Molecular and eco-physiological responses of soil-borne lead (Pb2+)-resistant bacteria for bioremediation and plant growth promotion under lead stress

Lead (Pb) is the 2nd known portentous hazardous substance after arsenic (As). Being highly noxious, widespread, non-biodegradable, prolonged environmental presence, and increasing accumulation, particularly in arable land, Pb pollution has become a serious global health concern requiring urgent remediation. Soil-borne, indigenous microbes from Pb-polluted sites have evolved diverse resistance strategies, involving biosorption, bioprecipitation, biomineralization, biotransformation, and efflux mechanisms, under continuous exposure to Pb in human-impacted surroundings. These strategies employ a wide range of functional bioligands to capture Pb and render it inaccessible for leaching. Recent breakthroughs in molecular technology and understanding of lead resistance mechanisms offer the potential for utilizing microbes as biological tools in environmental risk assessment. Leveraging the specific affinity and sensitivity of bacterial regulators to Pb2+ ions, numerous lead biosensors have been designed and deployed worldwide to monitor Pb bioavailability in contaminated sites, even at trace levels. Besides, the ongoing degradation of croplands due to Pb pollution poses a significant challenge to meet the escalating global food demands. The accumulation of Pb in plant tissues jeopardizes both food safety and security while severely impacting plant growth. Exploring Pb-resistant plant growth-promoting rhizobacteria (PGPR) presents a promising sustainable approach to agricultural practices. The active associations of PGPR with host plants have shown enhancements in plant biomass and stress alleviation under Pb influence. They thus serve a dual purpose for plants grown in Pb-contaminated areas. This review aims to offer a comprehensive understanding of the role played by Pb-resistant soil-borne indigenous bacteria in expediting bioremediation and improving the growth of Pb-challenged plants essential for potential field application, thus broadening prospects for future research and development.

Halotolerant Endophytic Bacteria Priestia flexa 7BS3110 with Hg2+ Tolerance Isolated from Avicennia germinans in a Caribbean Mangrove from Colombia

The mangrove ecosystems of the Department of Atlántico (Colombian Caribbean) are seriously threatened by problems of hypersalinization and contamination, especially by heavy metals from the Magdalena River. The mangrove plants have developed various mechanisms to adapt to these stressful conditions, as well as the associated microbial populations that favor their growth. In the present work, the tolerance and detoxification capacity to heavy metals, especially to mercury, of a halotolerant endophytic bacterium isolated from the species Avicennia germinans located in the Balboa Swamp in the Department of Atlántico was characterized. Diverse microorganisms were isolated from superficially sterilized A. germinans leaves. Tolerance to NaCl was evaluated for each of the obtained isolates, and the most resistant was selected to assess its tolerance to Pb2+, Cu2+, Hg2+, Cr3+, Co2+, Ni2+, Zn2+, and Cd2+, many of which have been detected in high concentrations in the area of study. According to the ANI and AAI percentages, the most halotolerant strain was identified as Priestia flexa, named P. flexa 7BS3110, which was able to tolerate up to 12.5% (w/v) NaCl and presented a minimum inhibitory concentrations (MICs) of 0.25 mM for Hg, 10 mM for Pb, and 15 mM for Cr3+. The annotation of the P. flexa 7BS3110 genome revealed the presence of protein sequences associated with exopolysaccharide (EPS) production, thiol biosynthesis, specific proteins for chrome efflux, non-specific proteins for lead efflux, and processes associated with sulfur and iron homeostasis. Scanning electron microscopy (SEM) analysis showed morphological cellular changes and the transmission electron microscopy (TEM) showed an electrodense extracellular layer when exposed to 0.25 mM Hg2+. Due to the high tolerance of P. flexa 7BS3110 to Hg2+ and NaCl, its ability to grow when exposed to both stressors was tested, and it was able to thrive in the presence of 5% (w/v) NaCl and 0.25 mM of Hg2+. In addition, it was able to remove 98% of Hg2+ from the medium when exposed to a concentration of 14 mg/L of this metalloid. P. flexa 7BS3110 has the potential to bioremediate Hg2+ halophilic contaminated ecosystems.

Draft genome analysis for Enterobacter kobei, a promising lead bioremediation bacterium

Lead pollution of the environment poses a major global threat to the ecosystem. Bacterial bioremediation offers a promising alternative to traditional methods for removing these pollutants, that are often hindered by various limitations. Our research focused on isolating lead-resistant bacteria from industrial wastewater generated by heavily lead-containing industries. Eight lead-resistant strains were successfully isolated, and subsequently identified through molecular analysis. Among these, Enterobacter kobei FACU6 emerged as a particularly promising candidate, demonstrating an efficient lead removal rate of 83.4% and a remarkable lead absorption capacity of 571.9 mg/g dry weight. Furthermore, E. kobei FACU6 displayed a remarkable a maximum tolerance concentration (MTC) for lead reaching 3,000 mg/L. To further investigate the morphological changes in E. kobei FACU6 in response to lead exposure, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed. These analyses revealed significant lead adsorption and intracellular accumulation in treated bacteria in contrast to the control bacterium. Whole-genome sequencing was performed to gain deeper insights into E. kobei's lead resistance mechanisms. Structural annotation revealed a genome size of 4,856,454 bp, with a G + C content of 55.06%. The genome encodes 4,655 coding sequences (CDS), 75 tRNA genes, and 4 rRNA genes. Notably, genes associated with heavy metal resistance and their corresponding regulatory elements were identified within the genome. Furthermore, the expression levels of four specific heavy metal resistance genes were evaluated. Our findings revealed a statistically significant upregulation in gene expression under specific environmental conditions, including pH 7, temperature of 30°C, and high concentrations of heavy metals. The outstanding potential of E. kobei FACU6 as a source of diverse genes related to heavy metal resistance and plant growth promotion makes it a valuable candidate for developing safe and effective strategies for heavy metal disposal.

Designed bacteria based on natural pbr operons for detecting and detoxifying environmental lead: A mini-review

Lead (Pb), a naturally occurring element, is redistributed in the environment mainly due to anthropogenic activities. Pb pollution is a crucial public health problem worldwide due to its adverse effects. Environmental bacteria have evolved various protective mechanisms against high levels of Pb. The pbr operon, first identified in Cupriavidus metallidurans CH34, encodes a unique Pb(II) resistance mechanism involving transport, efflux, sequestration, biomineralization, and precipitation. Similar pbr operons are gradually found in diverse bacterial strains. This review focuses on the pbr-encoded Pb(II) resistance system. It summarizes various whole-cell biosensors harboring artificially designed pbr operons for Pb(II) biomonitoring with fluorescent, luminescent, and colorimetric signal output. Optimization of genetic circuits, employment of pigment-based reporters, and screening of host cells are promising in improving the sensitivity, selectivity, and response range of whole-cell biosensors. Engineered bacteria displaying Pb(II) binding and sequestration proteins, including PbrR and its derivatives, PbrR2 and PbrD, for adsorption are involved. Although synthetic bacteria show great potential in determining and removing Pb at the nanomolar level for environmental protection and food safety, some challenges must be addressed to meet demanding application requirements.

Bio-mediated detoxification of heavy metal contaminated soil and phytotoxicity reduction using novel strain of Brevundimonas vancanneytii SMA3

Heavy metals pose a serious environmental threat on a global scale due to their toxicity towards livings. Therefore, removing harmful metals from the environment has become more challenging in recent years. The objective of this study is to isolate, examine, and characterize naturally existing bacteria that possess the ability to mitigate and detoxify heavy metals such as cadmium, mercury, and lead. The selected bacteria SMA3 actively demonstrated metal tolerance during screening and was then employed for biosorption study using a lab-scale technique. The bacterium belonged to Brevundimonas sp., according to 16 S rRNA analysis. To enhance the removal efficiency of SMA3, response surface methodology (RSM) was employed, resulting in the identification of optimized conditions (pH 7, temperature 30 °C and shaking speed 120 rpm) for achieving maximum removal percentage (69.5 % of Cd, 58.6 % of Hg, and 85.1 % of Pb) within 72 h. The structural changes induced by microbial treatment were demonstrated by comparing the findings of FESEM images and FTIR spectra confirming the disappearance of C ^ C, C]O peaks along with C]O, C-O-C, C-H, and O-H bond destabilization following bioaccumulation. Moreover, in terms of phytotoxicity evaluation, it was observed that the treated soil, containing both heavy metals and the selected potent bacterial strain, exhibited reduced toxicity, resulting in improved germination and growth parameters for the seeds of Solanum lycopersicum (tomato plant). Overall, the selected bacterial strain demonstrated its potential for effectively removing multiple metals from the metal contaminated environment.

