ftsZ is an essential cell division gene in Escherichia coli

Single-cell time-lapse analysis of depletion of the universally conserved essential protein YgjD

BACKGROUND

The essential Escherichia coli gene ygjD belongs to a universally conserved group of genes whose function has been the focus of a number of recent studies. Here, we put ygjD under control of an inducible promoter, and used time-lapse microscopy and single cell analysis to investigate the phenotypic consequences of the depletion of YgjD protein from growing cells.

RESULTS

We show that loss of YgjD leads to a marked decrease in cell size and termination of cell division. The transition towards smaller size occurs in a controlled manner: cell elongation and cell division remain coupled, but cell size at division decreases. We also find evidence that depletion of YgjD leads to the synthesis of the intracellular signaling molecule (p)ppGpp, inducing a cellular reaction resembling the stringent response. Concomitant deletion of the relA and spoT genes - leading to a strain that is uncapable of synthesizing (p)ppGpp - abrogates the decrease in cell size, but does not prevent termination of cell division upon YgjD depletion.

CONCLUSIONS

Depletion of YgjD protein from growing cells leads to a decrease in cell size that is contingent on (p)ppGpp, and to a termination of cell division. The combination of single-cell timelapse microscopy and statistical analysis can give detailed insights into the phenotypic consequences of the loss of essential genes, and can thus serve as a new tool to study the function of essential genes.

In vivo structure of the E. coli FtsZ-ring revealed by photoactivated localization microscopy (PALM)

The FtsZ protein, a tubulin-like GTPase, plays a pivotal role in prokaryotic cell division. In vivo it localizes to the midcell and assembles into a ring-like structure-the Z-ring. The Z-ring serves as an essential scaffold to recruit all other division proteins and generates contractile force for cytokinesis, but its supramolecular structure remains unknown. Electron microscopy (EM) has been unsuccessful in detecting the Z-ring due to the dense cytoplasm of bacterial cells, and conventional fluorescence light microscopy (FLM) has only provided images with limited spatial resolution (200-300 nm) due to the diffraction of light. Hence, given the small sizes of bacteria cells, identifying the in vivo structure of the Z-ring presents a substantial challenge. Here, we used photoactivated localization microscopy (PALM), a single molecule-based super-resolution imaging technique, to characterize the in vivo structure of the Z-ring in E. coli. We achieved a spatial resolution of ∼35 nm and discovered that in addition to the expected ring-like conformation, the Z-ring of E. coli adopts a novel compressed helical conformation with variable helical length and pitch. We measured the thickness of the Z-ring to be ∼110 nm and the packing density of FtsZ molecules inside the Z-ring to be greater than what is expected for a single-layered flat ribbon configuration. Our results strongly suggest that the Z-ring is composed of a loose bundle of FtsZ protofilaments that randomly overlap with each other in both longitudinal and radial directions of the cell. Our results provide significant insight into the spatial organization of the Z-ring and open the door for further investigations of structure-function relationships and cell cycle-dependent regulation of the Z-ring.

Estimating Z-ring radius and contraction in dividing Escherichia coli

We present a fluorescence recovery after photobleaching-based method for monitoring the progression of septal Z-ring contraction in dividing Escherichia coli cells. In a large number of cells undergoing division, we irreversibly bleached cytosolically expressed Enhanced Green Fluorescent Protein on one side of the septal invagination and followed the fluorescence relaxation on both sides of the septum. Since the relaxation time depends on the cross-sectional area of the septum, it can be used to determine the septal radius r. Assuming that the fraction of the observed cells with r-values in a given interval reflects the duration of that interval in the division process we could derive an approximate time-course for the contraction event, as a population average. By applying the method repeatedly on individual cells, the contraction process was also followed in real time. On a population average level, our data are best described by a linear contraction process in time. However, on the single cell level the contraction processes display a complex behaviour, with varying levels of activity. The proposed approach provides a simple yet versatile method for studying Z-ring contraction in vivo, and will help to elucidate its underlying mechanisms.

Examination of the interaction between FtsZ and MinCN in E. coli suggests how MinC disrupts Z rings

In Escherichia coli the Min system prevents Z ring assembly at cell poles by topologically regulating the division inhibitor MinC. The MinC protein has two domains of equal size and both domains can target FtsZ and block cell division in the proper context. Recently, we have shown that, along with MinD, the C-terminal domain of MinC (MinC(C)) competes with FtsA, and to a lesser extent with ZipA, for interaction with the C-terminal tail of FtsZ to block division. Here we explored the interaction between the N-terminal domain of MinC (MinC(N)) and FtsZ. A search for mutations in ftsZ that confer resistance to MinC(N) identified an alpha-helix at the interface of FtsZ subunits as being critical for the activity of MinC(N). Focusing on one such mutant FtsZ-N280D, we showed that it greatly reduced the FtsZ-MinC interaction and was resistant to MinC(N) both in vivo and in vitro. With these results, an updated model for the action of MinC on FtsZ is proposed: MinC interacts with FtsZ to disrupt two interactions, FtsZ-FtsA/ZipA and FtsZ-FtsZ, both of which are essential for Z ring formation.

Targeted gene knockouts reveal overlapping functions of the five Physcomitrella patens FtsZ isoforms in chloroplast division, chloroplast shaping, cell patterning, plant development, and gravity sensing

Chloroplasts and bacterial cells divide by binary fission. The key protein in this constriction division is FtsZ, a self-assembling GTPase similar to eukaryotic tubulin. In prokaryotes, FtsZ is almost always encoded by a single gene, whereas plants harbor several nuclear-encoded FtsZ homologs. In seed plants, these proteins group in two families and all are exclusively imported into plastids. In contrast, the basal land plant Physcomitrella patens, a moss, encodes a third FtsZ family with one member. This protein is dually targeted to the plastids and to the cytosol. Here, we report on the targeted gene disruption of all ftsZ genes in P. patens. Subsequent analysis of single and double knockout mutants revealed a complex interaction of the different FtsZ isoforms not only in plastid division, but also in chloroplast shaping, cell patterning, plant development, and gravity sensing. These results support the concept of a plastoskeleton and its functional integration into the cytoskeleton, at least in the moss P. patens.

