Localization Effect on the Metal Biosorption Capability of Recombinant Mammalian and Fish Metallothioneins inEscherichia coli

A unique Pb-binding flagellin as an effective remediation tool for Pb contamination in aquatic environment

Metal contaminants present persistent and deleterious threats to environmental ecosystems and human health. Microorganisms can rapidly develop protective mechanisms against metal toxicity, such as metallothionein production. The identification of biological factors related to these protective mechanisms is essential for effective metal remediation. This study presents a robust pathway to rapidly locate and characterize a Pb-binding flagellin in Serratia Se1998, which can bind Pb at a 16:1 Pb: protein ratio. A column gel electrophoresis system hyphenated with inductively coupled plasma mass spectrometry (ICP MS) was constructed to efficiently separate and identify Pb-binding proteins from the whole bacterial proteome. PCR and transgenic assays were used to elucidate the exact sequences and biological function of Pb-binding proteins and heterogeneous expression of Pb-binding flagellin in E. coli could significantly enhance Pb removal from aqueous solution by approximately 45%. This method provides a benchmark procedure to rapidly identify biological factors responsible for metal biosorption. Identification of this unique Pb-binding flagellin highlights that microorganisms can survive high metal stresses due to various complex biological pathways for metal detoxification and remediation.

The interaction between bacterial abundance and selected pollutants concentration levels in an arctic catchment (southwest Spitsbergen, Svalbard)

Persistent organic pollutants (POPs) have been a topic of interest in environmental sciences for >60years. POPs in the Arctic have been investigated since the 1970s, when first atmospheric measurements revealed the presence of these pollutants in the polar regions. Major contaminant transport routes to the Arctic include atmospheric and oceanic transport, as well as inflow from rivers and sea ice. The sources of pollutants, such as industry, power generators, vehicle and ship exhausts, introduce the PAHs, phenols, formaldehyde or metals into the Arctic. Transport via sea currents, however, can take several years. The highest concentration levels of total PAHs were observed in two samples from the tributaries in July 2015 and were 1069ngL^-1 and 3141ngL^-1 and in September 2015, the highest concentrations were observed in samples collected from Revvatnet lake and were 978ngL^-1 and 1823ngL^-1. The highest concentrations of trace elements in both months were 41μgL^-1 in the sample from the highest tributary (July 2015) and 79μgL^-1 in the same sample (September 2015). The purpose of this study was also to determine abundance of bacteria in the Arctic freshwater of different types. Microbes are omnipresent and represent diverse biological communities. In the freshwater ecosystems, microorganisms form the base of the food chain supporting higher trophic levels. Although microbes are generally thought to live in the warm regions of Earth, many of them develop in cold climates. In the Revelva catchment, the biggest number of bacteria were detected at the river estuary in July 2015 and at the sampling point located in the Revvatnet lake in September 2015. Generally, the bacterial abundance indices depended on nutrient levels to a small extent, showing the environment of the Revelva catchment not to be nutrient limited, which is in accordance with its rich biological life also in macroscale.

Mechanisms of removing pollutants from aqueous solutions by microorganisms and their aggregates: a review

With the public's enhanced awareness of eco-safety, environmentally benign measures based on microorganisms and microbial aggregates have become more accepted as methods of removing pollutants from aquatic systems. In this review, the application of microorganisms and microbial aggregates for removing pollutants from aqueous solutions is introduced and described based on mechanisms such as assimilation, adsorption, and biodegradation. The advantages of and future studies regarding the use of microorganisms and microbial aggregates to remove pollutants are discussed. Due to the limitation of a single microorganism species in adapting to heterogeneous conditions, this review demonstrates that the application of microbial aggregates consisting of multiple photoautotrophic and heterotrophic microorganisms, is a promising method of removing multiple pollutants from complex wastewaters and warrants further research.

