Brucella abortus Strain 2308 Wisconsin Genome: Importance of the Definition of Reference Strains

Abstract

Brucellosis is a bacterial infectious disease affecting a wide range of mammals and a neglected zoonosis caused by species of the genetically homogenous genus Brucella. As in most studies on bacterial diseases, research in brucellosis is carried out by using reference strains as canonical models to understand the mechanisms underlying host pathogen interactions. We performed whole genome sequencing analysis of the reference strain B. abortus 2308 routinely used in our laboratory, including manual curated annotation accessible as an editable version through a link at https://en.wikipedia.org/wiki/Brucella#Genomics. Comparison of this genome with two publically available 2308 genomes showed significant differences, particularly indels related to insertional elements, suggesting variability related to the transposition of these elements within the same strain. Considering the outcome of high resolution genomic techniques in the bacteriology field, the conventional concept of strain definition needs to be revised.

Keywords: Brucella; Brucella abortus; WGS; reference genome; reference strain.

FIGURE 1

Graphic representation of BLAST comparison of Brucella abortus 2308 (light gray bar), 2308W (light green bar) and 2308A (dark gray bar), visualized in ACT. Base pairs in kb coordinates are shown in the upper line for each chromosome. The red squares over the bars highlight an approximate region where the main differences among the genomes are found, and a zoom in is represented below. The red bars in the middle of the genomes’ bars indicate the regions are identical. White segments indicate deletions and the blue “hourglass-like” figure means an inversion. Chromosome I of 2308W shows the absence of three regions, which are present in the other two genomes. These regions coincide with contig breaks. At chromosome II, a 5.2 kb insertion is observed in 2308W and 2308A, and an inversion is present in 2308W. All deletions and inversions are surrounded by insertion elements.