Isolation,Identification,Degradation Characteristics Of Dichloroethane-degrading Bacteria

With the rapid development of industry,environmental and health issues have become more serious due to 1,2-dichloroethane widely being used and its high toxicity.Compared with traditional physical and chemical methods,biological treatment with high efficiency,low energy consumption and no secondary pollution will have broad application prospects in the repair of environmental pollution.In this thesis,a 1,2-dichloroethane-degrading bacterium T-2,which was able to utilize 1,2-dichloroethane as the sole carbon and energy source,was isolated from the activated sludge of a chemical plant in Zhejiang.According to the morphological,physiological and biochemical characteristics and sequence analysis of 16S rRNA,the strain was identified as Starkeya sp.T-2.Any relevant literatures about degradation of 1,2-DCA by the strain have not been found,so T-2 may be the new strain for 1,2-DCA degradation.The strain has been deposited in the China Center for Type Culture Collection(Wuhan).The accession number of the strain in CCTCC and GenBank are M 2011263 and JN606070,respectively.The optimal conditions for 1,2-DCA degradation were initial pH 7.0-8.0 and temperature 30 ?,respectively.The laws of the strain growth and 1,2-DCA degradation were discussed under the optimal conditions.Single factor experiments have been used to discuss the effects of 1,2-DCA concentration,yeast extracts addition,the concentration of Cl-,nitrogen source,(NH4)2SO4 concentration,trace elements and oxygen concentration on 1,2-DCA degradation,results shows:strain T-2 could rapidly and completely degrade low concentrations of 1,2-DCA,but could not when concentrations of 1,2-DCA increased to 800 mg·L-1 or more;The extra addition of yeast extracts could promote the strain growth and 1,2-DCA degradation;Strain T-2 could adapt high salt concentration,only when the Cl-concentration increased to 15 g·L-1,there was a harmful effect on 1,2-DCA degradation rate;T-2 could commonly use all organic nitrogen and most of inorganic nitrogen,(NH4)2SO4 was the best option and the optimum concentration in mineral salts medium was 1.8 g·L-1;In trace elements,CoCl2·6H2O,ZnCl2 and CuSO4-5H20 had larger impacts on 1,2-DCA degradation,and degradation rate would decrease obviously if mineral salts medium was absence of such three trace elements;1,2-DCA degradation also required certain amount of oxygen concentration.The 1,2-DCA degrading process followed the Haldane kinetics model.The maximum specific growth rate and specific degradation rate were 0.065 h-1 and 0.54 h-1,respectively,and the cell yield coefficient of the strain growing on 1,2-DCA was 0.191 mg-mg-1.Strain T-2 could mineralize 1,2-DCA finally into CO2 and H20 during growth.After complete degradation,carbon balance and chlorine balance were analysed by measuring the bacterial biomass,C02 generation,the amount of TOC and Cl-release,and the mineralization ratio was 45%.Cells played a main role in 1,2-DCA degradation and didn't require 1,2-DCA induction before direct degradation of 1,2-DCA and showed a high substrate specificity.The main metabolic intermediate identified by GC-MS was 2-chloroethanol.The metabolite suggested a possible metabolic pathway for 1,2-DCA biodegradation,in which 1,2-DCA firstly took off a Cl to generate 2-chloroethanol,which then followed two oxidation steps to chloroacetic acid,finally chloroacetic acid took off the other Cl to a simple organic compound entering the cycles of biochemical reactions.