Different mechanisms of bacterial survival/recovery from severe and sublethal heat stress

LAURA V. BUTTIGLIERO; ALEJANDRO M. VIALE

San Miguel de Tucumán

Congreso; XLV Reunión anual Sociadad Argentina de Investigación en Bioquímica y Biología Molecular; 2009

Sociadad Argentina de Investigación en Bioquímica y Biología Molecular

The roles and cooperation of the major folding chaperone of the Escherichia coli cytoplasm DnaK and its J protein cochaperones DnaJ, DjlA and CbpA in cell survival from severe heat stress at 50ºC were investigated by genetic procedures. As opposed to the isogenic parental strain, ΔdnaK and ΔdnaJΔcbpA mutants exhibited the most pronounced rate of bacterial inactivation at 50ºC. Measurements of intracellular protein aggregation indicated that only ΔdnaK and ΔdnaJΔcbpA mutants showed increased initial rate of aggregate formation at 50ºC as compared to the parental strain, although no differences in the final aggregation amount were found after 1 hour of heat treatment. This suggests that bacterial death from severe thermal challenge is not due to protein aggregation as has been suggested, but to other processes occurring after stress has abated, i. e., the recovery phase. Also, short exposure of parental strain to 50ºC causes growth arrest when stress is over. Moreover, and contrary to the dissolution of aggregates observed in bacteria exposed to sublethal temperatures, protein disaggregation was not necessary after a 50ºC heat shock to resume growth when physiological temperatures were reinstated. The overall results point to different mechanisms operating in response to moderate and severe heat stress, with DnaK along with DnaJ and CbpA being crucial for the recovery period.