ROLES OF THE ESCHERICHIA-COLI SMALL HEAT-SHOCK PROTEINS IBPA AND IBPBIN THERMAL-STRESS MANAGEMENT - COMPARISON WITH CLPA, CLPB, AND HTPG IN-VIVO

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 degrees C, but not at lower temperatures. However, the clpA, ht pG, and ibp null mutations did not reduce cell viability at 50 degrees C, When cultures were allowed to recover from transient exposure to 5 0 degrees C, all mutations except Delta ibp led to suboptimal growth a s the recovery temperature was raised, Deletion of the heat shock gene s clpB and htpG resulted in growth defects at 42 degrees C when combin ed with the dnaK756 or groES30 alleles, while the Delta ibp mutation h ad a detrimental effect only on the growth of dnaK756 mutants. Neither the overexpression of these heat shock proteins nor that of ClpA coul d restore the growth of dnaK756 or groES30 cells at high temperatures. Whereas increased levels of host protein aggregation were observed in dnaK756 and g7oES30 mutants at 46 degrees C compared to wild-type cel ls, none of the null mutations had a similar effect. These results sho w that the highly conserved E. coli small heat shock proteins are disp ensable and that their deletion results in only modest effects on grow th and viability at high temperatures. Our data also suggest that ClpB , HtpG, and IbpA and -B cooperate with the major E, coli chaperone sys tems in vivo.