Bacterial mercury resistance from atoms to ecosystems

Embedded elements in the IncPβ plasmids R772 and R906 can be mobilized and can serve as a source of diverse and novel elements

IncP plasmids are important contributors to bacterial adaptation. Their phenotypic diversity is due largely to accessory regions located in one or two specific parts of the plasmid. The accessory regions are themselves diverse, as judged from sequenced plasmids mostly isolated from non-clinical sources. To further understand the diversity, evolutionary history and functional attributes of the accessory regions, we compared R906 and R772, focusing on the oriV–trfA accessory region. These IncPβ plasmids were from porcine and clinical sources, respectively. We found that the accessory regions formed potentially mobile elements, Tn510 (from R906) and Tn511 (from R772), that differed internally but had identical borders. Both elements appeared to have evolved from a TnAO22-like mer transposon that had inserted into an ancestral IncPβ plasmid and then accrued additional transposable elements and genes from various proteobacteria. Structural comparisons suggested that Tn510 (and a descendent in pB10), Tn511 and the mer element in pJP4 represent three lineages that evolved from the same widely dispersed IncPβ carrier. Functional studies on Tn511 revealed that its mer module is inactive due to a merT mutation, and that its aphAI region is prone to deletion. More significantly, we showed that by providing a suitable transposase gene in trans, the defective Tn510 and Tn511 could transpose intact or in part, and could also generate new elements (stable cointegrates and novel transposons). The ingredients for assisted transposition events similar to those observed here occur in natural microcosms, providing non-self-mobile elements with avenues for dispersal to new replicons and for structural diversification. This work provides an experimental demonstration of how the complex embedded elements uncovered in IncP plasmids and in other plasmid families may have been generated.

Mercury bioremediation by mercury accumulating Enterobacter sp. cells and its alginate immobilized application

The effective microbial remediation of the mercury necessitates the mercury to be trapped within the cells without being recycled back to the environment. The study describes a mercury bioaccumulating strain of Enterobacter sp., which remediated mercury from the medium simultaneous to its growth. The transmission electron micrographs and electron dispersive X-ray analysis revealed the accumulation of remediated mercury as nano-size particles in the cytoplasm as well as on the cell wall. The Enterobacter sp. in the present work was able to accumulate mercury, without being engineered in its native form. The possibility of recovering the accumulated mercury from the cells is also indicated. The applicability of the alginate immobilized cells in removing mercury from synthetic and complex industrial effluent in a batch mode was amply demonstrated. The initial load of 7.3 mg l(-1) mercury in the industrial effluent was completely removed in 72 h. The cells immobilized in calcium alginate were similarly effective in the complete removal of 5 mg l(-1) HgCl(2) of mercury from the synthetic effluent in less than 72 h. The immobilized cells could be reused for multiple cycles.

Gene flow, mobile genetic elements and the recruitment of antibiotic resistance genes into Gram-negative pathogens

Antibiotics were one of the great discoveries of the 20th century. However, resistance appeared even in the earliest years of the antibiotic era. Antibiotic resistance continues to become worse, despite the ever-increasing resources devoted to combat the problem. One of the most important factors in the development of resistance to antibiotics is the remarkable ability of bacteria to share genetic resources via Lateral Gene Transfer (LGT). LGT occurs on a global scale, such that in theory, any gene in any organism anywhere in the microbial biosphere might be mobilized and spread. With sufficiently strong selection, any gene may spread to a point where it establishes a global presence. From an antibiotic resistance perspective, this means that a resistance phenotype can appear in a diverse range of infections around the globe nearly simultaneously. We discuss the forces and agents that make this LGT possible and argue that the problem of resistance can ultimately only be managed by understanding the problem from a broad ecological and evolutionary perspective. We also argue that human activities are exacerbating the problem by increasing the tempo of LGT and bacterial evolution for many traits that are important to humans.

A thermophilic bacterial origin and subsequent constraints by redox, light and salinity on the evolution of the microbial mercuric reductase

Mercuric reductase (MerA) is central to the mercury (Hg) resistance (mer) system, catalyzing the reduction of ionic Hg to volatile Hg(0). A total of 213 merA homologues were identified in sequence databases, the majority of which belonged to microbial lineages that occupy oxic environments. merA was absent among phototrophs and in lineages that inhabit anoxic environments. Phylogenetic reconstructions of MerA indicate that (i) merA originated in a thermophilic bacterium following the divergence of the Archaea and Bacteria with a subsequent acquisition in Archaea via horizontal gene transfer (HGT), (ii) HGT of merA was rare across phylum boundaries and (iii) MerA from marine bacteria formed distinct and strongly supported lineages. Collectively, these observations suggest that a combination of redox, light and salinity conditions constrain MerA to microbial lineages that occupy environments where the most oxidized and toxic form of Hg, Hg(II), predominates. Further, the taxon-specific distribution of MerA with and without a 70 amino acid N-terminal extension may reflect intracellular levels of thiols. In conclusion, MerA likely evolved following the widespread oxygenation of the biosphere in a thermal environment and its subsequent evolution has been modulated by the interactions of Hg with the intra- and extracellular environment of the organism.

Active transport, substrate specificity, and methylation of Hg(II) in anaerobic bacteria

The formation of methylmercury (MeHg), which is biomagnified in aquatic food chains and poses a risk to human health, is effected by some iron- and sulfate-reducing bacteria (FeRB and SRB) in anaerobic environments. However, very little is known regarding the mechanism of uptake of inorganic Hg by these organisms, in part because of the inherent difficulty in measuring the intracellular Hg concentration. By using the FeRB Geobacter sulfurreducens and the SRB Desulfovibrio desulfuricans ND132 as model organisms, we demonstrate that Hg(II) uptake occurs by active transport. We also establish that Hg(II) uptake by G. sulfurreducens is highly dependent on the characteristics of the thiols that bind Hg(II) in the external medium, with some thiols promoting uptake and methylation and others inhibiting both. The Hg(II) uptake system of D. desulfuricans has a higher affinity than that of G. sulfurreducens and promotes Hg methylation in the presence of stronger complexing thiols. We observed a tight coupling between Hg methylation and MeHg export from the cell, suggesting that these two processes may serve to avoid the build up and toxicity of cellular Hg. Our results bring up the question of whether cellular Hg uptake is specific for Hg(II) or accidental, occurring via some essential metal importer. Our data also point at Hg(II) complexation by thiols as an important factor controlling Hg methylation in anaerobic environments.

