Life without a wall or division machine in Bacillus subtilis

Abstract

The cell wall is an essential structure for virtually all bacteria, forming a tough outer shell that protects the cell from damage and osmotic lysis. It is the target of our best antibiotics. L-form strains are wall-deficient derivatives of common bacteria that have been studied for decades. However, they are difficult to generate and typically require growth for many generations on osmotically protective media with antibiotics or enzymes that kill walled forms. Despite their potential importance for understanding antibiotic resistance and pathogenesis, little is known about their basic cell biology or their means of propagation. We have developed a controllable system for generating L-forms in the highly tractable model bacterium Bacillus subtilis. Here, using genome sequencing, we identify a single point mutation that predisposes cells to grow without a wall. We show that propagation of L-forms does not require the normal FtsZ-dependent division machine but occurs by a remarkable extrusion-resolution mechanism. This novel form of propagation provides insights into how early forms of cellular life may have proliferated.

Listeria monocytogenesl‐forms respond to cell wall deficiency by modifying gene expression and the mode of division

“…With respect to Listeria L-forms, we found that important cell shape-associated genes and other genes such as ispA (Leaver et al, 2009) were not affected, at least in this strain. Still, it cannot be excluded that yet unrecognized mutations in other genes prevent correct synthesis or assembly of the wall or otherwise predispose to loss of the wall.…”

“…It might thus be possible that such a process, including formation of a Z-ring, membrane constriction and formation of new vesicles containing a copy of the genome can occur inside the L-forms. On the contrary, it was very recently reported that propagation and division of B. subtilis L-forms do not require FtsZ (Leaver et al, 2009). More research is needed in order to better understand this complex and novel process and to answer the many open questions such as spatial regulation of the division process and mechanism of genome transfer.…”

“…Earlier studies (Landman and Halle, 1963;Landman, 1968;Wyrinck and Gooder, 1977) mostly focused on Bacillus subtilis and the expression of factors known or suspected to be involved in PG synthesis (Henriques et al, 1998), teichoic acid synthesis (Honeyman and Stewart, 1989), or cell shape determination (Jones et al, 2001), but did not yield evidence that L-form transition could be due to mutation. A recent report (JoseleauPetit et al, 2007) suggested that unstable L-form-like variants of Escherichia coli retain low amounts of PG and require PG synthesis for growth, In contrast, Leaver et al (2009) showed that PG synthesis is not required for B. subtilis L-forms. Interestingly, the latter authors also identified a single point mutation which predisposes B. subtilis to grow without a wall.…”

“…It was recently reported that a single point mutation in ispA, whose product is involved in the formation of essential lipids in the isoprenoid pathway (Fujisaki et al, 1990), predisposes B. subtilis for formation of L-forms (Leaver et al, 2009). To determine if this or other mutations in several genes involved in cell division could possibly play a role for Listeria L-form transition, we analysed and compared the sequences of mreB, mreBH, mbl, ftsZ, ftsA and ispA from parent Scott A cells and L-forms derived thereof.…”

Supramolecular structure in the membrane of Staphylococcus aureus

“…Importantly, the division of L-forms of the rod-shaped bacterium Bacillus subtilis is freed from the requirement of the classical tubulin-like division component FtsZ (14). L-forms appear to divide by scission after blebbing, tabulation, or vesiculation dependent on an altered rate of membrane biosynthesis (15); this harks back perhaps to a more evolutionary primitive mechanism permitting cellular proliferation.…”