Internal glutamine and glutamate pools in Klebsiella pneumoniae grown under different conditions of nitrogen availability

Internal pool sizes of glutamine and glutamate in Klebsiella pneumoniae gro wn under nitrogen limitation or nitrogen sufficiency were measured to study the signal transduction of external nitrogen limitation. K pneumoniae cell s were grown in an anaerobic, ammonium-limited chemostat culture. At a grow th rate of 0.217 h(-1), the steady state ammonium concentration in the cult ure was 55 muM, correlating with repression of the nitrogen fixation (nif) genes. At growth rates below 0.138 h(-1), the ammonium concentration in the culture dropped below 0.5 muM and the nif genes became derepressed. During the transition from nitrogen sufficiency to nitrogen limitation, the inter nal glutamine pool in K. pneumoniae decreased by a factor of approximately 6. The glutamate pool, however, remained stable. Similarly, in anaerobic ba tch cultures with different limiting nitrogen sources, the glutamine pool g enerally decreased by a factor of 7 to 9 when nif gene derepression was ach ieved. All the limiting nitrogen sources used resulted in decreased growth rates compared with growth under nitrogen excess, suggesting an inverse rel ationship between glutamine pool size and doubling time. These studies indi cate that K. pneumoniae perceives external nitrogen limitation as internal glutamine limitation.