Evidence of methylmercury production and modification of the microbial community structure in estuary sediments contaminated with wastewater treatment plant effluents

The Seine's estuary (France) waters are the receptacle of effluents originating from wastewater treatment plants (WWTP). In this estuary, mudflats are deposition zones for sediments and their associated contaminants, and play an essential role in the mercury (Hg) biogeochemical cycle mainly due to indigenous microorganisms. Microcosms were used to assess the impact of WWTP-effluents on mercury methylation by monitoring Hg species (total dissolved Hg in porewater, methylmercury and total mercury) and on microbial communities in sediments. After effluent amendment, methylmercury (MeHg) concentrations increased in relation with the total Hg and organic matter content of the WWTP-effluents. A correlation was observed between MeHg and acid-volatile-sulfides concentrations. Quantification of sulfate-reducing microorganisms involved in Hg methylation showed no increase of their abundance but their activity was probably enhanced by the organic matter supplied with the effluents. WWTP-effluent spiking modified the bacterial community fingerprint, mainly influenced by Hg contamination and the organic matter amendment.

Nucleotide sequence of Pseudomonas aeruginosa conjugative plasmid pUM505 containing virulence and heavy-metal resistance genes

We determined the complete nucleotide sequence of conjugative plasmid pUM505 isolated from a clinical strain of Pseudomonas aeruginosa. The plasmid had a length of 123,322bp and contained 138 complete coding regions, including 46% open reading frames encoding hypothetical proteins. pUM505 can be considered a hybrid plasmid because it presents two well-defined regions. The first region corresponded to a larger DNA segment with homology to a pathogenicity island from virulent Pseudomonas strains; this island in pUM505 was comprised of genes probably involved in virulence and genes encoding proteins implicated in replication, maintenance and plasmid transfer. Sequence analysis identified pil genes encoding a type IV secretion system, establishing pUM505 as a member of the family of IncI1 plasmids. Plasmid pUM505 also contained virB4/virD4 homologues, which are linked to virulence in other plasmids. The second region, smaller in length, contains inorganic mercury and chromate resistance gene clusters both flanked by putative mobile elements. Although no genes for antibiotic resistance were identified, when pUM505 was transferred to a recipient strain of P. aeruginosa it conferred resistance to the fluoroquinolone ciprofloxacin. pUM505 also conferred resistance to the superoxide radical generator paraquat. pUM505 could provide Pseudomonas strains with a wide variety of adaptive traits such as virulence, heavy-metal and antibiotic resistance and oxidative stress tolerance which can be selective factors for the distribution and prevalence of this plasmid in diverse environments, including hospitals and heavy metal contaminated soils.

Characterization of the metabolically modified heavy metal-resistant Cupriavidus metallidurans strain MSR33 generated for mercury bioremediation

Background

Mercury-polluted environments are often contaminated with other heavy metals. Therefore, bacteria with resistance to several heavy metals may be useful for bioremediation. Cupriavidus metallidurans CH34 is a model heavy metal-resistant bacterium, but possesses a low resistance to mercury compounds.

Methodology/Principal Findings

To improve inorganic and organic mercury resistance of strain CH34, the IncP-1β plasmid pTP6 that provides novel merB, merG genes and additional other mer genes was introduced into the bacterium by biparental mating. The transconjugant Cupriavidus metallidurans strain MSR33 was genetically and biochemically characterized. Strain MSR33 maintained stably the plasmid pTP6 over 70 generations under non-selective conditions. The organomercurial lyase protein MerB and the mercuric reductase MerA of strain MSR33 were synthesized in presence of Hg²⁺. The minimum inhibitory concentrations (mM) for strain MSR33 were: Hg²⁺, 0.12 and CH₃Hg⁺, 0.08. The addition of Hg²⁺ (0.04 mM) at exponential phase had not an effect on the growth rate of strain MSR33. In contrast, after Hg²⁺ addition at exponential phase the parental strain CH34 showed an immediate cessation of cell growth. During exposure to Hg²⁺ no effects in the morphology of MSR33 cells were observed, whereas CH34 cells exposed to Hg²⁺ showed a fuzzy outer membrane. Bioremediation with strain MSR33 of two mercury-contaminated aqueous solutions was evaluated. Hg²⁺ (0.10 and 0.15 mM) was completely volatilized by strain MSR33 from the polluted waters in presence of thioglycolate (5 mM) after 2 h.

Conclusions/Significance

A broad-spectrum mercury-resistant strain MSR33 was generated by incorporation of plasmid pTP6 that was directly isolated from the environment into C. metallidurans CH34. Strain MSR33 is capable to remove mercury from polluted waters. This is the first study to use an IncP-1β plasmid directly isolated from the environment, to generate a novel and stable bacterial strain useful for mercury bioremediation.

Mercury bioaccumulation and simultaneous nanoparticle synthesis by Enterobacter sp. cells

A mercury resistant strain of Enterobacter sp. is reported. The strain exhibited a novel property of mercury bioaccumulation with simultaneous synthesis of mercury nanoparticles. The culture conditions viz. pH 8.0 and lower concentration of mercury promotes synthesis of uniform sized 2-5 nm, spherical and monodispersed intracellular mercury nanoparticles. The remediated mercury trapped in the form of nanoparticles is unable to vaporize back into the environment thus, overcoming the major drawback of mercury remediation process. The mercury nanoparticles were recoverable. The nanoparticles have been characterized by high resolution transmission electron microscopy, energy dispersive X-ray analysis, powder X-ray diffraction and atomic force microscopy. The strain can be exploited for metal bioaccumulation from environmental effluent and developing a green process for nanoparticles biosynthesis.

Genome sequence of the mercury-methylating strain Desulfovibrio desulfuricans ND132

Desulfovibrio desulfuricans strain ND132 is an anaerobic sulfate-reducing bacterium (SRB) capable of producing methylmercury (MeHg), a potent human neurotoxin. The mechanism of methylation by this and other organisms is unknown. We present the 3.8-Mb genome sequence to provide further insight into microbial mercury methylation.

