Identification and molecular analysis of PcsB, a protein required for cellwall separation of group B streptococcus

Group Il streptococcus (GBS) is the leading cause of bacterial sepsis and m eningitis in neonates. N-terminal sequencing of major proteins in the cultu re supernatant of a clinical isolate of GBS identified a protein of about 5 0 kDa which could be detected in all of 27 clinical isolates tested. The co rresponding gene, designated pcsB, was isolated from a GBS cosmid library a nd subsequently sequenced. The deduced PcsB polypeptide consists of 447 ami no acid residues (M-r, 46,754), carries a potential N-terminal signal pepti de sequence of 25 amino acids, and shows significant similarity to open rea ding 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 i nactivation of pcsB in the genome of GBS resulted in mutant strain Sep1 exh ibiting a drastically reduced growth rate compared to the parental GBS stra in and showing an increased susceptibility to osmotic pressure and to vario us antibiotics. Electron microscopic analysis of GBS mutant Sepl revealed g rowth in clumps, cell separation in several planes, and multiple division s epta within single cells. These data suggest a pivotal role of PcsB for cel l division and antibiotic tolerance of GBS.