Characterization of Caulobacter crescentus response to low temperature and identification of genes involved in freezing resistance

Free-living bacteria must respond to a wide range of temperature changes, and have developed specific mechanisms to survive in extreme environments. In this work we describe a remarkable resistance of mesophilic bacterium Caulobacter crescentus to several cycles of freezing at -80 °C, which was able to grow at low temperatures. Exponentially growing cells and late stationary-phase cells presented higher freezing resistance at both -20 and -80 °C than early stationary-phase cells. Cryotolerance was observed when log-phase cultures grown at 30 °C were preincubated at 5, 15 or 20 °C before freezing at -20 °C. A transposon library was screened to identify mutants sensitive to freezing at -80 °C and three strains presenting