Solute Transport Proteins and the Outer Membrane Protein NmpC Contribute to Heat Resistance of Escherichia coli AW1.7
ABSTRACTThis study aimed to elucidate determinants of heat resistance inEscherichia coliby comparing the composition of membrane lipids, as well as gene expression, in heat-resistantE. coliAW1.7 and heat-sensitiveE. coliGGG10 with or without heat shock. The survival ofE. coliAW1.7 at late exponential phase was 100-fold higher than that ofE. coliGGG10 after incubation at 60°C for 15 min. The cytoplasmic membrane ofE. coliAW1.7 contained a higher proportion of saturated and cyclopropane fatty acids than that ofE. coliGGG10. 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. coliGGG10 relative toE. coliAW1.7 upon heat shock at 50°C, indicating improved ribosome stability. The outer membrane porin NmpC and several transport proteins were overexpressed in exponentially growingE. coliAW1.7. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of membrane properties confirmed that NmpC is present in the outer membrane ofE. coliAW1.7 but not in that ofE. coliGGG10. Expression of NmpC inE. coliGGG10 increased survival at 60°C 50- to 1,000-fold. In conclusion, the outer membrane porin NmpC contributes to heat resistance inE. coliAW1.7, 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.