Live-Cell Imaging Enables Reporter-Free Monitoring Of The Circadian Rhythm In Individual Synechocystis Cells

Area of Science:

• Circadian Biology
• Microbiology
• Cell Biology

Background:

• In vivo monitoring of circadian rhythms typically relies on reporter genes, necessitating genetically modified strains.
• Understanding whether circadian rhythms operate at the individual cell level or through population effects is crucial.
• A reporter-free detection method for cyanobacterial batch cultures was previously established.

Purpose of the Study:

• To investigate if circadian rhythms in cyanobacteria are cell-autonomous or population-based.
• To analyze individual Synechocystis sp. PCC 6803 cells using advanced imaging and analysis techniques.
• To establish a reporter-free method for analyzing circadian rhythms in single cells.

Main Methods:

• Combined microfluidic cultivation with time-lapse microscopy for single-cell analysis.
• Utilized a deep learning workflow for cell segmentation of hundreds of time-lapse image sequences.
• Analyzed phase contrast brightness and backscatter properties of wildtype and mutant strains.

Main Results:

• Circadian gating of cell division was not observed in entrained Synechocystis cells.
• Individual cells exhibited circadian oscillations in average phase contrast brightness.
• Phase contrast and backscatter analyses indicated rhythmic changes in cellular refractive index.

Conclusions:

• Circadian rhythms in Synechocystis are not driven by cell division gating.
• Reporter-free analysis of single-cell phase contrast brightness is a viable method for circadian research.
• This approach advances the study of circadian rhythms by eliminating the need for reporter molecules.