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Harvard Biophysicist Howard Berg, Flagellum’s Discoverer, Lives On

David Coppedge
irreducible complexity
Image: Bacterial flagellar motor, from Unlocking the Mystery of Life, Illustra Media.

Howard C. Berg (1934-2021) passed away on December 31, 2021 at the age of 87. More than any other scientist, he brought to light the intricate biophysics occurring at the molecular scale in living organisms, particularly the peritrichous (multi-flagellated) bacterium Escherichia coli. Of his 120 scientific publications, he was most proud of his 1973 paper in Nature with the title “Bacteria swim by rotating their flagellar filaments.” It was the first known case of rotation in a biological organism — something other biologists had thought was impossible. 

At the end of that paper, Berg and Robert C. Anderson state, “If, as suggested by existing evidence, bacterial flagella rotate, the structures at the base of the flagellum deserve more attention than they have received thus far.” Since then, those structures were found to contain rotors, stators, a universal joint, and other components made of hundreds of proteins of twenty different types. Other examples of rotating biological motors have also been found: the archaeullum in archaea, and ATP synthase in all living organisms.

Whether he intended to or not, Berg helped propel the intelligent design movement. Who could look at a mechanical outboard motor and say it was a work of chance? Michael Behe couldn’t. Some of the first electron microscope images of the flagellum, undoubtedly from the Harvard lab, spoke for themselves: “That’s an outboard motor. That’s designed!” Behe might well have thought. “That’s no chance assemblage of parts.” The flagellum must have spoken to Berg himself to some degree. According to Scott Minnich in Unlocking the Mystery of Life, Howard Berg labeled the bacterial flagellum “the most efficient machine in the universe.” But how enthusiastic was this scientist about a mechanical marvel he spent his career observing?

“Died with His Boots On”

The tributes to Dr. Berg, such as one at Harvard’s website and another posted at The Scientist, describe him as both a hard-working and congenial character who “died with his boots on,” continuing his research to the end. This was echoed by another tribute in Current Biology. As a designer of equipment for observation, Berg was without peer. To follow the little creatures, he designed a microscope with servo motors that could follow a bacterium along three axes. 

Howard incessantly modified and improved the tracking microscope over the years, which gave him ample reason to visit the machine shop. He also built electrical and mechanical devices for performing various laboratory functions, including a foot-actuated plate-pourer and a Western blotting machine that had to be operated at its lowest setting lest it drive the proteins entirely through the membrane. The machine shop was his refuge — perhaps to the disappointment of his family. 

When cryo-electron microscopy was invented, allowing imaging of the flagellum at the molecular scale, Berg must have relished the high-resolution views compared to the fuzzy ones he first peered at in the 1970s. 

Assuming Evolution

There is no indication that Howard Berg ever strayed from the standard materialistic dogmas of evolution so prominent in academia. His last paper, a review article in Nature about bacterial motility published last year, assumes evolution four times:

  • “… bacteria have evolved several motility mechanisms…”
  • “… diverse bacteria… each have evolved distinct molecular mechanisms….”
  • “[two species] are not closely related, which indicates convergent evolution….”
  • “The evolutionary success … is likely to stem from its generality….” (Emphasis added.)

To what extent these are his statements or those of his co-author, Navish Wadhwa, I don’t know. Nor do I know what he thought about the intelligent design movement using the bacterial flagellum as an icon of design — a fact that could hardly have escaped his notice. Berg’s opinions about evolution, though, do not change the reality that the bacterial flagellum is a sophisticated molecular motor displaying irreducible complexity. It was already there waiting to be discovered. Berg simply found the right evidence, opening a path for many other scientists to look and wonder, like the scores of visitors who had come to Antony van Leeuwenhoek’s shop 300 years earlier to see the little “animalcules” (a wordplay on “molecules”) the Dutch merchant had discovered. What satisfaction Berg must have felt comparing his eyepiece with that of van Leeuwenhoek’s little hand-held device with which he had become the first one to witness bacteria swimming in liquid.

