We predict that the last bacterial common ancestor was a free-living flagellated, rod-shaped cell featuring a double membrane with a lipopolysaccharide outer layer, a Type III CRISPR-Cas system, Type IV pili, and the ability to sense and respond via chemotaxis.A rooted phylogeny resolves early bacterial evolution By Gareth A. Coleman, Adrián A. Davín, Tara A. Mahendrarajah, Lénárd L. Szánthó, Anja Spang, Philip Hugenholtz, Gergely J. Szöllősi, Tom A. Williams Science
A friend writes to say that most of the genes needed for flagella are present, including pili & flagella, with 70 gene families found.
Question: If the last common ancestor of the bacterium had a flagellum, what do we really know about the evolution of the flagellum? Isn’t that a bit like finding a stone laptop in a Neanderthal cave?
The findings, published in the journal Science today, demonstrate how integrating vertical descent and horizontal gene transfer can be used to infer the root of the bacterial tree and the nature of the last bacterial common ancestor.
Just as in plants and animals, the genomes of Bacteria are home to many different genes. However, Bacterial genes are not only inherited vertically from mother to daughter, but are also frequently exchanged horizontally between potentially distant family members. Amongst its many functions, horizontal gene sharing drives the rapid spread of antibiotic resistance amongst pathogenic Bacteria.
The combination of vertical and horizontal ancestry complicates how we think about evolutionary relationships among Bacteria, with the former best represented as a tree and the latter as a network. The team used phylogenetic methods that simultaneously consider the vertical and horizontal transmission of genes and found that, on average, genes travel vertically two-thirds of the time, suggesting that a tree provides a meaningful framework for interpreting bacterial evolution. University of Bristol, “Rooted tree key to understanding bacterial evolution, new study suggests” at Eurekalert
See also: Horizontal gene transfer: Sorry, Darwin, it’s not your evolution any more.