EXPRESSION OF THE CHIA GENE FROM SERRATIA MARCESCENS IN BOTH STRAIN E26 AND STRAIN NG13,NITROGEN-FIXING BACTERIA ASSOCIATED WITH RICE ROOT
chiA基因在稻根联合固氮菌E26和NG13中的表达

A 1.8 kb HinfI fragment carrying the chitinase gene (chiA) from Serratia marcescens was cloned into the expression vector pKK223-3 and the plasmid pMC71A, yielded the plasmid pKChiA and the plasmid pMChiA respectively. Both plasmid pKChiA and plasmid pMChiA were used to transform to the Enterobacter cloacae strain E26 and the Klebsiella oxytoca strain NG13, two nitrogen-fixing bacteria associated with rice root. The chiA gene could be highly expressed in the ChiA+ transformants of the strain E26 or the strain NG13. Cell location determination of the expressed chitinase showed that the enzyme existed not only in cell periplasm and cytoplasm, but also in extracellular broth. When the cultures were in the aftor logarithmic growthe phase, the distribution of the enzyme activity in extracellular broth, periplasm and cytoplasm were 23%-28%, 45%-51% and 21%-32%, respectively. The molecular weight of chitinase expressed in the ChiA+ transformants was 58 kD by SDS-PAGE analysis. The stability of the plasmid pMChiA in the transformants was better than that of the plasmid pKChiA.