Bpp0974, an adhesin of the avirulent phase from Bordetella parapertussis

CARRICA, MARIELA; GORGOJO, JUAN PABLO; VALDEZ, HUGO; DEBANDI, MARTINA; BAROLI, CARLOS; RODRIGUEZ, MARIA EUGENIA

Mendoza

Congreso; LVIII Congreso de la Sociedad Argentina de Investigaciones Bioquímicas (SAIB).; 2022

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular

B. parapertussis is an etiological agent of whooping cough, whose incidence has increased remarkably in the last years. This bacterium undergoes a phenotypic variation between the so-called virulent, intermediate and avirulent phases in response to environmental stimuli, such as temperature and exposure to modulating compounds. Due to the environmental conditions during transmission it has been suggested this pathogen reaches the host in avirulent phase, a phenotype that lack the expression of the main adhesin (filamentous haemagglutinin, FHA) required for bacterial attachment to host cells. Because bacterial attachment to the host cells is the first critical step of host colonization, bacterial adhesins expressed in avirulent phase might play a central role in B. parapertussis pathogenesis. In this study we searched for potential avirulent phase-expressed adhesins by means of comparative proteomics. We identified Bpp0974 expressed in avirulence, a protein that includes repetitive immunoglobulin-like domains, a von Willebrand Factor A domain, repetitive RTX motifs, a membrane retention domain, and a type I secretion target signal. All these features are characteristic of adhesins. The expression of Bpp0974 in the avirulent phase was confirmed by qRT-PCR and western blot. Interestingly, we observed that this protein remained highly expressed until the intermediate phase. We next built a B. parapertussis Bpp0974 in frame deletion mutant strain and checked it in attachment assays run in parallel with the wild type strain, both in avirulent and intermediate phases induced by modulating cultural conditions (high and intermediate concentrations of MgSO4 or nicotinic acid). We found that Bpp0974 is involved in the attachment of B. parapertussis to human bronchial epithelial (16HBE14o-) cell line, both in avirulent and intermediate phases. In agreement with its adhesin role, Bpp0974 was found involved in B. parapertussis biofilm formation during avirulent and intermediate phases, as determined by microtiter crystal violet assays, and bacterial entry into the cell where it is able to remain alive for days, as determined for polymixyn B protection assays. Taken together these results suggest that Bpp0974 might play a central role in the early steps of infection enabling host colonization while protecting the bacteria from the innate immunity until the environmental conditions induce the virulent phase in the infecting bacteria.