Wall teichoic acids are anionic, phosphate-rich polymers linked to the peptidoglycan of gram-positive bacteria. In
Bacillus subtilis, the predominant wall teichoic acid types are poly(glycerol phosphate) in strain 168 and poly(ribitol phosphate) in strain W23, and they are synthesized by the tagand targene products, respectively. Growing evidence suggests that wall teichoic acids are essential in B. subtilis; however, it is widely believed that teichoic acids are dispensable under phosphate-limiting conditions. In the work reported here, we carefully studied the dispensability of teichoic acid under phosphate-limiting conditions by constructing three new mutants. These strains, having precise deletions in tagB, tagF, and tarD, were dependent on xylose-inducible complementation from a distal locus ( amyE) for growth. The tarDdeletion interrupted poly(ribitol phosphate) synthesis in B. subtilisand represents a unique deletion of a targene. When teichoic acid biosynthetic proteins were depleted, the mutants showed a coccoid morphology and cell wall thickening. The new wall teichoic acid biogenesis mutants generated in this work and a previously reported tagDmutant were not viable under phosphate-limiting conditions in the absence of complementation. Cell wall analysis of B. subtilisgrown under phosphate-limited conditions showed that teichoic acid contributed approximately one-third of the wall anionic content. These data suggest that wall teichoic acid has an essential function in B. subtilisthat cannot be replaced by teichuronic acid.