Intracellular protein denaturation caused by severe heat stress does not lead to bacterial death

LAURA V. BUTTIGLIERO; ALEJANDRO M. VIALE

Puerto Madryn

Congreso; XLVI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Exposure of E. coli cultures to temperatures above 50ºC (severe heat stress, SHS) promotes cell death, an effect largely enhanced in bacteria lacking DnaK chaperones. Main SHS cell targets are not well defined, but intracellular protein denaturation/aggregation was proposed as a major heat inactivation factor. We studied whether SHS-induced protein denaturation compromises cell recovery from stress. Exposure of wild-type (wt) cells to 50ºC for short periods not causing substantial death in the population promoted growth arrest during subsequent incubation at 30ºC. Quali (SDS-PAGE) and quantitative (cell lysis) analyses indicated a rapid 7-10 fold SHS-mediated increase in intracellular protein denaturation, which was maintained during recovery at 30ºC and even after re-initiation of growth. Lack of DnaK caused massive death but only a slight increase in protein denaturation as compared to wt bacteria. Cell visualization using contrast phase microscopy showed neither morphological changes nor formation of protein aggregates due to SHS, a result also supported by buoyant density Percoll centrifugation analysis. The overall results indicate that even though SHS caused cytoplasmatic protein denaturation, it was not accompanied by massive formation of intracellular aggregates. Moreover, DnaK-mediated protein removal/reactivation was not necessary to maintain viability or to resume growth.