Cell wall polysaccharide alters the surface electric potential of Lacticaseibacillus paracasei strain Shirota and enhances acid tolerance

LCPS-1 is a cell wall polysaccharide (CWPS) of <i>Lacticaseibacillus paracasei</i> (formerly <i>Lactobacillus casei</i>) strain Shirota (LcS). LCPS-1 enhances the acid tolerance of LcS; however, the mechanism of action remains unclear. This study aimed to elucidate how LCPS-1 enhances LcS growth and survivability under acidic conditions. When cultured in media acidified with hydrochloric, lactic, or acetic acid, wild-type LcS showed significantly more growth than an LCPS-1-deficient mutant strain (<i>p</i> < 0.01), indicating that LCPS-1 confers enhanced protection against proton (<i>H</i> ⁺) stress. Wild-type LcS also exhibited a significant 73-83 % reduction (<i>p</i> < 0.01) in negative surface potential compared to that of the mutant. Additionally, wild-type LcS showed significantly more growth than the mutant (<i>p</i> < 0.01) in the presence of cupric oxide, which releases bactericidal Cu²⁺ ions. In contrast, wild-type LcS was slightly more susceptible than the mutant to lethal concentrations of hydroxide ions. These findings suggest that LCPS-1 modulates the surface electric potential of LcS cells, thereby influencing the interaction strength between the cell walls and environmental ions, ultimately altering the tolerance of the cells to ionic stress factors. These findings provide crucial insights into the role of CWPSs in modulating the surface electric potential of microorganisms, which affects microbial interactions with environmental ions. This enhanced understanding of CWPS function enables the development of more resilient probiotic strains, potentially improving their efficacy in various industrial and therapeutic applications.