粪产碱杆菌中ntrB基因调节胞外多糖合成的研究

In this study, suicide vector pJQ-cat-ntrB which contained the two homology fragments of ntrB gene was transformed into Agrobacterium sp. ATCC 31749 by triparental conjugation and then, an ntrB gene mutant was successfully constructed. Consumption rate of NH4Cl and KNO3 by the mutant declined as compared to wild strain. However, other nitrogenous compounds, such as glutamic acid and glutamine, were utilized normally. Curdlan productivity was severely impaired after ntrB gene was mutated and consequently, curdlan production dropped to 40% compared with the output of the wild strain in batch fermentation with NH4Cl as sole nitrogen source. On the other side, nitrogen limitation effect on curdlan synthesis was eliminated and curdlan was produced by ntrB mutant at nitrogen sufficient condition companied with a novel but unidentified polymer which was insoluble in alkali. Our results confirmed that the ntrB gene explicitly involved in regulating the biosynthesis of extracellular biopolymer in Agrobacterium sp. ATCC 31749 under nitrogen-limited condition and affected the utilization of a series of nitrogenous sources.