FtsZ placement in nucleoid-free bacteria

Interaction of Temporin-L Analogues with the E. coli FtsZ Protein

The research of new therapeutic agents to fight bacterial infections has recently focused on the investigation of antimicrobial peptides (AMPs), the most common weapon that all organisms produce to prevent invasion by external pathogens. Among AMPs, the amphibian Temporins constitute a well-known family with high antibacterial properties against Gram-positive and Gram-negative bacteria. In particular, Temporin-L was shown to affect bacterial cell division by inhibiting FtsZ, a tubulin-like protein involved in the crucial step of Z-ring formation at the beginning of the division process. As FtsZ represents a leading target for new antibacterial compounds, in this paper we investigated in detail the interaction of Temporin L with Escherichia coli FtsZ and designed two TL analogues in an attempt to increase peptide-protein interactions and to better understand the structural determinants leading to FtsZ inhibition. The results demonstrated that the TL analogues improved their binding to FtsZ, originating stable protein-peptide complexes. Functional studies showed that both peptides were endowed with a high capability of inhibiting both the enzymatic and polymerization activities of the protein. Moreover, the TL analogues were able to inhibit bacterial growth at low micromolar concentrations. These observations may open up the way to the development of novel peptide or peptidomimetic drugs tailored to bind FtsZ, hampering a crucial process of bacterial life that might be proposed for future pharmaceutical applications.

Both Enolase and the DEAD-Box RNA Helicase CrhB Can Form Complexes with RNase E in Anabaena sp. Strain PCC 7120

At present, little is known about the RNA metabolism driven by the RNA degradosome in cyanobacteria. RNA helicase and enolase are the common components of the RNA degradosome in many bacteria. Here, we provide evidence that both enolase and the DEAD-box RNA helicase CrhB can interact with RNase E in Anabaena (Nostoc) sp. strain PCC 7120 (referred to here as PCC 7120). Furthermore, we found that the C-terminal domains of CrhB and AnaEno (enolase of PCC 7120) are required for the interaction, respectively. Moreover, their recognition motifs for AnaRne (RNase E of PCC 7120) turned out to be located in the N-terminal catalytic domain, which is obviously different from those identified previously in Proteobacteria We also demonstrated in enzyme activity assays that CrhB can induce AnaRne to degrade double-stranded RNA with a 5' tail. Furthermore, we investigated the localization of CrhB and AnaRne by green fluorescent protein (GFP) translation fusion in situ and found that they both localized in the center of the PCC 7120 cytoplasm. This localization pattern is also different from the membrane binding of RNase E and RhlB in Escherichia coli Together with the previous identification of polynucleotide phosphorylase (PNPase) in PCC 7120, our results show that there is an RNA degradosome-like complex with a different assembly mechanism in cyanobacteria.IMPORTANCE In all domains of life, RNA turnover is important for gene regulation and quality control. The process of RNA metabolism is regulated by many RNA-processing enzymes and assistant proteins, where these proteins usually exist as complexes. However, there is little known about the RNA metabolism, as well as about the RNA degradation complex. In the present study, we described an RNA degradosome-like complex in cyanobacteria and revealed an assembly mechanism different from that of E. coli Moreover, CrhB could help RNase E in Anabaena sp. strain PCC 7120 degrade double-stranded RNA with a 5' tail. In addition, CrhB and AnaRne have similar cytoplasm localizations, in contrast to the membrane localization in E. coli.

The sequences of MinE responsible for its subcellular localization analyzed by competitive binding method in Escherichia coli

The subcellular localization of a protein is important for its proper function. Escherichia coli MinE is a small protein with clear subcellular localization, which provides a good model to study protein localization mechanism. In the present study, a series of recombinant minEs truncated in one end or in the middle regions, fused with egfp, was constructed, and these recombinant proteins could compete to function with the chromosomal MinE. Our results showed that the sequences related to the subcellular localization of MinE span several functional domains, demonstrating that MinE positioning in cells depends on multiple factors. The eGFP fusions with some truncated MinE from N-terminal resulted in different cell phenotypes and localization features, implying that these fusions can interfere chromosomal MinE's function, similar to MinE^36-88 phenotype in the previous report. The amino acid in the region (32-48) is sensitive to change MinE conformation and influence its dimerization. Some truncated protein structure could be unstable. Thus, the MinE localization is prerequisite for its proper anti-MinCD function and some new features of MinE were demonstrated. This approach can be extended for subcellular localization research for other essential proteins.

