Characterization of the protective response to FtsA imbalance-induced lysis in Streptococcus pneumoniae

HERNANDEZ MORFA, MIRELYS; ECHENIQUE J; VICTORIA E. ZAPPIA; NADIA B. OLIVERO; JAIME, ANDREA

Mendoza

Congreso; Reuniòn Anual de la Sociedad Argentina de nvestigacion en Bioquimica y Biol Molecular; 2022

SAIB

Cell division is a central process in bacteria and a prerequisite for pathogenicity. FtsZ, a tubulin homolog, and FtsA, an actin homolog, have fundamental roles in the bacterial division machinery. Division starts with the polymerization of FtsZ at the midcell and these protofilaments form a ring-like structure known as Z-ring. FtsZ assembly recruits other members of the divisome, such as FtsA that anchors the Z Ring to the membrane and recruits late-assemble proteins to complete the division. It has been demonstrated that a proper FtsA/FtsZ ratio is needed for cell division to occur. In Streptococcus pneumoniae, the relative amount of FtsA/FtsZ is 1:1.5. This relative abundance of FtsZ suggests that no-FtsA bound FtsZ is required during cell division. Here, we displayed that imbalances in the FtsA/FtsZ ratio due to overexpression of FtsA induced growth defects and bacterial lysis, while the FtsZ overproduction does not induce any morphological or growth defect. To identify putative protein-protein interaction, we performed a pull-down assay using GFP-Trap technology to compare the related proteins detected under native FtsA expression levels and a slight FtsA overexpression one without evidential morphological changes. Under native expression levels, the main hits were divisome proteins, such as FtsZ, while under overproduced FtsA conditions, we found an enrichment in stress response proteins. Among them, DnaK, a heat shock chaperone that binds to unfolded proteins, was the most relevant hit. Furthermore, it has been demonstrated that the two-component system CiaRH is important to maintain cell integrity helping S. pneumoniae to cope with lysis-inducing conditions. This protective effect involves the regulation of the major pneumococcal autolysin, LytA. We observed that autolysis induced by FtsA overexpression was abolished in the ΔlytA mutant, indicating the LytA dependence of this lytic event under these conditions. In addition, a ΔciaR mutation aggravates the lytic phenotype, which strengthens its protective role. The overexpression of FtsA produced cell wall alterations, evidenced by an increased propidium iodide uptake of the pneumococci, which might be the signal for the activation of LytA. The contrasting results obtained by overexpression of either FtsA or FtsZ support the idea that free FtsZ is needed for the division to occur and help to gain insight into how bacteria counter protein imbalances. In the case of an imbalance in the FtsA level, the CiaRH system is essential for the cell integrity of S. pneumoniae.