Unraveling the Role of Surface Mucus-Binding Protein and Pili in Muco-Adhesion of Lactococcus lactis

Abstract

Adhesion of bacteria to mucus may favor their persistence within the gut and their beneficial effects to the host. Interactions between pig gastric mucin (PGM) and a natural isolate of Lactococcus lactis (TIL448) were measured at the single-cell scale and under static conditions, using atomic force microscopy (AFM). In parallel, these interactions were monitored at the bacterial population level and under shear flow. AFM experiments with a L. lactis cell-probe and a PGM-coated surface revealed a high proportion of specific adhesive events (60%) and a low level of non-adhesive ones (2%). The strain muco-adhesive properties were confirmed by the weak detachment of bacteria from the PGM-coated surface under shear flow. In AFM, rupture events were detected at short (100−200 nm) and long distances (up to 600−800 nm). AFM measurements on pili and mucus-binding protein defective mutants demonstrated the comparable role played by these two surface proteinaceous components in adhesion to PGM under static conditions. Under shear flow, a more important contribution of the mucus-binding protein than the pili one was observed. Both methods differ by the way of probing the adhesion force, i.e. negative force contact vs. sedimentation and normal-to-substratum retraction vs. tangential detachment conditions, using AFM and flow chamber, respectively. AFM blocking assays with free PGM or O-glycan fractions purified from PGM demonstrated that neutral oligosaccharides played a major role in adhesion of L. lactis TIL448 to PGM. This study dissects L. lactis muco-adhesive phenotype, in relation with the nature of the bacterial surface determinants.

Atomic Force Microscopy of Biofilms—Imaging, Interactions, and Mechanics

“…This model is consistent with the previous interpretations of Gram-negative pili structure [87][88][89]. In a similar study, strains of Lactococcus lactis were immobilized onto polyethyleneimine (PEI)-coated cantilever, and adhesion to a pig gastric mucin-coated substrate was characterized [90]. In the study, long-range adhesion was found to be predominantly the result of pili-mediated binding, while surface adhesion was primarily mediated by mucus-binding adhesins.…”

From Genome to Phenotype: An Integrative Approach to Evaluate the Biodiversity of Lactococcus lactis

“…To support the second option, the functionality of L. lactis cell wall proteins was assessed in vivo using a ∆ srtA mutant [74]. Consistent with these data, the presence of various gene clusters associated with pili biogenesis, their efficient expression—for instance—in the plant TIL448 strain [57] and the ability to adhere to mucin, also conferred by the joint expression of a mucus-binding protein [58], reinforce lactococcal adhesion as a pivotal factor in transient persistence of L. lactis in the gut. Intestinal growth of L. lactis may also be a key parameter for increased fitness in the intestine.…”

Plasmid Complement of Lactococcus lactis NCDO712 Reveals a Novel Pilus Gene Cluster

“…A recent publication described a CRISPR-Cas system that was encoded by a lactococcal plasmid, although it was concluded not to be functional [20]. In addition, several genes related to lactococcal surface properties are carried on plasmids [21–23], such as aggL , a gene responsible for cell auto-aggregation, or genes responsible for adhesion to mucus [24]. …”

“…lactis strains also express proteinaceous surface appendages called pili [21,22,24]. Pili are known to have different functions in bacteria, including adhesion to surfaces (type I pili) or motility (type IV pili) [36–39].…”