They admit the difficulty of finding LBCA:
Higher life forms pass on their genetic code from parent to offspring via vertical gene transfer. As a result, the genome provides information on phylogenetic history. But bacteria are masters in another form of gene transfer, namely lateral gene transfer (LGT). This allows bacteria to exchange genetic information across different strains. This posed a major challenge in reconstructing the LBCA genome, as it renders the traditional phylogenetic methods incapable of inferring the root in the bacterial evolutionary tree.
For this reason, the researchers in Duesseldorf used biochemical networks together with thousands of individual trees. They investigated 1,089 anaerobic genomes and identified 146 protein families conserved in all bacteria. These proteins make up a nearly complete core metabolic network …
“We can infer with confidence that LBCA was most likely rod-shaped,” says Xavier. “If it was similar to Clostridia, it is possible that LBCA was able to sporulate.” This hypothesis was recently laid out by other researchers “and is highly compatible with our results,” says Xavier. Forming spores would allow early cells to survive the inhospitable environment of the early Earth.Heinrich-Heine University Duesseldorf, “In search of the first bacterium” at ScienceDaily
One senses that the reconstruction will be subject to considerable revision. It’s not entirely clear what “ancestry” means in a world of rampant horizontal gene transfer.
The paper is open access.
See also: Horizontal gene transfer: Sorry, Darwin, it’s not your evolution any more