Characteristics Of Cr(Ⅵ) Reduction By Marine Bacterium Pseudoalteromonas Sp.

Chromium (Cr) has been identified to pathogenic, teratogenic and carcinogenic effects, especially the Cr(VI), the toxicity, solubility and mobility of which is more dangerous. The release and discharge of Cr(VI) threaten seriously the environment.Among all the Cr pollution control methods, bioremediation has the advantages of cost saving and no secondary pollution, which has a broad application prospect. Microbial removal of Cr has two different ways:biological adsorption and reduction. While biological adsorption can be expressed that absorbing the Cr(VI) to cells directly, biological reduction is to put the Cr(VI) reduction into low toxicity and low mobility of Cr(III), which has more practical meaning. Some previous studies have reported that bacteria in different genus have the ability to reduce Cr(VI), which revealed a large number of Cr(VI) reductase in cell free extracts thatt included cytoplasmic solution and periplasmic space solution. However, there are few further analyses about whether Cr(VI) reductase is located in the cytoplasm or periplasmic space, and reduction process of periplasm enzyme to Cr(VI) keeps hitherto unknown.In this paper, Pseudoalteromonassp. CF10-13 (P. sp. CF10-13), was derived from the sediments of the South China Sea, which has efficient Cr(VI) reduction ability. The characteristics of Cr(VI) reduction in P. sp. CF10-13 were studied, which provided the theoretical guidance to explore the mechanism of microbial reduction of Cr (VI). The main research content is as follows:first of all, the characteristics of Cr(VI) reduction by P. sp. CF10-13 was analyzed by comparing different types of electron donor on the reduction of Cr (VI). It was showed that for resting cells, there are many electron donors, such as sodium acetate, sodium citrate, sodium lactate, sodium pyruvate, glucose and glycerol. Among these electron donors, sodium lactate was the obvious advantage one. In addition, sodium lactate could also promote the reducing Cr(VI) in growth cells, and 3 g/L sodium lactate was the best dosing quantity. The analysis of effect of elecron donor on reduction Cr(VI) showed that the existence of NO2- was likely to inhibit the reduction, while NO3- and SO42- had no significant effect on reduction activities. Analysis showed that there was no direct relationship between the oxidability of inorganic acid radical ion and microbial reduction activities. With dynamic model fitting the experimental data of different initial concentration of Cr(Ⅵ), it was found that the highest correlation coefficient was obtained in zero order reaction model, either the growth cells or resting cells When initial Cr(Ⅵ) concentration was set as 20-70 mg/L, pH=8.0,25℃ and 200 rpm.Next, the location of the bacteria Cr(Ⅵ) reductase in the bacteria and relative inductivity of enzyme was investigated by analysising of various active component cells reduction ability. The results of Cr(Ⅵ) reductase in P. sp. CF10-13 showed that Cr(Ⅵ) reductase that was a kind of soluble was locationed in the periplasmic space and cytoplasm, which could make same use of NADH and NADPH. The Cr-free cultivated cells could not reduce Cr(Ⅵ), while Cr cultivated cells had a 40% reduction rate, In addition, when P. sp. CF10-13 were cultivated exposure to Cr(VI) that was less than 5 mg/L and then were inoculated in LB culture medium containing 50 mg/L Cr(Ⅵ), the cells needed a period of stagnation before reducing Cr(Ⅵ). However, cells cultured in high concentration Cr(Ⅵ) had no stagnation. In conclusion, the Cr(Ⅵ) reductase in P. sp. CF10-13 was an inducible enzyme.Finally, the reduction process of Cr(Ⅵ) in P. sp. CF10-13 was studied and the results by the research of the accumulation of total chromium and hexavalent chromium content in the cell. It was showed that Cr(Ⅵ) entered the EPS firstly, then entered the intracellular periplasmic space and reduction reaction immediately, and Cr(Ⅲ) was discharged at last. The removal of total chromium mainly depended on the EPS. Using AFM and SEM, the results found that the cells cultured in the medium containing Cr had no precipitation in the cell surface. Using zeolite immobilization and adsorption of Cr(Ⅲ) microbes can significantly improve the removal rate of total chromium when reduction rate of Cr(Ⅵ) unchanged...