Contributions ofFrancisella tularensissubsp.novicidaChitinases and Sec Secretion System to Biofilm Formation on Chitin

Abstract

Francisella tularensis, the zoonotic cause of tularemia, can infect numerous mammals and other eukaryotes. Although studying F. tularensis pathogenesis is essential to comprehending disease, mammalian infection is just one step in the ecology of Francisella species. F. tularensis has been isolated from aquatic environments and arthropod vectors, environments in which chitin could serve as a potential carbon source and as a surface for attachment and growth. We show that F. tularensis subsp. novicida forms biofilms during the colonization of chitin surfaces. The ability of F. tularensis to persist using chitin as a sole carbon source is dependent on chitinases, since mutants lacking chiA or chiB are attenuated for chitin colonization and biofilm formation in the absence of exogenous sugar. A genetic screen for biofilm mutants identified the Sec translocon export pathway and 14 secreted proteins. We show that these genes are important for initial attachment during biofilm formation. We generated defined deletion mutants by targeting two chaperone genes (secB1 and secB2) involved in Sec-dependent secretion and four genes that encode putative secreted proteins. All of the mutants were deficient in attachment to polystyrene and chitin surfaces and for biofilm formation compared to wild-type F. novicida. In contrast, mutations in the Sec translocon and secreted factors did not affect virulence. Our data suggest that biofilm formation by F. tularensis promotes persistence on chitin surfaces. Further study of the interaction of F. tularensis with the chitin microenvironment may provide insight into the environmental survival and transmission mechanisms of this pathogen.

Cyclic Di-GMP Stimulates Biofilm Formation and Inhibits Virulence of Francisella novicida

“…3A). As shown previously (10,26), the wildtype U112 strain formed biofilms on borosilicate glass tubes. A strain lacking the entire FTN0451-FTN0456 cluster (KKF457) or a strain lacking just CdgA and CdgB (cdgA cdgB strain) was defective for biofilm formation, demonstrating that cdGMP signaling contributes to F. novicida biofilm formation.…”

“…F. novicida forms biofilms on abiotic and chitinous surfaces (10,26), and an orphan response regulator, QseB, has been shown to be important for biofilm formation. To investigate the contribution of cdGMP levels to F. novicida biofilm formation, we measured biofilms formed by various F. novicida strains with high or low cdGMP levels (Fig.…”

“…novicida forms biofilms in vitro, and this behavior is likely linked to its environmental persistence in aquatic habitats as well as possibly within tick and mosquito vectors (10,26). An orphan response regulator, QseB (FTN1465), is required for normal biofilm development (10), as is the Sec secretion system and several Sec-dependent secreted proteins, some of which are predicted to bind and/or degrade chitin (26). In the current study, we show that high cdGMP levels stimulate F. novicida biofilm formation and inhibit virulence, suggesting that differential cdGMP signaling within Francisella species may contribute in part to their relative virulence in humans.…”

The Acid Phosphatase AcpA Is SecretedIn Vitroand in Macrophages by Francisella spp

“…The expression of FPI genes is regulated by many transcriptional regulators (18), including MglA (29), SspA (12), FevR (8,11), MigR (9), PmrA (6,39), and Hfq (37,45). The FPI is thought to encode a type VI secretion system that is required for phagosomal disruption and intracellular replication (5), but FPI proteins can also be secreted by FPIindependent mechanisms, including type I secretion (2,24), a type IV pilus secretion system (25), and a Sec-dependent secretion system (33). In addition, Francisella spp.…”

Interactions of Francisella Tularensis With Components of the Host Fibrinolytic System

“…Additionally, Francisella has also been shown to infect protozoans such as Acanthamoeba castellanii (11) and has also been shown to reside in cysts of this amoeba for up to 3 weeks post-infection (12). Recent work has also shown the ability of F. tularensis subsp novicida to form biofilms on chitin (13), a component of many arthropods and invertebrates found in aqueous habitats, making this a possible method of both survival under nutrient poor conditions and transmission to mammalian hosts. Overall, these data suggest that the life cycle of Francisella in the environment is quite complex and that this pathogen is well-suited for survival in a variety of conditions, whether inside or outside its chosen host.…”