Researchers: The last bacterial common ancestor had a flagellum

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Gene transfers (movement of genes between bacterial lineages) have hampered traditional efforts to study bacterial evolution in deep time. Coleman et al. used a new method that combines the vertical and horizontal components of bacterial evolution to draw inferences about the the nature of the earliest Bacteria and the deepest divides in the bacterial tree/Gergely J. Szöll?si

The paper at Science seems paywalled but here it is at BioarXiv and here’s a pdf.

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?

That said, it’s nice to see horizontal gene transfer getting proper recognition:

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.

Comments

Regarding any theory about any last common ancestor, I'm not calling it proven, let alone a legitimate basis for further theorization, until we have one sitting in a laboratory where we can examine it. EvilSnack

It's difficult to trace a family tree, either horizontally or vertically, when you don't know all the branches. With larger animals and plants, fossils show the branches that have gone extinct, so we can extrapolate back from them along with the living branches. With bacteria, major groups or types have undoubtedly been lost with no possibility of tracing what they looked like. polistra

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