An evolutionary study of enzymes that produce and deactivate Vitamin A suggests that Vitamin A was “invented” not by animals, as generally thought, but by cyanobacteria. This is a surprising finding with respect to standard models of evolution. Vitamin A is medically important and cyanobacteria are ecologically very significant so the research may have impact both on healthcare and on the environment (Millard, Scanlan,* Gallagher, Marsh & Taylor* Mol. Biosyst. 2014)

This research was carried out by Warwick Chemistry undergraduate Connor Gallagher under the supervision of Prof. Scanlan and Drs. Marsh, Millard & Taylor thanks to an Underdgraduate Research Scholarship from the University.

Biosynthesis of retinoic acid from retinaldehyde (retinal) is catalysed by an aldehyde dehydrogenase (ALDH) and its oxidation by cytochrome P450 enzymes (CYPs). We have shown by phylogenetic analysis that the ALDHs and CYPs in the retinoic acid pathway in animals are much closer in evolutionary terms to cyanobacterial orthologs than would be expected from the standard models of evolution.

Maximum likelihood phylogenetic analyses, across all kingdoms, of both ALDH1a/2 aldehyde dehydrogenases and cytochrome P450 enzymes known to oxidise retinoic acid show surprising evolutionary proximities between animal and cyanobacterial proteins (and also planctomycetes in the case of ALDHs). We believe the simplest explanation consistent with these data, and with literature observations on the structures and functions of the enzymes, to be a lateral gene transfer event between the bacteria and animals.

Given the importance of retinoic acid biosynthesis to developmental biology and in medicine, our observations suggest that detailed research of the pathway in cyanobacteria could have an impact on human healthcare, as well as understanding of important ecosystems. Further studies of the evolutionary links between such apparently distant species may also be revealing.