The conserved C-terminal tail of FtsZ is required for the septal localization and division inhibitory activity of MinC(C)/MinD

The Escherichia coli Min system contributes to spatial regulation of cytokinesis by preventing assembly of the Z ring away from midcell. MinC is a cell division inhibitor whose activity is spatially regulated by MinD and MinE. MinC has two functional domains of similar size, both of which have division inhibitory activity in the proper context. However, the molecular mechanism of the inhibitory action of either domain is not very clear. Here, we report that the septal localization and division inhibitory activity of MinC(C)/MinD requires the conserved C-terminal tail of FtsZ. This tail also mediates interaction with two essential division proteins, ZipA and FtsA, to link FtsZ polymers to the membrane. Overproduction of MinC(C)/MinD displaces FtsA from the Z ring and eventually disrupts the Z ring, probably because it also displaces ZipA. These results support a model for the division inhibitory action of MinC/MinD. MinC/MinD binds to ZipA and FtsA decorated FtsZ polymers located at the membrane through the MinC(C)/MinD-FtsZ interaction. This binding displaces FtsA and/or ZipA, and more importantly, positions MinC(N) near the FtsZ polymers making it a more effective inhibitor.

Degradation of ppGpp by nudix pyrophosphatase modulates the transition of growth phase in the bacterium Thermus thermophilus

A major bacterial alarmone, guanosine 3',5'-bispyrophosphate (ppGpp), controls cellular growth under conditions of nutritional starvation. For most bacteria, intracellular ppGpp levels are tightly controlled by the synthesis/degradation cycle of RelA and SpoT activities. This study shows a novel ppGpp regulatory protein governing the cellular growth of Thermus thermophilus, Ndx8, a member of the Nudix pyrophosphatase family that degrades ppGpp to yield guanosine 3',5'-bisphosphate. The ndx8-null mutant strain exhibited early stage growth arrest accompanied by the stationary phase-specific morphologies and global transcriptional modulation under nutritionally defined conditions. Several possible substrate compounds of Ndx8, which specifically accumulated in the ndx8 mutant cells, were identified by employing a capillary electrophoresis time-of-flight mass spectrometry-based metabolomics approach. Among them, the hydrolytic activity of Ndx8 for ppGpp was significant not only in vitro but also in vivo. Finally, the elimination of ppGpp synthetic activity suppressed the observed phenotype of the ndx8 mutation, suggesting that the function of Ndx8 as a growth regulator is involved in ppGpp accumulation, which is thought to act as a trigger of the growth phase transition. These results suggest a novel mechanism of ppGpp-mediated growth control by the functional relay between Ndx8 and SpoT activity as ppGpp scavengers.

A vitamin B12-based system for conditional expression reveals dksA to be an essential gene in Myxococcus xanthus

Myxococcus xanthus is a prokaryotic model system for the study of multicellular development and the response to blue light. The previous analyses of these processes and the characterization of new genes would benefit from a robust system for controlled gene expression, which has been elusive so far for this bacterium. Here, we describe a system for conditional expression of genes in M. xanthus based on our recent finding that vitamin B12 and CarH, a MerR-type transcriptional repressor, together downregulate a photoinducible promoter. Using this system, we confirmed that M. xanthus rpoN, encoding sigma(54), is an essential gene, as reported earlier. We then tested it with ftsZ and dksA. In most bacteria, ftsZ is vital due to its role in cell division, whereas null mutants of dksA, whose product regulates the stringent response via transcriptional control of rRNA and amino acid biosynthesis promoters, are viable but cause pleiotropic effects. As with rpoN, it was impossible to delete endogenous ftsZ or dksA in M. xanthus except in a merodiploid background carrying another functional copy, which indicates that these are essential genes. B12-based conditional expression of ftsZ was insufficient to provide the high intracellular FtsZ levels required. With dksA, as with rpoN, cells were viable under permissive but not restrictive conditions, and depletion of DksA or sigma(54) produced filamentous, aberrantly dividing cells. dksA thus joins rpoN in a growing list of genes dispensable in many bacteria but essential in M. xanthus.

In vitro reconstitution of the initial stages of the bacterial cell division machinery

Fission of many prokaryotes as well as some eukaryotic organelles depends on the self-assembly of the FtsZ protein into a membrane-associated ring structure early in the division process. Different components of the machinery are then sequentially recruited. Although the assembly order has been established, the molecular interactions and the understanding of the force-generating mechanism of this dividing machinery have remained elusive. It is desirable to develop simple reconstituted systems that attempt to reproduce, at least partially, some of the stages of the process. High-resolution studies of Escherichia coli FtsZ filaments' structure and dynamics on mica have allowed the identification of relevant interactions between filaments that suggest a mechanism by which the polymers could generate force on the membrane. Reconstituting the membrane-anchoring protein ZipA on E. coli lipid membrane on surfaces is now providing information on how the membrane attachment regulates FtsZ polymer dynamics and indicates the important role played by the lipid composition of the membrane.

Cell-division inhibitors: new insights for future antibiotics

The growing problem of antibiotic resistance has been exacerbated by the use of new drugs that are merely variants of older overused antibiotics. While it is naive to expect to restrain the spread of resistance without controlling antibacterial usage, the desperate need for drugs with novel targets has been recognized by health organizations, industry and academia alike. The wealth of knowledge available about the bacterial cell-division pathway has aided target-driven approaches to identify novel inhibitors. Here, we discuss the therapeutic potential of inhibiting bacterial cell division, and review the progress made in this exciting new area of antibacterial discovery.

Reconstitution of contractile FtsZ rings in liposomes

FtsZ is a tubulin homolog and the major cytoskeletal protein in bacterial cell division. It assembles into the Z ring, which contains FtsZ and a dozen other division proteins, and constricts to divide the cell. We have constructed a membrane-targeted FtsZ (FtsZ-mts) by splicing an amphipathic helix to its C terminus. When mixed with lipid vesicles, FtsZ-mts was incorporated into the interior of some tubular vesicles. There it formed multiple Z rings that could move laterally in both directions along the length of the liposome and coalesce into brighter Z rings. Brighter Z rings produced visible constrictions in the liposome, suggesting that FtsZ itself can assemble the Z ring and generate a force. No other proteins were needed for assembly and force generation.

The great divide: coordinating cell cycle events during bacterial growth and division

The relationship between events during the bacterial cell cycle has been the subject of frequent debate. While early models proposed a relatively rigid view in which DNA replication was inextricably coupled to attainment of a specific cell mass, and cell division was triggered by the completion of chromosome replication, more recent data suggest these models were oversimplified. Instead, an intricate set of intersecting, and at times opposing, forces coordinate DNA replication, cell division, and cell growth with one another, thereby ensuring the precise spatial and temporal control of cell cycle events.

