Streptococcus gordonii Type I Lipoteichoic Acid Contributes to Surface Protein Biogenesis

Area of Science:

• Microbiology
• Bacterial Cell Envelope Structure and Function

Background:

• Lipoteichoic acid (LTA) is a vital polymer in Gram-positive bacterial cell envelopes, yet its precise physiological roles remain largely undefined.
• Previous studies indicate LTA absence impacts bacterial hydrophobicity, biofilm formation, and cell division, but the underlying mechanisms are unclear.

Purpose of the Study:

• To investigate the role of LTA in the surface protein presentation of *Streptococcus gordonii*.
• To elucidate the physiological consequences of LTA deficiency in *S. gordonii* and relate them to broader Gram-positive bacterial physiology.

Main Methods:

• Generation and utilization of a viable LTA-deficient *Streptococcus gordonii* strain.
• Label-free mass spectrometry analysis of cell wall fractions from wild-type and LTA-deficient strains.
• Chemical characterization of LTA structure in *S. gordonii*.

Main Results:

• LTA deficiency significantly altered the abundance of numerous cell surface proteins, including those involved in biofilm formation (SspA, SspB, SGO_0707), cell division (FtsE), cell wall biosynthesis (Pbp1a, Pbp2a), and stress response (DegP).
• These protein changes correlated with observed alterations in cell envelope homeostasis, biofilm formation, and adhesion to eukaryotic cells.
• *S. gordonii* produces a complex type I LTA, decorated with d-alanylations and glycosylations, similar to *Streptococcus suis*.

Conclusions:

• Lipoteichoic acid in *S. gordonii* plays a critical role in orchestrating the expression and presentation of cell surface proteins.
• LTA is essential for maintaining cell envelope homeostasis, facilitating biofilm formation, and mediating adhesion to host cells.
• These findings provide a mechanistic understanding of LTA's importance in Gram-positive bacteria, extending beyond *S. gordonii*.