Isolation And Identification Of A Cr(?)-reducing Bacteria WUST-Cr1 And Thereof Detoxification Of Hexavalent Chromium

Chromium and its compounds are widely used in electroplating,tanning and other fields,and a large amount of chromium residues and chromium-containing wastewaters are produced in the production process,the direct emissions of which are bound to bring pollution to the water and soil.Hexavalent Chromium(Cr(?))can seriously affect human health as well as the growth of plants and animals,and its pollution control has aroused widespread attention.The common treatment of Cr(?)is reducing Cr(?)from high toxicity,free to low toxicity,stable trivalent chromium(Cr(?))by physical,chemical or biological methods.The use of physical and chemical methods is expensive,and easy to lead to secondary pollution.In contrast,biological methods to treat Cr(?)pollution are highly welcome due to environmentally friendly,highly efficient,low cost,thorough detoxification,no secondary pollution,etc.showing a broad development prospects.In this study,a heavy metal Cr(?)was a target pollutant,and an indigenous strain was isolated from the soil contaminated with chromium dust,and was identified.The optimum culture conditions of WUST-Cr1 were determined.The preliminary analyses of reduction mechanism and reduction kinetics were performed.Finally,the synergistic effects of biochar(BC)and activated carbon(AC)on the reduction of hexavalent chromium were investigated.The main conclusions of this paper are as follows:(1)A high efficiently reducing bacteria WUST-Cr1 was isolated.According to its morphological and physiological properties and the analysis of its 16 S r DNA gene partial sequences,the Cr(?)reducing bacteria was identified as Lysinibacillus sp.(2)The optimum temperature,initial p H,rotary shaker speed and bacterial load for WUST-Cr1 were 35 ?,p H =7.0,150 rpm and inocula 2 %(v/v),respectively,under which 100 mg/L Cr(?)in LB was completely reduced by strain WUST-Cr(?)within 20 h.When Cr(?)is at low concentration,the Cr(?)reduction reaction is a zero order reaction.With the increase of Cr(?)in the system,the reaction rate constant decreases,and the reaction order is between zero and the first.(3)Cr(?)is directly reduced by strain WUST-Cr1 through enzymatic reaction.Chromium reductase is present in the cytoplasm,and the reduced Cr(III)is distributed in solution as well as in the cell in a small amount.And the cell itself is very weak in the adsorption capacity of hexavalent chromium.The strain WUST-Cr1 was sensitive to tetracycline,kanamycin and chloramphenicol,and is resistant to ampicillin and streptomycin.100 mg/L Cr(?)in LB was completely reduced by strain WUST-Cr1 in the presence of 50 ?g/m L streptomycin within 28 h under optimum condtions(p H = 7.0,35 ? and 150 rpm).(4)Both AC and BC could improve the reducing performance of strain WUST-Cr1,while BC had a greater synergistic effect on the reduction of Cr(?)by WUST-Cr1.The adsorption capacity of unmodified BC to Cr(?)was very weak.When BC and WUST-Cr1 were applied to hexavalent chromium,the addition of 5 %(w/v)BC could effectively improve the reducing ability of the strain.The addition of BC can significantly promote the growth of bacteria.A 47 % increase in biomass was obtained by the addition of BC compared with the negative control.