The heat shock gene, htpG, and thermotolerance in the cyanobacterium, Synechocystis sp. PCC 6803

The htpG null mutant was obtained by inserting a chloramphenicol resistance cassette (Cm(r)) in the htpG coding sequence. The htpG null mutant (delta htpG), delta hsp16.6, and the double mutant, delta htpG::hsp16.6 cells showed little growth disadvantage at 30 degrees C and 37 degrees C, but not at 40 degrees C. This suggests that HtpG and HSP16.6 proteins do not have an essential role during growth at normal and mildly elevated temperatures. Cell growth, cell survival rate, and oxygen electrode measurements demonstrated that delta htpG, delta hsp16.6, and delta htpG::hsp16.6 cells were sensitive to heat stress. Decreased basal and acquired thermotolerance was observed when mutants were heat shocked, with delta htpG::hsp16.6 being the most sensitive. A comparison of mutants showed that delta hsp16.6 was more sensitive to heat shock than delta htpG.