Roles of the Essential Protein FtsA in Cell Growth and Division in Streptococcus pneumoniae

Abstract

Streptococcus pneumoniae is an ovoid-shaped Gram-positive bacterium that grows by carrying out peripheral and septal peptidoglycan (PG) synthesis, analogous to model bacilli, such as Escherichia coli and Bacillus subtilis. In the model bacilli, FtsZ and FtsA proteins assemble into a ring at midcell and are dedicated to septal PG synthesis but not peripheral PG synthesis; hence, inactivation of FtsZ or FtsA results in long filamentous cells unable to divide. Here, we demonstrate that FtsA and FtsZ colocalize at midcell in S. pneumoniae and that partial depletion of FtsA perturbs septum synthesis, resulting in elongated cells with multiple FtsZ rings that fail to complete septation. Unexpectedly, complete depletion of FtsA resulted in the delocalization of FtsZ rings and ultimately cell ballooning and lysis. In contrast, depletion or deletion of gpsB and sepF, which in B. subtilis are synthetically lethal with ftsA, resulted in enlarged and elongated cells with multiple FtsZ rings, with deletion of sepF mimicking partial depletion of FtsA. Notably, cell ballooning was not observed, consistent with later recruitment of these proteins to midcell after Z-ring assembly. The overproduction of FtsA stimulates septation and suppresses the cell division defects caused by the deletion of sepF and gpsB under some conditions, supporting the notion that FtsA shares overlapping functions with GpsB and SepF at later steps in the division process. Our results indicate that, in S. pneumoniae, both GpsB and SepF are involved in septal PG synthesis, whereas FtsA and FtsZ coordinate both peripheral and septal PG synthesis and are codependent for localization at midcell.IMPORTANCE Streptococcus pneumoniae (pneumococcus) is a clinically important human pathogen for which more therapies against unexploited essential targets, like cell growth and division proteins, are needed. Pneumococcus is an ovoid-shaped Gram-positive bacterium with cell growth and division properties that have important distinctions from those of rod-shaped bacteria. Gaining insights into these processes can thus provide valuable information to develop novel antimicrobials. Whereas rods use distinctly localized protein machines at different cellular locations to synthesize peripheral and septal peptidoglycans, we present evidence that S. pneumoniae organizes these two machines at a single location in the middle of dividing cells. Here, we focus on the properties of the actin-like protein FtsA as an essential orchestrator of peripheral and septal growth in this bacterium.KEYWORDS FtsA, Gram-positive cocci, Streptococcus pneumoniae, cell division

Suppression and synthetic‐lethal genetic relationships of ΔgpsB mutations indicate that GpsB mediates protein phosphorylation and penicillin‐binding protein interactions in Streptococcus pneumoniaeD39

“…According to this model, interactions between EzrA and GpsB coordinate GpsB function with the dynamics of the midcell FtsZring, which mediates both septal and peripheral PG synthesis in ovococcus bacteria (Fig. 10) (see Land et al, 2013;Massidda et al, 2013;Tsui et al, 2014;Mura et al, 2016). GpsB functions to balance septal and peripheral PG synthesis by direct or indirect interactions with aPBP2a, bPBP2x and bPBP2b.…”

Bacterial Cell Division: Nonmodels Poised to Take the Spotlight

“…Depending on the strain background, the Δ mapZ phenotype may be less dramatic, indicating that there could be other redundant factors that may perform a similar role to that of MapZ (12). Another report shows that, FtsA, an essential protein in S. pneumoniae (80), is required for proper localization of FtsZ and may play a role in regulating peptidoglycan synthesis during both septation as well as lateral cell elongation (98). …”

Prevention of EloR/KhpA heterodimerization by introduction of site-specific amino acid substitutions renders the essential elongasome protein PBP2b redundant in Streptococcus pneumoniae

“…FtsZ forms the division ring, which functions as a scaffold for a number of proteins found in the elongasome and divisome. FtsZ is therefore present at the division zone during initiation of new septa, cell elongation and cross wall synthesis, but it is not required for the final stage of daughter cell separation (12, 17). KhpA-sfGFP and FtsZ fused to the fluorescent marker mKate2 were co-expressed in S. pneumoniae (strain AW198), and fluorescence microscopy images demonstrate that mid-cell located KhpA-sfGFP follows the same localization pattern as FtsZ (Fig.…”

“…Zheng and co-workers report that the levels of FtsA, which together with FtsZ assembles into the division ring (6, 17, 34, 35), were elevated two-to threefold in Δ eloR and Δ khpA mutants. Their results suggest that EloR and KhpA bind 5’ untranslated regions of mRNAs, including the ftsA transcript, resulting in altered translation rates (29).…”

“…In contrast to rod-shaped bacteria, S. pneumoniae lacks MreB, a cytoskeleton-like protein that moves the cell wall synthesis machinery in helical patterns perpendicular to the cell length (16). Instead, pneumococci elongate by inserting new peptidoglycan into the existing cell wall between the future cell equator and the septum in a circumferentially motion guided by the FtsZ/FtsA division ring (6, 17, 18). At some point during cell elongation, the divisome initiates septal cross wall synthesis.…”