Comparative analysis of hmuO function and expression in Corynebacterium species

Abstract

We have constructed defined deletions in the hmuO gene from Corynebacterium diphtheriae and Corynebacterium ulcerans and show that the C. ulcerans hmuO mutation results in a significant reduction in hemoglobin-iron utilization, whereas in C. diphtheriae strains, deletion of hmuO caused no or only partial reduction in the utilization of heme as an iron source. We also show that expression from the C. ulcerans hmuO promoter exhibits minimal regulation by iron and heme whereas transcription from the C. diphtheriae hmuO promoter shows both significant iron repression and heme-dependent activation. These findings indicate that variability in HmuO function and expression exists among Corynebacterium species.

FIG. 1.

Amino acid comparison between various Corynebacterium HmuO proteins and the human heme oxygenase HO-1. The numbers separated by a slash represent percent identity/similarity. Cd-NCTC, C. diphtheriae genome strain NCTC 13129 (8); Cd-C7, C7(−) strain; Cu, C. ulcerans 712; Cg, Corynebacterium glutamicum; Cjk, Corynebacterium jeikeium.

FIG. 2.

A. Alignment of the nucleotide sequences in the hmuO promoter region between C. ulcerans (CU) and C. diphtheriae C7 (CD). DtxR binding sites are underlined. rbs, putative ribosome binding site; ATG, start codon for hmuO. The arrow indicates the start of transcription in C. diphtheriae (19). B. Alignment of the 19-bp DtxR binding sites from CU712 and C. diphtheriae C7 with the DtxR consensus binding sequence. Residues represented by bold characters indicate the most highly conserved nucleotides.