Lima BP, Kho K, Nairn BL, Davies JR, Svensäter G, Chen R, Steffes A, Vreeman GW, Meredith TC, Herzberg MC. 2019. Streptococcus gordonii type I lipoteichoic acid contributes to surface protein biogenesis. mSphere 4:e00814- 19. https://doi.org/10.1128/mSphere.00814-19.
Lipoteichoic acid (LTA) is an abundant polymer of the Gram-positive bacterial cell envelope and is essential for many species. Whereas the exact function of LTA has not been elucidated, loss of LTA in some species affects hydrophobicity, biofilm formation, and cell division. Using a viable LTA-deficient strain of the human oral commensal Streptococcus gordonii, we demonstrated that LTA plays an impor- tant role in surface protein presentation. Cell wall fractions derived from the wild- type and LTA-deficient strains of S. gordonii were analyzed using label-free mass spectroscopy. Comparisons showed that the abundances of many proteins differed, including (i) SspA, SspB, and S. gordonii 0707 (SGO_0707) (biofilm formation); (ii) FtsE (cell division); (iii) Pbp1a and Pbp2a (cell wall biosynthesis and remodeling); and (iv) DegP (envelope stress response). These changes in cell surface protein presentation appear to explain our observations of altered cell envelope homeostasis, biofilm for- mation, and adhesion to eukaryotic cells, without affecting binding and coaggrega- tion with other bacterial species, and provide insight into the phenotypes revealed by the loss of LTA in other species of Gram-positive bacteria. We also characterized the chemical structure of the LTA expressed by S. gordonii. Similarly to Streptococcus suis, S. gordonii produced a complex type I LTA, decorated with multiple D- alanylations and glycosylations. Hence, the S. gordonii LTA appears to orchestrate ex- pression and presentation of cell surface-associated proteins and functions.