RESUMO
The Min system plays an important role in ensuring that cell division occurs at mid-cell in rod-shaped bacteria. In Escherichia coli, pole-to-pole oscillation of the Min proteins specifically inhibits polar septation. This system also prevents polar division in Bacillus subtilis during vegetative growth; however, the Min proteins do not oscillate in this organism. The Min system of B. subtilis plays a distinct role during sporulation, a process of differentiation which begins with an asymmetrical cell division. Here, we show that oscillation of the E. coli Min proteins can be reproduced following their introduction into B. subtilis cells. Further, we present evidence that the oscillatory behaviour of the Min system inhibits sporulation. We propose that an alternative Min system mechanism avoiding oscillation is evolutionarily important because oscillation of the Min system is incompatible with efficient asymmetrical septum formation and sporulation.
Assuntos
Bacillus subtilis/metabolismo , Proteínas de Bactérias/metabolismo , Polaridade Celular , Esporos Bacterianos/citologia , Bacillus subtilis/citologia , Bacillus subtilis/genética , Proteínas de Bactérias/genética , Divisão Celular , Escherichia coli/citologia , Escherichia coli/genética , Escherichia coli/metabolismo , Esporos Bacterianos/genética , Esporos Bacterianos/metabolismoRESUMO
Cytokinesis in bacteria is initiated by polymerization of the tubulin homologue FtsZ into a circular structure at midcell, the Z-ring. This structure functions as a scaffold for all other cell division proteins. Several proteins support assembly of the Z-ring, and one such protein, SepF, is required for normal cell division in Gram-positive bacteria and cyanobacteria. Mutation of sepF results in deformed division septa. It is unclear how SepF contributes to the synthesis of normal septa. We have studied SepF by electron microscopy (EM) and found that the protein assembles into very large (â¼50 nm diameter) rings. These rings were able to bundle FtsZ protofilaments into strikingly long and regular tubular structures reminiscent of eukaryotic microtubules. SepF mutants that disturb interaction with FtsZ or that impair ring formation are no longer able to align FtsZ filaments in vitro, and fail to support normal cell division in vivo. We propose that SepF rings are required for the regular arrangement of FtsZ filaments. Absence of this ordered state could explain the grossly distorted septal morphologies seen in sepF mutants.
Assuntos
Bacillus subtilis/fisiologia , Proteínas de Bactérias/metabolismo , Citocinese/fisiologia , Proteínas do Citoesqueleto/metabolismo , Bacillus subtilis/metabolismo , Cromatografia em Gel , GTP Fosfo-Hidrolases/metabolismo , Hidrólise , Microscopia Eletrônica , Microscopia de Fluorescência , Mutagênese , Reação em Cadeia da Polimerase , PolimerizaçãoRESUMO
In both rod-shaped Bacillus subtilis and Escherichia coli cells, Min proteins are involved in the regulation of division septa formation. In E. coli, dynamic oscillation of MinCD inhibitory complex and MinE, a topological specificity protein, prevents improper polar septation. However, in B. subtilis no MinE is present and no oscillation of Min proteins can be observed. The function of MinE is substituted by that of an unrelated DivIVA protein, which targets MinCD to division sites and retains them at the cell poles. We inspected cell division when the E. coli Min system was introduced into B. subtilis cells. Expression of these heterologous Min proteins resulted in cell elongation. We demonstrate here that E. coli MinD can partially substitute for the function of its B. subtilis protein counterpart. Moreover, E. coli MinD was observed to have similar helical localization as B. subtilis MinD.
Assuntos
Adenosina Trifosfatases/biossíntese , Bacillus subtilis , Proteínas de Ciclo Celular/biossíntese , Divisão Celular , Proteínas de Escherichia coli/biossíntese , Escherichia coli/genética , Proteínas de Membrana/biossíntese , Adenosina Trifosfatases/genética , Bacillus subtilis/citologia , Bacillus subtilis/metabolismo , Proteínas de Bactérias/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Polaridade Celular , Proteínas de Escherichia coli/genética , Teste de Complementação Genética , Proteínas Luminescentes , Proteínas de Membrana/genética , Microscopia de Fluorescência , Proteínas Recombinantes de Fusão/biossínteseRESUMO
The fluid mosaic model of membrane structure has been revised in recent years as it has become evident that domains of different lipid composition are present in eukaryotic and prokaryotic cells. Using membrane binding fluorescent dyes, we demonstrate the presence of lipid spirals extending along the long axis of cells of the rod-shaped bacterium Bacillus subtilis. These spiral structures are absent from cells in which the synthesis of phosphatidylglycerol is disrupted, suggesting an enrichment in anionic phospholipids. Green fluorescent protein fusions of the cell division protein MinD also form spiral structures and these were shown by fluorescence resonance energy transfer to be coincident with the lipid spirals. These data indicate a higher level of membrane lipid organization than previously observed and a primary role for lipid spirals in determining the site of cell division in bacterial cells.