Investigation of regulation of FtsZ assembly by SulA and development of a model for FtsZ polymerization

In Escherichia coli FtsZ organizes into a cytoskeletal ring structure, the Z ring, which effects cell division. FtsZ is a GTPase, but the free energy of GTP hydrolysis does not appear to be used for generation of the constriction force, leaving open the question of the function of the GTPase activity of FtsZ. Here we study the mechanism by which SulA, an inhibitor of FtsZ induced during the SOS response, inhibits FtsZ function. We studied the effects of SulA on the in vitro activities of FtsZ, on Z rings in vivo, and on a kinetic model for FtsZ polymerization in silico. We found that the binding of SulA to FtsZ is necessary but not sufficient for inhibition of polymerization, since the assembly of FtsZ polymers in the absence of the GTPase activity was not inhibited by SulA. We developed a new model for FtsZ polymerization that accounts for the cooperativity of FtsZ and could account for cooperativity observed in other linear polymers. When SulA was included in the kinetic scheme, simulations revealed that SulA with strong affinity for FtsZ delayed, but did not prevent, the assembly of polymers when they were not hydrolyzing GTP. Furthermore, the simulations indicated that SulA controls the assembly of FtsZ by binding to a polymerization-competent form of the FtsZ molecule and preventing it from participating in assembly. In vivo stoichiometry of the disruption of Z rings by SulA suggests that FtsZ may undergo two cooperative transitions in forming the Z ring.

Curcumin inhibits FtsZ assembly: an attractive mechanism for its antibacterial activity

The assembly and stability of FtsZ protofilaments have been shown to play critical roles in bacterial cytokinesis. Recent evidence suggests that FtsZ may be considered as an important antibacterial drug target. Curcumin, a dietary polyphenolic compound, has been shown to have a potent antibacterial activity against a number of pathogenic bacteria including Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus. We found that curcumin induced filamentation in the Bacillus subtilis 168, suggesting that it inhibits bacterial cytokinesis. Further, curcumin strongly inhibited the formation of the cytokinetic Z-ring in B. subtilis 168 without detectably affecting the segregation and organization of the nucleoids. Since the assembly dynamics of FtsZ protofilaments plays a major role in the formation and functioning of the Z-ring, we analysed the effects of curcumin on the assembly of FtsZ protofilaments. Curcumin inhibited the assembly of FtsZ protofilaments and also increased the GTPase activity of FtsZ. Electron microscopic analysis showed that curcumin reduced the bundling of FtsZ protofilaments in vitro. Further, curcumin was found to bind to FtsZ in vitro with a dissociation constant of 7.3±1.8 μM and the agent also perturbed the secondary structure of FtsZ. The results indicate that the perturbation of the GTPase activity of FtsZ assembly is lethal to bacteria and suggest that curcumin inhibits bacterial cell proliferation by inhibiting the assembly dynamics of FtsZ in the Z-ring.

The tubulin homologue FtsZ contributes to cell elongation by guiding cell wall precursor synthesis in Caulobacter crescentus

The tubulin homologue FtsZ is well known for its essential function in bacterial cell division. Here, we show that in Caulobacter crescentus, FtsZ also plays a major role in cell elongation by spatially regulating the location of MurG, which produces the essential lipid II peptidoglycan cell wall precursor. The early assembly of FtsZ into a highly mobile ring-like structure during cell elongation is quickly followed by the recruitment of MurG and a major redirection of peptidoglycan precursor synthesis to the midcell region. These FtsZ-dependent events occur well before cell constriction and contribute to cell elongation. In the absence of FtsZ, MurG fails to accumulate near midcell and cell elongation proceeds unperturbed in appearance by insertion of peptidoglycan material along the entire sidewalls. Evidence suggests that bacteria use both a FtsZ-independent and a FtsZ-dependent mode of peptidoglycan synthesis to elongate, the importance of each mode depending on the timing of FtsZ assembly during elongation.

Plastid division: evolution, mechanism and complexity

BACKGROUND

The continuity of chloroplasts is maintained by division of pre-existing chloroplasts. Chloroplasts originated as bacterial endosymbionts; however, the majority of bacterial division factors are absent from chloroplasts and the eukaryotic host has added several new components. For example, the ftsZ gene has been duplicated and modified, and the Min system has retained MinE and MinD but lost MinC, acquiring at least one new component ARC3. Further, the mechanism has evolved to include two members of the dynamin protein family, ARC5 and FZL, and plastid-dividing (PD) rings were most probably added by the eukaryotic host.

SCOPE

Deciphering how the division of plastids is coordinated and controlled by nuclear-encoded factors is key to our understanding of this important biological process. Through a number of molecular-genetic and biochemical approaches, it is evident that FtsZ initiates plastid division where the coordinated action of MinD and MinE ensures correct FtsZ (Z)-ring placement. Although the classical FtsZ antagonist MinC does not exist in plants, ARC3 may fulfil this role. Together with other prokaryotic-derived proteins such as ARC6 and GC1 and key eukaryotic-derived proteins such as ARC5 and FZL, these proteins make up a sophisticated division machinery. The regulation of plastid division in a cellular context is largely unknown; however, recent microarray data shed light on this. Here the current understanding of the mechanism of chloroplast division in higher plants is reviewed with an emphasis on how recent findings are beginning to shape our understanding of the function and evolution of the components.

CONCLUSIONS

Extrapolation from the mechanism of bacterial cell division provides valuable clues as to how the chloroplast division process is achieved in plant cells. However, it is becoming increasingly clear that the highly regulated mechanism of plastid division within the host cell has led to the evolution of features unique to the plastid division process.

Dynamic filaments of the bacterial cytoskeleton

Bacterial cells contain a variety of structural filamentous proteins necessary for the spatial regulation of cell shape, cell division, and chromosome segregation, analogous to the eukaryotic cytoskeletal proteins. The molecular mechanisms by which these proteins function are beginning to be revealed, and these proteins show numerous three-dimensional structural features and biochemical properties similar to those of eukaryotic actin and tubulin, revealing their evolutionary relationship. Recent technological advances have illuminated links between cell division and chromosome segregation, suggesting a higher complexity and organization of the bacterial cell than was previously thought.

Intracellular cytoskeletal elements and cytoskeletons in bacteria

Within a short period of time after the discovery of bacterial cytoskletons, major progress had been made in areas such as general spatial layout of cytoskeletons, their involvement in a variety of cellfunctions (shape control, cell division, chromosome segregation, cell motility). This progress was achieved by application of advanced investigation techniques. Homologs of eukaryotic actin, tubulin, and intermediate filaments were found in bacteria; cytoskeletal proteins not closely or not at all related to any of these major cytoskeletal proteins were discovered in a number of bacteria such as Mycoplasmas, Spiroplasmas, Spirochetes, Treponema, Caulobacter. A structural role for bacterial elongation factor Tu was indicated. On the basis of this new thinking, new approaches in biotechnology and new drugs are on the way.

