CTP regulates membrane-binding activity of the nucleoid occlusion protein Noc

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Noc protein binds to specific DNA sequences to coordinate cell division with chromosome segregation

Coordination of chromosome segregation and cytokinesis is crucial for efficient cell proliferation. In Bacillus subtilis, the nucleoid occlusion protein Noc protects the chromosomes by associating with the chromosome and preventing cell division in its vicinity. Using protein localization, ChAP‐on‐Chip and bioinformatics, we have identified a consensus Noc‐binding DNA sequence (NBS), and have shown that Noc is targeted to about 70 discrete regions scattered around the chromosome, though absent from a large region around the replication terminus. Purified Noc bound specifically to an NBS in vitro. NBSs inserted near the replication terminus bound Noc–YFP and caused a delay in cell division. An autonomous plasmid carrying an NBS array recruited Noc–YFP and conferred a severe Noc‐dependent inhibition of cell division. This shows that Noc is a potent inhibitor of division, but that its activity is strictly localized by the interaction with NBS sites in vivo. We propose that Noc serves not only as a spatial regulator of cell division to protect the nucleoid, but also as a timing device with an important role in the coordination of chromosome segregation and cell division.     

Short FtsZ filaments can drive asymmetric cell envelope constriction at the onset of bacterial cytokinesis

FtsZ, the bacterial homologue of eukaryotic tubulin, plays a central role in cell division in nearly all bacteria and many archaea. It forms filaments under the cytoplasmic membrane at the division site where, together with other proteins it recruits, it drives peptidoglycan synthesis and constricts the cell. Despite extensive study, the arrangement of FtsZ filaments and their role in division continue to be debated. Here, we apply electron cryotomography to image the native structure of intact dividing cells and show that constriction in a variety of Gram‐negative bacterial cells, including Proteus mirabilis and Caulobacter crescentus, initiates asymmetrically, accompanied by asymmetric peptidoglycan incorporation and short FtsZ‐like filament formation. These results show that a complete ring of FtsZ is not required for constriction and lead us to propose a model for FtsZ‐driven division in which short dynamic FtsZ filaments can drive initial peptidoglycan synthesis and envelope constriction at the onset of cytokinesis, later increasing in length and number to encircle the division plane and complete constriction.     

Molecular mechanism by which the nucleoid occlusion factor, SlmA, keeps cytokinesis in check

In Escherichia coli, cytokinesis is orchestrated by FtsZ, which forms a Z-ring to drive septation. Spatial and temporal control of Z-ring formation is achieved by the Min and nucleoid occlusion (NO) systems. Unlike the well-studied Min system, less is known about the anti-DNA guillotining NO process. Here, we describe studies addressing the molecular mechanism of SlmA (synthetic lethal with a defective Min system)-mediated NO. SlmA contains a TetR-like DNA-binding fold, and chromatin immunoprecipitation analyses show that SlmA-binding sites are dispersed on the chromosome except the Ter region, which segregates immediately before septation. SlmA binds DNA and FtsZ simultaneously, and the SlmA-FtsZ structure reveals that two FtsZ molecules sandwich a SlmA dimer. In this complex, FtsZ can still bind GTP and form protofilaments, but the separated protofilaments are forced into an anti-parallel arrangement. This suggests that SlmA may alter FtsZ polymer assembly. Indeed, electron microscopy data, showing that SlmA-DNA disrupts the formation of normal FtsZ polymers and induces distinct spiral structures, supports this. Thus, the combined data reveal how SlmA derails Z-ring formation at the correct place and time to effect NO.     

Isolation and Identification of a Novel Antifungal Protein from a Rhizobacterium Bacillus subtilis Strain F3

Bacillus subtilis strain F3, isolated from peach rhizosphere soil, is an antifungal bacterium against many plant pathogens. In this study, the antifungal protein was isolated and purified by ammonium sulphate and chromatography, then identified by mass spectrum analysis. By sequential chromatography of Sephadex G‐50, DEAE‐Sephadex A‐25 anion exchange and Sephadex G‐100, a fraction designated as F3A was isolated to show a single protein band in SDS‐PAGE and be antagonistic towards Monilinia fructicola. The peptide mass fingerprinting of the protein band of F3A had high similarity with the amino acid sequences of several flagellin protein of B. subtilis. There were seven amino acid fragments matched with the protein having the highest score, and sequence coverage was 33%. F3A showed a strongly inhibitory effect to the growth and sporulation of M. fructicola. There were little aerial hyphae and conidia at the antifungal zone, and the hyphae were abnormal with some cell wall collapse and several vacuoles in cells.     

Six New Acylphloroglucinols from Dryopteris championii

Six new acylphloroglucinols ( 1  –  6 ) were isolated from Dryopteris championii. Their structures were established on the basis of extensive analysis of spectroscopic data and comparison with reported data. The antibacterial activities of the isolates were evaluated against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, and Dickeya zeae.