Evidence that Listeria innocua modulates its membrane's stored curvature elastic stress, but not fluidity, through the cell cycle

This paper reports that the abundances of endogenous cardiolipin and phosphatidylethanolamine halve during elongation of the Gram-positive bacterium Listeria innocua. The lyotropic phase behaviour of model lipid systems that describe these modulations in lipid composition indicate that the average stored curvature elastic stress of the membrane is reduced on elongation of the cell, while the fluidity appears to be maintained. These findings suggest that phospholipid metabolism is linked to the cell cycle and that changes in membrane composition can facilitate passage to the succeding stage of the cell cycle. This therefore suggests a means by which bacteria can manage the physical properties of their membranes through the cell cycle.

Enhanced production of polyhydroxybutyrate by multiple dividing E. coli

BACKGROUND

Most bacteria are grown in a binary fission way meaning a bacterial cell is equally divided into two. Polyhydroxyalkanoates (PHA) can be accumulated as inclusion bodies by bacteria. The cell division way and morphology have been shown to play an important role in regulating the bacterial growth and PHA storages.

RESULTS

The common growth pattern of Escherichia coli was changed to multiple fission patterns by deleting fission related genes minC and minD together, allowing the formation of multiple fission rings (Z-rings) in several positions of an elongated cell, thus a bacterial cell was observed to be divided into more than two daughter cells at same time. To further improve cell growth and PHA production, some genes related with division process including ftsQ, ftsL, ftsW, ftsN and ftsZ, together with the cell shape control gene mreB, were all overexpressed in E. coli JM109 ∆minCD. The changing pattern of E. coli cell growth and morphology resulted in more cell dry weights (CDW) and more than 80 % polyhydroxybutyrate (PHB) accumulation increases compared to its binary fission control grown under the same conditions.

CONCLUSIONS

This study clearly demonstrated that combined over-expression genes ftsQ, ftsW, ftsN, ftsL and ftsZ together with shape control gene mreB in multiple division bacterial E. coli JM109 ∆minCD benefited PHA accumulation. Our study provides useful information on increasing the yield of PHA by changing the cell division pattern and cell morphology of E. coli.

The bacterial divisome: ready for its close-up

Bacterial cells divide by targeting a transmembrane protein machine to the division site and regulating its assembly and disassembly so that cytokinesis occurs at the correct time in the cell cycle. The structure and dynamics of this machine (divisome) in bacterial model systems are coming more clearly into focus, thanks to incisive cell biology methods in combination with biochemical and genetic approaches. The main conserved structural element of the machine is the tubulin homologue FtsZ, which assembles into a circumferential ring at the division site that is stabilized and anchored to the inner surface of the cytoplasmic membrane by FtsZ-binding proteins. Once this ring is in place, it recruits a series of transmembrane proteins that ultimately trigger cytokinesis. This review will survey the methods used to characterize the structure of the bacterial divisome, focusing mainly on the Escherichia coli model system, as well as the challenges that remain. These methods include recent super-resolution microscopy, cryo-electron tomography and synthetic reconstitution.

The keepers of the ring: regulators of FtsZ assembly

FtsZ, a GTPase distributed in the cytoplasm of most bacteria, is the major component of the machinery responsible for division (the divisome) in Escherichia coli. It interacts with additional proteins that contribute to its function forming a ring at the midcell that is essential to constrict the membrane. FtsZ is indirectly anchored to the membrane and it is prevented from polymerizing at locations where septation is undesired. Several properties of FtsZ are mediated by other proteins that function as keepers of the ring. ZipA and FtsA serve to anchor the ring, and together with a set of Zap proteins, they stabilize it. The MinCDE and SlmA proteins prevent the polymerization of FtsZ at sites other than the midcell. Finally, ClpP degrades FtsZ, an action prevented by ZipA. Many of the FtsZ keepers interact with FtsZ through a central hub located at its carboxy terminal end.

The Min system and other nucleoid-independent regulators of Z ring positioning

Rod-shaped bacteria such as E. coli have mechanisms to position their cell division plane at the precise center of the cell, to ensure that the daughter cells are equal in size. The two main mechanisms are the Min system and nucleoid occlusion (NO), both of which work by inhibiting assembly of FtsZ, the tubulin-like scaffold that forms the cytokinetic Z ring. Whereas NO prevents Z rings from constricting over unsegregated nucleoids, the Min system is nucleoid-independent and even functions in cells lacking nucleoids and thus NO. The Min proteins of E. coli and B. subtilis form bipolar gradients that inhibit Z ring formation most at the cell poles and least at the nascent division plane. This article will outline the molecular mechanisms behind Min function in E. coli and B. subtilis, and discuss distinct Z ring positioning systems in other bacterial species.