Simultaneous determination of mercury methylation and demethylation capacities of various sulfate-reducing bacteria using species-specific isotopic tracers

The use of species-specific isotopic tracers for inorganic and methyl mercury has allowed the simultaneous determination of the methylation and demethylation potentials of pure culture of isolated sulfate-reducing (SR) bacterial strains using low Hg species concentration levels (7 µg/L (199)Hg(II), 1 µg/L Me(201)Hg). A major advantage of the method reported here is that it can be used to follow simultaneously both the degradation of the species added but also the formation of their degradation products and thus the determination during the same incubation of the specific methylation/demethylation yields and rate constants. Methylation/demethylation capacities and extents have been found to differ between the tested strains and the tested conditions. The methylating/demethylating capacities of bacteria appear to be strain specific. All the methylating strains were found to demethylate methylmercury (MeHg). The active mechanism responsible for Hg methylation appears directly dependent on the bacterial activity but is not dependent on the metabolism used by the tested bacteria (sulfate reduction, fermentation, or nitrate respiration). The results provide confirmation that SR strains contribute to MeHg demethylation under anoxic conditions, leading to Hg(II) as the end product, consistent with the oxidative degradation pathway. Kinetic experiments have allowed specific transformation rate constants to be addressed for the two reversible processes and the reactivity of each isotopic tracer to be compared. The differential reactivity highlighted the different steps involved in the two apparent processes (i.e., uptake plus internal transformation of mercury species). Methylation appears as the slowest process, mainly controlled by the assimilation of Hg(II), whereas demethylation is faster and not dependent on the MeHg concentration.

Construction and characterization of a photosynthetic bacterium genetically engineered for Hg2+ uptake

A recombinant photosynthetic bacterium, Rhodopseudomonas palustris, was constructed to simultaneously express mercury transport system and metallothionein for Hg(2+) removal from heavy metal wastewater. The effects of essential process parameters, including pH, ionic strength and presence of co-ions on Hg(2+) uptake were evaluated. The results showed that compared with wild type R. palustris, recombinant strain displayed stronger resistance to toxic Hg(2+), and its Hg(2+) binding capacity was enhanced threefolds. In the range of pH 4-10, recombinant R. palustris maintained effective accumulation of Hg(2+). The presence of 10 mg L(-1) Mg(2+), Ca(2+), Zn(2+) or Ni(2+) did not significantly influence Hg(2+) bioaccumulation by recombinant R. palustris from solutions containing 0.2 mg L(-1) Hg(2+), while Na(+) and Cd(2+) posed serious adverse effect on Hg(2+) uptake. Furthermore, EDTA treatment experiment confirmed that different from wild type R. palustris that mainly absorbed Hg(2+) on the cell surface, recombinant R. palustris transported most of the bound Hg(2+) into the cells.

Arsenic removal from contaminated soil via biovolatilization by genetically engineered bacteria under laboratory conditions

In Rhodopseudomonas palustris, an arsM gene, encoding bacterial and archaeal homologues of the mammalian Cyt19 As(III) S-adenosylmethionine methytransferase, was regulated by arsenicals. An expression of arsM was introduced into strains for the methylation of arsenic. When arsM was expressed in Sphingomonas desiccabilis and Bacillus idriensis, it had 10 folds increase of methyled arsenic gas compared to wild type in aqueous system. In soil system, about 2.2%-4.5% of arsenic was removed by biovolatilization during 30 days. This study demonstrated that arsenic could be removed through volatilization from the contaminated soil by bacteria which have arsM gene expressed. These results showed that it is possible to use microorganisms expressing arsM as an inexpensive, efficient strategy for arsenic bioremediation from contaminated water and soil.

Methylmercury and sulfate-reducing bacteria in mangrove sediments from Jiulong River Estuary, China

Estuaries are important sites for mercury (Hg) methylation, with sulfate-reducing bacteria (SRB) thought to be the main Hg methylators. Distributions of total mercury (THg) and methylmercury (MeHg) in mangrove sediment and sediment core from Jiulong River Estuary Provincial Mangrove Reserve, China were determined and the possible mechanisms of Hg methylation and their controlling factors in mangrove sediments were investigated. Microbiological and geochemical parameters were also determined. Results showed that SRB constitute a small fraction of total bacteria (TB) in both surface sediments and the profile of sediments. The content of THg, MeHg, TB, and SRB were (350 +/- 150) ng/g, (0.47 +/- 0.11) ng/g, (1.4 x10(11) +/- 4.1 x 10(9)) cfu/g dry weight (dw), and (5.0 x 10(6) +/- 2.7 x 10(6)) cfu/g dw in surficial sediments, respectively, and (240 +/- 24) ng/g, (0.30 +/- 0.15) ng/g, (1.9 x 10(11) +/- 4.2 x 10(10)) cfu/g dw, and (1.3 x 10(6) +/- 2.0 x 10(6)) cfu/g dw in sediment core, respectively. Results showed that THg, MeHg, TB, MeHg/THg, salinity and total sulfur (TS) increased with depth, but total organic matter (TOM), SRB, and pH decreased with depth. Concentrations of MeHg in sediments showed significant positive correlation with THg, salinity, TS, and MeHg/THg, and significant negative correlation with SRB, TOM, and pH. It was concluded that other microbes, rather than SRB, may also act as main Hg methylators in mangrove sediments.

Diversity and characterization of mercury-resistant bacteria in snow, freshwater and sea-ice brine from the High Arctic

It is well-established that atmospheric deposition transports mercury from lower latitudes to the Arctic. The role of bacteria in the dynamics of the deposited mercury, however, is unknown. We characterized mercury-resistant bacteria from High Arctic snow, freshwater and sea-ice brine. Bacterial densities were 9.4 × 10(5), 5 × 10(5) and 0.9-3.1 × 10(3) cells mL(-1) in freshwater, brine and snow, respectively. Highest cultivability was observed in snow (11.9%), followed by freshwater (0.3%) and brine (0.03%). In snow, the mercury-resistant bacteria accounted for up to 31% of the culturable bacteria, but <2% in freshwater and brine. The resistant bacteria belonged to the Alpha-, Beta- and Gammaproteobacteria, Firmicutes, Actinobacteria, and Bacteriodetes. Resistance levels of most isolates were not temperature dependent. Of the resistant isolates, 25% reduced Hg(II) to Hg(0). No relation between resistance level, ability to reduce Hg(II) and phylogenetic group was observed. An estimation of the potential bacterial reduction of Hg(II) in snow suggested that it was important in the deeper snow layers where light attenuation inhibited photoreduction. Thus, by reducing Hg(II) to Hg(0), mercury-resistant bacteria may limit the supply of substrate for methylation processes and, hence, contribute to lowering the risk that methylmercury is being incorporated into the Arctic food chains.

