WhmD promotes the assembly of Mycobacterium smegmatis FtsZ: A possible role of WhmD in bacterial cell division

An adamantyl-caffeoyl-anilide exhibits broad-spectrum antibacterial activity by inhibiting FtsZ assembly and Z-ring formation

Several harmful bacteria have evolved resistance to conventional antibiotics due to their extensive usage. FtsZ, a principal bacterial cell division protein, is considered as an important drug target to combat resistance. We identified a caffeoyl anilide derivative, (E)-N-(4-(3-(3,4-dihydroxyphenyl)acryloyl)phenyl)-1-adamantylamide (compound 11) as a new antimicrobial agent targeting FtsZ. Compound 11 caused cell elongation in Mycobacterium smegmatis, Bacillus subtilis, and Escherichia coli cells, indicating that it inhibits cell partitioning. Compound 11 inhibited the assembly of Mycobacterium smegmatis FtsZ (MsFtsZ), forming short and thin filaments in vitro. Interestingly, the compound increased the rate of GTP hydrolysis of MsFtsZ. Compound 11 also impeded the assembly of Mycobacterium tuberculosis FtsZ. Fluorescence and absorption spectroscopic analysis suggested that compound 11 binds to MsFtsZ and produces conformational changes in FtsZ. The docking analysis indicated that the compound binds at the interdomain cleft of MsFtsZ. Further, it caused delocalization of the Z-ring in Mycobacterium smegmatis and Bacillus subtilis without affecting DNA segregation. Notably, compound 11 did not inhibit tubulin polymerization, the eukaryotic homolog of FtsZ, suggesting its specificity on bacteria. The evidence indicated that compound 11 exerts its antibacterial effect by impeding FtsZ assembly and has the potential to be developed as a broad-spectrum antimicrobial agent.

The Bacterial MtrAB Two-Component System Regulates the Cell Wall Homeostasis Responding to Environmental Alkaline Stress

Throughout the course of evolution, bacteria have developed signal transduction tools such as two-component systems (TCSs) to meet their demands to thrive even under the most challenging environmental conditions. One TCS called MtrAB is commonly found in Actinobacteria and is implicated in cell wall metabolism, osmoprotection, cell proliferation, antigen secretion, and biosynthesis of secondary metabolites. However, precisely how the MtrAB TCS regulates the bacterial responses to external environments remains unclear. Here, we report that the MtrAB TCS regulates the cell envelope response of alkali-tolerant bacterium Dietzia sp. strain DQ12-45-1b to extreme alkaline stimuli. We found that under alkaline conditions, an mtrAB mutant exhibited both reduced growth and abnormal morphology compared to the wild-type strain. Electrophoretic mobility shift assay analysis showed that MtrA binds the promoter of the mraZ gene critical for cell wall homeostasis, suggesting that MtrA directly controls transcription of this regulator. In conclusion, our findings demonstrate that MtrAB TCS is involved in controlling the bacterial response to alkaline stimuli by regulating the expression of the cell wall homeostasis regulator MraZ in Dietzia sp. DQ12-45-1b, providing novel details critical for a mechanistic understanding of how cell wall homeostasis is controlled. IMPORTANCE Microorganisms can be found in most extreme environments, and they have to adapt to a wide range of environmental stresses. The two-component systems (TCSs) found in bacteria detect environmental stimuli and regulate physiological pathways for survival. The MtrAB TCS conserved in Corynebacterineae is critical for maintaining the metabolism of the cell wall components that protects bacteria from diverse environmental stresses. However, how the MtrAB TCS regulates cell wall homeostasis and adaptation under stress conditions is unclear. Here, we report that the MtrAB TCS in Dietzia sp. DQ12-45-1b plays a critical role in alkaline resistance by modulating the cell wall homeostasis through the MtrAB-MraZ pathway. Thus, our work provides a novel regulatory pathway used by bacteria for adaptation and survival under extreme alkaline stresses.