Comparative secretomic and proteomic analysis reveal multiple defensive strategies developed by Vibrio cholerae against the heavy metal (Cd2+, Ni2+, Pb2+, and Zn2+) stresses

Vibrio cholerae is a common waterborne pathogen that can cause pandemic cholera in humans. The bacterium with heavy metal-tolerant phenotypes is frequently isolated from aquatic products, however, its tolerance mechanisms remain unclear. In this study, we investigated for the first time the response of such V. cholerae isolates (n = 3) toward the heavy metal (Cd2+, Ni2+, Pb2+, and Zn2+) stresses by comparative secretomic and proteomic analyses. The results showed that sublethal concentrations of the Pb2+ (200 μg/mL), Cd2+ (12.5 μg/mL), and Zn2+ (50 μg/mL) stresses for 2 h significantly decreased the bacterial cell membrane fluidity, but increased cell surface hydrophobicity and inner membrane permeability, whereas the Ni2+ (50 μg/mL) stress increased cell membrane fluidity (p < 0.05). The comparative secretomic and proteomic analysis revealed differentially expressed extracellular and intracellular proteins involved in common metabolic pathways in the V. cholerae isolates to reduce cytotoxicity of the heavy metal stresses, such as biosorption, transportation and effluxing, extracellular sequestration, and intracellular antioxidative defense. Meanwhile, different defensive strategies were also found in the V. cholerae isolates to cope with different heavy metal damage. Remarkably, a number of putative virulence and resistance-associated proteins were produced and/or secreted by the V. cholerae isolates under the heavy metal stresses, suggesting an increased health risk in the aquatic products.

Microbial functionalities and immobilization of environmental lead: Biogeochemical and molecular mechanisms and implications for bioremediation

The increasing environmental and human health concerns about lead in the environment have stimulated scientists to search for microbial processes as innovative bioremediation strategies for a suite of different contaminated media. In this paper, we provide a compressive synthesis of existing research on microbial mediated biogeochemical processes that transform lead into recalcitrant precipitates of phosphate, sulfide, and carbonate, in a genetic, metabolic, and systematics context as they relate to application in both laboratory and field immobilization of environmental lead. Specifically, we focus on microbial functionalities of phosphate solubilization, sulfate reduction, and carbonate synthesis related to their respective mechanisms that immobilize lead through biomineralization and biosorption. The contributions of specific microbes, both single isolates or consortia, to actual or potential applications in environmental remediation are discussed. While many of the approaches are successful under carefully controlled laboratory conditions, field application requires optimization for a host of variables, including microbial competitiveness, soil physical and chemical parameters, metal concentrations, and co-contaminants. This review challenges the reader to consider bioremediation approaches that maximize microbial competitiveness, metabolism, and the associated molecular mechanisms for future engineering applications. Ultimately, we outline important research directions to bridge future scientific research activities with practical applications for bioremediation of lead and other toxic metals in environmental systems.

Bioremediation potential of consortium Pseudomonas Stutzeri LBR and Cupriavidus Metallidurans LBJ in soil polluted by lead

Pollution by lead (Pb) is an environmental and health threat due to the severity of its toxicity. Microbial bioremediation is an eco-friendly technique used to remediate contaminated soils. This present study was used to evaluate the effect of two bacterial strains isolated and identified from Bizerte lagoon: Cupriavidus metallidurans LBJ (C. metallidurans LBJ) and Pseudomonas stutzeri LBR (P. stutzeri LBR) on the rate of depollution of soil contaminated with Pb from Tunisia. To determine this effect, sterile and non-sterile soil was bioaugmented by P. stutzeri LBR and C. metallidurans LBJ strains individually and in a mixture for 25 days at 30°C. Results showed that the bioaugmentation of the non-sterile soil by the mixture of P. stutzeri LBR and C. metallidurans LBJ strains gave the best rate of reduction of Pb of 71.02%, compared to a rate of 58.07% and 46.47% respectively for bioaugmentation by the bacterial strains individually. In the case of the sterile soil, results showed that the reduction rate of lead was in the order of 66.96% in the case of the mixture of the two bacterial strains compared with 55.66% and 41.86% respectively for the addition of the two strains individually. These results are confirmed by analysis of the leachate from the sterile and non-sterile soil which showed an increase in the mobility and bioavailability of Pb in soil. These promising results offer another perspective for a soil bioremediation bioprocess applying bacterial bioremediation.

Effects of cadmium and copper mixtures on antibiotic resistance genes in rhizosphere soil

The evolvement and development of antibiotic resistance in microorganisms may be influenced by metals; however, it is still unclear how cadmium (Cd) and copper (Cu) combined affect the distribution and presence of antibiotic-resistance genes (ARGs) in rhizosphere soil. The aims of this research were to (1) compare the distribution patterns of bacterial communities and ARGs in response to the effects of Cd and Cu both separately and combined; (2) explore the possible mechanisms underlying the variation in soil bacterial communities and ARGs in addition to the combined effects of Cd, Cu, and various environmental variables (nutrients, pH, etc.); and (3) provide a reference for assessing the risks of metals (Cd and Cu) and ARGs. The findings showed that the multidrug resistance genes acrA and acrB and the transposon gene intI-1 were present in high relative abundance in bacterial communities. Cadmium and Cu had a substantial interaction effect on the abundance of acrA, whereas Cu had a notable main effect on the abundance of intI-1. According to the network analysis, the strong links between bacterial taxa and specific ARGs revealed that most ARGs were hosted by Proteobacteria, Actinobacteria, and Bacteroidetes. According to structural equation modeling, Cd had a larger effect on ARGs than Cu. Compared to previous analyses of ARGs, bacterial community diversity had little effect on ARGs in this study. Overall, the results may have important consequences for determining the possible hazard of soil metals and extend the understanding of how Cd and Cu co-select ARGs in rhizosphere soils.

Impact of lead (Pb2+) on the growth and biological activity of Serratia marcescens selected for wastewater treatment and identification of its zntR gene-a metal efflux regulator

Microorganisms isolated from contaminated areas play an important role in bioremediation processes. They promote heavy metal removal from the environment by adsorbing ions onto the cell wall surface, accumulating them inside the cells, or reducing, complexing, or precipitating these substances in the environment. Microorganism-based bioremediation processes can be highly efficient, low-cost and have low environmental impact. Thus, the present study aimed to select Pb²⁺-resistant bacteria and evaluate the growth rate, biological activity, and the presence of genes associated with metal resistance. Serratia marcescens CCMA 1010, that was previously isolated from coffee processing wastewater, was selected since was able to growth in Pb²⁺ concentrations of up to 4.0 mM. The growth rate and generation time did not differ from those of the control (without Pb²⁺), although biological activity decreased in the first hour of exposure to these ions and stabilized after this period. The presence of the zntR, zntA and pbrA genes was analysed, and only zntR was detected. The zntR gene encodes a protein responsible for regulating the production of ZntA, a transmembrane protein that facilitates Pb²⁺ extrusion out of the cell. S. marcescens CCMA 1010 demonstrated a potential for use as bioindicator that has potential to be used in bioremediation processes due to its resistance to high concentrations of Pb²⁺, ability to grow until 24 h of exposure, and possession of a gene that indicates the existence of mechanisms associated with resistance to lead (Pb²⁺).

Lead biosorption efficiency of Levilactobacillus brevis MZ384011 and Levilactobacillus brevis MW362779: A response surface based approach

Lead (Pb) is a substantial contaminant in the environment and a potent toxin for living organisms. Current study describes probiotic characteristics of Pb-biosorbing lactic acid bacteria (LAB), and response surface methodology (RSM) based optimization of physical conditions for maximum Pb biosorption. A total of 18 LAB, isolated from carnivore feces (n = 8) and human breast milk (n = 9), along with one reference strain Lactobacillus acidophilus ATCC4356 were included in the study. Pb biosorption was strain specific. Eight strains, demonstrating ≥ 70 % lead biosorption, were selected for further testing. The lactobacillus-Pb complex was found to be stable and strains had a negative surface charge. The strains displayed good probiotic properties with the survival rate of 71-90 % in simulated gastric environment, 36-69 % in intestinal condition (1.8 % bile salts) and 55-72 % hydrophobicity. On the basis of excellent probiotic ability, Levilactobacillus brevis MZ384011 and Levilactobacillus brevis MW362779 were selected for optimization of physical conditions of Pb biosorption through RSM. Maximum biosorption was observed at pH 6 in 60 min at a cell density of 1 g/L. L. brevis MZ384011 and L. brevis MW362779 are recommended for experimentation on Pb toxicity amelioration and safety evaluation in in-vivo setting.

