Characterization of the gene cluster involved in allantoate catabolism and its transcriptional regulation by the RpiR-type repressor HpxU in Klebsiella pneumoniae.

Bacteria, fungi, and plants have metabolic pathways for the utilization of nitrogen present in purine bases. In Klebsiella pneumoniae, the genes responsible for the assimilation of purine ring nitrogen are distributed in three separated clusters. We characterized the gene cluster involved in the metabolism of allantoate (genes KPN_01761 to KPN_01771).

Role of YiaX2 in L-ascorbate transport in Klebsiella pneumoniae 13882.

The yiaK-S operon is required for aerobic growth on L-ascorbate in several Enterobacteriaceae. Here we present evidence that the yiaX2 gene belonging to the yiaK-S operon of Klebsiella pneumoniae 13882, which encodes a protein similar to the putative transporters classified as the major facilitator superfamily, is involved in the uptake of L-ascorbate. Concentration kinetic analysis yielded an apparent K(m) of YiaX2 for L-ascorbate of 161.

Quaternary structural transitions in the DeoR-type repressor UlaR control transcriptional readout from the L-ascorbate utilization regulon in Escherichia coli.

UlaR is a DNA binding protein of the DeoR family of eubacterial transcriptional repressors which maintains the utilization of the L-ascorbate ula regulon in a repressed state. The availability of L-ascorbate in the growth medium releases UlaR-mediated repression on the ula regulon, thereby activating transcription. The molecular details of this induction by L-ascorbate have remained elusive to date.

The yiaKLX1X2PQRS and ulaABCDEFG gene systems are required for the aerobic utilization of L-ascorbate in Klebsiella pneumoniae strain 13882 with L-ascorbate-6-phosphate as the inducer.

The capacity to both ferment and oxidize L-ascorbate has been widely documented for a number of enteric bacteria. Here we present evidence that all the strains of Klebsiella pneumoniae tested in this study ferment L-ascorbate using the ula regulon-encoded proteins. Under aerobic conditions, several phenotypes were observed for the strains.

Dual role of LldR in regulation of the lldPRD operon, involved in L-lactate metabolism in Escherichia coli.

The lldPRD operon of Escherichia coli, involved in L-lactate metabolism, is induced by growth in this compound. We experimentally identified that this system is transcribed from a single promoter with an initiation site located 110 nucleotides upstream of the ATG start codon. On the basis of computational data, it had been proposed that LldR and its homologue PdhR act as regulators of the lldPRD operon.

Aerobic L-ascorbate metabolism and associated oxidative stress in Escherichia coli.

The anaerobic utilization of L-ascorbate by gene products of the ula regulon in Escherichia coli has been widely documented. Under aerobic conditions, we have shown that this metabolism is only functional in the presence of casein acid hydrolysate. Transcriptional fusions and proteomic analysis indicated that both the ula regulon and the yiaK-S operon are required for the aerobic utilization of this compound.

Regulation of expression of the divergent ulaG and ulaABCDEF operons involved in LaAscorbate dissimilation in Escherichia coli.

The ula regulon, responsible for the utilization of L-ascorbate in Escherichia coli, is formed by two divergently transcribed operons, ulaG and ulaABCDEF. The regulon is negatively regulated by a repressor of the DeoR family which is encoded by the constitutive gene ulaR located downstream of ulaG. Full repression of the ula regulon requires simultaneous interaction of the repressor with both divergent promoters and seems to be dependent on repressor-mediated DNA loop formation, which is helped by the action of integration host factor.

The gene yjfQ encodes the repressor of the yjfR-X regulon (ula), which is involved in L-ascorbate metabolism in Escherichia coli.

Mutations in yjfQ allowed us to identify this gene as the regulator of the operon yjfS-X (ula operon), reported to be involved in L-ascorbate metabolism. Inactivation of this gene renders constitutive the expression of the ula operon, indicating that YjfQ acts as a repressor. We also demonstrate that this repressor regulates the nearby yjfR gene, which in this way constitutes a regulon with the ula operon.