A family of genus‐specific RNAs in tandem with DNA‐binding proteins control expression of the badA major virulence factor gene in Bartonella henselae

Abstract

Bartonella henselae is a gram‐negative zoonotic bacterium that causes infections in humans including endocarditis and bacillary angiomatosis. B. henselae has been shown to grow as large aggregates and form biofilms in vitro. The aggregative growth and the angiogenic host response requires the trimeric autotransporter adhesin BadA. We examined the transcriptome of the Houston‐1 strain of B. henselae using RNA‐seq revealing nine novel, highly‐expressed intergenic transcripts (Bartonella regulatory transcript, Brt1‐9). The Brt family of RNAs is unique to the genus Bartonella and ranges from 194 to 203 nucleotides with high homology and stable predicted secondary structures. Immediately downstream of each of the nine RNA genes is a helix‐turn‐helix DNA‐binding protein (transcriptional regulatory protein, Trp1‐9) that is poorly transcribed under the growth conditions used for RNA‐seq. Using knockdown or overexpressing strains, we show a role of both the Brt1 and Trp1 in the regulation of badA and also in biofilm formation. Based on these data, we hypothesize that Brt1 is a trans‐acting sRNA that also serves as a cis‐acting riboswitch to control the expression of badA. This family of RNAs together with the downstream Trp DNA‐binding proteins represents a novel coordinated regulatory circuit controlling expression of virulence‐associated genes in the bartonellae.

Bartonella Species, an Emerging Cause of Blood-Culture-Negative Endocarditis

“…Not surprisingly, we have shown that BadA plays an important role in biofilm formation by B. henselae, as a badA deletion mutant has an impaired ability to form biofilms (Fig. 8) (75). When our laboratory constructed nonpolar deletion mutants of the badA gene in both the Houston-1 type strain and the Marseille strain of B. henselae, they were shown to have a reduced ability to form biofilms.…”

“…Expression of TAA genes is also highly variable among different species, within strains of the same species (72), and even under different conditions (74). The expression of TAA genes correlates with autoaggregation and has also been recently shown to play an important role in biofilm formation by B. henselae (75). It is well known that these autoaggregative properties are more apparent in recent low-passage-number isolates.…”

“…Some Bartonella species, including B. grahamii and B. tribocorum, possess plasmids (36,78). The functions of plasmid-borne genes in these species are not well characterized but include putative small regulatory RNAs (75). Additional episomal DNA elements are the linear DNA fragments of a uniform 14-kb size that were observed in the cells of B. henselae (79).…”

“…Regulation of the badA gene has been attributed to the BatR/S two-component regulatory system (326) and the general stress response system (327). More recent studies have shown that a family of nine unannotated and highly transcribed RNAs designated Bartonella regulatory transcript (Brt1 to Brt9) found upstream of a putative transcriptional regulator protein are important in the regulation of badA (75).…”

“…The autoaggregative nature of low-passage-number Bartonella species grown under laboratory conditions is well known, and large aggregates of bacteria have been observed in histopathological specimens from patients with BA (387), verruga peruana (388), and CSD (389). The ability of B. henselae (75,76) and perhaps other Bartonella species to aggregate and form biofilms suggests that these bacterial communities are an integral component of the vegetative masses reported for endocarditis caused by Bartonella. Molecular studies and histopathology of heart valves from cases of Bartonella endocarditis demonstrate the presence of these bacteria on the surface of damaged valves (97,177).…”