Role of the Type III Secretion System in a Hypervirulent Lineage of Bordetella bronchiseptica

Abstract

Despite the fact that closely related bacteria can cause different levels of disease, the genetic changes that cause some isolates to be more pathogenic than others are generally not well understood. We use a combination of approaches to determine which factors contribute to the increased virulence of a Bordetella bronchiseptica lineage. A strain isolated from a host with B. bronchiseptica-induced disease, strain 1289, was 60-fold more virulent in mice than one isolated from an asymptomatically infected host, strain RB50. Transcriptome analysis and quantitative reverse transcription-PCR showed that the type III secretion system (TTSS) genes were more highly expressed by strain 1289 than strain RB50. Compared to strain RB50, strain 1289 exhibited greater TTSS-mediated cytotoxicity of a mammalian cell line. Additionally, we show that the increase in virulence of strain 1289 compared to that of RB50 was partially attributable to the TTSS. Using multilocus sequence typing, we identified another strain from the same lineage as strain 1289. Similar to strain 1289, we implicate the TTSS in the increased virulence of this strain. Together, our data suggest that the TTSS is involved in the increased virulence of a B. bronchiseptica lineage which appears to be disproportionately associated with disease. These data are consistent with the view that B. bronchiseptica lineages can have different levels of virulence, which may contribute to this species' ability to cause different severities of respiratory disease.

Transcriptional Profiling of the Iron Starvation Response in Bordetella pertussis Provides New Insights into Siderophore Utilization and Virulence Gene Expression

“…Some strains, including Tohama I, secreted modest levels of T3SS proteins and others secreted significantly higher levels; none of the B. pertussis strains produced the high Bsp22 levels observed in B. bronchiseptica RB50. It is possible that T3SS expression in B. pertussis is a strain-or lineage-variable trait, as has been proposed for B. bronchiseptica (26). No obvious correlation was observed between highly passaged laboratory-adapted B. pertussis isolates versus those that have been minimally passaged.…”

“…Analysis of the B. pertussis Tohama I derivative BP953 (81), carrying chromosomal fhaB-lacZ and ptx-phoA transcriptional fusions, revealed only modest elevation of fhaB and ptxA expression under iron-depleted growth conditions as compared with iron-replete conditions (46% and 14% increases in reporter activity after 48 h of culturing, respectively) (data not shown). Also among the B. pertussis genes showing elevated transcript abundance under iron starvation conditions were Bvg-dependent genes of the T3SS, which have been extensively analyzed in B. bronchiseptica (26,37,47,48,53,54,64,65,92,93). We examined the influence of iron starvation on Bordetella T3SS gene expression and protein production in greater detail (see below).…”

Comparative Analyses of a Cystic Fibrosis Isolate of Bordetella bronchiseptica Reveal Differences in Important Pathogenic Phenotypes

“…Since B. bronchiseptica is more genetically and clinically diverse than the other classical bordetellae, it was hypothesized that strains from different phylogenetic lineages of B. bronchiseptica utilize different sets of virulence factors (5,8,(12)(13)(14). Several studies have recently confirmed this hypothesis (15)(16)(17).…”

“…Additionally, dye-swap experiments, in which the fluorescent labels were exchanged to ensure that uneven incorporation did not confound our results, were performed analogously. Fluorescently labeled cDNA copies of the total RNA pool were prepared, and the two differentially labeled reactions to be compared were then mixed, followed by buffer exchange, purification, and concentration as described previously (15,16,33,35,36). The two differentially labeled reactions to be compared were combined and hybridized to an RB50-specific long-oligonucleotide microarray (35).…”

Enzymatic Carbon Dioxide Capture

“…Additionally, dye-swap experiments were performed analogously, in which the fluorescent labels were exchanged to ensure that uneven incorporation did not confound our results. Fluorescently-labeled cDNA copies of the total RNA pool were prepared by direct incorporation of fluorescent nucleotide analogs during a first-strand reverse transcription (RT) reaction [39,[45][46][47]. The two differentially labeled reactions were then combined and directly hybridized to a B. bronchiseptica strain RB50-specific long-oligonucleotide microarray [46].…”