Overexpression of PrfA Leads to Growth Inhibition ofListeria monocytogenesin Glucose-Containing Culture Media by Interfering with Glucose Uptake

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Abstract
Listeria monocytogenes strains expressing high levels of the virulence regulator PrfA (mutant PrfA* or wild-type PrfA) show strong growth inhibition in minimal media when they are supplemented with glucose but not when they are supplemented with glucose-6-phosphate compared to the growth of isogenic strains expressing low levels of PrfA. A significantly reduced rate of glucose uptake was observed in a PrCA*-overexpressing strain growing in LB supplemented with glucose. Comparative transcriptome analyses were performed with RNA isolated from a prfA mutant and an isogenic strain carrying multiple copies of prfA or prfA* on a plasmid. These analyses revealed that in addition to high transcriptional up-regulation of the known PrfA-regulated virulence genes (group I), there was less pronounced up-regulation of the expression of several phage and metabolic genes (group II) and there was strong down-regulation of several genes involved mainly in carbon and nitrogen metabolism in the PrfA*-overexpres sing strain (group III). Among the latter genes are the nrgAB, gltAB, and glnRA operons (involved in nitrogen metabolism), the ilvB operon (involved in biosynthesis of the branched-chain amino acids), and genes for some ABC transporters. Most of the down-regulated genes have been shown previously to belong to a class of genes in Bacillus subtilis whose expression is negatively affected by impaired glucose uptake. Our results lead to the conclusion that excess PrfA (or PrfA*) interferes with a component(s) essential for phosphotransferase system-mediated glucose transport.