Three
Corynebacterium species are capable of producing the diphtheria toxin:
C. diphtheriae,
C. ulcerans and, to a lesser extent,
C. pseudotuberculosis. The toxin is encoded by the
tox gene located within a prophage lysogenized in the bacterial chromosome (
1,
2). In developing countries, diphtheria is caused by toxigenic
C. diphtheriae. In developed countries, however, diphtheria-like infections caused by toxigenic
C. ulcerans have outnumbered those caused by toxigenic
C. diphtheriae (
3,
4).
Here, we present the draft genome sequences of two toxigenic
C. ulcerans strains. Strains LSPQ-04227 (NML 040264) and LSPQ-04228 (NML 130346) were isolated from two different patients, one from a blood sample and the other from a scar exudate following thoracic surgery. Both strains were identified as
C. ulcerans based on growth on Tinsdale plates (
5), biochemical profiles on bioMérieux API Coryne microbial identification strips, and 16S rRNA gene sequences. The presence of the
tox gene, typical of toxigenic strains, was confirmed by PCR (
6). An Elek's test (
7) confirmed the toxigenicity of both strains.
Both genomes were sequenced on an Ion Torrent PGM sequencer (Life Technologies, Carlsbad, CA). A total of 4,230,671 reads were sequenced for a total of 653 Mbp for isolate LSPQ-04227, while 2,672,954 reads were sequenced for a total of 468 Mbp for isolate LSPQ-04228. The quality of the raw sequence data was checked using FastQC (
http://www.bioinformatics.babraham.ac.uk/projects/fastqc/). SPAdes version 3.5 (
http://bioinf.spbau.ru/spades [
8]) was used to assemble each genome. The annotations were done using the NCBI Prokaryotic Genome Annotation Pipeline version 2.10 (
9).
The draft genome sequence of LSPQ-04227 is 2,428,218 bp, with an average G+C content of 53.4%. It consists of 10 contigs, ranging in size from 363 to 691,756 bp, with an
N50 of 543,718 bp. A total of 1,772 protein-coding sequences, 51 tRNAs, 5 rRNAs, and 342 pseudo-genes are predicted. The draft genome size of LSPQ-04228 is 2,439,377 bp, with an average G+C content of 53.4%. It consists of 23 contigs, ranging in size from 213 to 410,667 bp, with an N
50 of 276,589 bp. A total of 1,717 protein-coding sequences, 53 tRNAs, 11 rRNAs, and 424 pseudo-genes are predicted. In strain LSPQ-04227, the
tox gene is on contig 1 and covers nucleotide positions 202029 to 203711. In strain LSPQ-04228, the
tox gene is on contig 5, positions 77442 to 79124. Interestingly, whereas in
C. diphtheriae the
tox gene is carried by a lysogenic phage, here, an alignment of both
C. ulcerans tox genes and flanking sequences with
Corynebacterium phage sequences (
10,
11) showed an absence of phage-like sequences, with the exception of an integrase 32 kbp upstream the
tox gene.