Determining the effects of a spatially heterogeneous selection pressure on bacterial population structure at the sub-millimetre scale

A key interest of microbial ecology is to understand the role of environmental heterogeneity in shaping bacterial diversity and fitness. However, quantifying relevant selection pressures and their effects is challenging due to the number of parameters that must be considered and the multiple scales over which they act. In the current study, a model system was employed to investigate the effects of a spatially heterogeneous mercuric ion (Hg(2+)) selection pressure on a population comprising Hg-sensitive and Hg-resistant pseudomonads. The Hg-sensitive bacteria were Pseudomonas fluorescens SBW25::rfp and Hg-resistant bacteria were P. fluorescens SBW25 carrying a gfp-labelled, Hg resistance plasmid. In the absence of Hg, the plasmid confers a considerable fitness cost on the host, with µ(max) for plasmid-carrying cells relative to plasmid-free cells of only 0.66. Two image analysis techniques were developed to investigate the structure that developed in biofilms about foci of Hg (cellulose fibres imbued with HgCl(2)). Both techniques indicated selection for the resistant phenotype occurred only in small areas of approximately 178-353 μm (manually defined contour region analysis) or 275-350 μm (daime analysis) from foci. Hg also elicited toxic effects that reduced the growth of both Hg-sensitive and Hg-resistant bacteria up to 250 μm from foci. Selection for the Hg resistance phenotype was therefore highly localised when Hg was spatially heterogeneous. As such, for this model system, we define here the spatial scale over which selection operates. The ability to quantify changes in the strength of selection for particular phenotypes over sub-millimetre scales is useful for understanding the scale over which environmental variables affect bacterial populations.

Diversity and mobility of integrative and conjugative elements in bovine isolates of Streptococcus agalactiae, S. dysgalactiae subsp. dysgalactiae, and S. uberis

Bovine isolates of Streptococcus agalactiae (n = 76), Streptococcus dysgalactiae subsp. dysgalactiae (n = 32), and Streptococcus uberis (n = 101) were analyzed for the presence of different integrative and conjugative elements (ICEs) and their association with macrolide, lincosamide, and tetracycline resistance. The diversity of the isolates included in this study was demonstrated by multilocus sequence typing for S. agalactiae and pulsed-field gel electrophoresis for S. dysgalactiae and S. uberis. Most of the erythromycin-resistant strains carry an ermB gene. Five strains of S. uberis that are resistant to lincomycin but susceptible to erythromycin carry the lin(B) gene, and one has both linB and lnuD genes. In contrast to S. uberis, most of the S. agalactiae and S. dysgalactiae tetracycline-resistant isolates carry a tet(M) gene. A tet(S) gene was also detected in the three species. A Tn916-related element was detected in 30 to 50% of the tetracycline-resistant strains in the three species. Tetracycline resistance was successfully transferred by conjugation to an S. agalactiae strain. Most of the isolates carry an ICE integrated in the rplL gene. In addition, half of the S. agalactiae isolates have an ICE integrated in a tRNA lysine (tRNA(Lys)) gene. Such an element is also present in 20% of the isolates of S. dysgalactiae and S. uberis. A circular form of these ICEs was detected in all of the isolates tested, indicating that these genetic elements are mobile. These ICEs could thus also be a vehicle for horizontal gene transfer between streptococci of animal and/or human origin.

Direct measurement of mercury(II) removal from organomercurial lyase (MerB) by tryptophan fluorescence: NmerA domain of coevolved γ-proteobacterial mercuric ion reductase (MerA) is more efficient than MerA catalytic core or glutathione

Aerobic and facultative bacteria and archaea harboring mer loci exhibit resistance to the toxic effects of Hg(II) and organomercurials [RHg(I)]. In broad spectrum resistance, RHg(I) is converted to less toxic Hg(0) in the cytosol by the sequential action of organomercurial lyase (MerB: RHg(I) → RH + Hg(II)) and mercuric ion reductase (MerA: Hg(II) → Hg(0)) enzymes, requiring transfer of Hg(II) from MerB to MerA. Although previous studies with γ-proteobacterial versions of MerA and a nonphysiological Hg(II)-DTT-MerB complex qualitatively support a pathway for direct transfer between proteins, assessment of the relative efficiencies of Hg(II) transfer to the two different dicysteine motifs in γ-proteobacterial MerA and to competing cellular thiol is lacking. Here we show the intrinsic tryptophan fluorescence of γ-proteobacterial MerB is sensitive to Hg(II) binding and use this to probe the kinetics of Hg(II) removal from MerB by the N-terminal domain (NmerA) and catalytic core C-terminal cysteine pairs of its coevolved MerA and by glutathione (GSH), the major competing cellular thiol in γ-proteobacteria. At physiologically relevant concentrations, reaction with a 10-fold excess of NmerA over HgMerB removes ≥92% Hg(II), while similar extents of reaction require more than 1000-fold excess of GSH. Kinetically, the apparent second-order rate constant for Hg(II) transfer from MerB to NmerA, at (2.3 ± 0.1) × 10(4) M(-1) s(-1), is ∼100-fold greater than that for GSH ((1.2 ± 0.2) × 10(2) M(-1) s(-1)) or the MerA catalytic core (1.2 × 10(2) M(-1) s(-1)), establishing transfer to the metallochaperone-like NmerA domain as the kinetically favored pathway in this coevolved system.

Long-term Hg pollution-induced structural shifts of bacterial community in the terrestrial isopod (Porcellio scaber) gut

In previous studies we detected lower species richness and lower Hg sensitivity of the bacteria present in egested guts of Porcellio scaber (Crustacea, Isopoda) from chronically Hg polluted than from unpolluted environment. Basis for such results were further investigated by sequencing of 16S rRNA genes of mercury-resistant (Hgr) isolates and clone libraries. We observed up to 385 times higher numbers of Hgr bacteria in guts of animals from polluted than from unpolluted environment. The majority of Hgr strains contained merA genes. Sequencing of 16S rRNA clones from egested guts of animals from Hg-polluted environments showed elevated number of bacteria from Pseudomonas, Listeria and Bacteroidetes relatives groups. In animals from pristine environment number of bacteria from Achromobacter relatives, Alcaligenes, Paracoccus, Ochrobactrum relatives, Rhizobium/Agrobacterium, Bacillus and Microbacterium groups were elevated. Such bacterial community shifts in guts of animals from Hg-polluted environment could significantly contribute to P. scaber Hg tolerance.

