Comparative Analysis of Ionic Strength Tolerance between Freshwater and Marine Adhesins.

Bacterial adhesion is affected by environmental factors, such as ionic strength, pH, temperature, and shear forces. Therefore, marine bacteria must have developed adhesins with different compositions and structures than those of their freshwater counterparts to adapt to their natural environment. The dimorphic alphaproteobacterium is a marine budding bacterium in the clade uses a polar adhesin, the holdfast, located at the cell pole opposite the reproductive stalk, for surface attachment and cell-cell adhesion. The holdfast adhesin has been best characterized in , a freshwater member of the , and little is known about holdfast compositions and properties in marine Here, we use as a model to characterize holdfast properties in marine We show that freshwater and marine use similar genes in holdfast biogenesis and that these genes are highly conserved among the species in the two genera. We determine that produces a larger holdfast than and that the holdfasts have different chemical compositions, as they contain -acetylglucosamine and galactose monosaccharide residues and proteins but lack DNA. Finally, we show that holdfasts tolerate higher ionic strength than those of We conclude that marine holdfasts have physicochemical properties that maximize binding in high-ionic-strength environments. Most bacteria spend a large part of their life spans attached to surfaces, forming complex multicellular communities called biofilms. Bacteria can colonize virtually any surface, and therefore, they have adapted to bind efficiently in very different environments. In this study, we compare the adhesive holdfasts produced by the freshwater bacterium and a relative, the marine bacterium We show that holdfasts have a different morphology and chemical composition and tolerate high ionic strength. Our results show that the holdfast is an excellent model to study the effect of ionic strength on adhesion and provides insights into the physicochemical properties required for adhesion in the marine environment.