A comprehensive review on bio-stimulation and bio-enhancement towards remediation of heavy metals degeneration

Pollution of heavy metals is one of the risky contaminations that should be managed for all intents and purposes of general well-being concerns. The bioaccumulation of these heavy metals inside our bodies and pecking orders will influence our people in the future. Bioremediation is a bio-mechanism where residing organic entities use and reuse the squanders that are reused to one more form. This could be accomplished by taking advantage of the property of explicit biomolecules or biomass that is equipped for restricting by concentrating the necessary heavy metal particles. The microorganisms can't obliterate the metal yet can change it into a less harmful substance. In this unique circumstance, this review talks about the sources, poisonousness, impacts, and bioremediation strategies of five heavy metals: lead, mercury, arsenic, chromium, and manganese. The concentrations here are the ordinary strategies for bioremediation such as biosorption methods, the use of microbes, green growth, and organisms, etc. This review demonstrates the toxicity of heavy metal contamination degradation by biotransformation through bacterioremediation and biodegradation through mycoremediation.

Bacillus megaterium HgT21: a Promising Metal Multiresistant Plant Growth-Promoting Bacteria for Soil Biorestoration

The environmental deterioration produced by heavy metals derived from anthropogenic activities has gradually increased. The worldwide dissemination of toxic metals in crop soils represents a threat for sustainability and biosafety in agriculture and requires strategies for the recovery of metal-polluted crop soils. The biorestoration of metal-polluted soils using technologies that combine plants and microorganisms has gained attention in recent decades due to the beneficial and synergistic effects produced by its biotic interactions. In this context, native and heavy metal-resistant plant growth-promoting bacteria (PGPB) play a crucial role in the development of strategies for sustainable biorestoration of metal-contaminated soils. In this study, we present a genomic analysis and characterization of the rhizospheric bacterium Bacillus megaterium HgT21 isolated from metal-polluted soil from Zacatecas, Mexico. The results reveal that this autochthonous bacterium contains an important set of genes related to a variety of operons associated with mercury, arsenic, copper, cobalt, cadmium, zinc and aluminum resistance. Additionally, halotolerance-, beta-lactam resistance-, phosphate solubilization-, and plant growth-promotion-related genes were identified. The analysis of resistance to metal ions revealed resistance to mercury (HgII+), arsenate [AsO4]³-, cobalt (Co2+), zinc (Zn2+), and copper (Cu2+). Moreover, the ability of the HgT21 strain to produce indole acetic acid (a phytohormone) and promote the growth of Arabidopsis thaliana seedlings in vitro was also demonstrated. The genotype and phenotype of Bacillus megaterium HgT21 reveal its potential to be used as a model of both plant growth-promoting and metal multiresistant bacteria. IMPORTANCE Metal-polluted environments are natural sources of a wide variety of PGPB adapted to cope with toxic metal concentrations. In this work, the bacterial strain Bacillus megaterium HgT21 was isolated from metal-contaminated soil and is proposed as a model for the study of metal multiresistance in spore-forming Gram-positive bacteria due to the presence of a variety of metal resistance-associated genes similar to those encountered in the metal multiresistant Gram-negative Cupriavidus metallidurans CH34. The ability of B. megaterium HgT21 to promote the growth of plants also makes it suitable for the study of plant-bacteria interactions in metal-polluted environments, which is key for the development of techniques for the biorestoration of metal-contaminated soils used for agriculture.

Synthetic biology techniques to tackle heavy metal pollution and poisoning

The requirement for natural resources and energy increases continually with the increase in population. An inevitable result of this is soil, water, and air pollution with diverse pollutants, including heavy metals. Synthetic Biology involves using modular, interchangeable biological parts, devices in standard chassis or whole organisms to achieve a programmed result that can be quantified and optimized till it meets the required efficiency. This makes synthetic biology techniques very popular to tackle pressing global issues such as heavy metal poisoning. This review aimed to highlight various advancements as well as benefits, risks, and problems in synthetic biology techniques for detection, bioaccumulation, and biosorption of various heavy metals using engineered organisms. We found that while such an approach is cost-effective, accessible, and efficient, there are several inherent technological and ethical issues including but not limited to metabolic burden and consequences of use of genetically modified organisms respectively. Overcoming these hurdles will probably take time and innumerable conversations, and should be done through education and a culture of responsible research, rather than enforcing restrictions on the development of synthetic biology.

Effect of the phosphate solubilization and mineralization synergistic mechanism of Ochrobactrum sp. on the remediation of lead

Phosphate-solubilizing bacteria (PSB) promotes the formation of mineralized precipitation through phosphorous dissolution and mineralization, forming stable lead (Pb(II)) minerals and reducing the migration of Pb(II) in the environment. In this study, a Pb-tolerant strain Ochrobactrum sp. J023 from a contaminated soil around a battery factory in Jiangsu Province, China, was screened for experiments to investigate the phosphate solubilization and mineralization mechanism of this strain. The organic acids and the acid phosphatase produced by the bacteria have a synergistic effect on phosphate dissolution. When the pH of the culture medium decreased to the lowest 4.55, the amount of soluble phosphate and the activity of acid phosphatase reached the maximum 161.29 mg L^-1 and 61.98 U mL^-1, and there was a significant correlation between the concentration of soluble phosphate and the activity of acid phosphatase (R = 0.832**, P < 0.05). It was found that acetic acid played the most important role in the secreted organic acids. During the mineralization reaction, the extracellular polymeric substances (EPS) chelates part of the Pb(II) on the surface of the cell wall, preventing the metal Pb from penetrating into the cell, thus providing protection to the strain. Meanwhile, due to the nucleation sites provided by cell surface groups (carboxyl and phosphate groups), a large number of metal ions are absorbed to promote the formation of crystallization. The final mineralized product of Pb(II) by strain J023 was pyroxite (Pb₅(PO₄)₃X, where X = Cl, OH). The mechanism of phosphate dissolution and mineralization proposed by us is that the organic acids and acid phosphatases secreted by phosphate-solubilizing bacteria promote the increase of PO₄^3- concentration in the solution, the complexation of metal cations and cell surface groups will induce the formation of mineralized precipitation under the catalysis of enzyme. Therefore, it is a promising strategy for bioremediation of lead pollution by screening functional strains with strong abilities of phosphate solubility and mineralization.

Genome sequencing of biocontrol strain Bacillus amyloliquefaciens Bam1 and further analysis of its heavy metal resistance mechanism

Plant growth-promoting rhizobacteria (PGPR) or Biocontrol strains inevitably encounter heavy metal excess stress during the product's processing and application. Bacillus amyloliquefaciens Bam1 was a potential biocontrol strain with strong heavy metal resistant ability. To understand its heavy metal resistance mechanism, the complete genome of Bam1 had been sequenced, and the comparative genomic analysis of Bam1 and FZB42, an industrialized PGPR and biocontrol strain with relatively lower heavy metal tolerance, was conducted. The comparative genomic analysis of Bam1 and the other nine B. amyloliquefaciens strains as well as one Bacillus velezensis (genetically and physiologically very close to B. amyloliquefaciens) was also performed. Our results showed that the complete genome size of Bam1 was 3.95 Mb, 4219 coding sequences were predicted, and it possessed the highest number of unique genes among the eleven analyzed strains. Nine genes related to heavy metal resistance were detected within the twelve DNA islands of Bam1, while only two of them were detected within the seventeen DNA islands of FZB42. When compared with B. amyloliquefaciens type strain DSM7, Bam1 lacked contig L, whereas FZB42 lacked contig D and I, as well as just possessed contig B with a very small size. Our results could also deduce that Bam1 promoted its essential heavy metal resistance mainly by decreasing the import and increasing the export of heavy metals with the corresponding homeostasis systems, which are regulated by different metalloregulators. While Bam1 promoted its non-essential heavy metal resistance mainly by the activation of some specific or non-specific exporters responding to different heavy metals. The variation of the genes related to heavy metal resistance and the other differences of the genomes, including the different number and arrangement of contigs, as well as the number of the heavy metal resistant genes in Prophages and Genomic islands, led to the significant different resistance of Bam1 and FZB42 to heavy metals.

