Enzymatic activities and functional interdependencies of Bacillus subtilis lipoteichoic acid synthesis enzymes

Lipoteichoic acid (LTA) is an important cell wall polymer in Gram-positive bacteria. The enzyme responsible for polyglycerolphosphate LTA synthesis is LtaS, first described in Staphylococcus aureus. Four LtaS orthologues, LtaSBS, YfnI, YqgS and YvgJ, are present in Bacillus subtilis. Using an in vitro enzyme assay, we determined that all four proteins are Mn2+-dependent metal enzymes that use phosphatidylglycerol as a substrate. We show that LtaSBS, YfnI and YqgS can produce polymers, suggesting that these three proteins are bona-fide LTA synthases while YvgJ functions as an LTA primase, as indicated by the accumulation of a GroP-Glc2-DAG glycolipid. Western blot analysis of LTA produced by ltaSBS, yfnI, yqgS and yvgJ single, triple and the quadruple mutant, showed that LTA production was only abolished in the quadruple and the YvgJ-only expressing mutant. B. subtilis strains expressing YfnI in the absence of LtaSBS produced LTA of retarded mobility, presumably caused by an increase in chain length as suggested by a structural analysis of purified LTA. Taken together, the presented results indicate that the mere presence or absence of LTA cannot account for cell division and sporulation defects observed in the absence of individual enzymes and revealed an unexpected enzymatic interdependency of LtaS-type proteins in B. subtilis.