The response to heat stress was examined in Thermoanaerobacterium thermosulfurigenes EM1. Upon a temperature shift-up from 50 degrees to 62 degrees C, four heat shock proteins (hsps) were synthesized at an elevated level. Two proteins were found to be immunologically related to the Escherichia coli GroEL protein and the Mycobacterium tuberculosis hsp71 (DnaK similar protein), and the corresponding groE and dnaK homologous sequences were detected in the chromosome of T. thermosulfurigenes EM1. The heat shock response in this thermophile was transient, with a maximum synthesis of hsps between 10 and 15 min after the shock. The enhanced synthesis of DnaK and GroEL was consistent with increased mRNA levels of the genes, which reached a maximum 15 min after heat treatment.