Cell Wall Polysaccharide Alters the Surface Electric Potential of Lacticaseibacillus Paracasei Strain Shirota and Enhances Acid Tolerance

Abstract

LCPS-1 is a cell wall polysaccharide (CWPS) of Lacticaseibacillus paracasei (formerly known as Lactobacillus casei) strain Shirota (LcS). Although we have previously demonstrated that LCPS-1 enhances the acid tolerance of LcS, the mechanism remains unclear. This study aimed to elucidate how LCPS-1 enhances the growth and survivability of LcS under acidic conditions. Wild-type LcS showed significantly more growth than an LCPS-1-deficient mutant strain when cultured in media acidified with hydrochloric, lactic, or acetic acid (p < 0.01), indicating that LCPS-1 confers enhanced protection against proton (H+) stress. Wild-type LcS exhibited a 65 to 76 % reduction in negative surface potential compared to that of the mutant. Wild-type LcS also showed significantly more growth than the mutant (p < 0.01) in the presence of cupric oxide (CuO), which releases bactericidal Cu2+ ions. Conversely, wild-type LcS was slightly more susceptible than the mutant to lethal concentrations of hydroxide ions (OH-). These findings suggest that LCPS-1 modulates the surface electric potential of LcS cells, thereby influencing the strength of interactions between the cell walls and environmental ions and ultimately altering the tolerance of the cells to ionic stress factors. The findings of this study provide critical insights into the role of CWPSs in modulating the surface electric potential of microorganisms, which in turn affects microbial interactions with environmental ions. This enhanced understanding of CWPS function may enable the development of more resilient probiotic strains, potentially improving their efficacy in various industrial and therapeutic applications.

Keywords: Cell wall polysaccharide, Probiotics, Lacticaseibacillus paracasei, Zeta potential, Acid tolerance, survivability, Cu2+ ion