Z ring as executor of bacterial cell division

It has become apparent that bacteria possess ancestors of the major eukaryotic cytoskeletal proteins. FtsZ, the ancestral homologue of tubulin, assembles into a cytoskeletal structure associated with cell division, designated the Z ring. Formation of the Z ring represents a major point of both spatial and temporal regulation of cell division. Here we discuss findings concerning the structure and the formation of the ring as well as its spatial and temporal regulation.

FtsZ from divergent foreign bacteria can function for cell division in Escherichia coli

FtsZs from Mycoplasma pulmonis (MpuFtsZ) and Bacillus subtilis (BsFtsZ) are only 46% and 53% identical in amino acid sequence to FtsZ from Escherichia coli (EcFtsZ). In the present study we show that MpuFtsZ and BsFtsZ can function for cell division in E. coli provided we make two modifications. First, we replaced their C-terminal tails with that from E. coli, giving the foreign FtsZ the binding site for E. coli FtsA and ZipA. Second, we selected for mutations in the E. coli genome that facilitated division by the foreign FtsZs. These suppressor strains arose at a relatively high frequency of 10(-3) to 10(-5), suggesting that they involve loss-of-function mutations in multigene pathways. These pathways may be negative regulators of FtsZ or structural pathways that facilitate division by slightly defective FtsZ. Related suppressor strains were obtained for EcFtsZ containing certain point mutations or insertions of yellow fluorescent protein. The ability of highly divergent FtsZs to function for division in E. coli is consistent with a two-part mechanism. FtsZ assembles the Z ring, and perhaps generates the constriction force, through self interactions; the downstream division proteins remodel the peptidoglycan wall by interacting with each other and the wall. The C-terminal peptide of FtsZ, which binds FtsA, provides the link between FtsZ assembly and peptidoglycan remodeling.

The chromosome partitioning proteins Soj (ParA) and Spo0J (ParB) contribute to accurate chromosome partitioning, separation of replicated sister origins, and regulation of replication initiation in Bacillus subtilis

Soj (ParA) and Spo0J (ParB) of Bacillus subtilis belong to a conserved family of proteins required for efficient plasmid and chromosome partitioning in many bacterial species. Unlike most Par systems, for which intact copies of both parA and parB are required for the Par system to function, inactivating soj does not cause a detectable chromosome partitioning phenotype whereas inactivating spo0J leads to a 100-fold increase in the production of anucleate cells. This suggested either that Soj does not function like other ParA homologues, or that a cellular factor might compensate for the absence of soj. We found that inactivating smc, the gene encoding the structural maintenance of chromosomes (SMC) protein, unmasked a role for Soj in chromosome partitioning. A soj null mutation dramatically enhanced production of anucleate cells in an smc null mutant. To look for effects of a soj null on other phenotypes perturbed in a spo0J null mutant, we analysed replication initiation and origin positioning in (soj-spo0J)+, Deltasoj, Deltaspo0J and Delta(soj-spo0J) cells. All of the mutations caused increased initiation of replication and, to varying extents, affected origin positioning. Using a new assay to measure separation of the chromosomal origins, we found that inactivating soj, spo0J or both led to a significant defect in separating replicated sister origins, such that the origins remain too close to be spatially resolved. Separation of a region outside the origin was not affected. These results indicate that there are probably factors helping to pair sister origin regions for part of the replication cycle, and that Soj and Spo0J may antagonize this pairing to contribute to timely separation of replicated origins. The effects of Deltasoj, Deltaspo0J and Delta(soj-spo0J) mutations on origin positioning, chromosome partitioning and replication initiation may be a secondary consequence of a defect in separating replicated origins.

RNase E maintenance of proper FtsZ/FtsA ratio required for nonfilamentous growth of Escherichia coli cells but not for colony-forming ability

Inactivation or deletion of the RNase E-encoding rne gene of Escherichia coli results in the growth of bacterial cells as filamentous chains in liquid culture (K. Goldblum and D. Apirion, J. Bacteriol. 146:128-132, 1981) and the loss of colony-forming ability (CFA) on solid media. RNase E dysfunction is also associated with abnormal processing of ftsQAZ transcripts (K. Cam, G. Rome, H. M. Krisch, and J.-P. Bouché, Nucleic Acids Res. 24:3065-3070, 1996), which encode proteins having a central role in septum formation during cell division. We show here that RNase E regulates the relative abundances of FtsZ and FtsA proteins and that RNase E depletion results in decreased FtsZ, increased FtsA, and consequently an altered FtsZ/FtsA ratio. However, while restoration of the level of FtsZ to normal in rne null mutant bacteria reverses the filamentation phenotype, it does not restore CFA. Conversely, overexpression of a related RNase, RNase G, in rne-deleted bacteria restores CFA, as previously reported, without affecting FtsZ abundance. Our results demonstrate that RNase E activity is required to maintain a proper cellular ratio of the FtsZ and FtsA proteins in E. coli but that FtsZ deficiency does not account for the nonviability of cells lacking RNase E.

Borrelia burgdorferi ftsZ plays a role in cell division

ftsZ is essential for cell division in many microorganisms. In Escherichia coli and Bacillus subtilis, FtsZ plays a role in ring formation at the leading edge of the cell division septum. An ftsZ homologue is present in the Borrelia burgdorferi genome (ftsZ(Bbu)). Its gene product (FtsZ(Bbu)) is strongly homologous to other bacterial FtsZ proteins, but its function has not been established. Because loss-of-function mutants of ftsZ(Bbu) might be lethal, the tetR/tetO system was adapted for regulated control of this gene in B. burgdorferi. Sixty-two nucleotides of an ftsZ(Bbu) antisense DNA sequence under the control of a tetracycline-responsive modified hybrid borrelial promoter were cloned into pKFSS1. This construct was electroporated into a B. burgdorferi host strain carrying a chromosomally located tetR under the control of the B. burgdorferi flaB promoter. After induction by anhydrotetracycline, expression of antisense ftsZ RNA resulted in generation of filamentous B. burgdorferi that were unable to divide and grew more slowly than uninduced cells. To determine whether FtsZ(Bbu) could interfere with the function of E. coli FtsZ, ftsZ(Bbu) was amplified from chromosomal DNA and placed under the control of the tetracycline-regulated hybrid promoter. After introduction of the construct into E. coli and induction with anhydrotetracycline, overexpression of ftsZ(Bbu) generated a filamentous phenotype. This suggested interference of ftsZ(Bbu) with E. coli FtsZ function and confirmed the role of ftsZ(Bbu) in cell division. This is the first report of the generation of a B. burgdorferi conditional lethal mutant equivalent by tetracycline-controlled expression of antisense RNA.

