AUTHOR=Fang Shiuh-Bin , Huang Ching-Jou , Huang Chih-Hung , Wang Ke-Chuan , Chang Nai-Wen , Pan Hung-Yin , Fang Hsu-Wei , Huang Ming-Te , Chen Ching-Kuo 

TITLE=speG Is Required for Intracellular Replication of Salmonella in Various Human Cells and Affects Its Polyamine Metabolism and Global Transcriptomes

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.02245

DOI=10.3389/fmicb.2017.02245

ISSN=1664-302X

ABSTRACT=<p>The <italic>speG</italic> gene has been reported to regulate polyamine metabolism in <italic>Escherichia coli</italic> and <italic>Shigella</italic>, but its role in <italic>Salmonella</italic> remains unknown. Our preliminary studies have revealed that <italic>speG</italic> widely affects the transcriptomes of infected <italic>in vitro</italic> M and Caco-2 cells and that it is required for the intracellular replication of <italic>Salmonella enterica</italic> serovar Typhimurium (<italic>S</italic>. Typhimurium) in HeLa cells. In this study, we demonstrated that <italic>speG</italic> plays a time-dependent and cell type-independent role in the intracellular replication of <italic>S</italic>. Typhimurium. Moreover, high-performance liquid chromatography (HPLC) of four major polyamines demonstrated putrescine, spermine, and cadaverine as the leading polyamines in <italic>S</italic>. Typhimurium. The deletion of <italic>speG</italic> significantly increased the levels of the three polyamines in intracellular <italic>S</italic>. Typhimurium, suggesting the inhibitory effect of <italic>speG</italic> on the biosynthesis of these polyamines. The deletion of <italic>speG</italic> was associated with elevated levels of these polyamines in the attenuated intracellular replication of <italic>S</italic>. Typhimurium in host cells. This result was subsequently validated by the dose-dependent suppression of intracellular proliferation after the addition of the polyamines. Furthermore, our RNA transcriptome analysis of <italic>S</italic>. Typhimurium SL1344 and its <italic>speG</italic> mutant outside and inside Caco-2 cells revealed that <italic>speG</italic> regulates the genes associated with flagellar biosynthesis, fimbrial expression, and functions of types III and I secretion systems. <italic>speG</italic> also affects the expression of genes that have been rarely reported to correlate with polyamine metabolism <italic>in Salmonella</italic>, including those associated with the periplasmic nitrate reductase system, glucarate metabolism, the phosphotransferase system, cytochromes, and the succinate reductase complex in <italic>S</italic>. Typhimurium in the mid-log growth phase, as well as those in the <italic>ilv</italic>–<italic>leu</italic> and histidine biosynthesis operons of intracellular <italic>S</italic>. Typhimurium after invasion in Caco-2 cells. In the present study, we characterized the phenotypes and transcriptome effects of <italic>speG</italic> in <italic>S</italic>. Typhimurium and reviewed the relevant literature to facilitate a more comprehensive understanding of the potential role of <italic>speG</italic> in the polyamine metabolism and virulence regulation of <italic>Salmonella</italic>.</p>