Mechanism Study On Cr(Ⅵ) Removal By A Strain Of Bacillus Sp. Based On Characteristics Of NiR Enzyme

The mechanism of Cr (VI) removal by microorganism kept be attractive to researchers, many researches showed that Cr (VI) removal by bacteria was primarily due to enzymatic reactions. The sulfite reducing bacteria metabolites had good effects for Cr(VI) removal, and sulfite reductase usually possessed nitrite reduction activities, what’s more, dechromisation strains mostly contained nitrite reductase, but the studies of Cr(VI) removal by nitrite reductase was rarely reported. Therefore, this article discussed Cr (VI) removal mechanism of a predominant strain screened before from the perspective of nitrite reductase, taking a dechromisation predominant strain(Bacillus sp.) for example.Firstly, the Cr(VI) removal efficiency by the components of predominant strain were studied. The result showed that all of the supernate and precipitate from bacterial suspension and protoplast and cracking protoplast had the capability for dechromisation in different degree. The supernate’s capability of dechromisation was higher than precipitate of bacterial suspension. The protoplast’s capability of dechromisation was higher than cracking protoplast.Next, This paper explored four factors impact on enzyme activities by improved griess dyeing, after getting the nitrite reductase by fermentation and ultrasonication method, they were the temperature、pH、Cr(Ⅵ) induced concentration and magnetic field. The result showed that the optimal conditions of nitrite reductase collection was that the temperature was37℃, the pH was6.5, the Cr(Ⅵ) induced concentration was80mg/L, and the magnetic field intensity was15mT. The nitrite reductase activity reached to30U/mL. As the concentration of Cr(Ⅵ) induced increased, the enzyme activity increased first then fallen down. As the concentration was40and80mg/L, nitrite reductase activity increased4.5%and13.64%respectively. Therefore, Cr(Ⅵ) could induced the strain producing nitrite reductase. As the concentration was120mg/L, nitrite reductase maintained90%enzyme activity. As the concentration of Cr(Ⅵ)was between160and200mg/L, nitrite reduetase activity decreased by70.5%.Lastly, the correlation of nitrite reductase and Cr(Ⅵ) removal of predominated strain were explored by comparing the dechromisation rate of between nitrite reductase and cracking protoplast and between bacterial suspension with and without nitrite reductase. The result showed that the contribution of dechromisation rate of nitrite reductase was higher than10%(P<0.05) as the concentration of Cr(Ⅵ) was below100mg/L. The Cr(Ⅵ) removal rate of suspension with nitrite reductase was reached to52.8%when the concentration of Cr(Ⅵ) was60mg/L. The dechromisation rate of nitrite reductase was30%as the concentration of Cr(Ⅵ) was80mg/L. While the concentration of Cr(Ⅵ) was higher than120mg/L, there was no difference in dechromisation rate between the four components. The Cr(Ⅵ) removal rate and nitrite reductase activity were positively correlated with the nitrite reductase activity. Plus a magnetic field can enhance the vitality of nitrite reductase. In brief, the existence of nitrite reductase was one of the Cr (Ⅵ) removal mechanisms by Bacillus sp.