ABSTRACT
Pope, W., Haase-Pettingell, C. & King, J. (2004) Applied & Environmental Microbiology, in press.
Protein folding failure sets the high temperature limit on the growth of phage P22 in Salmonella serovar Typhimurium.
The high temperature limit for the growth of microorganisms varies greatly depending on their species and habitat. The importance of an organism’s ability to manage thermal stress is reflected in the ubiquitous distribution of the heat shock chaperones. Though many chaperones function to reduce protein folding defects, it has been difficult to identify the specific protein folding pathways that set the high temperature limit of growth for a given microorganism. We have investigated this for a simple system, phage P22 infection of Salmonella enterica serovar Typhimurium. Production of infectious particles exhibited a broad maximum of 150 phage/cell when host cells were grown between 30°C–39°C in minimal medium. Production of infectious phage declined sharply in the range of 40°C - 41°C, to below 1% by 42°C. The host cells maintained optimal division rates at these temperatures. The loss of phage infectivity was steeper than the loss of physical particles, suggesting that non-infectious particles were formed at higher temperatures. SDS-PAGE revealed a decrease in the tailspike adhesins assembled onto phage particles purified from cultures incubated at higher temperatures. The infectivity of these particles was restored by incubation in vitro with soluble tailspike trimers. Examination of tailspike folding and assembly in lysates of phage-infected cells confirmed that the fraction of polypeptide chains able to reach the native state in vivo decreased with increasing temperature, indicating a thermal folding rather than particle assembly defect. Thus, we believe that the folding pathway of the tailspike adhesin sets the high temperature limit for P22 formation in Salmonella serovar Typhimurium.
