Phytoremediation of Heavy Metals by Typha angustifolia in Hokersar Wetland of Kashmir

Remediation of heavy metals by macrophytes in wetlands is gaining importance, particularly in the wetlands and game reserves of international importance. Hokersar wetland, a Ramsar site, is a game reserve of international importance and is facing anthropogenic disturbances over the years. Keeping in view deleterious effect of heavy metals on all the facets of contaminated ecosystems need for removal of these contaminants has received lot of attention in the recent past. It is in this backdrop, heavy metal sequestration by Typha angustata, one of the common and abundant species growing in the wetland, was explored. The study was aimed to assess sequestration of heavy metals, such as Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn by T. angustata in the Hokersar wetland. The EF for all the investigated heavy metals was greater than one and TF of T. angustata was greater than one for Zn, Cr and Pb thereby making the species a hyper-accumulator for these elements. In conclusion, it can be stated that T. angustata, being a hyperaccumulator of Zn, Cr and Pb and accumulator for Fe, Mn, Al, Co, Cu, Ni and Cd can be exploited for heavy metal sequestration in the wetland system.

Pollution Intensity of Hazardous Metals, Microbiome and Potential Bacterial-Based Toxic Metal Sequestration of Coal Mine Drainage

Drains from coal mine remain a worrisome point source of toxic metal/metalloid pollutions to surface- and ground-waters worldwide, requiring sustainable remediation strategies. Understanding the microbial community subtleties through integrated metagenomic and geochemical data elicit selection of autochthonous bacteria consortium, spurring decommissioning of drains before discharge to hydrosphere. The drains contained characteristic sulphates (313.0 ± 15.9 mg/l), carbonate (253.0 ± 22.4 mg/l), and nitrate (86.6 ± 41.0 mg/l), having extreme tendencies to enrich receiving environments with extremely high pollution load index (3110 ± 942) for toxic metals/metalloid. The drains exerted severe degree of toxic metals/metalloid contamination (3,400,000 ± 240,000) and consequent astronomically high ecological risks in the order: Lead > Cadmium > Arsenic > Nickel > Cobalt > Iron > Chromium. Metagenome of the drains revealed dominance of Proteobacteria (50.8%) and Bacteroidetes (18.9%) among bacterial community, whereas, Ascomycota (60.8%) and Ciliophora (12.6%) dominated the eukaryotic community. A consortium of 7 autochthonous bacterial OTUs exhibited excellent urease activities (≥ 253 µmol urea/min.) with subsequent stemming of acidic pH to > 8.2 and sequestration of toxic metals (approx. 100% efficiency) as precipitates (15.6 ± 0.92 mg/ml). The coal mine drain is a point source for metals/metalloid pollution to surrounding hydrosphere, and its bioremediation is achievable with the bacteria consortium.

Lipoteichoic acid depletion in Lactobacillus impacts cell morphology and stress response but does not abolish mercury surface binding

Lipoteichoic acid (LTA) is a key component of the cell wall of most Gram-positive bacteria and plays many structural and functional roles. In probiotic lactobacilli, the function of LTA in mediating bacteria/host cross-talk has been evidenced and it has been postulated that, owing to its anionic nature, LTA may play a role in toxic metal sequestration by these bacteria. However, studies on this last aspect employing strains unable to synthesise LTA are lacking. We have inactivated the LTA polymerase encoding gene ltaS in two different Lactobacillus plantarum strains. Analysis of LTA contents in wild-type and ltaS mutant strains corroborated the role of this gene as a major contributor to LTA synthesis in L. plantarum. The mutant strains displayed strain-dependent anomalous cell morphologies that resulted in elongated or irregular cells with aberrant septum formation. They also exhibited higher sensitivity to several stresses (osmotic and heat) and to antimicrobials that target the cell wall. The toxicity of inorganic [(Hg(II)] and organic mercury (methyl-Hg) was also increased upon ltaS mutation in a strain-dependent manner. However, the mutant strains showed 0 to 50% decrease in their capacity of Hg binding compared to their corresponding parental strains. This result suggests a partial contribution of LTA to Hg binding onto the cell surface that was dependent on the strain and the Hg form.

Non-Enzymatic Antioxidant Responses of Mytilus galloprovincialis under Cadmium-Induced Oxidative Stress Risk

Exposure to metals is known to generate oxidative stress in living organisms, which are able to respond with the induction of antioxidant defenses, both enzymatic and non-enzymatic. The aim of this work is to study the correlation among several non-enzymatic component of the antioxidant system, that are physiologically related to both metal sequestration and defense against metal-induced oxidative stress, using the blue mussels (Mytilus galloprovincialis) as model organism. Specimens of this marine bivalve were experimentally exposed to cadmium (Cd), used as oxidative stress risk inducer. Cd, metallothionein (MT), glutathione (GSH), malondialdehyde (MDA) contents, and glutathione reductase (GR) activity in gills and in digestive glands were assessed at 0, 12, 24, 48, 72 and 96 h. The obtained results provide new data about the relationships among the non-enzymatic antioxidant cellular components considered in this study. These constitute the prompt physiological responses to the risk of oxidative stress in blue mussels exposed to Cd in controlled laboratory conditions.

Molecular Cloning and Heterologous Expression of Manganese(II)-Oxidizing Enzyme from Acremonium strictum Strain KR21-2

Diverse ascomycete fungi oxidize manganese(II) [Mn(II)] and produce Mn(III, IV) oxides in terrestrial and freshwater environments. Although multicopper oxidase (MCO) is considered to be a key catalyst in mediating Mn(II) oxidation in ascomycetes, the responsible gene and its product have not been identified. In this study, a gene, named mco1, encoding Mn(II)-oxidizing MCO from Acremonium strictum strain KR21-2 was cloned and heterologously expressed in the methylotrophic yeast Pichia pastoris. Based on the phylogenetic relationship, similarity of putative copper-binding motifs, and homology modeling, the gene product Mco1 was assigned to a bilirubin oxidase. Mature Mco1 was predicted to be composed of 565 amino acids with a molecular mass of 64.0 kDa. The recombinant enzyme oxidized Mn(II) to yield spherical Mn oxides, several micrometers in diameter. Zinc(II) ions added to the reaction mixture were incorporated by the Mn oxides at a Zn/Mn molar ratio of 0.36. The results suggested that Mco1 facilitates the growth of the micrometer-sized Mn oxides and affects metal sequestration through Mn(II) oxidation. This is the first report on heterologous expression and identification of the Mn(II) oxidase enzyme in Mn(II)-oxidizing ascomycetes. The cell-free, homogenous catalytic system with recombinant Mco1 could be useful for understanding Mn biomineralization by ascomycetes and the sequestration of metal ions in the environment