The role of uridylyltransferase in the control of Klebsiella pneumoniae nif gene regulation

The glnD gene in enteric bacteria encodes a uridylyltransferase/uridylyl-removing enzyme which acts as the primary nitrogen sensor in the nitrogen regulation (Ntr) system. We have investigated the role of this enzyme in transcriptional regulation of nitrogen fixation genes in Klebsiella pneumoniae by cloning glnD from this organism and constructing a null mutant by insertional inactivation of the chromosomal gene using the Ω interposon. K. pneumoniae glnD encodes a 102.3 kDa polypeptide which is highly homologous to the predicted products of both Escherichia coli glnD and Azotobacter vinelandii nfrX. The glnD-Ω mutant was unable to uridylylate P_II and was altered in adenylylation/deadenylylation of glutamine synthetase. Uridylyltransferase was required for derepression of ntr-regulated promoters such as glnAp2 and p nifL but was not involved in the nifspecific response to changes in nitrogen status mediated by the nifL product. We conclude that a separate, as yet uncharacterised, nitrogen control system may be responsible for nitrogen sensing by NifL.