Abstract
Some cyanobacteria exhibit compaction of DNA in synchrony with their circadian rhythms accompanying cell division. Since the structure is transient, it has not yet been described in detail. Here, we successfully visualize the ultrastructure of compacted DNA in the cyanobacterium Synechococcus elongatus PCC 7942 under rigorous synchronized cultivation by means of high-voltage cryo-electron tomography. In 3D reconstructions of rapidly frozen cells, the compacted DNA appears as an undulating rod resembling a eukaryotic condensed chromosome. The compacted DNA also includes many small and paired polyphosphate bodies (PPBs), some of which seem to maintain contact with DNA that appears to twist away from them, indicating that they may act as interactive suppliers and regulators of phosphate for DNA synthesis. These observations throw light on the duplication and segregation mechanisms of cyanobacterial DNA and point to an important role for PPBs.
Highlights
Cyanobacteria are unicellular photosynthetic prokaryotes that produce about 25% of all carbohydrates on Earth; they have supplied the Earth with oxygen for more than two billion years[1,2]
Cryo-electron tomography is a powerful tool to visualize the dynamical structure of biological specimens in 3D19, where one instant of a living cell is fixed by rapid freezing and directly observed by EM using a cryo-specimen holder
Growing S. elongatus PCC 7942 cells cultured under a 12 hours light/12 hours dark regime were observed by fluorescence microscopy after labeling with Hoechst 33342 (Fig. 1)
Summary
Cyanobacteria are unicellular photosynthetic prokaryotes that produce about 25% of all carbohydrates on Earth; they have supplied the Earth with oxygen for more than two billion years[1,2]. Prokaryotic cells show condensed DNA blobs or bundles, called nucleoid, in the cytoplasm, where ribosomes and multiple other complexes are effectively excluded to the periphery of the nucleoid[8,9,10,11] This is not known to develop into a dramatic display of transformation on the occasion of cell division as in eukaryotic chromosomes[12,13]. The DNA condensed gradually and showed a wavy rod-like shape under the light microscope just before cell division This phenomenon may be related to bacterial DNA synthesis during the light period and with its subsequent distribution to daughter cells at the end of the light period[16]. This rod-shaped body contained many small and paired polyphosphate bodies (PPBs), some of them attached to DNA that appears to twist away, indicating that they probably act as interactive suppliers and regulators of phosphate for DNA synthesis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
