Differentiated roles for MreB‐actin isologues and autolytic enzymes in Bacillus subtilis morphogenesis

Abstract

Cell morphogenesis in most bacteria is governed by spatiotemporal growth regulation of the peptidoglycan cell wall layer. Much is known about peptidoglycan synthesis but regulation of its turnover by hydrolytic enzymes is much less well understood. Bacillus subtilis has a multitude of such enzymes. Two of the best characterized are CwlO and LytE: cells lacking both enzymes have a lethal block in cell elongation. Here we show that activity of CwlO is regulated by an ABC transporter, FtsEX, which is required for cell elongation, unlike cell division as in Escherichia coli. Actin-like MreB proteins are thought to play a key role in orchestrating cell wall morphogenesis. B. subtilis has three MreB isologues with partially differentiated functions. We now show that the three MreB isologues have differential roles in regulation of the CwlO and LytE systems and that autolysins control different aspects of cell morphogenesis. The results add major autolytic activities to the growing list of functions controlled by MreB isologues in bacteria and provide new insights into the different specialized functions of essential cell wall autolysins.

FtsEX acts on FtsA to regulate divisome assembly and activity

“…10). The GLTDY motif is present in many Gram-negative but not Gram-positive bacteria, consistent with the observation that FtsEX is used for divisome assembly, activation, and septal cell wall hydrolysis in a Gramnegative bacterium like E. coli, but only used for cell wall hydrolysis in Gram-positive bacteria like Bacillus subtilis and Streptococcus pneumoniae (8,9,31,(44)(45)(46).…”

“…FtsEX has been studied in diverse bacterial species for its role in regulating cell wall hydrolysis (9,(44)(45)(46)(47), but its essential role in E. coli cell division, where it was discovered, remained enigmatic because it can be bypassed. Nevertheless, in medium with low osmolarity, FtsEX is essential for division (8,21,31,34).…”

“…Although FtsEX is a known component of the divisome in many Gram-negative bacteria, FtsEX in the Gram-positive bacterium Bacillus subtilis is involved in cell wall hydrolysis, but not at the septum (44)(45)(46)(47). Alignment of FtsA sequences from members of both groups revealed a motif (GLTDY) in FtsA of many Gramnegative bacteria that is not present in FtsA of Gram-positive bacteria (Fig.…”

Dynamic protein complexes for cell growth

“…Furthermore, in E. coli, the bifunctional PG synthases, PBP1A and PBP1B, have dedicated regulators, LpoA and LpoB, which localize independently to elongation and divisions sites, respectively (9,10). In contrast, some PG hydrolases require their regulators for localization (11,12), whereas others do not (13). It remains to be seen if the regulators and/or the PG enzymes associate dynamically with the PGEM (or the division machinery), but in cases of independent localization, it is unlikely that both form stable interactions with the moving macromolecular machineries.…”

The Blueprint of a Minimal Cell: MiniBacillus

“…UDPManNAc, UDP-N-acetylmannosamine. also needs the ABC transporter FtsEX and the small protein Mbl (149). Thus, the choice of LytE allowed a smaller number of genes.…”