Circadian clocks are nearly ubiquitous throughout life, appearing in eukaryotes and prokaryotes alike. They are an adaptation that evolved to modify metabolism and behavior in anticipation of the daily fluctuation in light and other environmental conditions. One of the simplest organisms to posses a circadian clock is the photoautotrophic cyanobacterium Synechococcus elongatus PCC 7942. As an organism wholly dependent on the sun's energy, its biology is structured around the day-night cycle. Its metabolism, gene expression, and cellular organization are regulated in a circadian manner.

Here, I investigate the potential role of circadian chromosome compaction in imparting rhythmicity to downstream gene expression. I used fluorescence microscopy to visualize chromosome compaction status and correlate it to rhythmic gene expression. I also investigated circadian changes in cellular organization using high-resolution cryo-electron tomography (CET) to visualize cells in a near-native state. I report interesting subcellular structures and features that have not been observed previously. In support of CET as a maturing tool for cell biology, I present data and considerations for sample preparation and downstream data analysis.