Functional insights into the high-molecular-mass penicillin- binding proteins of streptococcus agalactiae revealed by gene deletion and transposon mutagenesis analysis

Luchang Zhu, Prasanti Yerramilli, Layne Pruitt, Abhishek Mishra, Randall J. Olsen, Stephen B. Beres, Andrew S. Waller, James M. Musser

Research output: Contribution to journalArticlepeer-review

Abstract

High-molecular-mass penicillin-binding proteins (PBPs) are enzymes that catalyze the biosynthesis of bacterial cell wall peptidoglycan. The Gram-positive bacterial pathogen Streptococcus agalactiae (group B streptococcus [GBS]) produces five high-molecular-mass PBPs, namely, PBP1A, PBP1B, PBP2A, PBP2B, and PBP2X. Among these, only PBP2X is essential for cell viability, whereas the other four PBPs are individually dispensable. The biological function of the four nonessential PBPs is poorly characterized in GBS. We deleted the pbp1a, pbp1b, pbp2a, and pbp2b genes individually from a genetically well-characterized serotype V GBS strain and studied the phenotypes of the four isogenic mutant strains. Compared to the wild-type parental strain, (i) none of the pbp isogenic mutant strains had a significant growth defect in Todd-Hewitt broth supplemented with 0.2% yeast extract (THY) rich medium, (ii) isogenic mutant Dpbp1a and Dpbp1b strains had significantly increased susceptibility to penicillin and ampicillin, and (iii) isogenic mutant Dpbp1a and Dpbp2b strains had significantly longer chain lengths. Using saturated transposon mutagenesis and transposon insertion site sequencing, we determined the genes essential for the viability of the wild-type GBS strain and each of the four isogenic pbp deletion mutant strains in THY rich medium. The pbp1a gene is essential for cell viability in the pbp2b deletion background. Reciprocally, pbp2b is essential in the pbp1a deletion background. Moreover, the gene encoding RodA, a peptidoglycan polymerase that works in conjunction with PBP2B, is also essential in the pbp1a deletion background. Together, our results suggest functional overlap between PBP1A and the PBP2B-RodA complex in GBS cell wall peptidoglycan biosynthesis.

Original languageEnglish (US)
Article numbere00234-21
JournalJournal of bacteriology
Volume203
Issue number17
DOIs
StatePublished - Sep 2021

Keywords

  • Group B streptococcus
  • Penicillin-binding proteins
  • TraDIS

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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