Regulatory role of MlrA in transcription activation of csgD, the master regulator of biofilm formation in Escherichia coli

The transcription factor CsgD plays a key role in the control of biofilm formation in Escherichia coli by controlling the production of curli fimbriae and other biofilm components. In concert with its regulatory role, the promoter for the csgD operon is under the control of more than 10 regulatory factors, each monitoring a different condition or factor in stressful environments. Previously, we classified three factors (OmpR, RstA and IHF) as activators and two factors (CpxR and H-NS) as repressors, and found novel modes of their interplay. Here we describe an as yet uncharacterized regulator, MlrA, that has been suggested to participate in control of curli formation. Based on both in vivo and in vitro analyses, we identified MlrA as a positive factor of the csgD promoter by directly binding to its upstream region (-113 to -146) with a palindromic sequence of AAAATTGTACA(12N)TGTACAATTTT between the binding sites of two activators, IHF and OmpR. The possible interplay between three activators was analysed in detail.

[Application of mercury-resistant genes in bioremediation of mercurials in environments]

Mercury and its organic compounds, especially methylmercury are extremely hazardous pollutants that have been released into the environment in substantial quantities by natural events and anthropogenic activities. Due to the acute toxicity of these contaminants, there is an urgent need to develop an effective and affordable technology to remove them from the environments. Recently, attempts have been made to utilize bacterial mer operon-mediated reduction and volatilization of mercurials for environmental remediation of mercury pollution. However, application of this technology to the treatment of mercury-contaminated environments has been limited by social concerns about the release of volatile mercury that will become part of the local mercury cycle and repollute the environment again, into the ambient air. To improve this environmental problem, a new mercury scavenging mechanism that could be expressed in living cells and accumulates mercury from contaminated site without releasing mercury vapor is necessitated. To construct a new biocatalyst that is capable of specifically accumulating mercury from contaminated sites without releasing mercury vapor, we have genetically engineered bacteria and tobacco plant for removal of mercury from wastewater and soils, respectively, to express a mercury transport system and organomercurial lyase enzyme simultaneously, and overexpress polyphosphate, a chelator of divalent metals. The applicability of these new engineered biocatalysts in the environmental remediation of mercurials is evaluated and discussed in this review.

Growth responses to and accumulation of mercury by ectomycorrhizal fungi

Heavy metals have been shown to negatively affect the growth of ectomycorrhizal fungi (ECMF). In addition, ECMF have been shown to accumulate heavy metals and to protect host trees from metal toxicity. However, specific literature on the interactions between ECMF and mercury (Hg) is scant. This paper describes the responses of ECMF to Hg in axenic culture conditions. Six ECMF from an area with no known history of direct Hg contamination were tested to determine their sensitivity to Hg. ECMF were incubated on solid medium amended with Hg (0-50μM) as HgCl₂ and the effect of Hg on radial growth was determined. The effect of preexposure cultivation on Hg sensitivity, the effect of Hg on biomass production, and the ability to accumulate Hg were determined for four of the ECMF. At micromolar concentrations, Hg significantly inhibited the radial growth rate of ECMF. This inhibitory effect was lessened in some ECMF when an established colony was exposed to Hg. Mercury lowered biomass production by some ECMF, and ECMF accumulate Hg from a solid growth substrate in direct relation to the amount of Hg added to the media. Possible implications for ECMF communities in Hg-impacted areas are discussed.

Curli produced by Escherichia coli PHL628 provide protection from Hg(II)

The role of curli, amyloid extracellular fibers, in the tolerance of Escherichia coli PHL628 to Hg(II) was examined. Our findings indicate that by sorbing Hg(II) extracellularly, curli protect the cells. To our knowledge, this is the first time a protective role of curli against toxic metals has been demonstrated.

Expression and single-step purification of mercury transporter (merT) from Cupriavidus metallidurans in E. coli

The mercury transporter, merT, from Cupriavidus metallidurans was cloned into pRSET-C and expressed in various E. coli hosts. Expression of merT gene failed in common expression hosts like E. coli BL21(DE3), E. coli BL21(DE3)pLysS and E. coli GJ1158 due to expression induced toxicity. The protein was successfully expressed in E. coli C43(DE3) as inclusion bodies. The inclusion bodies were solubilized with Triton X-100 detergent. The detergent solubilized protein with N-terminal His-tag was purified in a single-step by immobilized metal affinity chromatography with a yield of 8 mg l(-1).

Ecological, groundwater, and human health risk assessment in a mining region of Nicaragua

The objective of the present study was to integrate the relative risk from mercury exposure to stream biota, groundwater, and humans in the Río Artiguas (Sucio) river basin, Nicaragua, where local gold mining occurs. A hazard quotient was used as a common exchange rate in probabilistic estimations of exposure and effects by means of Monte Carlo simulations. The endpoint for stream organisms was the lethal no-observed-effect concentration (NOECs), for groundwater the WHO guideline and the inhibitory Hg concentrations in bacteria (IC), and for humans the tolerable daily intake (TDI) and the benchmark dose level with an uncertainty factor of 10 (BMDLs(0.1)). Macroinvertebrates and fish in the contaminated river are faced with a higher risk to suffer from exposure to Hg than humans eating contaminated fish and bacteria living in the groundwater. The river sediment is the most hazardous source for the macroinvertebrates, and macroinvertebrates make up the highest risk for fish. The distribution of body concentrations of Hg in fish in the mining areas of the basin may exceed the distribution of endpoint values with close to 100% probability. Similarly, the Hg concentration in cord blood of humans feeding on fish from the river was predicted to exceed the BMDLs(0.1) with about 10% probability. Most of the risk to the groundwater quality is confined to the vicinity of the gold refining plants and along the river, with a probability of about 20% to exceed the guideline value.

