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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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Analysis of correlation of the position of foci along the cell length with that along the cell diameter. Graphs show the positions of foci of four loci in wt and Ndd-treated cells, as indicated in each panel, along the cell diameter (Y-axis) as a function of their position along the cell length (X-axis). The grey dots are individual foci. The red dots are sliding means of twenty adjacent foci (with a step of one focus). For the ori, right and NS-right loci in Ndd-untreated cells and for the ori and ter loci in Ndd-treated cells, the data from the different cell classes were combined, as these dataset do not statistically differ (see Figure 2). In the case of the ter locus in Ndd-untreated cells, only the data from cells with a single focus are plotted. The dotted lines show the mean position of foci calculated from the 90% central model.
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Figure 5: Analysis of correlation of the position of foci along the cell length with that along the cell diameter. Graphs show the positions of foci of four loci in wt and Ndd-treated cells, as indicated in each panel, along the cell diameter (Y-axis) as a function of their position along the cell length (X-axis). The grey dots are individual foci. The red dots are sliding means of twenty adjacent foci (with a step of one focus). For the ori, right and NS-right loci in Ndd-untreated cells and for the ori and ter loci in Ndd-treated cells, the data from the different cell classes were combined, as these dataset do not statistically differ (see Figure 2). In the case of the ter locus in Ndd-untreated cells, only the data from cells with a single focus are plotted. The dotted lines show the mean position of foci calculated from the 90% central model.

Mentions: Foci were sorted in ascending order of their distance to the closest pole (X-axis) and their position along the cell diameter was plotted (Y-axis, grey dots; Figure 5). No correlation appeared for any locus and calculated Pearson correlation coefficients were not significant (less than 0.05 in absolute value). The datasets of cell diameter position are de facto highly variable. Therefore, sliding means for 20 adjacent dots were calculated and plotted to help visualise patterns (red dots, Figure 5). Again no general relationship between position along one axis and position along the other could be established. Nevertheless the ori and right loci appeared to behave similarly and the NS-right locus tended to be closer than ori and right to the cell centre. The ter locus was more peripheral than other loci in cells with a single focus (red dots). The same analysis was performed for the ori and ter loci after Ndd treatment (Figure 5). For the ter locus, distributions of the two cell classes were combined since they were not significantly different (Additional file 1, Figure S4D). In both cases, the sliding mean was consistent with the peripheral location of the loci. Equivalent patterns were obtained for the right and NS-right loci in Ndd-treated cells (not shown). Foci located in the 0-0.1 cell length slice were more central than the other foci. This cell length slice corresponds to the cell poles, where the membrane curvature modifies the cell width distribution of foci. This effect was detected only in Ndd-treated cells due to the enrichment of loci in this cell slice compared to control cells (Additional file 1, Figure S4C).


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)

Analysis of correlation of the position of foci along the cell length with that along the cell diameter. Graphs show the positions of foci of four loci in wt and Ndd-treated cells, as indicated in each panel, along the cell diameter (Y-axis) as a function of their position along the cell length (X-axis). The grey dots are individual foci. The red dots are sliding means of twenty adjacent foci (with a step of one focus). For the ori, right and NS-right loci in Ndd-untreated cells and for the ori and ter loci in Ndd-treated cells, the data from the different cell classes were combined, as these dataset do not statistically differ (see Figure 2). In the case of the ter locus in Ndd-untreated cells, only the data from cells with a single focus are plotted. The dotted lines show the mean position of foci calculated from the 90% central model.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Analysis of correlation of the position of foci along the cell length with that along the cell diameter. Graphs show the positions of foci of four loci in wt and Ndd-treated cells, as indicated in each panel, along the cell diameter (Y-axis) as a function of their position along the cell length (X-axis). The grey dots are individual foci. The red dots are sliding means of twenty adjacent foci (with a step of one focus). For the ori, right and NS-right loci in Ndd-untreated cells and for the ori and ter loci in Ndd-treated cells, the data from the different cell classes were combined, as these dataset do not statistically differ (see Figure 2). In the case of the ter locus in Ndd-untreated cells, only the data from cells with a single focus are plotted. The dotted lines show the mean position of foci calculated from the 90% central model.
Mentions: Foci were sorted in ascending order of their distance to the closest pole (X-axis) and their position along the cell diameter was plotted (Y-axis, grey dots; Figure 5). No correlation appeared for any locus and calculated Pearson correlation coefficients were not significant (less than 0.05 in absolute value). The datasets of cell diameter position are de facto highly variable. Therefore, sliding means for 20 adjacent dots were calculated and plotted to help visualise patterns (red dots, Figure 5). Again no general relationship between position along one axis and position along the other could be established. Nevertheless the ori and right loci appeared to behave similarly and the NS-right locus tended to be closer than ori and right to the cell centre. The ter locus was more peripheral than other loci in cells with a single focus (red dots). The same analysis was performed for the ori and ter loci after Ndd treatment (Figure 5). For the ter locus, distributions of the two cell classes were combined since they were not significantly different (Additional file 1, Figure S4D). In both cases, the sliding mean was consistent with the peripheral location of the loci. Equivalent patterns were obtained for the right and NS-right loci in Ndd-treated cells (not shown). Foci located in the 0-0.1 cell length slice were more central than the other foci. This cell length slice corresponds to the cell poles, where the membrane curvature modifies the cell width distribution of foci. This effect was detected only in Ndd-treated cells due to the enrichment of loci in this cell slice compared to control cells (Additional file 1, Figure S4C).

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