Heliorhodopsins function in Gram-positive bacteria
Rhodopsins are light sensing proteins that span across all kingdoms of life. They absorb light using retinal. As a response to light, rhodopsins can function as ion pumps, channels, enzymes, and photo sensory receptors. Heliorhodopsins (HeRs) are a new rhodopsin family discovered in our lab. HeRs are present in all domains of life, they react to light, yet their end function is currently unknown. Recently, a HeR gene was discovered in a strain of Lactococcus lactis and in Alkalibacterium pelagium, another culturable bacterium related to L. lactis. Interestingly, acquisition of HeR genes happened several times within the order Lactobacillales, such that the heliorhodopsins from A. pelagium and L. lactis appear to have independent origins. We confirmed that the Lactococcus HeR (LlHeR) is transcribed in this L. lactis, and then over-expressed LlHeR and ApHeR in Escherichia coli. Next, mutant strains of L. lactis were used to perform RNASeq analysis in an attempt to shed light on LlHeR role in L. lactis.