Perpendicular planes of FtsZ arcs in spheroidal Escherichia coli cells

226

223

Summary Many recent reviews in the field of bacterial chromosome segregation propose that newly replicated DNA is actively separated by the functioning of specific proteins. This view is primarily based on an interpretation of the position of fluorescently labelled DNA regions and proteins in analogy to the active segregation mechanism in eukaryotic cells, i.e. to mitosis. So far, physical aspects of DNA organization such as the diffusional movement of DNA supercoil segments and their interaction with soluble proteins, leading to a phase separation between cytoplasm and nucleoid, have received relatively little attention. Here, a quite different view is described taking into account DNA–protein interactions, the large variation in the cellular position of fluorescent foci and the compaction and fusion of segregated nucleoids upon inhibition of RNA or protein synthesis. It is proposed that the random diffusion of DNA supercoil segments is transiently constrained by the process of co‐ transcriptional translation and translocation (transertion) of membrane proteins. After initiation of DNA replication, a bias in the positioning of transertion areas creates a bidirectionality in chromosome segre‐gation that becomes self‐enhanced when neigh‐bouring genes on the same daughter chromosome are expressed. This transertion‐mediated segregation model is applicable to multifork replication during rapid growth and to multiple chromosomes and plasmids that occur in many bacteria.

Section: Discussionmentioning

confidence: 99%

The role of co‐transcriptional translation and protein translocation (transertion) in bacterial chromosome segregation

Woldringh

2002

226

223

“…The FtsZ protein is the earliest known component of a ring (hoop) required for septation (Buddelmeijer and Beckwith, 2002; Lutkenhaus, 2002). However, the diameter of this structure is not set by self‐assembly because the Z ring contracts during cell division and incomplete arcs can initiate septation (Addinall and Lutkenhaus, 1996; Pas et al ., 2001; de Pedro et al ., 2001). Also, FtsZ polymerizes in vitro as straight filaments, flat sheets or tiny rings (Lutkenhaus and Addinall, 1997; Lu et al .…”

Section: Scaffoldsmentioning

confidence: 99%

Bacterial shape

Young

2003

156

115

SummaryIn free-living eubacteria an external shell of peptidoglycan opposes internal hydrostatic pressure and prevents membrane rupture and death. At the same time, this wall imposes on each cell a shape. Because shape is both stable and heritable, as is the ability of many organisms to execute defined morphological transformations, cells must actively choose from among a large repertoire of available shapes. How they do so has been debated for decades, but recently experiment has begun to catch up with theory. Two discoveries are particularly informative. First, specific protein assemblies, nucleated by FtsZ, MreB or Mbl, appear to act as internal scaffolds that influence cell shape, perhaps by correctly localizing synthetic enzymes. Second, defects in cell shape are correlated with the presence of inappropriately placed, metabolically inert patches of peptidoglycan. When combined with what we know about mutants affecting cellular morphology, these observations suggest that bacteria may fabricate specific shapes by directing the synthesis of two kinds of cell wall: a long-lived, rigid framework that defines overall topology, and a metabolically plastic peptidoglycan whose shape is directed by internal scaffolds.

“…As for the known systems that regulate Z-ring placement, S. aureus does not have a Min system (based on homology searches) but, although the existence of nucleoid occlusion has never been shown, a noc homologue is present in its genome, as well as in the genomes of other spherical bacteria that divide in either two or three planes. Importantly, most studies regarding choice of division planes in round cells used either Neisseria or E. coli round cells as models (Westling-Haggstrom et al, 1977;Begg and Donachie, 1998;Zaritsky et al, 1999;Pas et al, 2001;Ramirez-Arcos et al, 2001;Corbin et al, 2002). These organisms, however, have a Min system which is required for normal growth and division, and therefore are not the most appropriate models for the mode of division in three orthogonal planes used by S. aureus.…”

Section: Introductionmentioning

confidence: 99%

Absence of nucleoid occlusion effector Noc impairs formation of orthogonal FtsZ rings during Staphylococcus aureus cell division

Veiga

Jorge

Pinho

2011

SummaryThe Gram-positive pathogen Staphylococcus aureus divides by synthesizing the septum in three orthogonal planes over three consecutive division cycles. This process has to be tightly coordinated with chromosome segregation to avoid bisection of the nucleoid by the septum. Here we show that deletion of the nucleoid occlusion effector Noc in S. aureus results in the formation of Z-rings over the nucleoid, as well as in DNA breaks, indicating that Noc has an important role as an antiguillotine checkpoint that prevents septa from forming over the DNA. Furthermore, Noc deleted cells show multiple Z-rings which are no longer placed in perpendicular planes. We propose that the axis of chromosome segregation has a role in determining the placement of the division septum. This is achieved via the action of Noc which restricts the placement of the division septum to one of an infinite number of potential division planes that exist in S. aureus.