The Absence of E. coli Nucleoid-Associated Protein FIS at Low Temperature Induces an Adaptive Response that Leads To Genome Compaction in Small Rods

For Escherichia coli , an adaptive response to temperatures just above the minimum temperature of growth, 8°C, includes a change in morphology from rods to small rods. A study was initiated to determine the requirement of nucleoid-associated protein FIS for growth and genome compaction in the small rods at low temperature. Growth and nucleoid staining analyses revealed that the fis null mutant displayed decreased growth and initially formed filaments containing decondensed nucleoids at 12°C, indicating that FIS facilitates production of small rods with condensed nucleoids at low temperature. However, characterized by biphasic growth at low temperature, the fis null mutant exhibited increased growth, cell division, and nucleoid condensation following a lag phase. Furthermore, compacted circular-shaped nucleoids were formed near the onset of the second growth phase. Therefore E. coli responds to the absence of FIS by inducing an adaptive mechanism that causes a shift towards nucleoid condensation resulting in genome compaction in small rods. Furthermore, the deletion of sulA (encodes DNA damaged-induced cell division inhibitor SulA) in the fis null mutant resulted in suppression of the filamentous morphology. This indicates that the absence of FIS with nucleoid decondensation led to DNA damage, inducing cell division inhibition by SulA.