Isolation and identification of a wild amylase-producing bacterium and optimization of its fermentable conditions

Objective To isolate high amylase-producing strain from soil,and optimize its enzyme producing conditions to obtain more economical amylase.Method The plate dilution method was used to screen amylase-producing bacterial strains from the samples collected from soil with high starch content and waste water.The bacterial strains were identified based on morphological,physiological characteristics and phylogenetic analysis of 16S rDNA,and the effective enzyme production conditions were optimized through the optimization of various parameters such as carbon source,nitrogen source,ion concentration and UV mutagenesis.Iodine-starch method etc.were used to study the enzymatic properties of the crude extract.Result 19 wild-type strains producing more and stable enzyme were obtained.Among these strains,Z19 produced the highest amylase activity(up to 351.78 U/mL).It was identified as a strain of B.amyloliquefaciens based on morphological,physiological characteristics and phylogenetic analysis of 16S rDNA.The optimal fermentation conditions were established as follow: cornmeal as the carbon source;glutin as nitrogen source;the starch concentration at 0.5% while NaCl at 0.5% and CaCl2 at 0.25%;pH value 7.0 at 37 ℃.Under these conditions the enzyme activity was improved to 1 360.72 U/mL.Under the solid state fermentation,the optimal culture conditions were follows: the ratio of wheat bran to water was 1︰0.6 and the inoculum of strain was 0.1% at pH 7.0 for 120 hours.The enzyme activity was 1 504.2 U/mL.By studying enzymology property of Z19,its optimal reaction condition was 55 ℃ to 60 ℃ at pH 6.5.The concentration of substrate was 0.5%.Conclusion The strain Z19 with high enzyme activity was obtained and its fermentable condition is suitable for industrial production,which suggests an application prospects.