Engineering whole-cell microbial biosensors: Design principles and applications in monitoring and treatment of heavy metals and organic pollutants

Biosensors have been widely used as cost-effective, rapid, in situ, and real-time analytical tools for monitoring environments. The development of synthetic biology has enabled emergence of genetically engineered whole-cell microbial biosensors. This review updates the design and optimization principles for a diverse array of whole-cell biosensors based on transcription factors (TF) including activators or repressors derived from heavy metal resistance systems, alkanes, and aromatics metabolic pathways of bacteria. By designing genetic circuits, the whole-cell biosensors could be engineered to intelligently sense heavy metals (Hg²⁺, Zn²⁺, Pb²⁺, Au³⁺, Cd²⁺, As³⁺, Ni²⁺, Cu²⁺, and UO₂²⁺) or organic compounds (alcohols, alkanes, phenols, and benzenes) through one-component or two-component system-based TFs, transduce signals through genetic amplifiers, and response as various outputs such as cell fluorescence and bioelectricity for monitoring heavy metals and organic pollutants in real conditions, synthetic curli and surface metal-binding peptides for in situ bio-sorption of heavy metals. We further review strategies that have been implemented to optimize the selectivity and correlation between ligand concentration and output signal of the TF-based biosensors, so as to meet requirements of practical applications. The optimization strategies include protein engineering to change specificities, promoter engineering to improve sensitivities, and genetic circuit-based amplification to enhance dynamic ranges via designing transcriptional amplifiers, logic gates, and feedback loops. At last, we outlook future trends in developing novel forms of biosensors.

An insight into the mechanisms of homeostasis in extremophiles

The homeostasis of extremophiles is one that is a diamond hidden in the rough. The way extremophiles adapt to their extreme environments gives a clue into the true extent of what is possible when it comes to life. The discovery of new extremophiles is ever-expanding and an explosion of knowledge surrounding their successful existence in extreme environments is obviously perceived in scientific literature. The present review paper aims to provide a comprehensive view on the different mechanisms governing the extreme adaptations of extremophiles, along with insights and discussions on what the limits of life can possibly be. The membrane adaptations that are vital for survival are discussed in detail. It was found that there are many alterations in the genetic makeup of such extremophiles when compared to their mesophilic counterparts. Apart from the several proteins involved, the significance of chaperones, efflux systems, DNA repair proteins and a host of other enzymes that adapt to maintain functionality, are enlisted, and explained. A deeper understanding of the underlying mechanisms could have a plethora of applications in the industry. There are cases when certain microbes can withstand extreme doses of antibiotics. Such microbes accumulate numerous genetic elements (or plasmids) that possess genes for multiple drug resistance (MDR). A deeper understanding of such mechanisms helps in the development of potential approaches and therapeutic schemes for treating pathogen-mediated outbreaks. An in-depth analysis of the parameters - radiation, pressure, temperature, pH value and metal resistance - are discussed in this review, and the key to survival in these precarious niches is described.

Urinary lead level and colonization by antibiotic resistant bacteria: Evidence from a population-based study

BACKGROUND

Infection by antibiotic resistant bacteria (ARB) is a global health crisis and asymptomatic colonization increases risk of infection. Nonhuman studies have linked heavy metal exposure to the selection of ARB; however, few epidemiologic studies have examined this relationship. This study analyzes the association between urinary lead level and colonization by ARB in a nonclinical human population.

METHODS

Data came from the Survey of the Health of Wisconsin 2016-2017, and its ancillary Wisconsin Microbiome Study. Urinary lead levels, adjusted for creatinine, were used to assess exposure. ARB included methicillin resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), fluoroquinolone resistant Gram-negative bacilli (RGNB), and Clostridium difficile (C. diff), from skin, nose, and mouth swabs, and saliva and stool samples. Logistic regression, adjusted for covariates, was used to evaluate associations between Pb and ARB. Secondary analysis investigated Pb resistance from ARB isolates.

RESULTS

Among 695 participants, 239 (34%) tested positive for ARB. Geometric mean urinary Pb (unadjusted) was 0.286 µg/L (95% confidence intervals [CI] = 0.263, 0.312) for ARB negative participants and 0.323 µg/L (95% CI = 0.287, 0.363) for ARB positive participants. Models adjusted for demographics, diet, and antibiotic use showed elevated odds of positive colonization for those in the 95th percentile (vs. below) of Pb exposure (odds ratio [OR] = 2.05, 95% CI = 0.95, 4.44), and associations were highest in urban residents (OR = 2.85, 95% CI = 1.07, 7.59). RGNB isolates were most resistant to Pb.

DISCUSSION

These novel results suggest that Pb exposure is associated with increased colonization by ARB, and that RGNB are particularly resistant to Pb.

Development and optimization of heavy metal lead biosensors in biomedical and environmental applications

The detrimental impact of the heavy metal lead (Pb) on human health has been studied for years. The fact that Pb impairs human body has been established from countless painful and sad historical events. Nowadays, World Health Organization and many developmental countries have established regulations concerning the use of Pb. Measuring the blood lead level (BLL) is so far the only way to officially evaluate the degree of Pb exposure, but the so-called safety value (10 μg/dL in adults and 5 μg/dL in children) seems unreliable to represent the security checkpoint for children through daily intake of drinking water or physical contact with a lower contaminated level of Pb contents. In general, unsolved mysteries about the Pb toxicological mechanisms still remain. In this review article, we report on the methods to prevent Pb poison for further Pb toxicological research. We establish high-sensitivity Pb monitoring, and also report on the use of fluorescent biosensors such as genetically-encoded fluorescence resonance energy transfer-based biosensors built for various large demands such as the detection of severe acute respiratory syndrome coronavirus 2. We also contribute to the development and optimization of the FRET-based Pb biosensors. Our well-performed version of Met-lead 1.44 M1 has achieved a limit of detection of 10 nM (2 ppb; 0.2 μg/dL) and almost 5-fold in dynamic range (DR) supported for the real practical applications-that is, the in-cell Pb sensing device for blood and blood-related samples, and the Pb environmental detections in vitro. The perspective of our powerful Pb biosensor incorporated with a highly sensitive bio-chip of the portable device for quick Pb measurements will be addressed for further manipulation.

Bioavailability of arsenic, cadmium, lead and mercury as measured by intestinal permeability

In this study, the intestinal permeability of metal(loid)s (MLs) such as arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg) was examined, as influenced by gut microbes and chelating agents using an in vitro gastrointestinal/Caco-2 cell intestinal epithelium model. The results showed that in the presence of gut microbes or chelating agents, there was a significant decrease in the permeability of MLs (As-7.5%, Cd-6.3%, Pb-7.9% and Hg-8.2%) as measured by apparent permeability coefficient value (Papp), with differences in ML retention and complexation amongst the chelants and the gut microbes. The decrease in ML permeability varied amongst the MLs. Chelating agents reduce intestinal absorption of MLs by forming complexes thereby making them less permeable. In the case of gut bacteria, the decrease in the intestinal permeability of MLs may be associated to a direct protection of the intestinal barrier against the MLs or indirect intestinal ML sequestration by the gut bacteria through adsorption on bacterial surface. Thus, both gut microbes and chelating agents can be used to decrease the intestinal permeability of MLs, thereby mitigating their toxicity.

