Structural diversity and biological significance of lipoteichoic acid in Gram-positive bacteria: focusing on beneficial probiotic lactic acid bacteria

Abstract

Bacterial cell surface molecules are at the forefront of host-bacterium interactions. Teichoic acids are observed only in Gram-positive bacteria, and they are one of the main cell surface components. Teichoic acids play important physiological roles and contribute to the bacterial interaction with their host. In particular, lipoteichoic acid (LTA) anchored to the cell membrane has attracted attention as a host immunomodulator. Chemical and biological characteristics of LTA from various bacteria have been described. However, most of the information concerns pathogenic bacteria, and information on beneficial bacteria, including probiotic lactic acid bacteria, is insufficient. LTA is structurally diverse. Strain-level structural diversity of LTA is suggested to underpin its immunomodulatory activities. Thus, the structural information on LTA in probiotics, in particular strain-associated diversity, is important for understanding its beneficial roles associated with the modulation of immune response. Continued accumulation of structural information is necessary to elucidate the detailed physiological roles and significance of LTA. In this review article, we summarize the current state of knowledge on LTA structure, in particular the structure of LTA from lactic acid bacteria. We also describe the significance of structural diversity and biological roles of LTA.

Keywords: Lactobacillus spp.; glycolipid anchor; lactic acid bacteria; lipoteichoic acid; probiotics; repeating unit.

Fig. 1.

Overview of the Gram-positive cell surface architecture. Lipoteichoic acids are anchored to the cell membrane via glycolipids, while the wall-teichoic acids are covalently bound to cell wall peptidoglycan.

Fig. 2.

Typical structures of wall-teichoic and lipoteichoic acids. In most cases, R is H, d-alanine, and/or hexose. Typical hexose residues include glucose, galactose, and N-acetylglucosamine. GlcNAc, N-acetylglucosamine; MurNAc, N-acetylmuramic acid.

Fig. 3.

Bacterial species whose complete lipoteichoic acid structures are known. Details of lipoteichoic acid of such beneficial lactic acid bacteria as Lactobacillus spp., Lactococcus spp., and Leuconostoc spp. are relatively sparse compared with non-opportunistic and opportunistic pathogens.