Submitted to: Journal of Microbial and Biochemical Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2012
Publication Date: 4/1/2012
Citation: Liu, Y., Huang, L., Joerger, R.D., Gunther, N.W. 2012. Genes that are involved in high hydrostatic pressure treatments in a Listeria monocytogenes Scott A ctsR deletion mutant. Journal of Microbial and Biochemical Technology. 4:050-056.
Interpretive Summary: The bacterium, Listeria monocytogenes, is an important food-borne pathogen that causes disease in humans and animals. High hydrostatic pressure (HPP) has been used to control L. monocytogenes in food. However, a small portion of a bacterial population can be relatively resistant after a certain level of HHP is applied. This phenomenon is called a tailing effect, and it is a major challenge for the food industry. A pressure tolerant mutant (genetically modified strain) has been shown to be related to the tailing effect; however, the factors that contribute to the survival of this mutant bacterium subjected to HPP treatment remain unclear. DNA microarray technology is a powerful tool that can be used to study the expression of all of the genes possessed by a bacterium under different conditions. DNA microarrays were used to study the expression of genes in the pressure tolerant strain of L. monocytogenes when exposed to HPP. A number of genes were found to be affected by HPP, and thus these genes could potentially be investigated as targets for strategies to increase the susceptibility of L. monocytogenes to HPP, therefore, preventing the tailing effect. Information from this study enhances the understanding of how L. monocytogenes survives HHP and may assist in the design of effective, economically feasible HHP food processing treatments to control this pathogen.
Technical Abstract: Listeria monocytogenes is a food-borne pathogen of significant threat to public health. High Hydrostatic Pressure (HHP) treatment can be used to control L. monocytogenes in food. The CtsR (class three stress gene repressor) protein negatively regulates the expression of class III heat shock genes. A spontaneous pressure-tolerant ctsR L. monocytogenes deletion mutant 2-1 that was able to survive under HHP treatment was identified; however, there is only limited information about the mechanisms of survival and adaptation of this mutant in response to high pressure. Microarray technology was used to monitor the gene expression profiles of ctsR mutant 2-1 under pressure treatments. Total RNA was isolated from pressure-treated L. monocytogenes Scott A (450 Mpa, 3 min) ctsR mutant 2-1, labeled with fluorescent dyes, and hybridized to commercial oligonucleotide (35-mers) microarray chips representing the whole genome of L. monocytogenes. The gene expression changes determined by microarray assays were confirmed by real-time RT-PCR analyses. Compared to non-pressure-treated ctsR mutant 2-1, 14 genes were induced (> 2-fold increase) in the ctsR deletion mutant whereas 32 genes were inhibited (< -2-fold decrease). The induced genes included genes encoding proteins involved in synthesis of purines, pyrimidines, nucleosides, and nucleotides, transport and binding, transcription, cell membrane, DNA and energy metabolism, protein synthesis, and unknown functions. The inhibited genes included genes encoding proteins for transport and binding, cell envelope, transcription, amino acid biosynthesis, regulatory functions, cellular processes and central intermediary metabolism. This study enhances our understanding of how L. monocytogenes survives HHP and may contribute to the design of safe, accurate, and economically feasible HHP treatments for food processing.