Bacterial stress responses, with relations to food production and food safety

Bacteria respond to stress by induction of specific proteins (stress proteins) in order to continue growth or to increase survival. Because of this, exposure to sublethal stress conditions usually increase the tolerance to additional stress levels. Using a hierachical regulatory model as a tool in the unraveling of the regulatory networks we define a stimulon as the class of proteins, which are regulated by a specific stress condition. The stimulon can be subdevided into regulons, which are classes of proteins that share a common regulatory pathway. The lowest level of specification is the target, which is a single protein whose level is regulated in response to the stress condition. A target may belong to many regulons, and a regulon may belong to many stimulons.
The goal of the project is to identify stimulons, regulons, targets and regulatory networks involved in dairy related stress responses, and their role in the generation of stress resistance. The focus of the project is heat and osmotic stress together with the physiological stress resulting from shortage of purines, phosphate and glucose. The latter three conditions were chosen due to their generation of temperature stress cross-protection. We have selected the well characterized lactic acid bacterium Lactococcus lactis as a model organism for gram-positive dairy related bacteria.
The methodologies used include physiological analysis (survival and growth rate), proteomics (2D-GE of proteins coupled to mass spectrometry), Transcriptomics (analysis of mRNA levels from single or multible genes, with plans to include gene array techniques), & mutant construction and analysis (mutated in stress genes or regulatory genes).
Currently we are undertaking a detailed molecular analysis of the heat stress repressor, HrcA, and the purine specific activator, PurR, together with a proteomic, and transcriptional analysis of their respective regulons using regulatory mutants.