Bacillus subtilis α-Phosphoglucomutase Is Required for Normal Cell Morphology and Biofilm Formation

Peptidoglycan and wall teichoic acids (WTAs) are major constituents of the cell wall in many gram-positive bacteria. It has been proposed that lipoteichoic acids (LTAs), polymers anchored in the membrane, and WTAs contribute to the cell wall electrolyte properties, modulate the activity of peptidoglycan-degrading enzymes, and maintain cation homeostasis (24). The biology of WTAs and LTAs has been reviewed recently (17, 24). In Bacillus subtilis 168, poly(glycerolphosphate) [poly(Gro-P)], known as the major WTA, is glucosylated and d-alanylated at the C-2 position of the 1,3-phosphodiester-linked glycerol units (17, 24). Absence of either of these substituents does not affect cell viability, whereas the polymer backbone is an essential cell constituent (20). Glucosylation of poly(Gro-P) plays an essential role in the attachment of phage φ29 to B. subtilis 168 (34). Mutations associated with a φ29-resistant phenotype were mapped to three loci, gtaA, gtaB, and gtaC (35). Subsequently, analyses of gtaB-deficient mutants established that gtaB is the structural gene of the UTP:α-glucose-1-phosphate uridylyltransferase (28, 31), the enzyme that catalyzes the formation of UDP-glucose (UDP-Glc) from α-glucose 1-phosphate (α-Glc 1-P) and UTP. gtaA (rodD), which has been renamed tagE, encodes the enzyme for the transfer of glucosyl groups from UDP-Glc to the poly(Gro-P) moiety of the major WTA (10, 19). In addition, UDP-Glc is required for the polymerization of poly(glucosyl N-acetylgalactosamine phosphate), the minor WTA (17), as well as for the YpfP-governed synthesis of diglucosyldiacylglycerol, the membrane anchor for poly(Gro-P) which forms the main chain of LTA (12). Mutations leading to an α-phosphoglucomutase (α-PGM) deficiency (i.e., mutations associated with the inability to convert glucose 6-phosphate [Glc 6-P] to α-Glc 1-P) were mapped to the gtaC locus at 77° on the B. subtilis genome (1, 28). The gtaC mutants were, however, split into two subgroups; the PBSZ-sensitive mutants retained the designation gtaC, whereas the PBSZ-resistant mutants were renamed gtaE (28). Inspection of the B. subtilis 168 chromosome sequence (16) suggested that the α-PGM (EC 5.4.2.2) gene corresponds to yhxB, a 1,698-nucleotide open reading frame (encoding 565 amino acids) whose calculated map position is 85.9°. In the present study we found that gtaC and gtaE mutations map to yhxB (designated pgcA in this paper). Below we present evidence that the α-PGM deficiency correlates with altered cell morphology and impaired biofilm formation. To further characterize this phenotype, strains bearing mutations in the biosynthetic pathway downstream of the α-Glc 1-P formation step were investigated.