Transcriptomic analysis of Listeria monocytogenes in response to bile under aerobic and anaerobic conditions
Damayanti Chakravarty1, Gyan Sahukhal1, Mark Arwick2, Morgan Wright3, and Janet R. Donaldson1*
1Cell and Molecular Biology, The University of Southern Mississippi, Hattiesburg, MS
2Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University, Mississippi State, MS
3Department of Biological Sciences, Mississippi State University, Mississippi State, MS
Listeria monocytogenes is a dangerous food borne bacterium that is the third leading cause of death from food borne pathogens in the USA. Typically acquired through consumption of contaminated ready to eat products, such as cantaloupes and ice cream, L. monocytogenes must be able to sense and respond to bile encountered within the small intestine. Listeria monocytogenes possesses response mechanisms that allow it to survive the bacteridical effect of bile. Though these mechanisms have been identified, it is not known how this response occurs under physiologically relevant anaerobic conditions. Our hypothesis was genes involving pathogenesis are differentially regulated under conditions mimicking different parts of the gastrointestinal tract. Our investigation involved analyzing the transcriptome of L. monocytogenes following exposure to bile under aerobic or anaerobic conditions at a pH of either 7.5 or 5, mimicking different parts of the GI tract. After obtaining the raw RNA sequencing reads, data was analyzed using several softwares packaged into a bioinformatics pipeline. At the end of pipeline, differentially expressed genes were obtained and genes greater than ± 3 fold were selected for further study. Genes responsible for adhesion and intracellular survival were upregulated under anaerobic conditions. Genes responsible for two component system were also upregulated, which could indicate a potential novel stress recognition and response system. Interestingly, the pdeD gene, which codes for a known oxygen sensor and regulator of cyclic-di-GMP concentrations, was also upregulated at certain mimicking conditions. Expression of pdeD gene also increased under anaerobic conditions when measured in vitro. A pdeD mutant was constructed and was found to be sensitive to bile, as well as to intracellular growth. Concentration of c-di-GMP increased when the pdeD mutant was exposed to anaerobic environment compared to aerobic. These data indicate that c-di-GMP may be regulated in response to oxygen availability. This needs to be further analyzed in future directions.