Molecular Strategy for Survival at a Critical High Temperature in Eschierichia coli

Masayuki Murata,Taku Oshima,Naotake Ogasawara,Tomoyuki Kosaka,Hiroshi Nagamitsu,Hiroko Fujimoto,Kannikar Charoensuk,Kaori Nishimura,Satish Raina,Mamoru Yamada,Mick F Tuite

doi:10.1371/journal.pone.0020063

Abstract

The molecular mechanism supporting survival at a critical high temperature (CHT) in Escherichia coli was investigated. Genome-wide screening with a single-gene knockout library provided a list of genes indispensable for growth at 47°C, called thermotolerant genes. Genes for which expression was affected by exposure to CHT were identified by DNA chip analysis. Unexpectedly, the former contents did not overlap with the latter except for dnaJ and dnaK, indicating that a specific set of non-heat shock genes is required for the organism to survive under such a severe condition. More than half of the mutants of the thermotolerant genes were found to be sensitive to H2O2 at 30°C, suggesting that the mechanism of thermotolerance partially overlaps with that of oxidative stress resistance. Their encoded enzymes or proteins are related to outer membrane organization, DNA double-strand break repair, tRNA modification, protein quality control, translation control or cell division. DNA chip analyses of essential genes suggest that many of the genes encoding ribosomal proteins are down-regulated at CHT. Bioinformatics analysis and comparison with the genomic information of other microbes suggest that E. coli possesses several systems for survival at CHT. This analysis allows us to speculate that a lipopolysaccharide biosynthesis system for outer membrane organization and a sulfur-relay system for tRNA modification have been acquired by horizontal gene transfer.

Highlights

Responses of Escherichia coli to high temperatures have been extensively investigated, though previous studies have mainly focused on the response to a temperature up-shift around 42uC, a response known as a heat shock response (HSR) to induce the expression of a set of proteins, heat-shock proteins (HSPs) [1]
Thermosensitive mutants and thermotolerant genes In order to identify genes required for survival at critical high temperature (CHT) in E. coli, we screened for thermosensitive mutants from a single-gene knockout library [13], which had been constructed according to the one-step gene disruption method with an aph cassette [14] and for which each construct had been confirmed extensively [15]
Our experiments indicated that the parental strain used for construction of the disrupted library is able to grow at temperatures up to 47uC, this temperature being its CHT

Summary

Introduction

Responses of Escherichia coli to high temperatures have been extensively investigated, though previous studies have mainly focused on the response to a temperature up-shift around 42uC, a response known as a heat shock response (HSR) to induce the expression of a set of proteins, heat-shock proteins (HSPs) [1]. Based on the results showing that disrupted mutations of these genes caused a thermosensitive phenotype, we assumed that the cells require more ATP at a higher temperature.

Results

Conclusion