#134 – The bacterial flagellum according to an expert

A scientist who specifically studies the bacterial flagellum using some of the most cutting-edge research tools clears up a few myths and misconceptions.

Much of Dr. Michael Behe’s defense of Intelligent Design rests on claims made about the bacterial flagellum. It certainly has become his signature, and one could even say it’s become the symbol or mascot of the ID movement (like the polar bear became for the global warming movement). Some of his claims are often challenged by opponents of ID. To shed some light on the subject, we reached out to several scientists who actually work with the bacterial flagellum (Behe does not). Here, we speak to Dr. Nicholas Mitzke, who gives us a basic introduction to this bacterial machine, demystifying it and clearing up some misconceptions that have been built up around it. Points that we discussed included:

• misconception #1: the flagellum is not just one unique thing that cannot be altered in any way without completely losing its function. There are in fact thousands of different versions of the flagellum, each with differences in their amino acid sequence (which necessarily means their gene sequence was changed), and some of them are even missing certain protein parts, and yet all of these altered versions retain their function.
• misconception #2: the flagellum did not in fact arise through a series of intermediate steps, each intermediate being non-functional, before finally becoming a functional machine. Instead, we’re now getting glimpses of its evolutionary journey through various stages of different functionality.
• proteins in general can evolve, changing amino acid sequences in many ways, and yet retain their original shape, and therefore full function
• how the rotary engine in the flagellum converts chemical energy into a rotational movement; it uses an acid battery that spins an “electric” rotor
• the flagellum is made of multiple copies of 20 proteins; 99% of the flagellum is the long whip (tens of thousands of copies of one particular protein); the other 19 proteins are at the base of the flagellum, forming one machine that creates the flagellum (the “type III secretion system”) and another machine that rotates the flagellum (the motor).
• misconception #3: given the statement above, the type III secretion system is NOT a “devolved” flagellum
• misconception #4: cellular machines (like the flagellum) do not need a mechanic to assemble the different parts into a functional machine (a misconception based on our familiarity with human-made machines). Instead, cellular machines can make themselves!? Self assembly!!! [we talked about this in detail in episode #131]
• misconception #5: the flagellum motor does not work through pistons, gears, fan-belts, and other such moving parts (as might be misconstrued by the frequent references to the flagellum being “like the outboard engine of a boat”). Instead, they work through a series of simple shape-shifts … the protein parts just bend a bit this way or that, causing other subtle shape-shifts in their neighbors.
• we introduced another bacterial machine called the ATP-synthase, because this will become a key star in next week’s episode about the evolutionary origin story of the flagellum. It’s basically two small machines combined into one: an ion pump, and an energy molecule factory.
• we heard a very condensed version of that evolutionary origin story, one that links three very different bacterial machines (the type III secretion system, ATP synthase, and the flagellum), in order to whet listener’s appetite for next week’s episode. This story is very much like someone encountering a complete stranger, noticing some absolutely striking resemblances in facial features, and finding out that the stranger is a cousin/sibling they never knew about.

As always, tell us your thoughts on this topic.

To learn more about our guest expert, visit his faculty profile page.

If you enjoyed this episode, make sure you’ve listened to our interview with Michael Behe (or listen to it again, now that you’ve been informed). Also, if you haven’t already heard the other episodes in this mini-series, you might benefit from our basic introductions to how genes and proteins work.

Episode image by Raman Oza from Pixabay.

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