Identification and Molecular Analysis of PcsB, a Protein Required for Cell Wall Separation of Group B Streptococcus

Group B streptococcus (GBS) is the leading cause of bacterial sepsis and meningitis in neonates. N-terminal sequencing of major proteins in the culture supernatant of a clinical isolate of GBS identified a protein of about 50 kDa which could be detected in all of 27 clinical isolates tested. The corresponding gene, designated pcsB, was isolated from a GBS cosmid library and subsequently sequenced. The deduced PcsB polypeptide consists of 447 amino acid residues (M(r), 46,754), carries a potential N-terminal signal peptide sequence of 25 amino acids, and shows significant similarity to open reading frames of unknown function from different organisms and to the murein hydrolase P45 from Listeria monocytogenes. Northern blot analysis revealed a monocistronic transcriptional organization for pcsB in GBS. Insertional inactivation of pcsB in the genome of GBS resulted in mutant strain Sep1 exhibiting a drastically reduced growth rate compared to the parental GBS strain and showing an increased susceptibility to osmotic pressure and to various antibiotics. Electron microscopic analysis of GBS mutant Sep1 revealed growth in clumps, cell separation in several planes, and multiple division septa within single cells. These data suggest a pivotal role of PcsB for cell division and antibiotic tolerance of GBS.