Heavy metal resistance in Arthrobacter ramosus strain G2 isolated from mercuric salt-contaminated soil

Present study describes isolation of a multiple metal-resistant Arthrobacter ramosus strain from mercuric salt-contaminated soil. The isolate was found to resist and bioaccumulate several metals, such as cadmium, cobalt, zinc, chromium and mercury. Maximum tolerated concentrations for above metals were found to be 37, 525, 348, 1530 and 369 microM, respectively. The isolate could also reduce and detoxify redox-active metals like chromium and mercury, indicating that it has great potential in bioremediation of heavy metal-contaminated sites. Chromate reductase and mercuric reductase (MerA) activities in protein extract of the culture were found to be 2.3 and 0.17 units mg(-1) protein, respectively. MerA enzyme was isolated from the culture by (NH(4))(2)SO(4) precipitation followed by dye affinity chromatography and its identity was confirmed by nano-LC-MS/MS. Its monomeric molecular weight, and optimum pH and temperature were 57kDa, 7.4 and 55 degrees C, respectively. Thus, the enzyme was mildly thermophilic as compared to other MerA enzymes. K(m) and V(max) of the enzyme were 16.9 microM HgCl(2) and 6.2 micromol min(-1)mg(-1) enzyme, respectively. The enzyme was found to be NADPH-specific. To our knowledge this is the first report on characterization of MerA enzyme from an Arthrobacter sp.

Tackling metal regulation and transport at the single-molecule level

To maintain normal metal metabolism, organisms utilize dynamic cooperation of many biomacromolecules for regulating metal ion concentrations and bioavailability. How these biomacromolecules work together to achieve their functions is largely unclear. For example, how do metalloregulators and DNA interact dynamically to control gene expression to maintain healthy cellular metal level? And how do metal transporters collaborate dynamically to deliver metal ions? Here we review recent advances in studying the dynamic interactions of macromolecular machineries for metal regulation and transport at the single-molecule level: (1) The development of engineered DNA Holliday junctions as single-molecule reporters for metalloregulator-DNA interactions, focusing onMerR-family regulators. And (2) The development of nanovesicle trapping coupled with single molecule fluorescence resonance energy transfer (smFRET) for studying weak, transient interactions between the copper chaperone Hah1 and the Wilson disease protein. We describe the methodologies,the information content of the single-molecule results, and the insights into the biological functions of the involved biomacromolecules for metal regulation and transport. We also discuss remaining challenges from our perspective.

Tn502 and Tn512 are res site hunters that provide evidence of resolvase-independent transposition to random sites

In this study, we report on the transposition behavior of the mercury(II) resistance transposons Tn502 and Tn512, which are members of the Tn5053 family. These transposons exhibit targeted and oriented insertion in the par region of plasmid RP1, since par-encoded components, namely, the ParA resolvase and its cognate res region, are essential for such transposition. Tn502 and, under some circumstances, Tn512 can transpose when par is absent, providing evidence for an alternative, par-independent pathway of transposition. We show that the alternative pathway proceeds by a two-step replicative process involving random target selection and orientation of insertion, leading to the formation of cointegrates as the predominant product of the first stage of transposition. Cointegrates remain unresolved because the transposon-encoded (TniR) recombination system is relatively inefficient, as is the host-encoded (RecA) system. In the presence of the res-ParA recombination system, TniR-mediated (and RecA-mediated) cointegrate resolution is highly efficient, enabling resolution both of cointegrates involving functional transposons (Tn502 and Tn512) and of defective elements (In0 and In2). These findings implicate the target-encoded accessory functions in the second stage of transposition as well as in the first. We also show that the par-independent pathway enables the formation of deletions in the target molecule.

Is exposure to mercury a driving force for the carriage of antibiotic resistance genes?

The mercury resistance gene merA has often been found together with antibiotic resistance genes in human commensal Escherichia coli. To study this further, we analysed mercury resistance in collections of strains from various populations with different levels of mercury exposure and various levels of antibiotic resistance. The first population lived in France and had no known mercury exposure. The second lived in French Guyana and included a group of Wayampi Amerindians with a known high exposure to mercury. Carriage rates of mercury resistance were assessed by measuring the MIC and by detecting the merA gene. Mercury-resistant E. coli was found significantly more frequently in the populations that had the highest carriage rates of antibiotic-resistant E. coli and in parallel antibiotic resistance was higher in the population living in an environment with a high exposure to mercury, suggesting a possible co-selection. Exposure to mercury might be a specific driving force for the acquisition and maintenance of mobile antibiotic resistance gene carriage in the absence of antibiotic selective pressure.

Metagenomes from high-temperature chemotrophic systems reveal geochemical controls on microbial community structure and function

The Yellowstone caldera contains the most numerous and diverse geothermal systems on Earth, yielding an extensive array of unique high-temperature environments that host a variety of deeply-rooted and understudied Archaea, Bacteria and Eukarya. The combination of extreme temperature and chemical conditions encountered in geothermal environments often results in considerably less microbial diversity than other terrestrial habitats and offers a tremendous opportunity for studying the structure and function of indigenous microbial communities and for establishing linkages between putative metabolisms and element cycling. Metagenome sequence (14–15,000 Sanger reads per site) was obtained for five high-temperature (>65°C) chemotrophic microbial communities sampled from geothermal springs (or pools) in Yellowstone National Park (YNP) that exhibit a wide range in geochemistry including pH, dissolved sulfide, dissolved oxygen and ferrous iron. Metagenome data revealed significant differences in the predominant phyla associated with each of these geochemical environments. Novel members of the Sulfolobales are dominant in low pH environments, while other Crenarchaeota including distantly-related Thermoproteales and Desulfurococcales populations dominate in suboxic sulfidic sediments. Several novel archaeal groups are well represented in an acidic (pH 3) Fe-oxyhydroxide mat, where a higher O₂ influx is accompanied with an increase in archaeal diversity. The presence or absence of genes and pathways important in S oxidation-reduction, H₂-oxidation, and aerobic respiration (terminal oxidation) provide insight regarding the metabolic strategies of indigenous organisms present in geothermal systems. Multiple-pathway and protein-specific functional analysis of metagenome sequence data corroborated results from phylogenetic analyses and clearly demonstrate major differences in metabolic potential across sites. The distribution of functional genes involved in electron transport is consistent with the hypothesis that geochemical parameters (e.g., pH, sulfide, Fe, O₂) control microbial community structure and function in YNP geothermal springs.

