Saaki, T. | bioRxiv Science

bioRxiv2024

Divisome minimization shows that FtsZ and SepF can form an active Z-ring, and reveals BraB as a new cell division influencing protein in Bacillus subtilis

One of the aims of synthetic biology is the construction of a minimal cell. Since bacteria are the simplest life forms, they are the preferred blueprint for such a cell. In this study, we tried to find the minimal set of proteins required for division of a cell wall containing cell, using the bacterial model system Bacillus subtilis. Bacterial cytokinesis begins with polymerization of the tubulin homologue FtsZ at midcell into the Z-ring, which recruits the late cell division protein that synthesize the division septum. Assembly of FtsZ is carefully regulated, involving a dozen conserved cell division proteins. These proteins are not essential, but removing more than one is in many cases lethal. We made use of known suppressor mutations to find a gene deletion route that eventually enabled us to remove eight conserved cell division proteins: ZapA, MinC, MinJ, UgtP, ClpX, Noc, EzrA and FtsA. Only FtsZ and its membrane anchor SepF appeared to be required for Z-ring formation. Interestingly, SepF is also the FtsZ anchor in archaea, and both proteins may date back to the Last Universal Common Ancestor (LUCA). Curiously, viability was not greatly affected by the multiple deletions, although the frequency of cell division was considerably reduced. However, genome sequencing exposed the accumulation of several suppressor mutations, and revealed an unexpected cell division regulation function for the branched chain amino acid transporter BraB. The implications of these findings for the role of SepF in cell division, and the construction of a minimal cell division machinery are discussed.

microbiology↗

bioRxiv2017

Membrane curvature and the Tol-Pal complex determine polar localization of the chemoreceptor Tar in E. coli

Chemoreceptors are localized at the cell poles of Escherichia coli and other rod-shaped bacteria. Over the years different mechanisms have been put forward to explain this polar localization; from stochastic clustering, membrane curvature driven localization, interactions with the Tol-Pal complex, to nucleoid exclusion. To evaluate these mechanisms, we monitored the cellular localization of the aspartate chemoreceptor Tar in different deletion mutants. We did not find any indication for either stochastic cluster formation or nucleoid exclusion. However, the presence of a functional Tol-Pal complex appeared to be essential to retain Tar at cell poles. This finding also implies that the curvature of cell poles does not attract chemoreceptor complexes. Interestingly, Tar still accumulated at midcell in tol and in pal deletion mutants. In these mutants, the protein appears to gather at the base of division septa, a region characterised by strong membrane curvature. Chemoreceptors, like Tar, form trimer-of-dimers that bend the cell membrane due to a rigid tripod structure with an estimated curvature of approximately 37 nm. This curvature approaches the curvature of the cell membrane generated during cell division, and localization of chemoreceptor tripods at curved membrane areas is therefore energetically favourable as it lowers membrane tension. Indeed, when we introduced mutations in Tar that abolish the rigid tripod structure, the protein was no longer able to accumulate at midcell or cell poles. These findings favour a model where chemoreceptor localization in E. coli is driven by strong membrane curvature and association with the Tol-Pal complex.\n\nImportanceBacteria have exquisite mechanisms to sense and to adapt to the environment they live in. One such mechanism involves the chemotaxis signal transduction pathway, in which chemoreceptors specifically bind certain attracting or repelling molecules and transduce the signals to the cell. In different rod-shaped bacteria, these chemoreceptors localize specifically to cell poles. Here, we examined the polar localization of the aspartate chemoreceptor Tar in E. coli, and found that membrane curvature at cell division sites and interaction with the Tal-pol protein complex, localize Tar at cell division sites, the future cell poles. This study shows how membrane curvature can guide localization of proteins in a cell.

microbiology↗