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      High potential application in bioremediation of selenate by Proteus hauseri strain QW4

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          Abstract

          Background and Objective:

          Selenium is essential for biological systems at low concentrations and toxic at higher levels. Heavy metals and metalloids such as selenium are major contaminants in 40% of hazardous waste sites. Thus, bioremediation has been considered as an effective means of cleaning up of selenium-contaminated sites.

          Materials and Methods:

          In this study, 30 strains were isolated from wastewater samples collected from selenium-contaminated sites in Qom, Iran using the enrichment culture technique. One bacterial strain designated QW4, identified as Proteus hauseri by morphological, biochemical and 16S rRNA gene sequencing was studied for its ability to tolerate different concentrations of sodium selenate (100–800 mM). Also, the disk diffusion method was performed to determine resistance to some antibiotics

          Results:

          Strain QW4 showed maximum minimum inhibitory concentration (MIC) to selenate (760 mM). The maximum selenate removal was exhibited at 35 °C, while the removal activity reduced by 30.7% and 37% at 25 °C and 40 °C, respectively. The optimum pH and shaking incubator for removal activity was shown to be 7.0 and 150 rpm, with 60.2% and 60.3%, respectively. This bacterial strain was resistant to some antibiotics.

          Conclusion:

          The concentration of toxic sodium selenate (1000 μg/ml) in the supernatant of the bacterial culture medium decreased by 100% after 2 days and the color of the medium changed to red due to the formation of less toxic elemental selenium. Also, our results imply that heavy metal pollution may contribute to increased antibiotic resistance through indirect selection.

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          Most cited references9

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          Microbial resistance to metals in the environment.

          Many microorganisms demonstrate resistance to metals in water, soil and industrial waste. Genes located on chromosomes, plasmids, or transposons encode specific resistance to a variety of metal ions. Some metals, such as cobalt, copper, nickel, serve as micronutrients and are used for redox processes, to stabilize molecules through electrostatic interactions, as components of various enzymes, and for regulation of osmotic pressure. Most metals are nonessential, have no nutrient value, and are potentially toxic to microorganisms. These toxic metals interact with essential cellular components through covalent and ionic bonding. At high levels, both essential and nonessential metals can damage cell membranes, alter enzyme specificity, disrupt cellular functions, and damage the structure of DNA. Microorganisms have adapted to the presence of both nutrient and nonessential metals by developing a variety of resistance mechanisms. Six metal resistance mechanisms exist: exclusion by permeability barrier, intra- and extra-cellular sequestration, active transport efflux pumps, enzymatic detoxification, and reduction in the sensitivity of cellular targets to metal ions. The understanding of how microorganisms resist metals can provide insight into strategies for their detoxification or removal from the environment. Copyright 2000 Academic Press.
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            Reduction of selenite to elemental red selenium by Pseudomonas sp. Strain CA5.

            A Pseudomonas sp. that may be useful in bioremediation projects was isolated from soil. The strain is of potential value because it reduces selenite to elemental red selenium and is unusual in that it was resistant to high concentrations of both selenate and selenite. Exposure of the strain to 50, 100, and 150 mM selenite reduced growth by 28, 57, and 66%, respectively, while no change in growth was observed when the strain was exposed to 64 mM selenate, the highest level tested. Cells of the strain removed 1.7 mM selenite from the culture fluid during a 7-day incubation. A selenite reductase with a molecular weight of ~115 kD was detected in cell-free extracts and a protein with a molecular weight of ~700 kD was detected that reduced both selenate and nitrate. The bacterial isolate is a strict aerobe, reducing selenite to elemental red selenium under aerobic conditions only. Pseudomonas sp. strain CA5 might be useful as an inoculum for bioreactors used to harvest selenium from selenite-containing groundwater. 16S rRNA gene sequence alignment and fatty acid analysis were used to identify the bacterium as a novel species of Pseudomonas related to P. argentinensis, P. flavescens, and P. straminea.
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              Molecular cloning and characterization of the srdBCA operon, encoding the respiratory selenate reductase complex, from the selenate-reducing bacterium Bacillus selenatarsenatis SF-1.

              Previously, we isolated a selenate- and arsenate-reducing bacterium, designated strain SF-1, from selenium-contaminated sediment and identified it as a novel species, Bacillus selenatarsenatis. B. selenatarsenatis strain SF-1 independently reduces selenate to selenite, arsenate to arsenite, and nitrate to nitrite by anaerobic respiration. To identify the genes involved in selenate reduction, 17 selenate reduction-defective mutant strains were isolated from a mutant library generated by random insertion of transposon Tn916. Tn916 was inserted into the same genome position in eight mutants, and the representative strain SF-1AM4 did not reduce selenate but did reduce nitrate and arsenate to the same extent as the wild-type strain. The disrupted gene was located in an operon composed of three genes designated srdBCA, which were predicted to encode a putative oxidoreductase complex by the BLASTX program. The plasmid vector pGEMsrdBCA, containing the srdBCA operon with its own promoter, conferred the phenotype of selenate reduction in Escherichia coli DH5α, although E. coli strains containing plasmids lacking any one or two of the open reading frames from srdBCA did not exhibit the selenate-reducing phenotype. Domain structure analysis of the deduced amino acid sequence revealed that SrdBCA had typical features of membrane-bound and molybdopterin-containing oxidoreductases. It was therefore proposed that the srdBCA operon encoded a respiratory selenate reductase complex. This is the first report of genes encoding selenate reductase in gram-positive bacteria.
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                Author and article information

                Journal
                Iran J Microbiol
                Iran J Microbiol
                IJM
                IJM
                Iranian Journal of Microbiology
                Tehran University of Medical Sciences
                2008-3289
                2008-4447
                April 2015
                : 7
                : 2
                : 94-102
                Affiliations
                Department of Microbiology, Faculty of Basic Sciences, Qom Branch, Islamic Azad University, Qom, Iran
                Author notes
                [* ]Corresponding author: Mohaddeseh Khalilian, Address: Islamic Azad University, 15 Khordad Street, Qom, Iran. Tel: +98 9129175804, Fax: +98 2532611270, Email: m.khalilian88@ 123456yahoo.com
                Article
                ijm-7-94
                4662785
                26622970
                3196774f-59db-40e1-8775-d63ebfd7b29b
                © Tehran University of Medical Sciences

                This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License which allows users to read, copy, distribute and make derivative works for non-commercial purposes from the material, as long as the author of the original work is cited properly.

                History
                : March 2014
                : February 2015
                Categories
                Original Article

                Microbiology & Virology
                bioremediation,mic,proteus hauseri,sodium selenate
                Microbiology & Virology
                bioremediation, mic, proteus hauseri, sodium selenate

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