Derivation of pb(II)-sensing Escherichia coli cell-based biosensors from arsenic responsive genetic systems

Engineered Bacillus subtilis Biofilm@Biochar living materials for in-situ sensing and bioremediation of heavy metal ions pollution

The simultaneous sensing and remediation of multiple heavy metal ions in wastewater or soil with microorganisms is currently a significant challenge. In this study, the microorganism Bacillus subtilis was used as a chassis organism to construct two genetic circuits for sensing and adsorbing heavy-metal ions. The engineered biosensor can sense three heavy metal ions (0.1-75 μM of Pb2+ and Cu2+, 0.01-3.5 μM of Hg2+) in situ real-time with high sensitivity. The engineered B. subtilis TasA-metallothionein (TasA-MT) biofilm can specifically adsorb metal ions from the environment, exhibiting remarkable removal efficiencies of 99.5% for Pb2+, 99.9% for Hg2+and 99.5% for Cu2+ in water. Furthermore, this engineered strain (as a biosensor and absorber of Pb2+, Cu2+, and Hg2+) was incubated with biochar to form a hybrid biofilm@biochar (BBC) material that could be applied in the bioremediation of heavy metal ions. The results showed that BBC material not only significantly reduced exchangeable Pb2+ in the soil but also reduced Pb2+ accumulation in maize plants. In addition, it enhanced maize growth and biomass. In conclusion, this study examined the potential applications of biosensors and hybrid living materials constructed using sensing and adsorption circuits in B. subtilis, providing rapid and cost-effective tools for sensing and remediating multiple heavy metal ions (Pb2+, Hg2+, and Cu2+).

Label free electrochemical sensors for Pb(II) detection based on hemicellulose extracted from Opuntia Ficus Indica cactus

We aim to develop an electrochemical sensor for a divalent metal ion (lead II), a highly toxic water contaminant. We explore a sensor formed with a hemicellulose polysaccharide extracted from the Opuntia Ficus Indica cactus associated with agarose as a sensitive layer deposited on a gold electrode. This sensor combines the functional groups of hemicellulose that could form a complex with metal ions and agarose with gelling properties to form a stable membrane. The sensor demonstrated a loading ability of Pb2+, with higher affinity compared to other metal ions such as Hg2+, Ni2+, and Cu2+, thanks to the chemical structure of hemicellulose. The detection was measured by square wave voltammetry based on a well-defined redox peak of the metal ions. The sensor shows high sensitivity towards Pb2+ with a detection limit of 1.3 fM. The application in river and sea water using the standard addition method for lead detection was studied.

The characteristics and metabolic potentials of the soil bacterial community of two typical military demolition ranges in China

The response mechanism of soil microbiota in military polluted sites can effectively indicate the biotoxicity of ammunition. In this study, two military demolition ranges polluted soils of grenades and bullet were collected. According to high-throughput sequencing, after grenade explosion, the dominant bacteria in Site 1 (S1) are Proteobacteria (97.29 %) and Actinobacteria (1.05 %). The dominant bacterium in Site 2 (S2) is Proteobacteria (32.95 %), followed by Actinobacteria (31.17 %). After the military exercise, the soil bacterial diversity index declined significantly, and the bacterial communities interacted more closely. The indigenous bacteria in S1 were influenced more compared to those in S2. According to the environmental factor analysis, the bacteria composition can easily be influenced by heavy metals and organic pollutants, including Cu, Pb, Cr and Trinitrotoluene (TNT). About 269 metabolic pathways annotated in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were detected in bacterial communities, including nutrition metabolism (C, 4.09 %; N, 1.14 %; S, 0.82 %), external pollutant metabolism (2.52 %) and heavy metal detoxication (2.12 %), respectively. The explosion of ammunition changes the basic metabolism of indigenous bacteria, and heavy metal stress inhibits the TNT degradation ability of bacterial communities. The pollution degree and community structure influence the metal detoxication strategy at the contaminated sites together. Heavy metal ions in S1 are mainly discharged through membrane transporters, while heavy metal ions in S2 are mainly degraded through lipid metabolism and biosynthesis of secondary metabolites. The results obtained in this study can provide deep insight into the response mechanism of the soil bacterial community in military demolition ranges with composite pollutions of heavy metals and organic substances. CAPSULE: Heavy metal stress changed the composition, interaction and metabolism of indigenous communities in military demolition ranges, especially the TNT degradation process.

Multifunctional nanomaterials and nanocomposites for sensing and monitoring of environmentally hazardous heavy metal contaminants

The applications of conventional sensors are limited by the long response time, high cost, large detection limit, low sensitivity, complicated usage and low selectivity. These sensors are nowadays replaced by Nanocomposite-based modalities and nanomaterials which are known for their high selectivity and physical and chemical properties. These nanosensors effectively detect heavy metal contaminants in the environment as the discharge of heavy metals into natural water as a result of human activity has become a global epidemic. Exposure to these toxic metals might induce many health-related complications, including kidney failure, brain injury, immune disorders, muscle paleness, cardiac damage, nervous system impairment and limb paralysis. Therefore, designing and developing novel sensing systems for the detection and recognition of these harmful metals in various environmental matrices, particularly water, is of extremely important. Emerging nanotechnological approaches in the past two decades have played a key role in overcoming environmentally-related problems. Nanomaterial-based fabrication of chemical nanosensors has widely been applied as a powerful analytical tool for sensing heavy metals. Portability, high sensitivity, on-site detection capability, better device performance and selectivity are all advantages of these nanosensors. The detection and selectivity have been improved using molecular recognition probes for selective binding on different nanostructures. This study aims to evaluate the sensing properties of various nanomaterials such as metal-organic frameworks, fluorescent materials, metal-based nanoparticles, carbon-based nanomaterials and quantum dots and graphene-based nanomaterials and quantum dots for heavy metal ions recognition. All these nano-architectures are frequently served as effective fluorescence probes to directly (or by modification with some large or small biomolecules) sense heavy metal ions for improved selectivity. However, efforts are still needed for the simultaneous designing of multiple metal ion-based detection systems, exclusively in colorimetric or optical fluorescence nanosensors for heavy metal cations.