Characterization of cytoplasmic fibril structures found in gliding cells of Saprospira sp

The cytoplasmic fibril structures of Saprospira sp. strain SS98-5 grown on a low-nutrient agar medium were purified from cell lysates treated with Triton X-100 and were observed by electron microscopy to be about 7 nm in width and 200-300 nm in length. SDS-PAGE of the fibril structures exhibited a single protein band with a molecular mass of 61 kDa. A Saprospira cytoplasmic fibril protein (SCFP), which is a subunit of the fibril structures, was digested with trypsin to oligopeptides and analyzed for amino acid sequences. A partial nucleotide sequence of the SCFP gene was determined after PCR using primers designated from the amino acid sequences of the oligopeptides. SCFP gene including DNA fragments were detected by Southern hybridization using the PCR product for an SCFP gene as a probe and were cloned to determine whole nucleotide sequences. The SCFP gene indicated relatively higher similarity to conserved hypothetical phage tail sheath proteins. A Western immunoblotting analysis showed that SCFP was significantly expressed in gliding cells as compared with nongliding cells. The above findings with the previously reported results suggest that the cytoplasmic fibril structures are possibly related to the gliding motility of Saprospira sp. strain SS98-5.

Probing the domain structure of FtsZ by random truncation and insertion of GFP

Random transposon-mediated mutagenesis has been used to create truncations and insertions of green fluorescent protein (GFP), and Venus-yellow fluorescent protein (YFP), in Escherichia coli FtsZ. Sixteen unique insertions were obtained, and one of them, in the poorly conserved C-terminal spacer, was functional for cell division with the Venus-YFP insert. The insertion of enhanced GFP (eGFP) at this same site was not functional; Venus-YFP was found to be superior to eGFP in other respects too. Testing the constructs for dominant negative effects led to the following general conclusion. The N-terminal domain, aa 1-195, is an independently folding domain that can poison Z-ring function when expressed without a functional C-terminal domain. The effects were weak, requiring expression of the mutant at 3-5 times the level of wild-type FtsZ. The C-terminal domain, aa 195-383, was also independently folding, but had no activity in vivo. The differential activity of the N- and C-terminal domains suggests that FtsZ protofilament assembly is directional, with subunits adding primarily at the bottom of the protofilament. Directional assembly could occur by either a treadmilling or a dynamic instability mechanism.

Characterization of FtsZ homolog from hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1

The gene of bacterial type ftsZ homolog in hyperthermophilic archaeon, Pyrococcus kodakaraensis KOD1 (Pk-ftsZ), was identified. The gene product of the Pk-ftsZ gene is composed of 380 amino acids with a molecular mass of 41,354 Da. In the deduced amino acid sequence of the Pk-ftsZ gene, a glycine-rich sequence (Gly-Gly-Gly-Thr-Gly-Ala-Gly) implicated in GTP binding was well conserved. The Pk-ftsZ gene was overexpressed using Escherichia coli as a host and the recombinant protein was purified. The purified Pk-FtsZ protein exhibited GTPase activity with optimum temperatures higher than 80 degrees C. However, the protein showed little GTPase activity at 40 degrees C, indicating that a high reaction temperature is required for the GTPase activity in accordance with the thermophilic nature of P. kodakaraensis KOD1. The GTP-binding ability of Pk-FtsZ protein could also be detected by UV-induced cross-linking of a protein to [alpha-32P] GTP. The Pk-ftsZ gene was expressed in E. coli cells with a temperature-sensitive ftsZ mutation, E. coli ftsZ84 (ts), but its mutant phenotype of elongated cell form at a nonpermissive temperature (42 degrees C) could not be compensated, possibly because of the thermophilic nature of the Pk-FtsZ. Pk-FtsZ could form protofilaments in a GTP-dependent manner at 90 degrees C. Results of phylogenetic analysis suggest that there might be additional factors required for formation of the Z ring in P. kodakaraensis KOD1.

Overexpression of the ftsZ gene from Corynebacterium glutamicum (Brevibacterium lactofermentum) in Escherichia coli

Our goal in this work was to overexpress the essential cell division FtsZ protein from Corynebacterium glutamicum (Brevibacterium lactofermentum) (FtsZCG) in Escherichia coli to produce anti-FtsZCG polyclonal antibodies. Previous results from our laboratory showed that ftsZCG was not expressed in E. coli in a sufficient amount to purify FtsZCG. However, when ftsZCG (without upstream sequences) was transcriptionally fused to the T7 promoter, different truncated FtsZCG proteins (28-32 kDa) were overexpressed in E. coli, and in all cases, stop codons were created because of DNA deletions or rearrangements. Nevertheless, we were able to overexpress and purify an N-terminally hexa-His-tagged FtsZCG from uninduced E. coli cells carrying a pET-28a(+) derivative, yielding about 5 mg of 98% pure protein per 100-mL culture.

Insertion-duplication mutagenesis of Salmonella enterica and related species using a novel thermosensitive vector

We constructed a novel temperature-sensitive vector as a tool for gene disruption by insertion-duplication mutagenesis (IDM) in Salmonella enterica and related species. A phoN insertion mutant was proven highly stable during growth in LB medium and during infection of macrophage cells in the absence of selection pressure. By progressive shortening of a phoN fragment, the minimal length for effective insertional mutagenesis driven by homologous recombination was determined to be 50 bp, allowing to disrupt even short genes that could not yet be subjected to site-specific IDM. We also showed that plasmid excision from the chromosome restores the wild-type genotype with a reliability of 98%. Intracellular recovery of the excised vector provides the option to switch between two genotypes and thus to rapidly attribute the observed mutant phenotype to the targeted gene. In addition, a fragment library was used to measure the integration rate at various chromosomal sites that varies greatly by at least 2.5 magnitudes, independently from the length of the cloned fragment.