Lead Drives Complex Dynamics of a Conjugative Plasmid in a Bacterial Community

Plasmids carrying metal resistance genes (MRGs) have been suggested to be key ecological players in the adaptation of metal-impacted microbial communities, making them promising drivers of bio-remediation processes. However, the impact of metals on plasmid-mediated spread of MRGs through selection, plasmid loss, and transfer is far from being fully understood. In the present study, we used two-member bacterial communities to test the impact of lead on the dispersal of the IncP plasmid pKJK5 from a Pseudomonas putida KT2440 plasmid donor and two distinct recipients, Variovorax paradoxus B4 or Delftia acidovorans SPH-1 after 4 and 10 days of mating. Two versions of the plasmid were used, carrying or not carrying the lead resistance pbrTRABCD operon, to assess the importance of fitness benefit and conjugative potential for the dispersal of the plasmid. The spread dynamics of metal resistance conveyed by the conjugative plasmid were dependent on the recipient and the lead concentration: For V. paradoxus, the pbr operon did not facilitate neither lead resistance nor variation in plasmid spread. The growth gain brought by the pbr operon to D. acidovorans SPH-1 and P. putida KT2440 at 1 mM Pb enhanced the spread of the plasmid. At 1.5 mM Pb after 4 days, the proteomics results revealed an oxidative stress response and an increased abundance of pKJK5-encoded conjugation and partitioning proteins, which most likely increased the transfer of the control plasmid to D. acidovorans SPH-1 and ensured plasmid maintenance. As a consequence, we observed an increased spread of pKJK5-gfp. Conversely, the pbr operon reduced the oxidative stress response and impeded the rise of conjugation- and partitioning-associated proteins, which slowed down the spread of the pbr carrying plasmid. Ultimately, when a fitness gain was recorded in the recipient strain, the spread of MRG-carrying plasmids was facilitated through positive selection at an intermediate metal concentration, while a high lead concentration induced oxidative stress with positive impacts on proteins encoding plasmid conjugation and partitioning.

Chromium pollution and its bioremediation mechanisms in bacteria: A review

Environment pollution is at its peak and is creating havoc for living beings. Industrial wastes containing toxic pollutants have contributed to a great extent in this disastrous environment pollution. Chromium (Cr³⁺/Cr⁶⁺) is highly toxic and one of the most common environmental pollutants because of its extensive use in industries especially tanneries. Lack of efficient treatment methods has resulted in extensive chromium pollution. Bioremediation of chromium using bacteria is very thoughtful due to its eco-friendly and cost-effective outcome. Bacteria possess numerous mechanisms such as biosorption, reduction, efflux or bioaccumulation, naturally or acquired to counter the toxicity of chromium. This review focuses on the bacterial responses against chromium toxicity and scope for their application in bioremediation. The differences and similarities between Gram negative and positive bacteria against chromium are also highlighted. Further, the knowledge gap and future prospects are also discussed in order to fill these gaps and overcome the problem associated with real-time applicability of bacterial bioremediation.

Gut microbes modulate bioaccessibility of lead in soil

Metabolic uptake of lead (Pb) is controlled by its bioaccessibility. Most studies have examined bioaccessibility of Pb in the absence of gut microbes, which play an important role in the metabolic uptake of nutrients and metal(loid)s in intestine. In this study, we examined the effect of three gut microbes, from various locations in the gut, on the bioaccessibility of soil ingested Pb. The gut microbes include Lactobacillus acidophilus, Lactobacillus rhamnosus and Escherichia coli. Lead toxicity to these three microbes was also examined at various pH values. Bioaccessibility of Pb was measured using gastric and intestinal extractions. Both Pb spiked and Pb-contaminated shooting range field soils were used to measure Pb bioaccessibility in the presence and absence of gut microbes. The results indicated that Pb toxicity to gut microbes, as measured by LD₅₀ value, decreased with increasing pH, and was higher for Lactobacillus species. Gut microbes decreased the bioaccessible Pb; the effect was more pronounced at low pH, mimicking gastric conditions than in conditions closer to the intestine. Lead adsorption by these microbes increased at the higher pH tested, and E. coli adsorbed higher amounts of Pb than did the Lactobacillus species. The effect of gut microbes on reducing Pb bioaccessibility may be attributed to microbially-induced immobilization of Pb through adsorption, precipitation, and complexation reactions. The study demonstrates that bioaccessibility and subsequently bioavailability of metal(loid)s can be modulated by gut microbes, and it is important to undertake bioaccessibility measurements in the presence of gut microbes.

Effects of Land Use and Pollution Loadings on Ecotoxicological Assays and Bacterial Taxonomical Diversity in Constructed Wetlands

Freshwater ecosystems are affected by anthropogenic alterations. Different studies have extensively studied the concentrations of metals, nutrients, and water quality as measurements of pollution in freshwater ecosystems. However, few studies have been able to link these pollutants to bioindicators as a risk assessment tool. This study aimed to examine the potential of two bioindicators, plant ecotoxicological assays and sediment bacterial taxonomic diversity, in ecological risk assessment for six freshwater constructed wetlands in a rapidly urbanizing watershed with diverse land uses. Sediment samples were collected summer, 2015 and 2017, and late summer and early fall in 2016 to conduct plant ecotoxicological assays based on plant (Lepidium, Sinapis and Sorghum) growth inhibition and identify bacterial taxonomical diversity by the 16S rRNA gene sequences. Concentrations of metals such as lead (Pb) and mercury (Hg) (using XRF), and nutrients such as nitrate and phosphate (using HACH DR 2800TM spectrophotometer) were measured in sediment and water samples respectively. Analyses of response patterns revealed that plant and bacterial bioindicators were highly responsive to variation in the concentrations of these pollutants. Hence, this opens up the scope of using these bioindicators for ecological risk assessment in constructed freshwater wetland ecosystems within urbanizing watersheds.

Characterization of a Bacillus megaterium strain with metal bioremediation potential and in silico discovery of novel cadmium binding motifs in the regulator, CadC

Bioremediation of toxic metal ions using bacterial strains is a promising tool. Metal binding motifs in microbial proteins are involved in the regulation and transport of such toxic metals for metal detoxification. A bacterial strain designated TWSL_4 with metal (Cu, Cd, and Pb) resistance and removal ability was isolated and identified as a Bacillus megaterium strain using 16S rRNA gene analysis. An operon with 2 open reading frames (ORFs) was identified, cloned, and sequenced. ORF1 and ORF2 were identical to the cadmium efflux system accessory protein (CadC) and cadmium-translocating P-type ATPases (CadA) of B. megaterium strain YC4-R4 respectively. A protein homology search using Swiss model retrieved no crystal structures for CadC and CadA of Bacillus sp.. CadC of TWSL_4 had a sequence identity of 53% to the CadC (121aa) protein and 51.69% to the CadC crystal structure (1U2W.1.B; GMQE=0.75) of Staphylococcus sp. pI258. Molecular dynamic simulation studies revealed the presence of three metal binding regions in CadC of TWSL_4, [ASP7-TYR9], [ASP100-HIS102], and [LYS113-ASP116]. This is the first report showing evidence for the presence of Cd²⁺ and Zn²⁺ metal binding motifs in the CadC regulator of the Bacillus megaterium cad operon. The bacterial strain TWSL_4 was also found to contain two different P type ATPases encoding genes, cadA and zosA involved in metal resistance. Furthermore, the metal bioremediation potential of strain TWSL_4 was confirmed using an industrial effluent. KEY POINTS: • Isolation of a metal-resistant bacterial strain with potential for industrial bioremediation. • Discovery of novel Cd binding sites in CadC of the cad operon from B. megaterium. • Involvement of aspartic acid in the coordination of metal ions (Cd²⁺).

Lead accumulation in photosynthetic Euglena gracilis depends on polyphosphates and calcium

Worldwide increasing levels of lead in water systems require the search for efficient ecologically friendly strategies to remove it. Hence, lead accumulation by the free-living algae-like Euglena gracilis and its effects on cellular growth, respiration, photosynthesis, chlorophyll, calcium, and levels of thiol- and phosphate-molecules were analyzed. Photosynthetic cells were able to accumulate 4627 mg lead/kg_DW after 5 days of culture with 200 μM Pb²⁺. Nevertheless, exposure to 50, 100 and 200 μM Pb²⁺ for up to 8 days did not modify growth, viability, chlorophyll content and oxygen consumption/production. Enhanced biosynthesis of thiol molecules and polyphosphates, i.e. the two canonical metal ion chelation mechanisms in E. gracilis, was not induced under such conditions. However, in cells cultured in the absence of phosphate, lead accumulation and polyphosphate content markedly decreased, while culturing in the absence of sulfate did not modify the accumulation of this metal. In turn, the total amount of intracellular calcium slightly increased as the amount of intracellular lead increased, whereas under Ca²⁺ deficiency lead accumulation doubled. Therefore, the results indicated that E. gracilis is highly resistant to lead through mechanisms mediated by polyphosphates and Ca²⁺ and can in fact be classified as a lead hyperaccumulator microorganism.

