Single-cell imaging and analysis of cyanobacteria

I have a close working relationship with the Cameron Lab at CU Boulder, where we use fluorescence microscopy to study cyanobacteria. I have contributed to studies studying the degradation of bacterial microcompartments, understanding how genes are passed down through generations, as well as showing that mechanical forces play a role in the regulation of photosynthesis.

Mechanical forces affect the regulation of photosynthesis

Fluorescence microscopy images of cyanobacteria

The natural chlorophyll pigments in cyanobacteria naturally fluoresce. The intensity of fluorescence provides a real-time readout of the photosynthetic capacity of the cell. The photon energy absorbed by the pigment will either be transferred to the electron transport chain, resulting in biomass production, or it is released as light. Therefore, the brighter the cell, the less able it is to carry out photosynthesis. Using this property, we found that cells became bright when pressing against a neighboring cell. Upon further investigation, we found that mechanical confinement of cyanobacterial cells led to the physical decoupling of the light harvesting antennae, thereby reducing the cells' ability to absorb light. These results provide the first evidence that mechanical processes could be a mechanism in which these photosynthetic organisms regulate their growth in physically constrained growth environments. Our findings were reported in Nature Microbiology 5, 757-767 (2020).

Degradation of a bacterial microcompartment

Kymograph showing carboxysome localization and intensity over time

Cyanobacteria possess a unique microcompartment called the carboxysome, which consists of a protein shell encapsulating an ezymatic core. The carboxysome plays an important role in carbon fixation. It enables CO2 to be concentrated within, thereby increasing the efficiency of the carbon fixation process. While the biogenesis of the carboxysome has previously studied, the subsequent activity and eventual degradation of this microcompartment was previously unknown. Using optical microscopy, we showed the first evidence of carboxysome degradation by fluorescently labeling and tracking the carboxysome. Our findings suggest that shell breakage is the main cause of inactivation of this microcompartment. We also observed recruitment of the exposed enzymatic core towards the membrane, indicating the existence of a previously unknown recycling or repair pathway. Our findings were reported in Science Advances 6 eaba1269 (2020).

How genes are inherited in polyploid organisms

Kymograph showing carboxysome localization and intensity over time

In this study, we looked at how genetic inheritance occurs in polyploid bacteria, which have multiple, identical chromosome copies. The effect of increasing chromosome copy number is currently unclear. In this experiment, we fluorescently labeled chromosomes and observed how these chromosomes were passed on through different generations. I developed the image analysis tools to count the number of chromosomes within each cell, enabling them to be tracked over successive generations. By using CRISPR-interference to inhibit essential cell functions, such as growth and division, we were also able to study the effect of growth rate on chromosome dynamics. To our surprise, we found that cells were surprisingly resilient to manipulations of chromosome number, even continuing to grow for a period of time in the absence of chromosomes altogether. This paper is currently being revised for resubmission. A preprint is available on bioRxiv.