Identification of New Factors Modulating Adhesion Abilities of the Pioneer Commensal Bacterium Streptococcus salivarius

Abstract

Biofilm formation is crucial for bacterial community development and host colonization by Streptococcus salivarius, a pioneer colonizer and commensal bacterium of the human gastrointestinal tract. This ability to form biofilms depends on bacterial adhesion to host surfaces, and on the intercellular aggregation contributing to biofilm cohesiveness. Many S. salivarius isolates auto-aggregate, an adhesion process mediated by cell surface proteins. To gain an insight into the genetic factors of S. salivarius that dictate host adhesion and biofilm formation, we developed a screening method, based on the differential sedimentation of bacteria in semi-liquid conditions according to their auto-aggregation capacity, which allowed us to identify twelve mutations affecting this auto-aggregation phenotype. Mutations targeted genes encoding (i) extracellular components, including the CshA surface-exposed protein, the extracellular BglB glucan-binding protein, the GtfE, GtfG and GtfH glycosyltransferases and enzymes responsible for synthesis of cell wall polysaccharides (CwpB, CwpK), (ii) proteins responsible for the extracellular localization of proteins, such as structural components of the accessory SecA2Y2 system (Asp1, Asp2, SecA2) and the SrtA sortase, and (iii) the LiaR transcriptional response regulator. These mutations also influenced biofilm architecture, revealing that similar cell-to-cell interactions govern assembly of auto-aggregates and biofilm formation. We found that BglB, CshA, GtfH and LiaR were specifically associated with bacterial auto-aggregation, whereas Asp1, Asp2, CwpB, CwpK, GtfE, GtfG, SecA2 and SrtA also contributed to adhesion to host cells and host-derived components, or to interactions with the human pathogen Fusobacterium nucleatum. Our study demonstrates that our screening method could also be used to identify genes implicated in the bacterial interactions of pathogens or probiotics, for which aggregation is either a virulence trait or an advantageous feature, respectively.

Functional and Genomic Characterization of Ligilactobacillus salivarius TUCO-L2 Isolated From Lama glama Milk: A Promising Immunobiotic Strain to Combat Infections

“…The srr proteins mediate several interactions of S. salivarius with the environment and have thus emerged as the crucial host attachment factors involved in the colonization of mucosal surfaces by this commensal bacterium. Electron microscopy analysis of the TUCO-L2 strain demonstrated the presence of fibrin-like structures on bacterial surface; however, the density of the structures was significantly lower than that reported in S. salivarius (Couvigny et al, 2017(Couvigny et al, , 2018. It is tempting to speculate that two srr proteins may have a similar function in L. salivarius TUCO-L2 that enables colonization of the bacteria in various mucosal tissues in llamas.…”

Developing natural products as potential anti-biofilm agents

“…It was reported that cell surface-associated proteins such as Aap and SasG were involved in Staphylococcus epidermidis initiating attachment and Aap protein contains G5 domain, which was responsible for bacterial intercellular cell adhesion [8]. Extracellular components, including the surface-exposed protein, the extracellular glucan-binding protein and the glycosyltransferases (GtfE, GtfG and GtfH), also play an important role in cell adhesive abilities [9]. Sortase A (SrtA), a transpeptidase that can anchor cell surface proteins, also elicits extracellular localization and biofilm formation during infection of Gram-positive bacteria, such as Staphylococcus aureus Biofilm starts from bacteria initial attachment, and then develops into irreversible attachment.…”

Identification and localization of proteins associated with the formation of Streptococcus gordonii and Fusobacterium nucleatum biofilms

“…The oral cavity is a complex bacterial ecosystem composed of multiple microorganisms that intimately coexist [26][27][28][29][30]. Bio lms are one way they coexist [31,32], and they develop thanks to multiple mechanisms associated with protein expression [33][34][35][36][37]. However, the literature on this subject is still scarce [18,37,38].…”