Seeing chromosome segregation in bacteria

Research Areas:

Developmental biology, Cell biology, Microbiology, Chromosome segregation

Imaging Needs:

Precise localization in living bacterial cells over time

Imaging System:
  • Leica DM16000B microscope with adaptive focus
  • Prior Pro Scan motorized stage
  • Hamamatsu ORCA-Flash4.0 sCMOS camera
  • Leica MM AF software package
  • Metamorph for fluorescence quantification
Imaging Bacteria

Achieving the resolution and sensitivities needed to visualize bacterial cells is not just the domain of the ORCA-Flash4.0. Find out how Ashley Cadby and colleagues visualize cell wall growth in bacteria using Hamamatsu’s ImagEM camera. Read now.

THE QUESTION

How do bacterial cells ensure each daughter cell gets one and only one copy of the chromosome during cell division?

Unlike eukaryotic cells, chromosome replication and segregation is closely coordinated with cell division. The tight choreography requires that each region of the chromosome moves to a specific part of the cell at precisely defined times during the cell cycle.

THE BARRIERS

Much of the previous work on bacterial replication and chromosome segregation has focused on Caulobacter crescentus, Escherichia coli, and Pseudomonas aeruginosa, with the finding that the mechanics of the process differs among different bacterial species. Understanding how chromosome replication and segregation works in Myxococcus xanthus, a model social bacteria, required Harms, et al,1 to take a closer look at the process in M. xanthus.

THE SOLUTION

Tracking of Chromosome and Replisome Dynamics in Myxococcus xanthus Reveals a Novel Chromosome Arrangement.
Andrea Harms, Anke Treuner-Lange, Dominik Schumacher, Lotte Søgaard-Andersen
PLoS Genet. 2013 September; 9(9): e1003802. PMCID: PMC3778016.

Harms, et al,1 used YFP- and mCherry-labeled proteins that bind to specific regions of the chromosome during replication to visualize where the chromosome localizes at different points in the cell cycle. To image living cells over time, they took advantage of the high resolution and fast frame rates of Hamamatsu’s ORCA-Flash4.0 camera.

By tracking where label localized relative to the cell perimeter as the cell cycle progressed, Harms, et al,1 were able to show that the M. xanthus chromosome, unlike slow-growing cells of E. coli, is arranged about a longitudinal axis with ori, the origin of replication, in the subpolar region of the old pole and ter, the site where replication terminates, in the subpolar region of the new pole. The ori of one newly-replicated chromosome is positioned during segregation to the opposite pole while the other chromosome is kept in place. This sets up the ter region of both chromosomes to locate towards the midcell, the site where the new pole will form once cell division is complete.

THE POSSIBILITIES

Imaging bacteria can be technically demanding due to their small size. Accurately localizing protein complexes, and protein-DNA complexes, within bacteria even more so. Harms, et al,1 used Hamamatsu’s new ORCA-Flash4.0 to obtain the imaging speed and resolution they needed for understanding chromosome segregation in M. xanthus. Find out what other microbiologists are discovering with Hamamatsu’s cameras—read Exciting Insights into Cell Growth.

References

  1. Harms, et al. Tracking of Chromosome and Replisome Dynamics in Myxococcus xanthus Reveals a Novel Chromosome Arrangement. PLoS Genet. 2013 September; 9(9): e1003802. PMCID: PMC3778016.
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