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The terminal region of the E. coli chromosome localises at the periphery of the nucleoid.

Meile JC, Mercier R, Stouf M, Pages C, Bouet JY, Cornet F - BMC Microbiol. (2011)

Bottom Line: Observed apparent distributions of fluorescent-tagged loci of the E. coli chromosome along the cell diameter were compared with simulated distributions calculated using a range of cell width positioning models.Our approach allows to reliably observing the positioning of chromosome loci along the width of E. coli cells.The terminal region of the chromosome is preferentially located at the periphery of the nucleoid consistent with its specific roles in chromosome organisation and dynamics.

View Article: PubMed Central - HTML - PubMed

Affiliation: Université de Toulouse, Université Paul Sabatier, Laboratoire de Microbiologie et Génétique Moléculaires, F-31000 Toulouse, France.

ABSTRACT

Background: Bacterial chromosomes are organised into a compact and dynamic structures termed nucleoids. Cytological studies in model rod-shaped bacteria show that the different regions of the chromosome display distinct and specific sub-cellular positioning and choreographies during the course of the cell cycle. The localisation of chromosome loci along the length of the cell has been described. However, positioning of loci across the width of the cell has not been determined.

Results: Here, we show that it is possible to assess the mean positioning of chromosomal loci across the width of the cell using two-dimension images from wide-field fluorescence microscopy. Observed apparent distributions of fluorescent-tagged loci of the E. coli chromosome along the cell diameter were compared with simulated distributions calculated using a range of cell width positioning models. Using this method, we detected the migration of chromosome loci towards the cell periphery induced by production of the bacteriophage T4 Ndd protein. In the absence of Ndd production, loci outside the replication terminus were located either randomly along the nucleoid width or towards the cell centre whereas loci inside the replication terminus were located at the periphery of the nucleoid in contrast to other loci.

Conclusions: Our approach allows to reliably observing the positioning of chromosome loci along the width of E. coli cells. The terminal region of the chromosome is preferentially located at the periphery of the nucleoid consistent with its specific roles in chromosome organisation and dynamics.

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Distributions of foci along the cell diameter in Ndd-treated cells. (A) Micrographs of Ndd-treated cells showing the relocation of chromosomal DNA towards the cell periphery. Legend as for Figure 1B (parS site inserted at the ori locus). (B) Distributions of foci of the indicated loci along the cell diameter. Legend as for Figure 2C. (C) Legend as for Figure 2D.
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Figure 4: Distributions of foci along the cell diameter in Ndd-treated cells. (A) Micrographs of Ndd-treated cells showing the relocation of chromosomal DNA towards the cell periphery. Legend as for Figure 1B (parS site inserted at the ori locus). (B) Distributions of foci of the indicated loci along the cell diameter. Legend as for Figure 2C. (C) Legend as for Figure 2D.

Mentions: The position of a fluorescent focus along the width of the cell cannot be directly determined using 2-D wide-field microscopy. Indeed, a focus located near the cell periphery may appear at the centre of the cell diameter or at the edge according to the orientation of the cell cylinder with respect to the focal plan. Nevertheless, since the orientations of the cell cylinder are expected to be random for a population of rod-shaped bacteria deposited on a plane surface, the mean position of particular foci can be calculated from the apparent distributions of foci along the cell diameter. We therefore measured the apparent distance along the cell diameter between foci and the membrane (Figure 1C). The datasets obtained were then compared with distributions calculated for different models of positioning across the width of the cell (Methods). We defined five slices of equivalent surface in a quarter of the cell section and calculated the expected distributions of foci according to the various models of positioning (the 2-D apparent foci distributions for various 3-D localisation patterns are shown in Figures 2, 3 and 4).


The terminal region of the E. coli chromosome localises at the periphery of the nucleoid.

Meile JC, Mercier R, Stouf M, Pages C, Bouet JY, Cornet F - BMC Microbiol. (2011)

Distributions of foci along the cell diameter in Ndd-treated cells. (A) Micrographs of Ndd-treated cells showing the relocation of chromosomal DNA towards the cell periphery. Legend as for Figure 1B (parS site inserted at the ori locus). (B) Distributions of foci of the indicated loci along the cell diameter. Legend as for Figure 2C. (C) Legend as for Figure 2D.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3040692&req=5

Figure 4: Distributions of foci along the cell diameter in Ndd-treated cells. (A) Micrographs of Ndd-treated cells showing the relocation of chromosomal DNA towards the cell periphery. Legend as for Figure 1B (parS site inserted at the ori locus). (B) Distributions of foci of the indicated loci along the cell diameter. Legend as for Figure 2C. (C) Legend as for Figure 2D.
Mentions: The position of a fluorescent focus along the width of the cell cannot be directly determined using 2-D wide-field microscopy. Indeed, a focus located near the cell periphery may appear at the centre of the cell diameter or at the edge according to the orientation of the cell cylinder with respect to the focal plan. Nevertheless, since the orientations of the cell cylinder are expected to be random for a population of rod-shaped bacteria deposited on a plane surface, the mean position of particular foci can be calculated from the apparent distributions of foci along the cell diameter. We therefore measured the apparent distance along the cell diameter between foci and the membrane (Figure 1C). The datasets obtained were then compared with distributions calculated for different models of positioning across the width of the cell (Methods). We defined five slices of equivalent surface in a quarter of the cell section and calculated the expected distributions of foci according to the various models of positioning (the 2-D apparent foci distributions for various 3-D localisation patterns are shown in Figures 2, 3 and 4).

Bottom Line: Observed apparent distributions of fluorescent-tagged loci of the E. coli chromosome along the cell diameter were compared with simulated distributions calculated using a range of cell width positioning models.Our approach allows to reliably observing the positioning of chromosome loci along the width of E. coli cells.The terminal region of the chromosome is preferentially located at the periphery of the nucleoid consistent with its specific roles in chromosome organisation and dynamics.

View Article: PubMed Central - HTML - PubMed

Affiliation: Université de Toulouse, Université Paul Sabatier, Laboratoire de Microbiologie et Génétique Moléculaires, F-31000 Toulouse, France.

ABSTRACT

Background: Bacterial chromosomes are organised into a compact and dynamic structures termed nucleoids. Cytological studies in model rod-shaped bacteria show that the different regions of the chromosome display distinct and specific sub-cellular positioning and choreographies during the course of the cell cycle. The localisation of chromosome loci along the length of the cell has been described. However, positioning of loci across the width of the cell has not been determined.

Results: Here, we show that it is possible to assess the mean positioning of chromosomal loci across the width of the cell using two-dimension images from wide-field fluorescence microscopy. Observed apparent distributions of fluorescent-tagged loci of the E. coli chromosome along the cell diameter were compared with simulated distributions calculated using a range of cell width positioning models. Using this method, we detected the migration of chromosome loci towards the cell periphery induced by production of the bacteriophage T4 Ndd protein. In the absence of Ndd production, loci outside the replication terminus were located either randomly along the nucleoid width or towards the cell centre whereas loci inside the replication terminus were located at the periphery of the nucleoid in contrast to other loci.

Conclusions: Our approach allows to reliably observing the positioning of chromosome loci along the width of E. coli cells. The terminal region of the chromosome is preferentially located at the periphery of the nucleoid consistent with its specific roles in chromosome organisation and dynamics.

Show MeSH
Related in: MedlinePlus