title: Enzyme(s) responsible for tellurite reducing activity in a moderately halophilic bacterium, Salinicoccus iranensis strain QW6.
abstract: Oxyanions of tellurium, like tellurate (TeO4 (2-)) and tellurite (TeO3 (2-)), are highly toxic for most microorganisms. There are a few reports on the bacterial tellurite resistance mechanism(s). Salinicoccus iranensis, a Gram-positive halophilic bacterium, shows high tellurite resistance and NADH-dependent tellurite reduction activity in vitro. Since little is known regarding TeO3 (2-) resistance mechanisms in halophilic microorganisms, here one of the enzymatic reduction activities presented in this microorganism is investigated. To enhance the enzymatic activity during purification, the effect of different parameters including time, inoculation, different pHs, different tellurite concentrations and different salts were optimized. We also examined the tellurite removal rates by diethyldithiocarbamate (DDTC) during optimization. In the culture medium the optimum conditions obtained showed that at 30 h, 2 % inoculum, pH 7.5, without tellurite and with 5 % NaCl (w/v) the highest enzyme activity and tellurite removal were observed. Results of the purification procedure done by hydroxyapatite batch-mode, ammonium sulfate precipitation, followed by phenyl-Sepharose and Sephadex G-100 column chromatography, showed that the enzyme consisted of three subunits with molecular masses of 135, 63 and 57 kDa. In addition to tellurite reduction activity, the enzyme was able to reduce nitrate too. Our study extends the knowledge regarding this process in halophilic microorganisms. Besides, this approach may suggest an application for the organism or the enzyme itself to be used for bioremediation of polluted areas with different contaminants due to its nitrate reductase activity.
authors.affiliation: Extremophiles Laboratory, Department of Microbiology, Faculty of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, P.O. Box 14155-6455, Tehran, Iran.
authors.forename: Sana
authors.initials: S
authors.lastname: Alavi
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Amoozegar
authors.forename: Khosro
authors.initials: K
authors.lastname: Khajeh
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001711:Biotransformation; D055049:Salt Tolerance; D040141:Staphylococcaceae / Q000201:enzymology*; D013691:Tellurium / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C026660:tellurous acid; D013691:Tellurium