A suicide vector p JQ-ntrB-cat containing tw o homobgous sequence of n trB gene was transformed into A grobacterium sp. A TCC 31749 by triparental conjugation and then, an ntrB gene m utantw as successfully constructed . It was found that the consumption rate of NH4Cland KNO3 by the mutant declined as com pared to the w ild strain. H ow ever, other nitrogenous com pounds, such as glutam ic acid and glutam ine, w ere utilized by the tw o strains in noun al behavi)r. The capacity of cuidlan production w as severely in paired by the m utation of ntrB gene. Consequently, cuidlan concentration obtained by the m utant strain w as dropped to 40% com paring w ith that of the w ild strain in batch feim entation with N H 4 C las sole nitrogen source. 0 n the other side, nitrogen lin itation effect on cuidlan synthesis w as elin inated and cuidlan w as produced by ntrB m utantunder nitrogen sufficient condition com panied w ith a probably novel but unidentified polymer which was insoluble in alkali solution. The results confirmed that the ntrB gene explicitly involved in regulating the biosynthesis of extracellular biopolym er in A grobacterium sp . A TCC 31749 under nitrogen lin ited condition and affected the utilization of a series of nitrogenous sources.%利用三亲本接合方法将含有ntrB基因两端同源序列的自杀载体pJQ-ntrB-cat导入土壤杆菌(Agrobacterium sp.ATCC 31749)中,获得了ntrB基因突变株.结果表明,ntrB突变株对NH4Cl和KNO3的利用能力有所下降.当分别以谷氨酸和谷氨酰胺为氮源时,ntrB突变株生长状况与野生菌相同.ntrB基因的突变导致土壤杆菌的胞外多糖--热凝胶合成能力显著降低:当以NH4Cl为唯一氮源时,热凝胶产量仅为野生株的40%.另外,ntrB突变株在氮源充足时仍然能合成胞外多糖,同时有不溶解于碱液的未知聚合物产生.本研究证明氮源代谢双组分之一的ntrB基因参与调节菌体在氮源限制条件下胞外多糖的合成以及调控菌体对NH4Cl和KNO3等氮源的利用.
展开▼
