The transmembrane segment of TagH is required for wall teichoic acid transport under heat stress in Bacillus subtilis

Wall teichoic acids (WTAs) are anionic polymers that are covalently linked to peptidoglycan and play important roles in cell shape determination, cell division, autolysis, pathogenesis and antibiotic resistance in Gram-positive bacteria. In Bacillus subtilis, WTA is synthesized in the cytoplasm and translocated by an ABC transporter, TagGH. In this study, we found that the transmembrane segment of TagH is required for WTA transport under high temperatures. Cells expressing TagH302-FL (a construct fused to the 6×FLAG tag after the transmembrane segment, which lacks the C-terminal extracellular domain) grew normally at high temperatures, similar to those expressing the full-length TagH-FL fusion. In contrast, cells expressing TagH275-FL, which lacks both the transmembrane segment and the extracellular domain, exhibited a temperature-sensitive phenotype at temperatures above 49 °C and a growth defect at 50 °C. Interestingly, this growth defect was dissolved by an additional incubation at 37 °C. A similar temperature-sensitive phenotype was observed in cells expressing an N-terminal 6×FLAG tag fusion of TagH275. Immunofluorescence microscopy (IFM) indicated that TagG and TagH are localized on the cytoplasmic membrane in a patch-like manner. In addition, the C-terminal-truncated forms, TagH275-FL and TagH302-FL, were localized in similar patch-like patterns at 37 °C; only foci for TagH275-FL were remarkably reduced at high temperatures. Moreover, cell surface decoration with WTA was considerably reduced in cells harbouring TagH275-FL at high temperature, supporting the results of IFM observation. These results suggest that the transmembrane segment of TagH plays an important role in WTA export at high temperatures.