Isolation and Identification of Heavy Metal Tolerant Bacteria from Tannery Effluents

Abstract

IntroductionThe direct discharge of effluents from tanneries into bodies of water has become a growing environmental problem. Most of these wastewaters are extremely complex mixtures containing inorganic and organic compounds 1 . The tannery operation consists of converting the raw hide or skin into leather, which can be used in the manufacture of a wide range of products. Consequently, the tanning industry is a potentially pollutionintensive industry. Chemical impurities mostly comprise of the following dissolved substances: inorganic salt cations such as Fe 2+ , Zn 2+ , Cu 2+ , Ca + , Na + , etc., anion such as SO 4 2-, NO 3 -, PO 4 3-; organic parameters such as Dissolved Oxygen (DO), Total Dissolved Solids (TDS) 2 .Heavy metal contamination is widespread. Heavy metals are often defined as a group of metals whose atomic density is greater than 5 gram per cubic centimeter 3-5 . In nature, there are about 50 heavy metals of special concern because of their toxicological effect to human beings and other living organisms like microorganisms 6 . Metals play a vital role in the metabolic processes of the biota. Some of the heavy metals are essential and are required by the organisms as micro nutrients (Co, Cu, Ni, Fe, Mn and Zn, etc.) and are known as 'trace elements' 6 . They are involved in redox processes, in order to stabilize molecules through electrostatic interactions, as catalysts in enzymatic reactions, and regulating the osmotic balance 7 . On the other hand, some other heavy metals have no biological role and are detrimental to the organisms even at very low concentration (Cr, Cd, Hg, Pb, etc.). However, at high levels both of the essential and non-essential metals become toxic to the organisms as well as human being.These heavy metals influence the microbial population by affecting their growth, morphology, biochemical activities and ultimately resulting in decreased biomass and diversity 8 . Heavy metals can damage the cell membranes, alter enzymes specificity, disrupt cellular functions and damage the structure of DNA. Toxicity of these heavy metals occurs through the displacement of essential metals from their native binding sites or through ligand interactions 6 . Also, toxicity can occur as a result of alterations in the conformational structure of the nucleic acids and proteins and interference with oxidative phosphorylation and osmotic balance 6, 9 .Due to the selective pressure from the metal in the growth environment, microorganisms have evolved various mechanisms to resist the heavy metal stress. Several metal resistance mechanisms have been identified: exclusion by permeability barrier, intra and extra cellular sequestration, active transport, efflux pumps, enzymatic detoxification, and reduction in the sensitivity of the cellular targets to metal ions 6, 9 . Most mechanism reported involves the efflux of metal ions outside the cell, and genes for tolerance mechanisms have been found on both chromosomes and plasmids. Bacteria that are resistant to and grow on metals play an important role i...

Role of heavy metals on antibiotic resistance properties in lactose fermenting isolates collected from textile industry effluents

“…Bangladesh has a significant number of textile, dying and tannery industries, however, till now there were no systemic and extensive studies in this area except some random and small scale studies; for instance, Ashikuzzaman et al (2015) studied gram positive bacteria with heavy metal resistance isolated from textile effluents. In addition, Md et al (2009) studied on chromium resistance bacteria and Hossain and Anwar (2012) reported on chromium and copper resistance bacteria isolated from tannery effluents. As a result, the present study was a sure systemic and a small-scale effort to study on gram negative lactose fermenting Enterobacteriaceae providing emphasis on mostly phenotypic characterization.…”