Interplay of virulence factors and signaling molecules: albumin and calcium-mediated biofilm regulation in <i>Bordetella bronchiseptica</i>

<i>Bordetella bronchiseptica,</i> a respiratory pathogen capable of infecting various mammals, including humans, is associated with chronic infections. <i>B. bronchiseptica</i> can form biofilm-like structures <i>in vivo</i>, providing tolerance against environmental stresses. Recent studies have highlighted the role of cyclic diguanylate monophosphate (c-di-GMP) in this process <i>in vitro</i>: elevated c-di-GMP levels stimulate biofilm formation, whereas phosphodiesterase (PDE) activation reduces biofilms. Respiratory secretions, which contain albumin and calcium at higher concentrations than standard growth media, promote an increase in the amount and extracellular localization of the adenylate cyclase toxin (ACT), an important virulence factor of <i>Bordetella spp</i>. Secreted ACT, present in the extracellular medium or attached to the outer membrane, inhibits biofilm formation. Based on these observations, we hypothesized that serum albumin and calcium together inhibit biofilm formation and explored the potential role of c-di-GMP in this process. Our findings suggest that serum albumin and calcium inhibit <i>B. bronchiseptica</i> biofilm formation through two potentially independent mechanisms: one involving ACT secretion and another promoting c-di-GMP degradation. In the presence of albumin and calcium, intracellular levels of c-di-GMP were reduced, and specific PDEs appear to be involved in this process. In addition, albumin and calcium stimulated the secretion of the adhesin BrtA. This study contributes to the understanding of the mechanisms governing <i>B. bronchiseptica</i> biofilm formation and its modulation by host factors.IMPORTANCE<i>Bordetella bronchiseptica</i>, a respiratory pathogen capable of infecting various mammals, forms biofilms that enhance its ability to withstand environmental stresses. This study reveals that host-derived factors, specifically serum albumin and calcium, inhibit biofilm formation through two independent mechanisms: increasing adenylate cyclase toxin secretion and promoting the degradation of cyclic diguanylate monophosphate (c-di-GMP), a key biofilm regulator. These findings provide insights into how host conditions influence <i>B. bronchiseptica</i> biofilm dynamics, shedding light on the complex interactions between pathogen and host that contribute to infection persistence. Understanding these mechanisms may inform strategies to mitigate chronic infections caused by <i>B. bronchiseptica</i>.