A Novel Z-Ring Associated Protein ZapA-Like Protein (PA5407) From Pseudomonas aeruginosa Promotes FtsZ to Form Double Filaments

Bacterial cell division is initiated by the assembly of the contraction ring (Z-ring), which consists of the self-assembled FtsZ protofilaments and dozens of other associate proteins. ZapA, a regulatory protein found in almost all bacteria, stabilizes FtsZ protofilaments to form bundles and enhances the Z-ring condensation. Here, we reported that another small protein from Pseudomonas aeruginosa, ZapA-Like protein (ZapAL; PA5407), is a new FtsZ associated protein. ZapAL exists in many Pseudomonas species and shares only 20% sequence identity to ZapA. ZapAL interacts with FtsZ and induces FtsZ to form long straight double filaments; in comparison, ZapA promotes long bundles with multiple FtsZ filaments. ZapAL has only a mild effect on GTPase activity of FtsZ, which is reduced by around 26% when 10 μM ZapAL is added in the solution. However, to study their assembly dynamics using light-scattering assay, we found that FtsZ-ZapAL double filament is stable and no depolymerization process is observed, which is different from ZapA. Further research found that ZapA and ZapL are likely to form heterodimers. The bundles formed by the mixture of FtsZ-ZapA-ZapAL will depolymerize after GTP is hydrolyzed. Consistent with ZapAL interaction with FtsZ in vitro, the expression of ZapAL-GFP was observed as a narrow band or spots in the middle of the cells, suggesting that it is a component of bacterial division machinery. Similar to ZapA, ZapAL is also not essential for bacterial cell division. Little changes were observed when zapAL gene was deleted, or overexpressed under normal conditions; however, overexpression of ZapAL caused zapA-deficient cells to grow approximately two times longer, showing a mild bacterial division defect. Although we still do not know the exact physiological roles of ZapAL, our results suggest that ZapAL is a novel Z-ring associate protein, which may work together with ZapA to stabilize the FtsZ protofilament and Z-ring structure.

Single-molecule imaging reveals that Z-ring condensation is essential for cell division in Bacillus subtilis

Although many components of the cell division machinery in bacteria have been identified^1,2, the mechanisms by which they work together to divide the cell remain poorly understood. Key among these components is the tubulin FtsZ, which forms a Z ring at the midcell. FtsZ recruits the other cell division proteins, collectively called the divisome, and the Z ring constricts as the cell divides. We applied live-cell single-molecule imaging to describe the dynamics of the divisome in detail, and to evaluate the individual roles of FtsZ-binding proteins (ZBPs), specifically FtsA and the ZBPs EzrA, SepF and ZapA, in cytokinesis. We show that the divisome comprises two subcomplexes that move differently: stationary ZBPs that transiently bind to treadmilling FtsZ filaments, and a moving complex that includes cell wall synthases. Our imaging analyses reveal that ZBPs bundle FtsZ filaments together and condense them into Z rings, and that this condensation is necessary for cytokinesis.

Mutation of G51 in SepF impairs FtsZ assembly promoting ability of SepF and retards the division of Mycobacterium smegmatis cells

The role of FtsZ-associated proteins in the regulation of the assembly dynamics of Mycobacterium smegmatis FtsZ is not clear. In this work, we examined the effect of M. smegmatis SepF on the assembly and stability of M. smegmatis FtsZ polymers. We discovered a single dominant point mutation in SepF (G51D or G51R) that renders the protein inactive. SepF promoted the polymerization of FtsZ, induced the bundling of FtsZ filaments, stabilized FtsZ filaments and reduced the GTPase activity of FtsZ. Surprisingly, both G51D-SepF and G51R-SepF neither stabilized FtsZ filaments nor showed a discernable effect on the GTPase activity of FtsZ. The binding affinity of SepF to FtsZ was found to be stronger than the binding affinity of G51R/D-SepF to FtsZ. Interestingly, the binding affinity of SepF to G51R-SepF was determined to be 45 times stronger than FtsZ. In addition, the interaction of SepF with G51R-SepF was found to be 2.6 times stronger than SepF-SepF interaction. Furthermore, G51R-SepF impaired the ability of SepF to promote the assembly of FtsZ. In addition, the overexpression of G51R-SepF in M. smegmatis mc² 155 cells retarded the proliferation of these cells and increased the average length of the cells. The results indicated that SepF positively regulates the assembly of M. smegmatis FtsZ and the G51 residue has an important role in the functioning of SepF.

Bacterial Cell Division: Nonmodels Poised to Take the Spotlight

The last three decades have witnessed an explosion of discoveries about the mechanistic details of binary fission in model bacteria such as Escherichia coli, Bacillus subtilis, and Caulobacter crescentus. This was made possible not only by advances in microscopy that helped answer questions about cell biology but also by clever genetic manipulations that directly and easily tested specific hypotheses. More recently, research using understudied organisms, or nonmodel systems, has revealed several alternate mechanistic strategies that bacteria use to divide and propagate. In this review, we highlight new findings and compare these strategies to cell division mechanisms elucidated in model organisms.