Mutations in the GTP-binding and synergy loop domains of Mycobacterium tuberculosis ftsZ compromise its function in vitro and in vivo

The Mycobacterium tuberculosis FtsZ (FtsZ(TB)), unlike other eubacterial FtsZ proteins, shows slow GTP-dependent polymerization and weak GTP hydrolysis activities [E.L. White, L.J. Ross, R.C. Reynolds, L.E. Seitz, G.D. Moore, D.W. Borhani, Slow polymerization of Mycobacterium tuberculosis FtsZ, J. Bacteriol. 182 (2000) 4028-4034]. In an attempt to understand the biological significance of these findings, we created mutations in the GTP-binding (FtsZ(G103S)) and GTP hydrolysis (FtsZ(D210G)) domains of FtsZ and characterized the activities of the mutant proteins in vitro and in vivo. We show that FtsZ(G103S) is defective for binding to GTP and polymerization activities, and exhibited reduced GTPase activity whereas FtsZ(D210G) protein is proficient in binding to GTP, showing reduced polymerization activity but did not show any measurable GTPase activity. Visualization of FtsZ-GFP structures in ftsZ merodiploid strains by fluorescent microscopy revealed that FtsZ(D210G) is proficient in associating with Z-ring structures whereas FtsZ(G103S) is not. Finally, we show that Mycobacterium smegmatis ftsZ mutant strains producing corresponding mutant FtsZ proteins are non-viable indicating that mutant FtsZ proteins cannot function as the sole source for FtsZ, a result distinctly different from that reported for Escherichia coli. Together, our results indicate that optimal GTPase and polymerization activities of FtsZ are required to sustain cell division in mycobacteria and that the same conserved mutations in different bacterial species have distinct phenotypes.

Mutants of FtsZ targeting the protofilament interface: effects on cell division and GTPase activity

The bacterial cell division protein FtsZ assembles into straight protofilaments, one subunit thick, in which subunits appear to be connected by identical bonds or interfaces. These bonds involve the top surface of one subunit making extensive contact with the bottom surface of the subunit above it. We have investigated this interface by site-directed mutagenesis. We found nine bottom and eight top mutants that were unable to function for cell division. We had expected that some of the mutants might poison cell division substoichiometrically, but this was not found for any mutant. Eight of the bottom mutants exhibited dominant negative effects (reduced colony size) and four completely blocked colony formation, but this required expression of the mutant protein at four to five times the wild-type FtsZ level. Remarkably, the top mutants were even weaker, most showing no effect at the highest expression level. This suggests a directional assembly or treadmilling, where subunit addition is primarily to the bottom end of the protofilament. Selected pairs of top and bottom mutants showed no GTPase activity up to 10 to 20 microM, in contrast to the high GTPase activity of wild-type FtsZ above 1 muM. Overall, these results suggest that in order for a subunit to bind a protofilament at the 1 microM K(d) for elongation, it must have functional interfaces at both the top and bottom. This is inconsistent with the present model of the protofilament, as a simple stack of subunits one on top of the other, and may require a new structural model.

The effects of ftsZ mutation on the production of recombinant protein in Bacillus subtilis

In this paper, the possibility of using a mutation of ftsZ as a pseudo-spore mutant is investigated. ftsZ, which is essential for cell division and sporulation of Bacillus subtilis, was placed under the spac promoter, which is inducible with isopropyl thiogalactose (IPTG). Cell growth of the ftsZ mutant and its beta-galactosidase activity under the aprE promoter were compared with the wild type. In the presence of 1 mM IPTG, cell growth of the ftsZ mutant was almost the same as that of the wild type and its sporulation frequency was slightly lower than that of the wild type. However, under uninduced conditions, cell growth of ftsZ mutant was severely impaired. When induced with 0.2 mM IPTG, the ftsZ mutant showed about 13 times higher beta-galactosidase activity than the wild type. When the ftsZ mutant was used for secretory production of subtilisin, only three times higher extracellular subtilisin activity was measured, compared with the wild type. By real-time PCR investigation, it was revealed that the ftsZ mutant intracellular mRNA level for subtilisin was more than 16 times higher, compared with the wild type. However, it appears that the secretion pathway is somewhat damaged in the ftsZ mutant. These results suggest that the cell division mutant can also be used like a sporulation mutant to produce recombinant proteins, with a precise control of cell growth and induction.

A decreased level of FtsZ is responsible for inviability of RNase E-deficient cells

The endoribonuclease RNase E, encoded by the essential gene rne, plays a major role in cellular RNA metabolism, i.e. maturation of functional RNAs such as rRNA and tRNA, degradation of many mRNAs and processing of the ftsZ mRNA which encodes the essential cell division protein FtsZ. RNase E function is somehow regulated by the RNA binding protein Hfq. We found that temperature-sensitive colony formation of a rne-1 mutant was partially suppressed by introduction of a hfq::cat mutation. Neither accumulation of rRNA and tRNA(Phe) precursors nor incomplete processing of ftsZ mRNA in the rne-1 mutant was rescued by the hfq::cat mutation. However, the amount of FtsZ protein that was decreased in the rne-1 mutant was recovered up to a level similar to that of wild-type cells by the hfq::cat mutation. Overproduction of Hfq inhibited cell division because of decreased expression of FtsZ. Artificial expression of the FtsZ protein from a plasmid-borne ftsZ gene partially suppressed the temperature-sensitivity of the rne-1 mutant. These results suggest that the decreased level of FtsZ is, at least in part, responsible for the inviability of RNase E-deficient cells.

Human S100B protein interacts with the Escherichia coli division protein FtsZ in a calcium-sensitive manner

S100B is a small, dimeric EF-hand calcium-binding protein abundant in vertebrates. Upon calcium binding, S100B undergoes a conformational change allowing it to interact with a variety of target proteins, including the cytoskeletal proteins tubulin and glial fibrillary acidic protein. In both cases, S100B promotes the in vitro disassembly of these proteins in a calcium-sensitive manner. Despite this, there is little in vivo evidence for the interaction of proteins such as tubulin with S100B. To probe these interactions, we studied the expression of human S100B in Escherichia coli and its interaction with the prokaryotic ancestor of tubulin, FtsZ, the major protein involved in bacterial division. Expression of S100B protein in E. coli results in little change in FtsZ protein levels, causes a filamenting bacterial phenotype characteristic of FtsZ inhibition, and leads to missed rounds of cell division. Further, S100B localizes to positions similar to those of FtsZ in bacterial filaments: the small foci at the poles, the mid-cell positions, and between the nucleoids at regular intervals. Calcium-dependent physical interaction between S100B and FtsZ was demonstrated in vitro by affinity chromatography, and this interaction was severely inhibited by the competitor peptide TRTK-12. Together these results indicate that S100B interacts with the tubulin homologue FtsZ in vivo, modulating its activity in bacterial cell division. This approach will present an important step for the study of S100 protein interactions in vivo.

Assembly dynamics of the bacterial cell division protein FTSZ: poised at the edge of stability

FtsZ is a prokaryotic tubulin homolog that assembles into a ring at the future site of cell division. The resulting "Z ring" forms the framework for the division apparatus, and its assembly is regulated throughout the bacterial cell cycle. A highly dynamic structure, the Z ring exhibits continual subunit turnover and the ability to rapidly assemble, disassemble, and, under certain circumstances, relocalize. These in vivo properties are ultimately due to FtsZ's capacity for guanosine triphosphate (GTP)-dependent, reversible polymerization. FtsZ polymer stability appears to be fine-tuned such that subtle changes in its assembly kinetics result in large changes in the Z ring structure. Thus, regulatory proteins that modulate FtsZ's assembly dynamics can cause the ring to rapidly remodel in response to developmental and environmental cues.

