The Burkholderia cepacia fur gene: co-localization with omlA and absence of regulation by iron

The ferric uptake regulator (Fur) functions as a transcription repressor of many genes in bacteria in response to iron, but the presence of a functional equivalent of this protein has not been demonstrated in Burkholderia cepacia. A segment of the Burkholderia pseudomallei fur gene was amplified using degenerate primers and used to identify chromosomal restriction fragments containing the entire fur genes of B. cepacia and B. pseudomallei. These fragments were cloned and sequenced, revealing the Fur protein of both species to be a polypeptide of 142 amino acids possessing a high degree of amino acid sequence identity to Fur of other members of the β subclass of the Proteobacteria. Primer extension analysis demonstrated that transcription of B. cepacia fur originated from a single promoter located 36 bp upstream from the fur translation initiation codon. The Fur polypeptide of B. cepacia was shown to functionally substitute for Fur in an Escherichia coli fur mutant. Single copy fur–lacZ fusions were constructed and used to examine the regulation of B. cepacia fur. The B. cepacia fur promoter was not responsive to iron availability, the presence of hydrogen peroxide or the superoxide generator methyl viologen. In addition, fur expression was not significantly influenced by carbon source. Interestingly, the presence of the divergently transcribed omlA/smpA gene upstream of fur in some members of the γ subclass of the Proteobacteria is retained in several genera within the β taxon, including Burkholderia.