The Nucleoid Occlusion SlmA Protein Accelerates the Disassembly of the FtsZ Protein Polymers without Affecting Their GTPase Activity

Division site selection is achieved in bacteria by different mechanisms, one of them being nucleoid occlusion, which prevents Z-ring assembly nearby the chromosome. Nucleoid occlusion in E. coli is mediated by SlmA, a sequence specific DNA binding protein that antagonizes FtsZ assembly. Here we show that, when bound to its specific target DNA sequences (SBS), SlmA reduces the lifetime of the FtsZ protofilaments in solution and of the FtsZ bundles when located inside permeable giant vesicles. This effect appears to be essentially uncoupled from the GTPase activity of the FtsZ protofilaments, which is insensitive to the presence of SlmA·SBS. The interaction of SlmA·SBS with either FtsZ protofilaments containing GTP or FtsZ oligomers containing GDP results in the disassembly of FtsZ polymers. We propose that SlmA·SBS complexes control the polymerization state of FtsZ by accelerating the disassembly of the FtsZ polymers leading to their fragmentation into shorter species that are still able to hydrolyze GTP at the same rate. SlmA defines therefore a new class of inhibitors of the FtsZ ring different from the SOS response regulator SulA and from the moonlighting enzyme OpgH, inhibitors of the GTPase activity. SlmA also shows differences compared with MinC, the inhibitor of the division site selection Min system, which shortens FtsZ protofilaments by interacting with the GDP form of FtsZ.

Following the fate of bacterial cells experiencing sudden chromosome loss

Chromosomal DNA is a constant source of information, essential for any given cell to respond and adapt to changing conditions. Here, we investigated the fate of exponentially growing bacterial cells experiencing a sudden and rapid loss of their entire chromosome. Utilizing Bacillus subtilis cells harboring an inducible copy of the endogenous toxin yqcG, which encodes an endonuclease, we induced the formation of a population of cells that lost their genetic information simultaneously. Surprisingly, these DNA-less cells, termed DLCs, did not lyse immediately and exhibited normal cellular morphology for a period of at least 5 h after DNA loss. This cellular integrity was manifested by their capacity to maintain an intact membrane and membrane potential and cell wall architecture similar to those of wild-type cells. Unlike growing cells that exhibit a dynamic profile of macromolecules, DLCs displayed steady protein and RNA reservoirs. Remarkably, following DLCs by time lapse microscopy revealed that they succeeded in synthesizing proteins, elongating, and dividing, apparently forming de novo Z rings at the midcell position. Taken together, the persistence of key cellular events in DLCs indicates that the information to carry out lengthy processes is harbored within the remaining molecular components.

IMPORTANCE

Perturbing bacterial growth by the use of antibiotics targeting replication, transcription, or translation has been a subject of study for many years; however, the consequences of a more dramatic event, in which the entire bacterial chromosome is lost, have not been described. Here, we followed the fate of bacterial cells encountering an abrupt loss of their entire genome. Surprisingly, the cells preserved an intact envelope and functioning macromolecules. Furthermore, cells lacking their genome could still elongate and divide hours after the loss of DNA. Our data suggest that the information stored in the transient reservoir of macromolecules is sufficient to carry out complex and lengthy processes even in the absence of the chromosome. Based on our study, the formation of DNA-less bacteria could serve as a novel vaccination strategy, enabling an efficient induction of the immune system without the risk of bacterial propagation within the host.

Spatial coordination between chromosomes and cell division proteins in Escherichia coli

To successfully propagate, cells need to coordinate chromosomal replication and segregation with cell division to prevent formation of DNA-less cells and cells with damaged DNA. Here, we review molecular systems in Escherichia coli that are known to be involved in positioning the divisome and chromosome relative to each other. Interestingly, this well-studied micro-organism has several partially redundant mechanisms to achieve this task; none of which are essential. Some of these systems determine the localization of the divisome relative to chromosomes such as SlmA-dependent nucleoid occlusion, some localize the chromosome relative to the divisome such as DNA translocation by FtsK, and some are likely to act on both systems such as the Min system and newly described Ter linkage. Moreover, there is evidence that E. coli harbors other divisome-chromosome coordination systems in addition to those known. The review also discusses the minimal requirements of coordination between chromosomes and cell division proteins needed for cell viability. Arguments are presented that cells can propagate without any dedicated coordination between their chromosomes and cell division machinery at the expense of lowered fitness.