Excellence in Research: Coupling of DNA Replication and Cell Division at Low Temperature in E. coli

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Adverse environmental conditions such as extreme temperatures can have deleterious effects on cellular structures, processes and growth. Bacteria often encounter temperatures that are at or near their minimum temperature of growth. At temperatures just above the minimum temperature of growth, bacteria adapt and grow by inducing physiological changes that counteract the damaging effects of the cold stress. The long term goal of this project is to characterize the adaptive response to cold stress and identify factors that determine the minimum temperature of growth. In the bacterium Escherichia coli, an adaptive physiological change in response to low temperature is a decrease in cell size. Several proteins that function in DNA replication and cell division are specifically required for this adaptation. This research project aims to determine the connection between replication and cell division that facilitates growth and small cell size at cold temperatures. Broader impacts include the importance of understanding bacterial survival at cold temperatures because of our use of refrigeration in preserving and selling food. Additionally, the project will broaden participation by providing closely-mentored, hands-on research experience to train undergraduate students from groups that are underrepresented in STEM fields.The E. coli minimum temperature of growth is just above 8oC. The cells adapt to low temperature by increasing cell division and thereby reducing cell size. Compared to the large rods formed at 37oC, wild type E. coli are smaller rods at temperatures just above 8oC and filamentous rods at temperatures below the minimum temperature of growth. Late cell division proteins FtsN and DedD, which stimulate septal peptidoglycan synthesis and septation, are specifically required for growth and the formation of small rods at low temperature. A nucleoid-associated protein that enhances DNA replication is also required for growth and the production of the small rods. This project aims to test the hypothesis that replication and cell division are intricately linked, facilitating the small cell size and enabling growth at low temperatures. This hypothesis will be tested using two approaches. Flow cytometric and nucleoid staining analyses of the various cold-sensitive mutants will be performed to investigate the requirement for specific cell division and nucleoid-associated proteins for DNA replication at low temperature. Genetic screens will be done to identify suppressors of the cold-sensitive mutations, thereby elucidating the proteins required to couple DNA replication and cell division at low temperature. This research project should give novel insights into the differential requirements for the progression of the cell cycle as a function of temperature.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.