Genome Sequence of a Copper-Resistant Strain of Acidovorax citrulli Causing Bacterial Fruit Blotch of Melons.

Bacterial fruit blotch (BFB) of melons is a seed-borne disease caused by Acidovorax citrulli. We determined the draft genome of A. citrulli Tw6. The strain was isolated from a watermelon collected from Beijing, China. The A. citrulli Tw6 genome contains 5,080,614 bp and has a G+C content of 68.7 mol%.

GENOME ANNOUNCEMENT

Bacterial fruit blotch (BFB) of melons leads to important economic losses to cucurbits worldwide (1–3). This seed-borne disease is caused by the Gram-negative bacterium Acidovorax citrulli. The management of BFB would involve the use of resistant cultivars; however, it is difficult to select resistant cultivars because of the high level of genetic diversity of A. citrulli. Therefore, copper bactericides have widely been used to control BFB (4, 5). The long-term use of copper bactericides has led to the development of copper-resistant (Cur) strains of A. citrulli, resulting in difficulties in disease control. Previous reports have shown that A. citrulli can be classified into two genetically distinct groups (6). In 2007, a draft genome sequence of A. citrulli AAC00-1, which belongs to group 2 (GenBank accession no. NC_008752), was reported. Compared to strain A. citrulli AAC00-1 and other A. citrulli strains, strain Tw6 was found to show an unexpectedly high capacity for tolerating copper sprays and antibiotics. In order to study the copper metabolism of A. citrulli, we announce here the determination of the draft genome of strain A. citrulli Tw6, which was isolated from a watermelon seedling displaying leaf scorch symptoms in Beijing, China.

The genome of this strain was sequenced with massively parallel sequencing (MPS) Illumina technology. Two DNA libraries were constructed, a paired-end library with an insert size of 300 to 400 bp, and a mate-pair library with an insert size of 5 kb. Using Velvet version 1.2.07, we assembled the genome into 25 scaffolds, with an average length of 203,224 bases. The largest one was 768,921 bases. Among the large scaffolds, the N50 contig size was 527,712 bases. Gene prediction was performed on the A. citrulli strain AAC00-1 genome assembly using GeneMarkS (http://topaz.gatech.edu/) (7). A whole-genome BLAST search (E value, ≤1e-5; minimal alignment length, ≥40%) was performed against 5 databases. They are the TREMBL (computer-annotated supplement to Swiss-Prot) (8), nonredundant (NR) protein (9), Swiss-Prot (10), Clusters of Orthologous Groups (COG) (11), and Gene Ontology (GO) (12) databases.

The genome contains a single circular chromosome of 5,080,614 bp, with a G+C content of 68.7%. The total coding genes are 4,491,540 bp, with a coding ratio of 88.41%. A total of 4,759 protein-coding genes were identified in the genome, with an average length of 943 bp. There are three rRNAs and 48 tRNAs.

Nucleotide sequence accession numbers.

This whole-genome shotgun project has been deposited at DDBJ/EMBL/GenBank under the accession no. JXDJ00000000. The version described in this paper is version JXDJ01000000.