Bacterial tolerance strategies against lead toxicity and their relevance in bioremediation application

Among heavy metals, lead (Pb) is a non-essential metal having a higher toxicity and without any crucial known biological functions. Being widespread, non-biodegradable and persistent in every sphere of soil, air and water, Pb is responsible for severe health and environmental issues, which need appropriate remediation measures. However, microbes inhabiting Pb-contaminated area are found to have evolved distinctive mechanisms to successfully thrive in the Pb-contaminated environment without exhibiting any negative effects on their growth and metabolism. The defensive strategies used by bacteria to ameliorate the toxic effects of lead comprise biosorption, efflux, production of metal chelators like siderophores and metallothioneins and synthesis of exopolysaccharides, extracellular sequestration and intracellular bioaccumulation. Lead remediation technologies by employing microbes may appear as potential advantageous alternatives to the conventional physical and chemical means due to specificity, suitability for applying in situ condition and feasibility to upgrade by genetic engineering. Developing strategies by designing transgenic bacterial strain having specific metal binding properties and metal chelating proteins or higher metal adsorption ability and using bacterial activity such as incorporating plant growth-promoting rhizobacteria for improved Pb resistance, exopolysaccharide and siderophores and metallothionein-mediated immobilization may prove highly effective for formulating bioremediation vis-a-vis phytoremediation strategies.

Lead bioaccumulation mediated by Bacillus cereus BPS-9 from an industrial waste contaminated site encoding heavy metal resistant genes and their transporters

This study explores the soil microorganisms for their Lead bioremediation capability. The MIC values of the six Lead resistant bacteria were evaluated, and the AAS studies of these isolates estimated their Lead accumulation percentage. The results showed that the isolate namely Bacillus cereus BPS-9 as identified based on 16S rDNA gene sequences was shown to have the highest Lead accumulation potential (79.26 %) and also selected for bioaccumulation studies. Despite the reduction in growth rate, the superoxide dismutase activity of B. cereus BPS-9 was increased with a rise in the concentration of Lead manifested through increased nitro-blue tetrazolium (NBT) reduction from 3.94 % to 77.48 %. Moreover, the biosorption capacity of B. cereus BPS-9 was 193.93 mg/g and the Langmuir isotherm model showed a value of R² = 0.9. Furthermore, the FTIR analysis also established the role of C-H, C=C, N=N, N-H, and C-O functional groups in Lead adsorption and the SEM micrographs showed that the cells of B. cereus BPS-9 became dense, adhered and distorted after Lead adsorption. Finally, the In-silico results obtained by functional analysis through SEED viewer of the whole genome of B. cereus deciphered the presence of genes encoding heavy metal resistant proteins and transporters for the efflux of heavy metals.

Long-term continuous and real-time in situ monitoring of Pb(II) toxic contaminants in wastewater using solid-state ion selective membrane (S-ISM) Pb and pH auto-correction assembly

Lead (Pb) contaminants in wastewater have inhibited microbial activities and thus exerted high energy consumption in wastewater treatment plants (WWTPs). Current Pb monitoring has been conducted ex situ and off line, unable to affect real-time proactive control and operation. This study targets the crucial challenge of better and faster Pb monitoring by developing novel mm-sized screen-printed solid-state ion-selective membrane (S-ISM) Pb sensors with low-cost, high accuracy and long-term durability and that enable real-time in situ monitoring of Pb(II) ion contamination down to low concentrations (15 ppb-960 ppb) in wastewater. An innovative pH auto-correction data-driven model was built to overcome the inextricable pH inferences on Pb(II) ISM sensors in wastewater. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) analysis showed (3,4-ethylenedioxythiophene, EDOT) deposited onto the mm-sized screen-printed carbon electrodes using electropolymerization effectively alleviated the interferences from dissolved oxygen and improved long-term stability in wastewater. Monte Carlo simulation of the nitrification process predicted that real-time, and high accurate in situ monitoring of Pb(II) in wastewater and swift feedback control could save ∼53 % of energy consumption by alleviating the errors from pH and DO impacts in WWTPs.

Metal-induced bacterial interactions promote diversity in river-sediment microbiomes

Anthropogenic metal contamination results in long-term environmental selective pressure with unclear impacts on bacterial communities, which comprise key players in ecosystem functioning. Since metal contamination poses serious toxicity and bioaccumulation issues, assessing their impact on environmental microbiomes is important to respond to current environmental and health issues. Despite elevated metal concentrations, the river sedimentary microbiome near the MetalEurop foundry (France) shows unexpected higher diversity compared with the upstream control site. In this work, a follow-up of the microbial community assembly during a metal contamination event was performed in microcosms with periodic renewal of the supernatant river water. Sediments of the control site were gradually exposed to a mixture of metals (Cd, Cu, Pb and Zn) in order to reach similar concentrations to MetalEurop sediments. Illumina sequencing of 16S rRNA gene amplicons was performed. Metal-resistant genes, czcA and pbrA, as well as IncP plasmid content, were assessed by quantitative PCR. The outcomes of this study support previous in situ observations showing that metals act as community assembly managers, increasing diversity. This work revealed progressive adaptation of the sediment microbiome through the selection of different metal-resistant mechanisms and cross-species interactions involving public good-providing bacteria co-occurring with the rest of the community.

Fetal and early postnatal lead exposure measured in teeth associates with infant gut microbiota

BACKGROUND

Lead (Pb) is an environmentally ubiquitous heavy metal associated with a wide range of adverse health effects in children. Both lead exposure and the early life microbiome- which plays a critical role in human development-have been linked to similar health outcomes, but it is unclear if the adverse effects of lead are partially driven by early life gut microbiota dysbiosis. The objective of this study was to examine the association between in utero and postnatal lead levels (measured in deciduous baby teeth) and early life bacterial and fungal gut microbiota in the first year of life.

METHODS

Data from the Wayne County Health, Environment, Allergy and Asthma Longitudinal Study (WHEALS) birth cohort were analyzed. Tooth lead levels during the 2nd and 3rd trimesters and postnatally (<1 year of age) were quantified using high-resolution microspatial mapping of dentin growth rings. Early life microbiota were measured in stool samples collected at approximately 1 and 6 months of age, using both 16S rRNA (bacterial) and ITS2 (fungal) sequencing. Of the 1,258 maternal-child pairs in WHEALS, 146 had data on both tooth metals and early life microbiome.

RESULTS

In utero tooth lead levels were significantly associated with gut fungal community composition at 1-month of age, where higher levels of 2nd trimester tooth lead was associated with lower abundances of Candida and Aspergillus and higher abundances of Malassezia and Saccharomyces; 3rd trimester lead was also associated with lower abundances of Candida. Though lead did not significantly associate with the overall structure of the infant gut bacterial community, it associated with the abundance of some specific bacterial taxa, including the increased abundance of Collinsella and Bilophila and a decreased abundance of Bacteroides taxa.

CONCLUSIONS

The observed associations between lead exposure and infant gut microbiota could play a role in the impact of lead on childhood development. Given the paucity of research examining these associations in humans-particularly for fungal microbiota-further investigation is needed.

Potential application of Pseudomonas stutzeri W228 for removal of copper and lead from marine environments

High concentrations of metals in the environment alter bacterial diversity, selecting resistant and tolerant species. The study evaluated the selection of a potential bacterial strain from Sepetiba Bay-Rio de Janeiro, Brazil marine sediments to remove Cu and Pb. The bacterial strain isolated from the sediments was used in three different bioassays: (1) Cu at concentrations of 0 (control), 6 and 50 μg.mL^-1; (2) Pb at concentrations of 0 (control), 6 and 50 μg.mL^-1; (3) Cu + Pb in concentrations of 3 μg.mL^-1 Cu + 3 μg.mL^-1 Pb (6 μg.mL^-1) and 25 μg.mL^-1 Cu + 25 μg.mL^-1 Pb (50 μg.mL^-1). The number of cells and the enzymatic activities of dehydrogenases and esterases were quantified. Results of taxonomic identification indicated the selection of the Pseudomonas stutzeri W228 strain, showing a greater degree of similarity (±73%) with the database used. There was no significant variation in the number of cells, 10⁸ cells.mL^-1, which represents a high biomass production in the presence of stressors. However, we observed a reduction in dehydrogenase activity at all tested concentrations of Cu, Pb and Cu + Pb. The activity of esterase increased, indicating a higher energy demand to complete the bacterial life cycle. The study showed significant results for the absorption of Pb by the extracellular polymeric substances (EPS) and the efflux of Cu. The capacity of Pb absorption by EPS can be considered a resistance mechanism, as well as the efflux of Cu, so that the available EPS sites could be occupied by the most toxic ions demonstrating that Pseudomonas stutzeri is resistant to Pb and Cu.

