ABSTRACT
@#ObjectiveTo screen a high alkaline xylanase-producing strain,subject to molecular identification and characterization of enzymatic property,and optimize its fermentation condition.MethodsThe farmland soil samples from Shanxi,Henan and Zhejiang Provinces were collected aseptically,from which the high xylanase-producing strains were screened by enrichment culture,isolation and identification of 16S r DNA,and determined for enzymatic properties.The carbon source(xylan,lactose,soluble starch,sucrose,bran and glucose),nitrogen source[ammonium oxalate,peptone,yeast powder,(NH_4)_2SO_4,NH_4Cl,Na NO_3,urea,beef extract,bean powder,KNO_3,(NH_4)_2HPO_4or random mixture of two of peptone,yeast powder,beef extract,(NH_4)_2HPO_4and bean powder],metal ion[CuCl_2,MgCl_2,ZnCl_2,Al_2(SO_4)_3,CoCl_2,MnCl_2,AgNO_3,NaCl,CaCl_2,FeCl_2,BaCl_2 and FeCl_3],pH value(3.0～10.0)in medium and the fermentation temperature(25,28,30,33,35,37 and 40℃)were optimized by single factor test,while the contents of components[xylan,(NH_4)_2HPO_4and bean powder]by response surface method.The high alkaline xylanase-producing strain was fermented by using the optimized medium under the optimized condition,and determined for xylanase activity,and the result was compared with that predicated in model.ResultsA high alkaline xylanase-producing strain named as SX6-18 was screened and identified as Paemibacillus based on 16s rDNA sequence analysis.The xylanase produced by the strain maintained more than 70%of relative activity at temperatures of 25～55℃and pH 6.0～10.0.Mg(2+)promoted while Fe(2+)promoted while Fe(3+),Mn(3+),Mn(2+)and Cu(2+)and Cu(2+)inhibited the activity of xylanase.The optimal carbon source,nitrogen source and metal ion of the medium were xylan,bean powder+(NH_4)_2HPO_4 and Fe(2+)inhibited the activity of xylanase.The optimal carbon source,nitrogen source and metal ion of the medium were xylan,bean powder+(NH_4)_2HPO_4 and Fe(3+),while the optimal p H value and temperature for fermentation were 8.0 and 30℃，respectively.However,the optimal component contents were 15.00 g/L xylan,3.03 g/L(NH_4)_2HPO_4and 3.28 g/L bean powder.The activity of xylanase cultured in optimized medium under opti-mized condition for fermentation reached 701.08 U/m L,which was closed to the expected value(693.96 U/m L).ConclusionA high alkaline xylanase-producing strain SX6-18 was successfully screened,which maintained relatively high enzyme activity in alkaline condition.This study laid a foundation of application of xylanase in papermaking and washing fields.
ABSTRACT
The development of high-efficiency, low-toxicity, and low-residue green pesticides is the main trend of pesticide research, and the microbial-derived antibiotics are one of the essential parts of green pesticides and play a significant role in agriculture. With the development of microbial genomics technology, metabolic engineering, high-throughput screening and other technologies, the research on new microbial-derived antibiotics has entered a new stage in agriculture. Here we briefly summarize the types of new microbial-derived antibiotics developed in agriculture over the past decade. We also introduce the research strategies for high-yield breeding and fermentation of antibiotic-producing strains in agriculture. This review may provide references for the future development of agricultural antibiotics.