D-alanylation of lipoteichoic acid contributes to biofilm formation and acidogenesis capacity of Streptococcusmutans

• Published in: Microbial pathogenesis Vol. 169; p. 105666
• Main Authors: Wu, Minjing, Huang, Shan, Du, Jingyun, Li, Yijun, Jiang, Shan, Zhan, Ling, Huang, Xiaojing
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-08-2022
• Subjects: Acidogenesis; Biofilm formation; D-alanylation; Lipoteichoic acid; Streptococcus mutans; D-alanylation; Acidogenesis; Biofilm formation; Lipoteichoic acid; Streptococcus mutans
• ISSN: 0882-4010; 1096-1208
• DOI: 10.1016/j.micpath.2022.105666

D-alanylation of Lipoteichoic acid (LTA) is considered to be essential for virulence factors expression in Gram-positive microorganism. The effects of the D-alanylation of LTA on biofilm formation and acidogenesis of Streptococcus mutans (S. mutans) are still not clearly understood.
This study was designed to investigate the impact of D-alanylation of LTA on biofilm formation and acidogenesis of S. mutans and explore the related mechanisms.
We compared the biofilm formation process by fluorescence microscope observation of LTA D-alanylation blocking strain with that of the wildtype strain. Auto-aggregation, cell surface charge, and polysaccharide production assays were performed to investigate the related mechanisms. pH drop assay and glycolysis pH drop-down analysis were carried out to evaluate the acidogenesis capacity of S. mutans after LTA D-alanylation blocking. To identify the biofilm formation and adhesive-related genes expressions of S. mutans mutant, qRT-PCR was performed.
After blocking off the D-alanylation of LTA, S. mutans could not form the three-dimensional structural biofilm, in which cells were scattered on the substratum as small clusters. The auto-aggregation was prompted due to the mutant strain cell morphology change (*p < 0.05). Furthermore, more negative charges were found on the mutant strain cells surfaces and fewer water-insoluble glucans were produced in mutant biofilm (*p < 0.05). The adhesion capacity of the S. mutans biofilm was impaired after LTA D-alanylation blocking (*p < 0.05). Biofilm formation and adhesive-related genes expressions decreased (*p < 0.05), especially at the early stages of biofilm formation. S. mutans mutant strains exhibited suppressed acidogenesis because its glycolytic activity was impaired.
The results of this study suggest that blocking of LTA D-alanylation disrupts normal biofilm formation in S. mutans predominantly if not entirely by altering intercellular auto-aggregation, cell adhesion, and extracellular matrix formation. Moreover, our study results suggest that the LTA D-alanylation plays an important role in S. mutans acidogenesis by altering glycolytic activity. These findings add to the knowledge about mechanisms underlying biofilm formation and acid tolerance in S. mutans.
•The D-alanylation of LTA influences the amount of S. mutans biofilm formation and its profile.•The effects of D-Alanylation of LTA on S. mutans biofilm include alterations to auto-aggregation, adhesion, and extracellular matrix formation.•LTA D-alanylation plays a critical role in the acidogenesis of S. mutans by modifying glycolytic activity.•These findings contribute to our understanding of how biofilm is formed and how S. mutans withstands an acidic environment.