Speaker Calendar » 2017 Weiss
The concept of a last universal ancestor of all cells (Luca) is central to the study of early evolution and life's origin, yet information about how and where Luca lived is lacking. To investigate the microbial ecology of Luca, we constructed clusters and phylogenetic trees for 6.1 million protein coding genes in 1,981 prokaryotic genomes in order to identify proteins that, irrespective of universal distribution, i) trace to Luca through presence in archaea and bacteria yet ii) lack evidence of interdomain lateral gene transfer in the individual gene phylogeny. Among 286,514 protein clusters, the trees of 355 (~0.1%) show evidence for vertical intradomain inheritance from Luca. The functions of these 355 genes characterize Luca as anaerobic, CO2-fixing, H2-dependent with a Wood-Ljungdahl pathway, N2-fixing, and thermophilic. Luca's biochemistry was replete with FeS clusters and radical reaction mechanisms. Its cofactors reveal dependence upon transition metals, flavins, S-adenosyl methionine (SAM), coenzyme A, ferredoxin, molybdopterin, corrins, and selenium. Its genetic code required nucleoside modifications and SAM dependent methylations. The 355 phylogenies identify clostridia and methanogens, whose modern lifestyles resemble Luca's, as basal among their respective domains. Luca inhabited a geochemically active environment rich in H2, CO2, and iron.