Almost No Inertia

Berg mentions Antony van Leeuwenhoek in a 30-minute video about bacterial motility posted at Harvard University’s website and on YouTube, recorded in 2014. He even holds up a replica of the small device and describes its excellent optics. In Part 2 of his lecture on YouTube, he gives more detail about the structure of the flagellum and its operation. One interesting aspect of the flagellum many ID advocates may not realize is that the viscosity of water at the scale of a bacterium is very high. The Reynolds number (a dimensionless number correlating inertia to viscosity) is extremely low, which means that a bacterium like E. coli experiences almost no inertia in water. When the motor stops rotating, the bacterium stops moving. To keep from being buffeted by Brownian motion, the flagellum must overcome several physical constraints.

Berg describes these counterintuitive properties of water at the molecular level and shows how the spiral shape of the filament is optimized for motility in such conditions. He also explains why the run-and-tumble strategy is the best for following a concentration gradient at that scale. The flagellar motor itself, as we know, exhibits irreducible complexity enough, but it is also regulated by a signal transduction system composed of other machines that monitor concentrations of desirable or undesirable substances and guide the motor toward or away from them by changing the direction of its rotation. (How this works in peritrichous bacteria with bundles of flagella working together looks like a good research project for design scientists.)

Additional Optimization Perfections

Dr. Berg describes additional optimization perfections, such as the manner in which protein building blocks are injected through the hollow filament to the tip when the flagellum is built or repaired. These molecules barely fit through the filament, like pistons in a cylinder, but move quickly and efficiently to the tip, he explains, because of the time intervals between their insertion. The tribute in Current Biology mentions a final encore to his work:

At the age of 87, he was awarded an NSF grant to test experimentally the prediction that the stator unit that drives rotation of the bacterial flagellum is itself a rotary machine. This work will be carried on by the remaining members of his lab under the supervision of a former student of Howard’s, Aravinthan Samuel, now a Professor of Physics at Harvard.

All of these properties of the flagellar motor shout design, but in the videos, Berg speaks in a subdued tone about them, sharing his graphs and experimental results in academic vernacular. He ends by saying, with only a modest and calm modicum of delight, 

E. coli has a large number of tricks; it’s been fiddling around for billions of years. And we keep finding these things, and they’re surprising, because we hadn’t imagined that they occur, but E. coli is smarter than we are.

It was probably his normal disposition as a scientist to exercise moderation, or perhaps he was a little camera-shy while being recorded for the iBiology channel. But it’s hard to conceive of a scientist this close to a prime example of biological engineering not being excited about it. Curiosity must have driven him to devote so much of his life’s work to this biological marvel, but who knows why he didn’t jump from his eyepiece and shout “That’s an outboard motor!” There’s also a remote possibility that he didn’t want to express too much passion about what had become an icon of intelligent design. 

He might have outsourced his own ebullience to van Leeuwenhoek, whom he quoted at the beginning of Part 1. In a translation by biographer Clifford Dobell, the Dutch merchant said, 

This was for me, among all the marvels that I have discovered in nature, the most marvelous of all; and I must say, for my part, that no more pleasant sight has ever yet come before my eyes than these many thousands of living creatures, seen all alive in a drop of water, moving among one another, each several creature having its own proper motion.

So even with his restrained, matter-of-fact manner, Howard Berg may have internally shared that feeling with his predecessor.

Further Reading

Want to learn more? Howard Berg wrote two books available on Amazon: 

Random Walks in Biology (1993) has five-star ratings on Amazon by laymen. It appears devoted to physical concepts related to bacterial motility, not matters of origins.

E. coli in Motion (2004) is a more technical (and expensive) book. Springer-Link gives the table of contents and this abstract from the Epilogue:

I have told you some things about a free-living organism only one micron in size. It is equipped with sensors that count molecules of interest in its environment, coupled to a readout device that computes whether these counts are going up or down. The output is an intracellular signal that modulates the direction of rotation of a set of rotary engines, each turning a propeller with variable pitch. Each engine (or motor) is driven, in turn, by several force-generating elements (like pistons), powered by a transmembrane ion flux. In addition to a gear shift(labeled forward and reverse but prone to shift on its own) there is a stator, a rotor, a drive shaft, a bushing, and a universal joint.

The site also displays a portion of his Chapter 12, “Rotary Motor,” where he calls the flagellum motor “a nanotechnologist’s dream (or nightmare).” There are additional excerpts from other chapters, such as “Flagellar Motion” and “Optimal Control.”

Some of Dr. Berg’s 120 scientific papers can also be consulted. His 1973 paper is behind a paywall at Nature.

Or see the website of Berg’s lab at Harvard, with a statement about its research goals.