Cell wall polysaccharides enhance surface hydrophilicity and improve tolerance to alcohol and surfactants in Lacticaseibacillus paracasei strain Shirota

Cell wall polysaccharides (CWPSs) form the outermost interface of many bacteria; however, the mechanisms by which they regulate surface physicochemical properties and tolerance to chemical stress remain unclear. Lacticaseibacillus paracasei strain Shirota (LcS) produces a high-molecular-weight CWPS (LCPS-1) that contributes to gastrointestinal stress resistance. In this study, we compared wild-type LcS with an LCPS-1-deficient Δ cps mutant to determine how LCPS-1 affects cell-surface hydrophobicity and tolerance to hydrophobic and amphipathic compounds. In microbial adhesion-to-hydrocarbons assays, the Δ cps mutant showed increased partitioning into hexadecane, with only 26–31% of the cells remaining in the aqueous phase at high hexadecane ratios compared with 82–88% for the wild type. Consistent with enhanced surface hydrophobicity, the Δ cps mutant was more sensitive to bile acids, showing reduced survival at ≥20 mM cholic acid, ≥0.6 mM chenodeoxycholic acid, and ≥1.0 mM deoxycholic acid, along with reduced minimum inhibitory concentrations (MICs) for cholic and chenodeoxycholic acids. Loss of LCPS-1 also reduced survival and lowered the MICs for short-chain alcohols and bactericidal surfactants. These findings support a model in which LCPS-1 forms a hydrophilic surface layer that limits interfacial adhesion and reduces the effective exposure of the cytoplasmic membrane to hydrophobic chemicals. Overall, our results identify CWPSs as gene-encoded determinants that enable bacteria to modulate surface properties and enhance tolerance to chemical stress in both host-associated and environmental settings. IMPORTANCE Bacteria are covered by layers of surface sugars that influence their interaction with the environment; however, the actual role of these layers remains unclear. This study demonstrates that a major cell wall polysaccharide layer in Lacticaseibacillus paracasei strain Shirota makes the cell surface more hydrophilic and helps the bacterium withstand bactericidal hydrophobic chemicals. Without this polysaccharide layer, cells became more hydrophobic and more susceptible to bile acids, short-chain alcohols, and commonly used bactericidal disinfectants. These results support the idea that a hydrophilic sugar layer reduces the contact between hydrophobic compounds and the cell membrane. To our knowledge, this is among the first studies showing that cell wall polysaccharides can increase surface hydrophilicity and thereby improve resistance to hydrophobic stress.