Sobrevivência ao frio e congelamento em uma alfaproteobacteria

RESEARCH LETTER

Characterization of Caulobacter crescentus response to low temperature and identi¢cation of genes involved in freezing resistance
ˆ Ricardo R. Mazzon, Elza A.S. Lang, Vania S. Braz & Marilis V. Marques
ˆ ´ ˜ ˜ Department of Microbiology, Instituto de Ciencias Biomedicas, Universidade de Sao Paulo, Sao Paulo, SP, Brazil

Correspondence: Marilis V. Marques, Av. ˜ Prof. Lineu Prestes, 1374, Sao Paulo 05508900, SP, Brazil. Tel.: [phone]; fax: [phone]; e-mail: [e-mail] Present address: Elza A.S. Lang, Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA. Received 29 May 2008; revised 11 August 2008; accepted 12 August 2008. First published online 17 September 2008. DOI:10.1111/j.1574-6968.2008.01337.x Editor: Skorn Mongkolsuk Keywords cryotolerance; freezing survival; Caulobacter crescentus .

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 À 80 1C, which was able to grow at low temperatures. Exponentially growing cells and late stationary-phase cells presented higher freezing resistance at both À 20 and À 80 1C than early stationary-phase cells. Cryotolerance was observed when log-phase cultures grown at 30 1C were preincubated at 5, 15 or 20 1C before freezing at À 20 1C. A transposon library was screened to identify mutants sensitive to freezing at À 80 1C and three strains presenting o 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 1C, with the RNA helicase mutant presenting a