Discovery of a novel MarR-type transcriptional regulator that controls cell death in Bacillus subtilis biofilms

Pulcherriminic acid (PA) is a cyclic-L-leu-L-leu di-peptide produced by Bacillus subtilis during biofilm formation. When secreted, PA strongly chelates extracellular iron and forms a reddish- brown pigment, pulcherrimin. Production of pulcherriminic acid and formation of pulcherrimin modulate iron homeostasis in B. subtilis. Pulcherriminic acid also functions as an antioxidant to protect cells from increasing oxidative stress during biofilm formation. We previously showed that PA is involved in gene regulation, differentially regulating hundreds of genes in B. subtilis. One of the strongly upregulated genes by PA is yhjH, encoding a putative MarR-type transcription repressor. In this study, we characterized the regulation of the yhjH gene by PA, by PchR, a known transcription repressor for PA biosynthesis, and by YhjH itself. We also found that high expression of yhjH triggers rapid cell lysis in B. subtilis. Results from RNA-seq suggest that YhjH differentially regulates about 180 genes, among which there is a significant number of prophage genes. Lastly, we propose that YhjH be re-named as PcdR, for "pulcherriminic acid cell death regulator".