Structure and conformational dynamics of the metalloregulator MerR upon binding of Hg(II)

The bacterial metalloregulator MerR is the index case of an eponymous family of regulatory proteins, which controls the transcription of a set of genes (the mer operon) conferring mercury resistance in many bacteria. Homodimeric MerR represses transcription in the absence of mercury and activates transcription upon Hg(II) binding. Here, the average structures of the apo and Hg(II)-bound forms of MerR in aqueous solution are examined using small-angle X-ray scattering, indicating an extended conformation of the metal-bound protein and revealing the existence of a novel compact conformation in the absence of Hg(II). Molecular dynamics (MD) simulations are performed to characterize the conformational dynamics of the Hg(II)-bound form. In both small-angle X-ray scattering and MD, the average torsional angle between DNA-binding domains is approximately 65 degrees. Furthermore, in MD, interdomain motions on a timescale of approximately 10 ns involving large-amplitude (approximately 20 A) domain opening-and-closing, coupled to approximately 40 degrees variations of interdomain torsional angle, are revealed. This correlated domain motion may propagate allosteric changes from the metal-binding site to the DNA-binding site while maintaining DNA contacts required to initiate DNA underwinding.

Efficient use and recycling of the micronutrient iodide in mammals

Daily ingestion of iodide alone is not adequate to sustain production of the thyroid hormones, tri- and tetraiodothyronine. Proper maintenance of iodide in vivo also requires its active transport into the thyroid and its salvage from mono- and diiodotyrosine that are formed in excess during hormone biosynthesis. The enzyme iodotyrosine deiodinase responsible for this salvage is unusual in its ability to catalyze a reductive dehalogenation reaction dependent on a flavin cofactor, FMN. Initial characterization of this enzyme was limited by its membrane association, difficult purification and poor stability. The deiodinase became amenable to detailed analysis only after identification and heterologous expression of its gene. Site-directed mutagenesis recently demonstrated that cysteine residues are not necessary for enzymatic activity in contrast to precedence set by other reductive dehalogenases. Truncation of the N-terminal membrane anchor of the deiodinase has provided a soluble and stable source of enzyme sufficient for crystallographic studies. The structure of an enzyme.substrate co-crystal has become invaluable for understanding the origins of substrate selectivity and the mutations causing thyroid disease in humans.

Global regulation of food supply by Pseudomonas putida DOT-T1E

Pseudomonas putida DOT-T1E was used as a model to develop a "phenomics" platform to investigate the ability of P. putida to grow using different carbon, nitrogen, and sulfur sources and in the presence of stress molecules. Results for growth of wild-type DOT-T1E on 90 different carbon sources revealed the existence of a number of previously uncharted catabolic pathways for compounds such as salicylate, quinate, phenylethanol, gallate, and hexanoate, among others. Subsequent screening on the subset of compounds on which wild-type DOT-TIE could grow with four knockout strains in the global regulatory genes Deltacrc, Deltacrp, DeltacyoB, and DeltaptsN allowed analysis of the global response to nutrient supply and stress. The data revealed that most global regulator mutants could grow in a wide variety of substrates, indicating that metabolic fluxes are physiologically balanced. It was found that the Crc mutant did not differ much from the wild-type regarding the use of carbon sources. However, certain pathways are under the preferential control of one global regulator, i.e., metabolism of succinate and d-fructose is influenced by CyoB, and l-arginine is influenced by PtsN. Other pathways can be influenced by more than one global regulator; i.e., l-valine catabolism can be influenced by CyoB and Crp (cyclic AMP receptor protein) while phenylethylamine is affected by Crp, CyoB, and PtsN. These results emphasize the cross talk required in order to ensure proper growth and survival. With respect to N sources, DOT-T1E can use a wide variety of inorganic and organic nitrogen sources. As with the carbon sources, more than one global regulator affected growth with some nitrogen sources; for instance, growth with nucleotides, dipeptides, d-amino acids, and ethanolamine is influenced by Crp, CyoB, and PtsN. A surprising finding was that the Crp mutant was unable to flourish on ammonium. Results for assayed sulfur sources revealed that CyoB controls multiple points in methionine/cysteine catabolism while PtsN and Crc are needed for N-acetyl-l-cysteamine utilization. Growth of global regulator mutants was also influenced by stressors of different types (antibiotics, oxidative agents, and metals). Overall and in combination with results for growth in the presence of various stressors, these phenomics assays provide multifaceted insights into the complex decision-making process involved in nutrient supply, optimization, and survival.

Organomercurials removal by heterogeneous merB genes harboring bacterial strains

Organomercury lyase (MerB) is a key enzyme in bacterial detoxification and bioremediation of organomercurials. However, the merB gene is often considered as an ancillary component of the mer operon because there is zero to three merB genes in different mer operons identified so far. In this study, organomercurials' removal abilities of native mercury-resistant bacteria that have one or multiple merB genes were examined. Each heterogeneous merB genes from these bacteria was further cloned into Escherichia coli to investigate the substrate specificity of each MerB enzyme. The merB1 gene from Bacillus megaterium MB1 conferred the highest volatilization ability to methylmercury chloride, ethylmercury chloride, thimerosal and p-chloromercuribenzoate, while the merB3 from B. megaterium MB1 conferred the fastest mercury volatilization activity to p-chloromercuribenzoate. The substrate specificities among these MerB enzymes show the necessity for selecting the appropriate bacteria strains or MerB enzymes to apply them in bioremediation engineering for cleaning up specific organomercurial contaminations.

Temporal bacterial diversity associated with metal-contaminated river sediments

The temporal activity, abundance and diversity of microbial communities were evaluated across a metal-contamination gradient around a Superfund site in Montana. In order to analyze short-term variability, samples were collected from six sites on four occasions over 12 months. Measurements of community activity, diversity and richness, quantified by dehydrogenase activity and through denaturant gradient gel electrophoresis (DGGE), respectively, were higher at contaminated sites adjacent to the smelter, relative to reference sites. 16S rRNA gene copy numbers, measured by quantitative PCR, showed seasonal variability, yet were generally higher within polluted sediments. Jaccard similarity coefficients of DGGE profiles, found sites to cluster based primarily on geographical proximity rather than geochemical similarities. Intra-site clustering of the most polluted sites also suggests a stable metal-tolerant community. Sequences from DGGE-extracted bands were predominantly Beta and Gammaproteobacteria, although the communities at all sites generally maintained a diverse phylogeny changing in composition throughout the sampling period. Spearman's rank correlations analysis found statistically significant relationships between community composition and organic carbon (r-value = 0.786) and metals (r-values As = 0.65; Cu = 0.63; Zn = 0.62). A diverse and abundant community at the most polluted site indicates that historical contamination selects for a metal-resistant microbial community, a finding that must be accounted for when using the microbial community within ecosystem monitoring studies. This study highlights the importance of using multiple time-points to draw conclusions on the affect of metal contamination.