Staphylococcus aureus lacking a functional MntABC manganese import system has increased resistance to copper

S. aureus USA300 isolates utilize the copBL and copAZ gene products to prevent Cu intoxication. We created and examined a ΔcopAZ ΔcopBL mutant strain (cop-). The cop- strain was sensitive to Cu and accumulated intracellular Cu. We screened a transposon (Tn) mutant library in the cop- background and isolated strains with Tn insertions in the mntABC operon that permitted growth in the presence of Cu. The mutations were in mntA and they were recessive. Under the growth conditions utilized, MntABC functioned in manganese (Mn) import. When cultured with Cu, strains containing a mntA::Tn accumulated less Cu than the parent strain. Mn(II) supplementation improved growth when cop- was cultured with Cu and this phenotype was dependent upon the presence of MntR, which is a repressor of mntABC transcription. A ΔmntR strain had an increased Cu load and decreased growth in the presence of Cu, which was abrogated by the introduction of mntA::Tn. Over-expression of mntABC increased cellular Cu load and sensitivity to Cu. The presence of a mntA::Tn mutation protected iron-sulfur (FeS) enzymes from inactivation by Cu. The data presented are consistent with a model wherein defective MntABC results in decreased cellular Cu accumulation and protection to FeS enzymes from Cu poisoning.

Discrimination of heavy metal acclimated environmental strains by chemometric analysis of FTIR spectra

Heavy metal acclimated bacteria are profoundly the preferred choice for bioremediation studies. Bacteria get acclimated to toxic concentrations of heavy metals by induction of specific enzymes and genetic selection favoring new metabolic abilities leading to activation of one or several of resistance mechanisms creating bacterial populations with differences in resistance profile and/or level. Therefore, to use in bioremediation processes, it is important to discriminate acclimated bacterial populations and choose a more resistant strain. In this study, we discriminated heavy metal acclimated bacteria by using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and multivariate analysis methods namely Hierarchical Cluster Analysis (HCA), Principal Component Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA). Two acclimation methods, acute and gradual, were used which cause differences in molecular changes resulting in bacterial populations with different molecular and resistance profiles. Brevundimonas sp., Gordonia sp., and Microbacterium oxydans were exposed to the toxic concentrations of Cd (30 μg/ml) or Pb (90 μg/ml) by using broth medium as a growth media. Our results revealed that PCA and HCA clearly discriminated the acute-acclimated, gradual-acclimated, and control bacteria from each other in protein, carbohydrate, and whole spectral regions. Furthermore, we classified acclimated (acute and gradual) and control bacteria more accurately by using SIMCA with 99.9% confidence. This study demonstrated that heavy metal acclimated and control group bacteria can be discriminated by using chemometric analysis of FTIR spectra in a powerful, cost-effective, and handy way. In addition to the determination of the most appropriate acclimation procedure, this approach can be used in the detection of the most resistant bacterial strains to be used in bioremediation studies.

MALDI-TOF-MS and 16S rRNA characterization of lead tolerant metallophile bacteria isolated from saffron soils of Kashmir for their sequestration potential

Toxic metal contamination in soils due industrialization is nowadays a concern to the scientists worldwide. The current study deals with the evaluation of response and tolerance by isolated metallophilic bacteria in different lead concentrations (100 ppm to 1000 ppm). By taking optical densities of the isolates, the minimum inhibitory concentration (MIC) of Pb²⁺ were determined.16S rRNA and MALDI-TOF MS were used for the identification of the bacteria. Total of 37 isolates were observed, among them 04 (Staphylococcus equorum, Staphylococcus warneri, Bacillus safensis and Bacillus thuringiensis), isolated were detected having efficacy of Pb²⁺tolerance and sequestration at varying MIC. Furthermore, B. thuringiensis was observed to have highest (900 ppm) tolerance for lead and lowest (500 ppm) for Staphylococcus warneri. Moreover, the highest (65.3%) sequestration potential has been observed for B. thuringiensis and least (52.8%) for S. warneri. The tolerance and sequestration potential properties of these isolated species can be utilised to exterminate heavy metals and reduce their toxicity from the contaminated environment.

Sorption Mechanism and Optimization Study for the Bioremediation of Pb(II) and Cd(II) Contamination by Two Novel Isolated Strains Q3 and Q5 of Bacillus sp

The use of bacterial strains as agents in bioremediation processes could reduce the harmfulness of potential toxic elements (PTEs) from water and soil with low or even no impact on the natural ecosystems. In this study, two new metal resistant-bacterial strains (Q3 and Q5) of Bacillus sp. were isolated from a sulfurous spring and their potential (as pure cultures or mixed) to remove Pb(II) and Cd(II) from an aqueous matrix was evaluated and optimized using response surface methodology (RSM). The optimal conditions for Cd(II) removal from all tested strains combinations were observed at an initial pH 5, a temperature of 38 °C, and an initial Cd(II) concentration of 50 mg L-1, while the performance of bacterial strains on Pb(II) removal was strongly correlated to initial pH and temperature conditions. Moreover, the efficiency of bacterial strains in removing both PTEs, Pb(II) and Cd(II), from an aqueous matrix was considerably higher when they were used as a mixed culture rather than pure. According to field emission SEM (FESEM) and EDS analysis, the two bacterial strains showed different mechanisms in removing Cd(II): Bacillus sp. Q5 bio-accumulated Cd(II) in its periplasmic space, whereas Bacillus sp. Q3 bio-accumulated Cd(II) on its cell surface. On the other hand, Pb(II) is removed by chemical precipitation (lead sulfide) induced by both Bacillus sp. Q3 and Q5. This study discloses new aspects of Pb(II) and Cd(II) bioremediation mechanisms in Bacillus species that can be extremely useful for designing and operating novel PTEs bioremediation processes.

Disruption of RIM15 confers an increased tolerance to heavy metals in Saccharomyces cerevisiae

OBJECTIVE

The aim of this study was to identify genes related to a heavy metal tolerance and to elucidate the tolerance mechanism in a eukaryote model using Saccharomyces cerevisiae.

RESULTS

In this study, one strain tolerant to up to 50 μM Pb(NO₃)₂ and 30 μM CdCl₂ was isolated by screening a transposon-mediated mutant library and the disrupted gene was determined to be RIM15. In addition, this gene's characteristics related to heavy metals-tolerance was proved by deletion and overexpressing of this corresponding gene. The transposon mutant grew faster than the control strain and showed an obvious reduction in the intracellular level of reactive oxygen species (ROS) with activation of MSN4 and CTT1 in YPD medium containing 50 μM Pb(NO₃)₂ and 30 μM CdCl₂ respectively.

CONCLUSIONS

Disruption of RIM15 in S. cerevisiae results in increased tolerance to heavy metal stress.

Dynamic proteome responses to sequential reduction of Cr(VI) and adsorption of Pb(II) by Pannonibacter phragmitetus BB

Here, the microbial responses to Cr(VI) and Pb(II) with bio-removal of the metals in water by Pannonibacter phragmitetus BB were explored. The comparative bacterial proteomics showed that the intracellular and extracellular Cr(VI) reduction proteins, Pb(II) adsorption by the lipoprotein and sugar-related bacterial proteins, as well as Pb(II) precipitation by phosphate and OH^- were vital to the bio-removal of Cr(VI) and Pb(II). Moreover, the influx and efflux channels of Cr(VI) and Cr(III), Pb(II) transporters, extracellular siderophores for Pb(II) complexation and antioxidant proteins enabled the strain BB to resist the toxicity of Cr(VI) and Pb(II). In addition, the dynamic expression levels of the proteins related to reduction and transportation of Cr(VI), and adsorption, transportation and complexation of Pb(II) were dependent on the corresponding metal, respectively. The anti-oxidative stress system, such as superoxide dismutase, and Na⁺/H⁺ antiporters played central roles in the protein-protein interaction network to resist and detoxify Cr(VI) and Pb(II). The results of our study provide a novel insight for the physiological responses of the strain BB to the combined stresses of Pb(II) and Cr(VI).

