title: Characterization of Caulobacter crescentus response to low temperature and identification of genes involved in freezing resistance.
abstract: 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 degrees 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 degrees C than early stationary-phase cells. Cryotolerance was observed when log-phase cultures grown at 30 degrees C were preincubated at 5, 15 or 20 degrees C before freezing at -20 degrees C. A transposon library was screened to identify mutants sensitive to freezing at -80 degrees C and three strains presenting <10% survival were isolated. Identification of genes disrupted in each mutant showed that they encoded an AddA family DNA helicase, a DEAD/DEAH box RNA helicase and a putative RND (resistance, nodulation, cell division) efflux system component. These strains showed longer generation times than wild-type cells when growing at 15 degrees C, with the RNA helicase mutant presenting a severe growth defect. These analyses suggest that the singular intrinsic resistance to freezing of C. crescentus is in fact a consequence of several independent traits, especially the maintenance of a proper degree of supercoiling of nucleic acids.
authors.affiliation: Department of Microbiology, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Ricardo R
authors.initials: RR
authors.lastname: Mazzon
authors.forename: Elza A S
authors.initials: EA
authors.lastname: Lang
authors.forename: Vânia S
authors.initials: VS
authors.lastname: Braz
authors.forename: Marilis V
authors.initials: MV
authors.lastname: Marques
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D016935:Caulobacter crescentus / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism / Q000502:physiology; D003080:Cold Temperature; D003470:Culture Media; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D004251:DNA Transposable Elements; D005615:Freezing; D015964:Gene Expression Regulation, Bacterial; D015723:Gene Library; D018869:Heat-Shock Response; D009154:Mutation; D020365:RNA Helicases / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D004251:DNA Transposable Elements; D004265:DNA Helicases; D020365:RNA Helicases