Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2012
Publication Date: 12/19/2012
Citation: Liu, Y., Morgan, S.L., Ream, A.R., Huang, L. 2012. Gene expression profiling of a nisin-sensitive Listeria monocytogenes Scott A CtsR deletion mutant. Journal of Industrial Microbiology and Biotechnology. 40(5):495-505. Interpretive Summary: The bacterium, Listeria monocytogenes, is an important food-borne pathogen that causes disease in humans and animals. Nisin is a bacteriocin (toxin that can kill bacteria) that can be used to control L. monocytogenes in food. A pressure tolerant mutant (genetically modified strain) has been shown to be sensitive to nisin, however, the factors that contribute to the sensitivity of this mutant bacterium subjected to nisin 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 nisin. A number of genes were found to be affected by nisin treatment, and thus these genes could potentially be investigated as targets for antimicrobial treatments to control L. monocytogenes. Information from this study enhances the understanding of how L. monocytogenes survives under nisin treatment and may assist in the design of effective and economically feasible antimicrobial treatments to control this pathogen.
Technical Abstract: Listeria monocytogenes is a food-borne pathogen of significant threat to public health. Nisin is the only bacteriocin that can be used as a food preservative. Due to its antimicrobial activity, it can be used to control Listeria monocytogenes in food; however, the antimicrobial mechanism of nisin activity in Listeria monocytogenes is unknown. The CtsR (class three stress gene repressor) protein negatively regulates the expression of class III heat shock genes. A spontaneous pressure-tolerant ctsR deletion mutant that showed increased sensitivity to nisin has been identified. Microarray technology was used to monitor the gene expression profiles of the ctsR mutant under nisin treatments. Total RNA was isolated from the nisin-treated (20 micrograms per milliliter) ctsR mutant and L. monocytogenes Scott A wild type and hybridized to commercial oligonucleotide (35-mers) microarray chips representing the whole genome of L. monocytogenes. Compared to the nisin-treated wild type, 123 genes were up-regulated (> 2-fold increase) in the ctsR deletion mutant whereas 4 genes were down-regulated (< -2-fold decrease). The up-regulated genes included genes encoding for ribosomal proteins, membrane proteins, cold-shock domain proteins, translation initiation and elongation factors, cell division, a ATP-dependent ClpC protease, a putative accessory gene regulator protein D, transport and binding proteins, a beta-glucoside-specific phosphotransferase system (PTS); IIABC component, and hypothetical proteins. The down-regulated genes included genes that encode for virulence, a transcriptional regulator, stress proteins, and hypothetical proteins. The gene expression changes determined by microarray assays were confirmed by real-time RT-PCR analyses. This study enhances our understanding of how nisin interacts with the ctsR gene product in L. monocytogenes and may contribute to the understanding of the antibacterial mechanisms of nisin.