Heavy Metal Toxicity in Armed Conflicts Potentiates AMR in A. baumannii by Selecting for Antibiotic and Heavy Metal Co-resistance Mechanisms

Acinetobacter baumannii has become increasingly resistant to leading antimicrobial agents since the 1970s. Increased resistance appears linked to armed conflicts, notably since widespread media stories amplified clinical reports in the wake of the American invasion of Iraq in 2003. Antimicrobial resistance is usually assumed to arise through selection pressure exerted by antimicrobial treatment, particularly where treatment is inadequate, as in the case of low dosing, substandard antimicrobial agents, or shortened treatment course. Recently attention has focused on an emerging pathogen, multi-drug resistant A. baumannii (MDRAb). MDRAb gained media attention after being identified in American soldiers returning from Iraq and treated in US military facilities, where it was termed "Iraqibacter." However, MDRAb is strongly associated in the literature with war injuries that are heavily contaminated by both environmental debris and shrapnel from weapons. Both may harbor substantial amounts of toxic heavy metals. Interestingly, heavy metals are known to also select for antimicrobial resistance. In this review we highlight the potential causes of antimicrobial resistance by heavy metals, with a focus on its emergence in A. baumanni in war zones.

Advances in characterizing microbial community change and resistance upon exposure to lead contamination: Implications for ecological risk assessment

Recent advancement in molecular techniques has spurred waves of studies on responses of microorganisms to lead contamination exposure, leveraging detailed phylogenetic analyses and functional gene identification to discern the effects of lead toxicity on microbial communities. This work provides a comprehensive review of recent research on (1) microbial community changes in contaminated aquatic sediments and terrestrial soils; (2) lead resistance mechanisms; and (3) using lead resistance genes for lead biosensor development. Sufficient evidence in the literature, including both in vitro and in situ studies, indicates that exposure to lead contamination inhibits microbial activity resulting in reduced respiration, suppressed metabolism, and reduced biomass as well as altered microbial community structure. Even at sites where microbial communities do not vary compositionally with contamination levels due to extremely long periods of exposure, functional differences between microbial communities are evident, indicating that some microorganisms are susceptible to lead toxicity as others develop resistance mechanisms to survive in lead contaminated environments. The main mechanisms of lead resistance involve extracellular and intracellular biosorption, precipitation, complexation, and/or efflux pumps. These lead resistance mechanisms are associated with suites of genes responsible for specific lead resistance mechanisms and may serving as indicators of lead contamination in association with dominance of certain phyla. This allows for development of several lead biosensors in environmental biotechnology. To promote applications of these advanced understandings, molecular techniques, and lead biosensor technology, perspectives of future work on using microbial indicators for site ecological assessment is presented.

Urinary lead concentration and composition of the adult gut microbiota in a cross-sectional population-based sample

BACKGROUND

Lead (Pb) is a ubiquitous environmental contaminant with an array of detrimental health effects in children and adults, including neurological and immune dysfunction. Emerging evidence suggests that Pb exposure may alter the composition of the gut microbiota, however few studies have examined this association in human populations. The purpose of this study was to examine the association between urinary Pb concentration and the composition of the adult gut microbiota in a population-based sample of adults.

METHODS

Data used in this study were collected as part of the Survey of the Health of Wisconsin (SHOW) and its ancillary microbiome study. The SHOW is a household-based health examination survey of Wisconsin residents, collecting a variety of survey data on health determinants and outcomes, as well as objective measurements of body habitus, and biological specimens including urine. The ancillary microbiome study added additional questions and biological specimen collection, including stool, from participants age 18+. Pb concentration was analyzed in urine samples, and gut microbiota composition was assessed using DNA sequencing of the 16S rRNA V4 region, extracted from stool samples. Data processing and statistical analyses were performed in mothur, Python, R, and SAS.

RESULTS

Of 696 participants, urinary Pb concentration was highest in those age 70+, females, those with a high school diploma or lower, current and former smokers, and those without indoor pets. In adjusted models, increasing urinary Pb levels were associated with increases in microbial α-diversity (p = 0.071) and richness (p = 0.005). Differences in microbial β-diversity were significantly associated (p = 0.003) with differences in urinary Pb level. Presence of Proteobacteria, including members of the Burkholderiales, was significantly associated with increased urinary Pb.

CONCLUSION

These results suggest that Pb exposure is associated with differences in the composition of the adult gut microbiota in a population-based human sample. Further investigation of this association is warranted.

Recombinant Fusion Protein PbrD Cross-Linked to Calcium Alginate Nanoparticles for Pb Remediation

Lead (Pb) pollution arising from industrial and mining activities has led to widespread environmental toxicity, particularly in South Africa. Humans exposed to Pb are reported to suffer from detrimental health impacts that can lead to fatalities. As such, there is an urgent need to remediate Pb from the environment. In this study, we propose the use of a Pb-specific recombinant fusion metalloprotein, rPbrD surface-cross-linked onto calcium alginate nanoparticles (CANPs) for the biosorption of Pb(II) from aqueous solution. The prepared biosorbents were characterized using scanning electron microscopy, transmission electron microscopy, and dynamic light scattering. Their ability to biosorb soluble Pb(II) was determined by inductively coupled plasma mass spectroscopy and their adsorption mechanism was described according to the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich adsorption isotherms. The rate of Pb uptake for bare CANPs and rPbrD-CANPs at a concentration of 100 mg/L metal was 3.34 and 8.82 mg/g, respectively, within 30 min. The adsorption data for the bare CANPs best fit the Langmuir isotherm, whereas the adsorption data for rPbrD-CANPs best fitted the Freundlich isotherm. Based on the sorption intensity (n) and the separation factor (R _L), both biosorbents represent a favorable adsorption system. These findings suggest that the proposed nanobiosorbent is a promising candidate for the recovery of Pb ions present in high concentrations such as acid mine drainage or industrial effluent.

Removal of Pb (II), As (III), and Cr (VI) by nitrogen-starved Papiliotrema laurentii strain RY1

Heavy metals such as lead, chromium, and metalloid like arsenic dominate the pinnacle in posing a threat to life. Being environment-friendly, elucidating the mechanism by which microorganisms detoxify such elements has always been an active field of research hitherto. In the present study, we have investigated the capability of nitrogen-deprived Papiliotrema laurentii strain RY1 toward enhanced tolerance and neutralizing toxic elements. There were biosorption and bioprecipitation of lead and chromium at the cell surfaces. Bioprecipitation mechanisms included the formation of lead phosphates and pyromorphites from lead, grimaldite from chromium. Transcripts such as metallothionein, aquaporins, and arsenical pump-driving ATPase have been surmised to be involved in the detoxification of elements. Furthermore, activation of antioxidant defense mechanisms for the cells for each of the elements should contribute towards yeast's propagation. The efficiency of removal of elements for live cells and immobilized cells were high for lead and chromium. To the best of our knowledge, this is the first report of such high tolerance of lead, arsenic, and chromium for any yeast. The yeast showed such varied response under dual stress due to nitrogen starvation and in the presence of respective elements. The yeast possesses promising potentials in nitrogen deprived and enriched environments to aid in bioremediation sectors.

Molecular characterization of acutely and gradually heavy metal acclimated aquatic bacteria by FTIR spectraoscopy

In the environment, bacteria can be exposed to the concentration gradient of toxic heavy metals (gradual) or sudden high concentration of them (acute). In both situations, bacteria get acclimated to toxic heavy metal concentrations. Acclimation causes metabolic and molecular changes in bacteria. In this study, we aimed to understand whether there are differences between molecular profiles of the bacteria (Brevundimonas, Gordonia and Microbacterium) which are under acute or gradual exposure to cadmium or lead by using ATR-FTIR spectroscopy. Our results revealed the differences between the acclimation groups in membrane dynamics including changes in the structure and composition of the membrane lipids and proteins. Furthermore, protein concentrations decreased in acclimated bacterial groups. Also, a remarkable increase in exopolymer production occurred in acclimated groups. Interestingly, bacteria under acute cadmium exposure produced the significantly higher amount of exopolymer than they did under gradual exposure. On the contrary, under lead exposure gradually acclimate strains produced significantly higher amounts of exopolymer than those of acutely acclimated ones. This information can be used in bioremediation studies to obtain bacterial strains producing a higher amount of exopolymer.