Kinetics and intensity of the expression of genes involved in the stress response tightly induced by phenolic acids in Lactobacillus plantarum.

In Lactobacillus plantarum, PadR, the negative transcriptional regulator of padA encoding the phenolic acid decarboxylase, is divergently oriented from padA. Moreover, it forms an operonic structure with usp1, a genewhose products display homology with proteins belonging to the UspA family of universal stress proteins. PadR is inactivated by the addition of p-coumaric, ferulic or caffeic acid to the culture medium. In order to better characterize the stress response of this bacterium to phenolic acids, we report here the kinetics and quantitative expression by qRT-PCR of the 3 genes from the padA locus. The expression of the 3 genes is very low in the non-induced condition, while the addition of 1.2 mMp-coumaric acid induces an increase in the expression of padA, padR and usp1 by factors of 8,000, 37 and 13, respectively. These maximum relative transcript levels are obtained after 5 min of induction at the end of the exponential growth phase, while phenolic acid decarboxylase activity, not detectable before induction, is increased by a factor of 8,000 in 10 min. The apparent half-life of padA mRNA is about 1.4 min. The padA-padR system displays dynamic characteristics that are valuable to the development of tools for gene expression in this bacterium.