Solute Transport Proteins and the Outer Membrane Protein NmpC Contribute to Heat Resistance of Escherichia coli AW1.7

This study aimed to elucidate determinants of heat resistance inEscherichia coli by comparing the composition of membrane lipids, as well as gene expression, in heat-resistantE. coli AW1.7 and heat-sensitiveE. coli GGG10 with or without heat shock. The survival ofE. coli AW1.7 at late exponential phase was 100-fold higher than that ofE. coli GGG10 after incubation at 60°C for 15 min. The cytoplasmic membrane ofE. coli AW1.7 contained a higher proportion of saturated and cyclopropane fatty acids than that ofE. coli GGG10. Microarray hybridization of cDNA libraries obtained from exponentially growing or heat-shocked cultures was performed to compare gene expression in these two strains. Expression of selected genes from different functional groups was quantified by quantitative PCR. DnaK and 30S and 50S ribosomal subunits were overexpressed inE. coli GGG10 relative toE. coli AW1.7 upon heat shock at 50°C, indicating improved ribosome stability. The outer membrane porin NmpC and several transport proteins were overexpressed in exponentially growingE. coli AW1.7. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of membrane properties confirmed that NmpC is present in the outer membrane ofE. coli AW1.7 but not in that ofE. coli GGG10. Expression of NmpC inE. coli GGG10 increased survival at 60°C 50- to 1,000-fold. In conclusion, the outer membrane porin NmpC contributes to heat resistance inE. coli AW1.7, but the heat resistance of this strain is dependent on additional factors, which likely include the composition of membrane lipids, as well as solute transport proteins.