#135 – The expert’s fascinating version of how the flagellum really came to be

Three internationally-recognized, world experts on the bacterial flagellum connect the dots regarding the evolutionary origin of the flagellum, and draw some compelling comparisons to the evolutionary emergence of the Bible!

Three episodes ago, Dr. Michael Behe used the bacterial flagellum as Exhibit A in his defense of the Intelligent Design proposal. Last week, we heard Dr. Nicholas Matzke, who actually does cutting edge research on the flagellum, give his understanding of the bacterial flagellum, with comparisons to claims frequently made by the ID community.

In this episode, we hear three world-leading scientific experts on the flagellum discussing the latest scientific data on an amazing evolutionary journey which seems to explain the origin of the flagellum. Those three are Drs. Matthew Baker (University of New South Wales, Australia), Mark Pallen (University of East Anglia, UK), and Nick Matzke (University of Aukland, New Zealand).

Some of the technical points they discussed include:

• how to make direct measurements of individual flagellum motors freshly isolated from a test tube of bacteria
• why is there so much interest in the bacterial flagellum ….. why have so many researchers using such high-tech equipment studied this thing?
• the flagellum is not just one unchangeable thing (as ID proponents will often suggest); instead, the broad scientific community agrees that there are MANY different kinds of bacterial flagella (hundreds of thousands), each with different genetic sequences, and some of which seem to be missing parts, and yet still work for their hosts
• at the heart of two bacterial nanomachines there is a third nanomachine called “the type III secretion system” whose function is to squirt out proteins; the one in the flagellum squirts out the proteins that make the long propellor whip, while the one in “the injectosome” squirts out the toxins that the bacteria uses to capture its prey
• these are two examples of machines built on top of machines – Mark referred to it as “a modular system”
• there is yet another bacterial nanomachine — “the “ATP-synthase” — whose function it is to generate energy molecules called ATP; given how fundamental this function is, ATP-synthase is probably one of the oldest of cellular machines
• there are many striking similarities (genetic; structural; functional) between ATP-synthase and the type III secretory system, which suggests a common ancestral origin; in other words, those two very different enzymes seem to have both descended from yet another earlier enzymatic precursor
• there is some reason to suggest that the precursor for the type III secretory system (and for ATP-synthase) might have been related to one that modifies RNA, an enzyme called RNA-helicase; one of those reasons is the fact that all three are made up of six globular proteins that form a ring wrapped around a central filament of protein (in the case of the type III secretory system) or a filament of RNA (in the case of RNA-helicase), and all three spin like rotary motors as they do their job
• the type III secretory system is NOT a devolved bacterial flagellum (as ID proponents will often claim)

Altogether, the evidence starts to point to a possible scenario involving a recurring theme of gene duplication with subsequent modification of the copies, followed by selection for a useful function:

• an ancient primordial gene for an enzyme that comprised a rotary motor that spins around some filament was duplicated
• those two primordial gene copies morphed and diverged such that one specialized for RNA (the helicase) and the other specialized for proteins (becoming a generic protein pump)
• somewhere in that transition, one of those two new genes duplicated, and the resulting copy started to code for a rotary engine that ran in reverse and latched onto a protein to drive it to generate ATP (ATP synthase)
• the gene for the generic protein pump was duplicated and the copies began to specialize for pumping certain subsets of proteins … one for flagellar proteins (thereby becoming a propellor, the bacterial flagellum) …. and the other one for toxins (thereby becoming a weapon, the injectosome)

Parts of this story are more speculative than others, but the emerging picture is looking quite clear that the bacterial flagellum is the product of a long evolutionary journey. That hypothesis then prompts new research questions which flesh out the details of this evolutionary journey. There was an extended conversation about how genes/proteins can change/morph over time and take on entirely new functions …. and how this phenomenon is precisely paralleled by the evolution of language (the words loyal, legal, and lawful all have a common ancestral origin), and even of the Bible itself!

I asked our guests to comment on Michael Behe’s claim that secular scientists themselves are doing the scientific work of Intelligent Design by “doing their experiments from a Design perspective without calling it that.” Admittedly, it’s pretty hard for scientists to say anything about evolution without using wording such as “this protein/trait is designed to enable the animal to XYZ” or “this organism evolved toward being able to XYZ.” This is goal-oriented language … wording that conveys purpose, meaning, direction, guidance … otherwise known as “teleological” language. One response to this assertion was that it can also be “sloppy language,” just like humans have the tendency to refer to Earth as “her” or to a truck as “him.”

I also asked our guests if it is possible to meet the ID proponents in the middle by saying that there is indeed “a designer”, but that designer is the cell itself (which orchestrates the genetic changes) and evolutionary pressures (which select out the good stuff). One guest replied provocatively, but entirely legitimately, that if ID proponents insist on personifying “the designer” by referring to him/her/it as intelligent, then how do they explain the flagellum being so well designed to move the bacterium around through the human host’s body in order to mediate such nasty, devastating, destructive disease outcomes.

Interesting conversation indeed!

As always, tell us your thoughts on this topic …

Find more information about our guests at Nicholas Matzke’s profile, Mark Pallen’s profile, and Matthew Baker’s profile.

Episode image by Arek Socha from Pixabay.

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