Abstract:Curdlan is water-insoluble polysaccharides from Agrobacterium sp.ATCC 31749 after cell growth has ceased due to nitrogen exhaustion.The involvement of nitrogen regulatory systems in curdlan production is not surprising,but the mechanism is not known.To explore homeostatic responses to N limitation and the relationships between nitrogen regulation protein NtrC and curdlan synthesis,differences of expression level between Agrobacterium sp.ATCC 31749 and the ntrC mutant under nitrogen sufficient and nitrogen limitation were correlated by real-time PCR.For Agrobacterium sp.ATCC 31749 wild type,four nitrogen metabolism-associated genes(ntrB,glnA,glnB,nifR)and six carbon metabolism-associated genes(exoC,exoN,crd,cisY,ndk,glmU)relative expression level were improved differently under nitrogen limitation.The results indicated that Agrobacterium sp.regulated the whole celluar metabolism(nitrogen assimilation、carbon metabolism and energy metabolism etc.) and channeled the carbon flux into curdlan synthesis for energy storage under adverse condition.NtrC protein was involved in regulating curdlan production,and curdlan synthesis-associated enzymes were regulated at not only transcriptional level but also translational level.Curdlan synthesis capacity of the ntrC mutant decreased severely while relative expression level of the crd gene increased as compared to the wild type under nitrogen-limited conditions.It is speculated that the NtrC protein may not be transcription factor of the crd gene.