Cadmium biosorption by polyvinyl alcohol immobilized recombinant Escherichia coli

Recombinant Escherichia coli expressing human metallothionein protein was immobilized with polyvinyl alcohol (PVA) for the removal of cadmium from solution. The adsorption ability was strongly affected by pH with optimal performance at pH 5.0, while it was less sensitive to temperature over the range of 20-42 degrees C. The adsorption kinetics and equilibrium of PVA-immobilized cells was best described by pseudo-second order model and Langmuir isotherm, respectively. Over the Cd concentrations range of 10-150 mg/l, PVA-cells had the highest Cd removal percentage (82.7%) at 10mg Cd/l and a biomass loading of 15.4 wt.%. Better adsorption ability was obtained when biomass loading was increased, as the highest adsorption capacity of 4.29 mg/g was achieved at 33.0 wt.% of biomass (initial Cd concentration=100mg/l). An aqueous solution of 0.01 M Na(3)NTA displayed the best desorption efficiency (57-89%) for four A/D cycles, while 51-61% of the original adsorption capacity was retained after regeneration.

Metallothionein expression in HaCaT and C6 cell lines exposed to cadmium

Metallothioneins (MT) are low-molecular weight, cysteine-rich metal-binding proteins. MT play a role in the homeostasis of essential metals such as zinc (Zn) and copper (Cu), detoxification of toxic metals such as cadmium (Cd) and protection against oxidative stress. In this study, we examined the expression of MT in HaCaT and C6 cells as a strategy to enhance protection against Cd-mediated toxicity. At basal level, HaCaT cells showed higher MT level than C6 cells which could explain the resistance of HaCaT cells. Western blot showed that C6 cells treated with 20micromol/L Cd for 24h did not express any MT. MT were initially expressed in the cytoplasmic or periplasmic compartment and were then translocated in the nucleus after 24h treatment by Cd both in HaCaT and C6 cells. In addition, the cell treatment with Cd was followed by an increase in the cellular zinc level but the electrophoretic mobility shift assay (EMSA) experiment did not show any translocation of metal-responsive transcription factor-1 (MTF-1) to the nucleus of HaCaT cells. These absence of translocation could be due to the presence of MT in these cells at the basal state. The translocation study in HaCaT cells suggested that the MT translocation in the nucleus was greater than observed in C6 cells. The latter observation could explain HaCaT cells resistance to Cd concentrations up to 50micromol/L. Our results suggested that the C6 cell sensitivity was correlated with the decrease in MT level at 20micromol/L Cd occurring after the transcription of MT gene.

Biosorption of nickel, chromium and zinc by MerP-expressing recombinant Escherichia coli

Escherichia coli hosts able to over-express metal-binding proteins (MerP) originating from Gram-positive (Bacillus cereus RC607) and Gram-negative (Pseudomonas sp. K-62) bacterial strains were used to adsorb Ni(2+), Zn(2+) and Cr(3+) in aqueous solutions. The initial adsorption rate and adsorption capacity were determined to evaluate the performance of the biosorbents. With the expression of MerP protein, the metal adsorption capacity of the recombinant strains for Ni(2+), Zn(2+) and Cr(3+) significantly improved. The cells carrying Gram-positive merP gene (GB) adsorbed Zn(2+) and Cr(3+) at a capacity of 22.3 and 0.98 mmol/g biomass, which is 121% and 72% higher, respectively, over that of the MerP-free host cells. Adsorption capacity of the cells carrying Gram-negative merP gene (GP) also increased 144% and 126% for Zn(2+) and Cr(3+), respectively. Both recombinant strains also exhibited 24% and 5% enhancement in adsorption of Ni(2+) for GB and GP, respectively. The initial adsorption rate of the recombinant biosorbents was also higher than that of the MerP-free host, suggesting an increased metal-binding affinity with MerP expression. Severe cell damage on GB biosorbent was observed after Cr(3+) adsorption, probably due to the metal toxicity effect on the cells.