DFT studies of the degradation mechanism of methyl mercury activated by a sulfur-rich ligand

We describe theoretical insights into the mechanism of Hg-C bond protonolysis in methyl mercury coordinated by the tris(2-mercapto-1-tert-butylimidazolyl)hydroborato ligand, the structural and functional analogue of the organomercurial lyase MerB. Different cleavage pathways including both frontside and backside attack transition states were systematically studied by the hybrid density functional method B3LYP. Dependence of Hg-C bond activation on the primary sulfur coordination number of mercury was elaborated, and conceptual DFT indexes were suggested to be more appropriate than gross charge of atom sites in interpreting the dependence. Furthermore, absence of configurational inversion in MerB-catalyzed reactions was accounted for by examinations of the backside protonolysis pathways in the present system. Lastly, a rationalization was provided about the choice between different characteristics of transition states including both four-center and six-center ones.

Changes in the non-protein thiol pool and production of dissolved gaseous mercury in the marine diatom Thalassiosira weissflogii under mercury exposure

Two detoxification mechanisms working in the marine diatom Thalassiosira weissflogii to cope with mercury toxicity were investigated. Initially, the effect of mercury on the intracellular pool of non-protein thiols was studied in exponentially growing cultures exposed to sub-toxic HgCl(2) concentrations. T. weissflogii cells responded by synthesizing metal-binding peptides, named phytochelatins (PCs), besides increasing the intracellular pool of glutathione and gamma-glutamylcysteine (gamma-EC). Intracellular Hg and PC concentrations increased with the Hg concentration in the culture medium, exhibiting a distinct dose-response relationship. However, considerations of the PCs-SH:Hg molar ratio suggest that glutathione could also be involved in the intracellular mercury sequestration. The time course of the non-protein thiol pool and Hg intracellular concentration shows that PCs, glutathione and gamma-EC represent a rapid cellular response to mercury, although their role in Hg detoxification seems to lose importance at longer incubation times. The occurrence of a process of reduction of Hg(II) to Hg degrees and subsequent production of dissolved gaseous mercury (DGM) was also investigated at lower Hg concentrations, at which the PC synthesis doesn't seem to be involved. The significant (P<0.01) correlation between the cellular density in solution and the production of DGM suggests that this diatom is capable of directly producing DGM, both in light and dark conditions. This finding has been confirmed by the absence of DGM production in the culture media containing formaldehyde-killed cells. Finally, the relationship between these two different pathways of Hg detoxification is discussed.

Species-specific stable isotope fractionation of mercury during Hg(II) methylation by an anaerobic bacteria (Desulfobulbus propionicus) under dark conditions

This work reports the first results on the stable isotope fractionation of Hg during methylation by anaerobic bacteria under dark conditions. The GC-MC-ICPMS methodology employed is capable of simultaneously measuring the species-specific isotopic composition of different Hg species within the same sample. We have studied Hg isotopic fractionation caused by methylation of Hg(II) standard reference material NIST-3133 in the presence of the pure bacterial strain Desulfobulbus propionicus MUD10 (DSM 6523) under fermentative conditions. We have measured the isotopic composition of Hg(II) and monomethyl mercury (MMHg) in these cultures as a function of time and calculated delta-values for both species versus the starting material (NIST-3133) as a delta-zero standard. Two different strategies for the incubation were applied: single sampling cultures and a continuous sampling culture. The results obtained have shown that under the conditions employed in this work the methylation of Hg(II) causes mass-dependent fractionation of the Hg isotopes for both Hg(II) substrate and produced MMHg. Such a process occurred under the exponential growth of the bacteria which preferentially methylate the lighter isotopes of Hg. After 96 h for the continuous culture and 140 h for the single sampling cultures, we observed a change in the fractionation trend in the samples at a similar cell density value (ca. 6.0 x 10(7) cells mL(-1)) which suggests the increasing contribution of a simultaneous process balancing methylation extent such as demethylation. Assuming that Rayleigh type fractionation conditions are met before such suppression, we have obtained a alpha(202/198) fractionation factor of 1.0026 +/- 0.0004 for the single sampling cultures.

A general profile for the MerR family of transcriptional regulators constructed using the semi-automated Provalidator tool

Provalidator is a web-based tool that facilitates the design and validation of generalized profiles of protein families in prokaryotes. This tool combines the nearly full automation of profile building with a search for family members in all available databases. The tool is useful for assigning a given protein to a specific family, and is also useful for genome mining in annotated prokaryotic genomes. The tool is freely available at http://www.bactregulators.org. As proof of concept we constructed a profile that best defines the MerR family of transcriptional regulators. The profile created includes functional residues that are part of the helix-turn-helix DNA binding domain and accessory elements defined as wings 1 and 2, suggesting that members of the MerR family of regulators may exhibit conserved 3D structure in the region that defines the family profile. The profile defined for MerR was used to search for members of this family in the Swiss-Prot and TrEMBL databases, and also to identify members of the family in the genome of Pseudomonas putida. One of these identified regulators was found to be involved in zinc tolerance, showing the usefulness of identifying family members and assigning phenotypes.

Single-molecule study of metalloregulator CueR-DNA interactions using engineered Holliday junctions

To maintain normal metal metabolism, bacteria use metal-sensing metalloregulators to control transcription of metal resistance genes. Depending on their metal-binding states, the MerR-family metalloregulators change their interactions with DNA to suppress or activate transcription. To understand their functions fundamentally, we study how CueR, a Cu(1+)-responsive MerR-family metalloregulator, interacts with DNA, using an engineered DNA Holliday junction (HJ) as a protein-DNA interaction reporter in single-molecule fluorescence resonance energy transfer measurements. By analyzing the single-molecule structural dynamics of the engineered HJ in the presence of various concentrations of both apo- and holo-CueR, we show how CueR interacts with the two conformers of the engineered HJ, forming variable protein-DNA complexes at different protein concentrations and changing the HJ structures. We also show how apo- and holo-CueR differ in their interactions with DNA, and discuss their similarities and differences with other MerR-family metalloregulators. The surprising finding that holo-CueR binds more strongly to DNA than to apo-CueR suggests functional differences among MerR-family metalloregulators, in particular in their mechanisms of switching off gene transcription after activation. The study also corroborates the general applicability of engineered HJs as single-molecule reporters for protein-DNA interactions, which are fundamental processes in gene replication, transcription, recombination, and regulation.