Identification of the chain-dispersing peptidoglycan hydrolase LytB of Streptococcus gordonii.

Riccardo Arrigucci,Gianni Pozzi

doi:10.1371/journal.pone.0176117

Riccardo Arrigucci, Gianni Pozzi

Open Access

https://doi.org/10.1371/journal.pone.0176117

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Abstract

Bacterial cell division ends with the separation of the daughter cells, a process that requires peptidoglycan hydrolases (PGHs). Bacteria lacking cell separating PGHs are impaired in cell separation with the formation of long chains or clusters. We identified a gene in Streptococcus gordonii encoding for a putative glucosaminidase (lytB). The lytB isogenic mutant grew in long bacterial chains and resulted in impaired biofilm formation. Purified recombinant LytB showed a murolytic activity on Micrococcus lysodeikticus cell suspension and was able to disperse the long chains of the mutant, restoring the wild type diplococci/short chain phenotype. LytB protein was localized only in culture supernatant cell fraction of S. gordonii, and co-cultures of wild type and lytB mutant showed a significant reduction of bacterial chain length, indicating that LytB is a secreted enzyme. Our results demonstrate that LytB is a secreted peptidoglycan hydrolase required for S. gordonii cell separation.

Highlights

Bacteria produce enzymes able to cleave their own protective peptidoglycan cell wall
peptidoglycan hydrolases (PGHs) are involved in many bacterial physiological processes as autolysis, competence development, biofilm formation, sporulation, cell wall elongation and turnover, cell division and cell separation, and their classification is based on the catalytic activity on the different peptidoglycan bonds: N-acetylmuramyl-L-Alanine amidases, endopeptidases, carboxypeptidases, N-acetyl-β-D-muramidases, N-acetyl-β-D-glucosaminidases, and lytic transglycosylases [3, 4]
When the early stationary phase bacterial cultures were observed under a light microscope, we observed that the wild type strain grew in short chains and diplococci, whereas GP1485 formed long bacterial chains and aggregates that were dispersed by vortexing (Fig 2B)

Summary

Introduction

Bacteria produce enzymes able to cleave their own protective peptidoglycan cell wall. The number of peptidoglycan hydrolases (PGHs) encoded by a bacterial genome varies among species. Gram positive bacteria from Streptococcus and Lactobacillus genus possess a relative small number of PGHs [1], while 35 peptidoglycan hydrolases have been identified in Bacillus subtilis [2]. PGHs are involved in many bacterial physiological processes as autolysis, competence development, biofilm formation, sporulation, cell wall elongation and turnover, cell division and cell separation, and their classification is based on the catalytic activity on the different peptidoglycan bonds: N-acetylmuramyl-L-Alanine amidases, endopeptidases, carboxypeptidases, N-acetyl-β-D-muramidases, N-acetyl-β-D-glucosaminidases, and lytic transglycosylases [3, 4]. Several PGHs involved in daughter cells separation have been identified. In the human pathogen Streptococcus pneumoniae, the deletion of lytB gene causes the formation of long chains of non-separated cells that can be dispersed by the addition of purified recombinant

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Conclusion