacterial strains with an increased potential to be pathogenic to humans. For example, the presence of a 20-gene copper pathogenicity island is highlighted since bacteria containing this gene cluster could be readily isolated from copper-fed pigs, and many pathogenic strains, including Escherichia coli O104:H4, contain this potential virulence factor, suggesting a potential link between copper supplements in livestock and the evolution of pathogens.

Transcriptome Response to Heavy Metals in Sinorhizobium meliloti CCNWSX0020 Reveals New Metal Resistance Determinants That Also Promote Bioremediation by Medicago lupulina in Metal-Contaminated Soil.

The symbiosis of the highly metal-resistant Sinorhizobium meliloti CCNWSX0020 and Medicago lupulina has been considered an efficient tool for bioremediation of heavy metal-polluted soils. However, the metal resistance mechanisms of S. meliloti CCNWSX00200 have not been elucidated in detail. Here we employed a comparative transcriptome approach to analyze the defense mechanisms of S. meliloti CCNWSX00200 against Cu or Zn exposure. Six highly upregulated transcripts involved in Cu and Zn resistance were identified through deletion mutagenesis, including genes encoding a multicopper oxidase (CueO), an outer membrane protein (Omp), sulfite oxidoreductases (YedYZ), and three hypothetical proteins (a CusA-like protein, a FixH-like protein, and an unknown protein), and the corresponding mutant strains showed various degrees of sensitivity to multiple metals. The Cu-sensitive mutant (ΔcueO) and three mutants that were both Cu and Zn sensitive (ΔyedYZ, ΔcusA-like, and ΔfixH-like) were selected for further study of the effects of these metal resistance determinants on bioremediation. The results showed that inoculation with the ΔcueO mutant severely inhibited infection establishment and nodulation of M. lupulina under Cu stress, while inoculation with the ΔyedYZ and ΔfixH-like mutants decreased just the early infection frequency and nodulation under Cu and Zn stresses. In contrast, inoculation with the ΔcusA-like mutant almost led to loss of the symbiotic capacity of M. lupulina to even grow in uncontaminated soil. Moreover, the antioxidant enzyme activity and metal accumulation in roots of M. lupulina inoculated with all mutants were lower than those with the wild-type strain. These results suggest that heavy metal resistance determinants may promote bioremediation by directly or indirectly influencing formation of the rhizobium-legume symbiosis.IMPORTANCE Rhizobium-legume symbiosis has been promoted as an appropriate tool for bioremediation of heavy metal-contaminated soils. Considering the plant-growth-promoting traits and survival advantage of metal-resistant rhizobia in contaminated environments, more heavy metal-resistant rhizobia and genetically manipulated strains were investigated. In view of the genetic diversity of metal resistance determinants in rhizobia, their effects on phytoremediation by the rhizobium-legume symbiosis must be different and depend on their specific assigned functions. Our work provides a better understanding of the mechanism of heavy metal resistance determinants involved in the rhizobium-legume symbiosis, and in further studies, genetically modified rhizobia harboring effective heavy metal resistance determinants may be engineered for the practical application of rhizobium-legume symbiosis for bioremediation in metal-contaminated soils.

The Microevolution and Epidemiology of Staphylococcus aureus Colonization during Atopic Eczema Disease Flare

Staphylococcus aureus is an opportunistic pathogen and variable component of the human microbiota. A characteristic of atopic eczema (AE) is colonization by S. aureus, with exacerbations associated with an increased bacterial burden of the organism. Despite this, the origins and genetic diversity of S. aureus colonizing individual patients during AE disease flares is poorly understood. To examine the microevolution of S. aureus colonization, we deep sequenced S. aureus populations from nine children with moderate to severe AE and 18 non-atopic children asymptomatically carrying S. aureus nasally. Colonization by clonal S. aureus populations was observed in both AE patients and control participants, with all but one of the individuals carrying colonies belonging to a single sequence type. Phylogenetic analysis showed that disease flares were associated with the clonal expansion of the S. aureus population, occurring over a period of weeks to months. There was a significant difference in the genetic backgrounds of S. aureus colonizing AE cases versus controls (Fisher exact test, P = 0.03). Examination of intra-host genetic heterogeneity of the colonizing S. aureus populations identified evidence of within-host selection in the AE patients, with AE variants being potentially selectively advantageous for intracellular persistence and treatment resistance.

Microbial metal resistance and metabolism across dynamic landscapes: high-throughput environmental microbiology.

Multidimensional gradients of inorganic compounds influence microbial activity in diverse pristine and anthropogenically perturbed environments. Here, we suggest that high-throughput cultivation and genetics can be systematically applied to generate quantitative models linking gene function, microbial community activity, and geochemical parameters. Metal resistance determinants represent a uniquely universal set of parameters around which to study and evaluate microbial fitness because they represent a record of the environment in which all microbial life evolved. By cultivating microbial isolates and enrichments in laboratory gradients of inorganic ions, we can generate quantitative predictions of limits on microbial range in the environment, obtain more accurate gene annotations, and identify useful strategies for predicting and engineering the trajectory of natural ecosystems.

Bacterial resistance to arsenic protects against protist killing

Protists kill their bacterial prey using toxic metals such as copper. Here we hypothesize that the metalloid arsenic has a similar role. To test this hypothesis, we examined intracellular survival of Escherichia coli (E. coli) in the amoeba Dictyostelium discoideum (D. discoideum). Deletion of the E. coli ars operon led to significantly lower intracellular survival compared to wild type E. coli. This suggests that protists use arsenic to poison bacterial cells in the phagosome, similar to their use of copper. In response to copper and arsenic poisoning by protists, there is selection for acquisition of arsenic and copper resistance genes in the bacterial prey to avoid killing. In agreement with this hypothesis, both copper and arsenic resistance determinants are widespread in many bacterial taxa and environments, and they are often found together on plasmids. A role for heavy metals and arsenic in the ancient predator-prey relationship between protists and bacteria could explain the widespread presence of metal resistance determinants in pristine environments.

Microbial copper resistance: importance in biohydrometallurgy.

SummaryIndustrial biomining has been extensively used for many years to recover valuable metals such as copper, gold, uranium and others. Furthermore, microorganisms involved in these processes can also be used to bioremediate places contaminated with acid and metals. These uses are possible due to the great metal resistance that these extreme acidophilic microorganisms possess. In this review, the most recent findings related to copper resistance mechanisms of bacteria and archaea related to biohydrometallurgy are described. The recent search for novel metal resistance determinants is not only of scientific interest but also of industrial importance, as reflected by the genomic sequencing of microorganisms present in mining operations and the search of those bacteria with extreme metal resistance to improve the extraction processes used by the biomining companies.