| In this thesis,a bacterial strain hydrolyzing gamma-decalactone was isolated from soil samples and the preserved strains by laboratory.The bacterium was identified based on the phylogenetic relationship,and its growth conditions were optimized.Moreover,we established the method for enzyme assays and optimal conditions of gamma-decalactone hydrolysis.Based on observations of cell and colony morphology,biophysiology and biochemistry,the strain X6 was primarily identified as Bacillus cereus, which has been confirmed by 16S rDNA sequence information.By single factor and perpendicular tests,the fermentation medium was optimized:sucrose 1.0%;glucose 0.5%;peptone 1.0%;yeast extract 0.5%; K2HPO4 0.2%;MgSO4 0.1%;NaCl 0.5%;no pH adjustment.The culture conditions were listed below:temperature 30℃;pH 6.5;volume of medium 90ml;rotation speed 160rpm.The yield of biomass was 15g/l approximately.Several drying procedures including refrigeration,heat,air or vacuum drying were used to make the dry bacterial biomass.It was found that the enzyme activity was preserved well under vacuum drying.Different buffers was tested,and the results indicated that the bacterium has the best enzyme activity and enantiomeric excess values in the phosphate buffer（pH 6.5、0.2 mol/l）.The supplement of low-concentration Arabic gum in the reaction solution improved its conversion rate while the conversion rate and enantiomeric excess number were 40.2%and 61.5%,respectively.The reaction system of gamma-decalactone hydrolysis included the following components:phosphate buffer 20ml;Arabic gum solution 2.0ml; dry bacterium 0.05g;racemic gamma-decalactone 0.5ml.The reaction conditions,e.g.,concentration of bacterial biomass and substrate、temperature and time of reaction,were optimized and listed below: gamma-decalactone 0.7ml;drying biomass 0.08g;temperature 28℃in water bath;reaction time 12 hours.Under those optimized conditions,the conversion rate and enantiomeric excess number were 46.5%and 81.3%, respectively. |
PDF Full Text Request