Dispersed mode of Staphylococcus aureus cell wall synthesis in the absence of the division machinery

We have developed several new fluorescent staining procedures that enabled us to study the synthesis of cell wall material in the spherical Gram-positive bacterium Staphylococcus aureus. The results obtained support previous proposals that these cells synthesize new wall material specifically at cell division sites, in the form of a flat circular plate that is subsequently cleaved and remodelled to produce the new hemispherical poles of the daughter cells. We have shown that formation of the septal peptidoglycan is dependent on the key cell division protein FtsZ, which recruits penicillin-binding protein (PBP) 2. Unexpectedly, in FtsZ-depleted cells, the cell wall synthetic machinery becomes dispersed and new wall material is made in dispersed patches over the entire surface of the cells, which increase in volume by up to eightfold before lysing. The results have implications for understanding the nature of S. aureus morphogenesis and for inhibitors of cell division proteins as drug targets.

Discovery of a small molecule that inhibits cell division by blocking FtsZ, a novel therapeutic target of antibiotics

The emergence of bacterial resistance to antibiotics is a major health problem and, therefore, it is critical to develop new antibiotics with novel modes of action. FtsZ, a tubulin-like GTPase, plays an essential role in bacterial cell division, and its homologs are present in almost all eubacteria and archaea. During cell division, FtsZ forms polymers in the presence of GTP that recruit other division proteins to make the cell division apparatus. Therefore, inhibition of FtsZ polymerization will prevent cells from dividing, leading to cell death. Using a fluorescent FtsZ polymerization assay, the screening of >100,000 extracts of microbial fermentation broths and plants followed by fractionation led to the identification of viriditoxin, which blocked FtsZ polymerization with an IC50 of 8.2 microg/ml and concomitant GTPase inhibition with an IC50 of 7.0 microg/ml. That the mode of antibacterial action of viriditoxin is via inhibition of FtsZ was confirmed by the observation of its effects on cell morphology, macromolecular synthesis, DNA-damage response, and increased minimum inhibitory concentration as a result of an increase in the expression of the FtsZ protein. Viriditoxin exhibited broad-spectrum antibacterial activity against clinically relevant Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci, without affecting the viability of eukaryotic cells.

Dynamic FtsZ polymerization is sensitive to the GTP to GDP ratio and can be maintained at steady state using a GTP-regeneration system

In vitro polymerization of the essential bacterial cell division protein FtsZ, in the presence of GTP, is rapid and transient due to its efficient binding and hydrolysis of GTP. In contrast, the in vivo polymeric FtsZ structure which drives cell division - the Z-ring - is present in cells for extended periods of time whilst undergoing constant turnover of FtsZ. It is demonstrated that dynamic polymerization of Escherichia coli FtsZ in vitro is sensitive to the ratio of GTP to GDP concentration. Increase of GDP concentration in the presence of a constant GTP concentration reduces both the duration of FtsZ polymerization and the initial light-scattering maximum which occurs upon addition of GTP. It is also demonstrated that by use of a GTP-regeneration system, polymers of FtsZ can be maintained in a steady state for up to 85 min, while preserving their dynamic properties. The authors therefore present the use of a GTP-regeneration system for FtsZ polymerization as an assay more representative of the in vivo situation, where FtsZ polymers are subject to a constant, relatively high GTP to GDP ratio.

In vivo characterization of Escherichia coli ftsZ mutants: effects on Z-ring structure and function

We have characterized the in vivo phenotypes of 17 mutations of Escherichia coli ftsZ. In particular, we determined whether these mutations can complement a null ftsZ phenotype, and we demonstrated that two noncomplementing mutations show partial dominant-negative behavior. We performed immunofluorescence microscopy to determine whether these mutants could assemble into normal or abnormal structures in vivo. The mutants separated into four classes-those that complemented the null and formed normal FtsZ rings, those that complemented the null but formed aberrant FtsZ structures, those that formed aberrant FtsZ structures and did not complement, and those that were unable to form any FtsZ structures. We did not find any mutations that produced nonfunctional Z rings of normal appearance. Surprisingly, some mutants that produced extensively spiraled Z-ring structures divided and grew with a normal doubling time. The analysis was carried out using a complementation system based on an ftsZ deletion strain, a temperature-sensitive rescue plasmid, and a complementation vector that placed mutated ftsZ alleles under the control of the pBAD promoter, which offered several advantages over previous systems.

Conditional expression of Mycobacterium smegmatis ftsZ, an essential cell division gene

To understand the role of Mycobacterium smegmatis ftsZ (ftsZ(smeg)) in the cell division process, the ftsZ gene was characterized at the genetic level. This study shows that ftsZ(smeg) is an essential gene in that it can only be disrupted in a merodiploid background carrying another functional copy. Expression of ftsZ(smeg) in M. smegmatis from a constitutively active mycobacterial promoter resulted in lethality whereas that from a chemically inducible acetamidase (ami) promoter led to FtsZ accumulation, filamentation and cell lysis. To further understand the roles of ftsZ in cell division a conditionally complementing ftsZ(smeg) mutant strain was constructed in which ftsZ expression is controlled by acetamide. Growth in the presence of 0.2 % acetamide increased FtsZ levels approximately 1.4-fold, but did not decrease viability or change cell length. Withdrawal of acetamide reduced FtsZ levels, decreased viability, increased cell length and eventually lysed the cells. Finally, it is shown that ftsZ(smeg) function in M. smegmatis can be replaced with the Mycobacterium tuberculosis counterpart, indicating that heterologous FtsZ(tb) can independently initiate the formation of Z-rings and catalyse the septation process. It is concluded that optimal levels of M. smegmatis FtsZ are required to sustain cell division and that the cell division initiation mechanisms are similar in mycobacteria.

