BtaE: a novel B. suis 1330 adhesin from the type II autotransporter family

RUIZ-RANWEZ, M.V.; POSADAS, D. M.; AROCENA, G.M.; ABDIAN, P; MARTÍN, F.A.; SIEIRA, R.; ZORREGUIETA, A

Buenos Aires

Congreso; International Research Conference Including the 64th Brucellosis Research Conference; 2011

Some steps of Brucella infection have been exhaustively studied while others such as adhesion and invasion to host cells remain poorly explored. We found that BmaC, a member from the monomeric autotransporter family of Brucella suis participates in the adhesion to epithelial cells in vitro probably through the interaction with fibronectin molecules. The role of an autotransporter in the attachment of Brucella to the host encouraged us to explore whether other members of the autotransporter family may also be involved in the adhesion step. Based on bioinformatical approaches we identified in the B. suis 1330 genome a putative adhesin from the type II autotransporter family (Type V Secretion System), which was named BtaE (for Brucella trimeric autotransporter). A btaE mutant of B. suis 1330 was generated by a clean gene deletion.  Since the protein could promote its own secretion to the bacterial surface, we pursued a heterologous approach. Therefore, btaE was expressed in a non-adherent and non-invasive E. coli strain to evaluate if BtaE is able to confer adhesive properties to this strain. Policlonal antibodies against a peptide of BtaE were generated in mouse. Interestingly, the B. suis ΔbtaE showed a strong reduction in the ability to attach and invade HeLa cells. Nevertheless, the loss in the invasion seemed to be consequence of the decrease in adhesion. The wild type gene cloned into pBBRMCS with its own promoter complemented the adhesion phenotype of the ΔbtaE mutant. The ΔbtaE mutant was not affected in the replication rate in both HeLa or macrophages model cells, suggesting that BtaE is not required in later stages of cell infection. By immunofluorescense we observed that BtaE is exposed on the bacterial surface, as expected for an adhesin. In order to identify host molecules that could act as receptors or ligands of BtaE, we evaluated adhesion to several components of the extracellular matrix of the wild type, the ΔbtaE and the E. coli expressing btaE,. The results consistently showed that BtaE can interact with hialuronic acid. Our results support the idea that BtaE is involved in the adhesion of B. suis to the host, proving evidence of the importance of this stage during the infection process. Besides, functional and expression differences between the members of the autotransporter families within or between Brucella species may contribute to a differential tissue tropism and/or host preference.