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Journal of Bacteriology, October 1998, p. 5165-5172, Vol. 180, No. 19
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Roles of the Escherichia coli Small Heat Shock Proteins IbpA and IbpB in Thermal Stress Management: Comparison with ClpA, ClpB, and HtpG In Vivo

Jeffrey G. Thomasdagger and François Baneyx*

Department of Chemical Engineering, University of Washington, Seattle, Washington 98195

Received 24 April 1998/Accepted 30 July 1998

We have constructed an Escherichia coli strain lacking the small heat shock proteins IbpA and IbpB and compared its growth and viability at high temperatures to those of isogenic cells containing null mutations in the clpA, clpB, or htpG gene. All mutants exhibited growth defects at 46°C, but not at lower temperatures. However, the clpA, htpG, and ibp null mutations did not reduce cell viability at 50°C. When cultures were allowed to recover from transient exposure to 50°C, all mutations except Delta ibp led to suboptimal growth as the recovery temperature was raised. Deletion of the heat shock genes clpB and htpG resulted in growth defects at 42°C when combined with the dnaK756 or groES30 alleles, while the Delta ibp mutation had a detrimental effect only on the growth of dnaK756 mutants. Neither the overexpression of these heat shock proteins nor that of ClpA could restore the growth of dnaK756 or groES30 cells at high temperatures. Whereas increased levels of host protein aggregation were observed in dnaK756 and groES30 mutants at 46°C compared to wild-type cells, none of the null mutations had a similar effect. These results show that the highly conserved E. coli small heat shock proteins are dispensable and that their deletion results in only modest effects on growth and viability at high temperatures. Our data also suggest that ClpB, HtpG, and IbpA and -B cooperate with the major E. coli chaperone systems in vivo.

* Corresponding author. Mailing address: Department of Chemical Engineering, University of Washington, Box 351750, Seattle, WA 98195. Phone: (206) 685-7659. Fax: (206) 685-3451. E-mail: baneyx{at}cheme.washington.edu.

dagger Present address: Department of Chemical Engineering, University of Texas, Austin, TX 78712.

Journal of Bacteriology, October 1998, p. 5165-5172, Vol. 180, No. 19
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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