Bvgr regulates the transcription of a wide variety of genes in Bordetella bronchiseptica, including virulence factors.

SEN-KILIC; SISTI, FEDERICO; WONG, TING; FERNANDEZ, JULIETA; GUTIERREZ, MARÍA DE LA PAZ; DAMRON, F. HEATH

Congreso; PABMB-SAIB 2019; 2019

Bordetella bronchiseptica (Bb) is a pathogenic bacterium that causes respiratory infections in animals. Bb virulence factors are regulated by several mechanisms, being the most well-characterized the Bordetella three component system, BvgASR. When this system is active, the response regulator BvgA activates the expression of virulence-activated genes. On the contrary, BvgR represses the transcription of some virulence-repressed genes, such as Bb flagellin. No DNA binding domain has been described for BvgR. To date, microarray analyses have been used to identify some genes controlled by BvgR but the totality of the genes regulated by BvgR is unknown. In order to characterize more deeply the BvgR regulon, we performed RNA seq on RNA samples from a wild type Bb (Bb WT) and a mutant in bvgR (Bb bvgR-). Comparing the bvgR mutant to the wild type revealed differential expression of 319 genes, of which 221 and 98 were upregulated or downregulated, respectively. Among the upregulated genes we could detect the entire flagellar and chemotaxis genes regulons; the flagella master regulator encoded by flhD was the most highly upregulated gene. In addition, several transcriptional regulators, chaperons, heat shock proteins and proteins related to the second messenger c-di-GMP metabolism were found differently expressed between the strains.The transcriptomic analysis also revealed 98 genes with higher expression in Bb WT than in Bb BvgR-, some of which encoded for virulence factors such as bipA and Type Three Secretion System proteins. qRT-PCR and western blots confirmed these data. In order to evaluate the impact of the downregulation of the TTSS on Bb bvgR-, cytotoxicity assays on J774 macrophages were performed. A decrease in the percent LDH release induced by Bb bvgR- confirmed that this strain is less cytotoxic than Bb WT. Altogether, these data indicate that BvgR regulates a complex network of genes and different phenotypes such as motility and cytotoxicity. In future studies we will further characterize the downstream regulatory networks controlled by BvgR.