Spatio-temporal organisation of cell wall elongation machineries in Bacillus subtilis
Organisation spatio-temporelle des systèmes impliquées dans l'élongation de la paroi cellulaire chez Bacillus subtilis
Résumé
The cell wall (CW) is the physical determinant of bacteria’s shape. It is an external layer of the cell mostly composed of peptidoglycan (PG) creating a rigid mesh. The PG unit consists of two saccharides and five peptides. Units are assembled by transglycosylation (saccharide-saccharide bond) and transpeptidation (peptide-peptide bond). The CW’s size is modulated according to the cell’s cycle and must be lengthened during cell elongation. The PeptidoGlycan Elongation Machinery (PGEM) synthesizes and incorporates new PG units into this structure during cell growth. It is composed of two complementary mechanisms: the Rod system and class A Penicillin Binding Proteins (PBPs). The first one is the major one for PG synthesis during cell elongation. It is composed of the central component MreB protein, the transglycosylase RodA, the transpeptidases PBP2a and PBP2H, two bPBPs, and MreCD (Domínguez-Escobar et al., 2011). The aPBPs are capable of transglycosylation and transpeptidation. The major one is PBP1 (Kawai et al., 2019). Those two machineries are autonomous but should be coordinated (Cho et al., 2016). This study focuses on their spatio-temporal organization during cell elongation. MreB proteins polymerize into membrane-associated filaments. The active form represents a third exhibiting circumferential motion around cell’s periphery, the remaining show random or constrained diffusion but their role is unknown (Billaudeau et al. 2017). PBP1 has been shown to have a random diffusion along the cell but its active form has a very show diffusion (Cho et al., 2016). To study the localization and dynamics of those proteins, the Dense Mapping approach (Salomon et al., 2020) generates maps from (single) particle tracking ((S)PT) with a limited number of trajectories without degradation of the spatial resolution. This approach is adapted to the constrains of bacteria (i.e. small cell volume and limited amount of observed molecules).
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