Discovery of intracellular heme-binding protein HrtR, which controls heme efflux by the conserved HrtB-HrtA transporter in Lactococcus lactis.

Most commensal and food bacteria lack heme biosynthesis genes. For several of these, the capture of environmental heme is a means of activating aerobic respiration metabolism. Our previous studies in the Gram-positive bacterium Lactococcus lactis showed that heme exposure strongly induced expression of a single operon, called here hrtRBA, encoding an ortholog of the conserved membrane hrt (heme-regulated transporter) and a unique transcriptional regulator that we named HrtR.

Impact of aeration and heme-activated respiration on Lactococcus lactis gene expression: identification of a heme-responsive operon.

Lactococcus lactis is a widely used food bacterium mainly characterized for its fermentation metabolism. However, this species undergoes a metabolic shift to respiration when heme is added to an aerobic medium. Respiration results in markedly improved biomass and survival compared to fermentation.