Cytoplasmic chaperones involved in bacterial survival from extreme thermal challenge

LAURA V. BUTTIGLIERO; ALEJANDRO M. VIALE

Rosario

Congreso; V Congreso Argentino de Microbiología General (SAMIGE); 2008

Sociedad Argentina de Microbiología General

A number of treatments based in elevation of temperature constitute commonly employed means for the control of food- and water-borne poisoning or spoilage bacteria. Some of these technologies, such as Minimal Processing, involve the use of mild heat treatments at temperatures close above the enterobacterial adaptation zone, i.e., 50 to 60º C. Bacteria, however, may survive in substantial numbers these thermal treatments, challenging predictions on their bactericidal effectiveness. Different cytoplasmic chaperone systems participate in the adaptation and growth of bacteria under sub-lethal temperatures, but their roles in the preservation of cell viability under extreme conditions are not completely understood. Therefore, a detailed study of the bacterial mechanisms promoting increased resistance to heat inactivation may provide useful data for the design of safer treatments to control food-borne microbial risk simultaneously minimizing product over-processing. We investigated the roles and cooperation of the Escherichia coli cytoplasmic chaperones in cell survival from extreme heat stress by genetic procedures. Mutants lacking the sigma32 stress factor (delta rpoH), which are unable to fulfill the normal heat stress response, exhibited an increased rate of bacterial inactivation when exposed to 50º C. This increased heat sensitivity was comparable to that obtained for mutants specifically deficient in DnaK (delta dnaK), one of the main cytoplasmic sigma32-dependent chaperones, thus pointing to this system as the main responsible for extreme heat resistance. Remarkably, mutants lacking DnaJ (delta dnaJ), the physiological DnaK co-chaperone, were more resistant than delta dnaK mutants to the heat challenge. However, delta dnaJ delta cbpA double mutants showed similar sensitivity as delta dnaK cells, indicating synergistic actions between DnaJ and CbpA in cell survival from extreme heat stress. The overall data suggests that an “expanded” and fully functional DnaK system is pivotal for the preservation of cell viability from extreme thermal challenge.