Characterization of the ftsZ gene from Ehrlichia chaffeensis, Anaplasma phagocytophilum, and Rickettsia rickettsii, and use as a differential PCR target

Degenerate primers corresponding to highly conserved regions of previously characterized ftsZ genes were used to PCR amplify a portion of the ftsZ gene from the genomic DNA of Ehrlichia chaffeensis (ftsZ(Ech)), Anaplasma phagocytophilum (ftsZ(Ap)), and Rickettsia rickettsii (ftsZ(Rr)). Genome walking was then used to amplify the 5' and 3' termini of the genes. The DNA sequences of the resulting amplification products yielded open reading frames coding for proteins with molecular masses of 42.0, 45.7, and 48.3 kDa for A. phagocytophilum, E. chaffeensis, and R. rickettsii, respectively. These homologs are 20 to 70 amino acids longer than the FtsZ proteins characterized in bacteria such as Escherichia coli and Bacillus subtilis, but do not possess the large extended carboxyl-termini found in the FtsZ proteins of Bartonella, Rhizobium, and Agrobacterium species. The functional domains important for FtsZ activity are conserved within the ehrlichial and rickettsial FtsZ protein sequences. The R. rickettsii FtsZ sequence is highly homologous to the FtsZ protein previously described for Rickettsia prowazekii (89% identity), and identical to the FtsZ protein of Rickettsia conorii. The percent identity observed between the A. phagocytophilum and E. chaffeensis FtsZ proteins is only 79% and is particularly low in the carboxyl-terminal region (15.8% identity). Primers were designed to PCR amplify a portion of the variable carboxyl-terminal region of the ftsZ gene, and used to differentiate each agent based on the size of the amplicons: A. phagocytophilum, 278 bp; E. chaffeensis, 341 bp; and Rickettsia spp., 425 bp.

Productive interaction between the chromosome partitioning proteins, ParA and ParB, is required for the progression of the cell cycle in Caulobacter crescentus

In Caulobacter crescentus the partitioning proteins ParA and ParB operate a molecular switch that couples chromosome partitioning to cytokinesis. Homologues of these proteins have been shown to be important for the stable inheritance of F-plasmids and the prophage form of bacteriophage P1. In C. crescentus, ParB binds to sequences adjacent to the origin of replication and is required for the initiation of cell division. Additionally, ParB influences the nucleotide-bound state of ParA by acting as a nucleotide exchange factor. Here we have performed a genetic analysis of the chromosome partitioning protein ParB. We show that C. crescentus ParB, like its plasmid homologues, is composed of three domains: a carboxyl-terminal dimerization domain; a central DNA-binding, helix-turn-helix domain; and an amino-terminal domain required for the interaction with ParA. In vivo expression of amino-terminally deleted parB alleles has a dominant lethal effect resulting in the inhibition of cell division. Fluorescent in situ hybridization experiments indicate that this phenotype is not caused by a chromosome partitioning defect, but by the reversal of the amounts of ATP- versus ADP- bound ParA inside the cell. We present evidence suggesting that amino-terminally truncated and full-length, wild-type ParB form heterodimers which fail to interact with ParA, thereby reversing the intracellular ParA-ATP to ParA-ADP ratio. We hypothesize that the amino-terminus of ParB is required to regulate the nucleotide exchange of ParA which, in turn, regulates the initiation of cell division.

A widely conserved bacterial cell division protein that promotes assembly of the tubulin-like protein FtsZ

Cell division in bacteria is mediated by the tubulin-like protein FtsZ, which assembles into a structure known as the Z ring at the future site of cytokinesis. We report the discovery of a Z-ring-associated protein in Bacillus subtilis called ZapA. ZapA was found to colocalize with the Z ring in vivo and was capable of binding to FtsZ and stimulating the formation of higher-order assemblies of the cytokinetic protein in vitro. The absence of ZapA alone did not impair cell viability, but the absence of ZapA in combination with the absence of a second, dispensable division protein EzrA caused a severe block in cytokinesis. The absence of ZapA also caused lethality in cells producing lower than normal levels of FtsZ or lacking the division-site-selection protein DivIVA. Conversely, overproduction of ZapA reversed the toxicity of excess levels of the division inhibitor MinD. In toto, the evidence indicates that ZapA is part of the cytokinetic machinery of the cell and acts by promoting Z-ring formation. Finally, ZapA is widely conserved among bacteria with apparent orthologs in many species, including Escherichia coli, in which the orthologous protein exhibited a strikingly similar pattern of subcellular localization to that of ZapA. Members of the ZapA family of proteins are likely to be a common feature of the cytokinetic machinery in bacteria.

The tubulin ancestor, FtsZ, draughtsman, designer and driving force for bacterial cytokinesis

We discuss in this review the regulation of synthesis and action of FtsZ, its structure in relation to tubulin and microtubules, and the mechanism of polymerization and disassembly (contraction) of FtsZ rings from a specific nucleation site (NS) at mid cell. These topics are considered in the light of recent immunocytological studies, high resolution structures of some division proteins and results indicating how bacteria may measure their mid cell point.

Unique and overlapping roles for ZipA and FtsA in septal ring assembly in Escherichia coli

ZipA and FtsA are essential division proteins in Escherichia coli that are recruited to the division site by interaction with FtsZ. Utilizing a newly isolated temperature-sensitive mutation in zipA we have more fully characterized the role of ZipA. We confirmed that ZipA is not required for Z ring formation; however, we found that ZipA, like FtsA, is required for recruitment of FtsK and therefore all downstream division proteins. In the absence of FtsA or ZipA Z rings formed; however, in the absence of both, new Z rings were unable to form and preformed Z rings were destabilized. Consistent with this, we found that an FtsZ mutant unable to interact with both ZipA and FtsA was unable to assemble into Z rings. These results demonstrate that ZipA and FtsA are both required for recruitment of additional division proteins to the Z ring, but either one is capable of supporting formation and stabilization of Z rings.

kdsA mutations affect FtsZ-ring formation in Escherichia coli K-12

No one has, as yet, addressed the relationship between the nature of the outer membrane and cell division. kdsA encodes 3-deoxy-D-manno-octulosonic acid (KDO) 8-phosphate synthetase which catalyses the first step in the synthesis of KDO, the linker between lipid A and oligosaccharide of lipopolysaccharide (LPS). Seven temperature-sensitive mutants containing missense mutations in kdsA were affected in the production of KDO and all mutants stopped dividing at 41 degrees C and formed filaments with either one or no FtsZ ring. All observed defects were reversed by the plasmid-borne wild-type kdsA gene. Western blotting analysis, however, demonstrated that the amount of FtsZ protein was not affected by the mutation. The mutants were more susceptible to various hydrophobic materials, such as novobiocin, eosin Y and SDS at 36 degrees C. Methylene blue, however, restored kdsA mutant growth. Plasmid-borne wild-type msbA, encoding a lipid A transporter in the ABC family, partially suppressed kdsA mutation. A mutation of lpxA, functioning at the first stage in lipid A biosynthesis, inhibited both cell division and growth, producing short filaments. These results indicate that the instability of the outer membrane, caused by the defect in KDO biosynthesis, affects FtsZ-ring formation.