Bacterial Flagella—Icon of the Intelligent Design Movement

Magnificent and Miraculous Microbes

There are many extraordinary examples of design in the microbial world. In this chapter, two examples are given: the bacterial flagella and the production of a blood red pigment in Serratia marcescens. The molecular machinery of the bacterial flagella is magnificent. The amazing ability for Serratia marcescens, a rod-shaped bacterium, to produce a pigment that resembles blood is “miraculous.”

Bacterial Flagella—Icon of the Intelligent Design Movement

We begin with Michael Behe who made the bacterial flagellum a popular argument for intelligent design in Darwin’s Black Box, using them to illustrate the concept of irreducible complexity. The flagellum is a corkscrew-shaped, hair-like appendage attached to the cell surface acting like a propeller, allowing the bacterium to swim.

The bacterial flagellum is an irreducibly complex process. An irreducibly complex system is one that requires several interlacing parts to be present at the same time, where the removal of one or more parts causes the whole system to malfunction. Destroy one part and the whole system falls apart. The purported mechanism of evolution, on the other hand, is that a new trait will confer a selective survival advantage, and thus enable its possessors to compete better than organisms without the trait. In neo-Darwinian evolution, a new trait would have to be completely developed—no halfway measures would do. Given this requirement, new features are so complex that neo-Darwinian gradualism is very improbable because an incompletely developed trait would offer no selective advantage.

The Mousetrap Example

Dr. Michael J. Behe, biochemistry professor and author of the 1996 blockbuster book Darwin’s Black Box, has challenged the classical neo-Darwinian explanation that intricate cell structures arose by chance. In the book, he uses the flagellum to introduce the concept of “irreducible complexity.” If a structure is so complex that all its parts must initially be present in a suitably functioning manner, it is said to be irreducibly complex. All the parts of a bacterial flagellum must be present from the start in order to function at all. According to Darwinian theory, any component that doesn’t offer an advantage to an organism (i.e., doesn’t function) will be lost or discarded. How such a structure could have evolved in a gradual, step-by-step process as required by classical Darwinian evolution is an insurmountable obstacle to evolutionists. How a flagellum is used, however, adds an additional level of complexity to the picture.

Some bacteria have a single flagellum located at the end of a rod-shaped cell. To move in an opposite direction, a bacterium simply changes the direction the flagellum rotates. Other bacteria have a flagellum at both ends of the cell, using one for going in one direction and the other for going in the opposite direction. A third group of bacteria has many flagella surrounding the cell. They wrap themselves together in a helical bundle at one end of the cell and rotate in unison to move the cell in one direction. To change direction, the flagella unwrap, move to the opposite end of the cell, reform the bundle, and again rotate in a coordinated fashion. The structural complexity and finely tuned coordination of flagella attests to the work of a Master Engineer who designed and created flagella to function in a wonderfully intricate manner.

You might call it the Maker’s molecular outboard motor. Its most interesting aspect is that it is attached to and rotated by a tiny, electrical “motor” made of different kinds of protein. Like an electrical motor, the flagellum contains a rod (drive shaft), a hook (universal joint), L- and P-rings (bushings/bearings), S- and M-rings (rotor), and a C-ring and stud (stator). The flagellar filament (propeller) is attached to the flagellar motor via the hook. To function completely, the flagellum requires over 40 different proteins. The electrical power driving the motor is supplied by the voltage difference developed across the cell membrane. This motor is one of the nature’s best molecular machines!

Some scientists have called bacterial flagella the “most efficient machine in the universe” with its self assembly and repair, water-cooled rotary engine, proton motive-force drive system, forward and reverse gears, operating speeds of 6,000 to 17,000 rpm, direction-reversing capability, and hard-wired signal-transduction system with short-term memory.

Bacterial Flagellum: Paradigm for Design in Yersinia, Example 1

After Michael Behe made the bacterial flagellum a popular argument for intelligent design in Darwin’s Black Box, Scott Minnich joined the ranks of the intelligent design movement. Dr. Minnich, a geneticist and associate professor of microbiology at the University of Idaho, takes the argument to the next level by describing how this design paradigm led to new insights in his research. Minnich has been studying bacterial flagella for over 15 years and has published work in the following areas: the structure and function of flagella in Yersinia and Salmonella species; assembly blueprints and genetic instructions; detail descriptions of the transcriptional and translational regulator genes; and integrating motility with signal transduction (chemotaxis).

Yersinia enterocolitica

In extensive research, Scott Minnich has discovered that bacterial flagella provide a paradigm for design. Minnich has been working with the genetics and flagella structure of Yersinia enterocolitica (cousin of Yersinia pestis, pathogen of bubonic plague) for more than a decade. Y. enterocolitica, a cause of foodborne infection (like E. coli or Campylobacter) is commonly found in the intestines of livestock. It causes food infections due to contaminated meat and dairy products. It causes enteric fever and may produce severe, life-threatening infections.

After describing over 30 individual proteins that make up its rotary-motor mechanism (close to 50 in the entire flagellum), Minnich noticed that the basal body of the flagellum produced a toxic secretion when the bacterium was under stress. If Yersinia was kept “happy” at 20 ºC (68 ºF) and in good environmental conditions (i.e., low osmotic saline), the basal body produced a hook and filament—the remaining portions of the flagellum. Minnich had predicted from his genetic studies that a good design would be used for diverse purposes, like engineer-designed structures that serve dual functions. It is good genetic efficiency or optimal genetic design (minimum cost/benefit ratio). Even before observing this in humans, he predicted what would happen.

Yersinia was quite motile in its environment and could propel its rotary motor at up to 100 rpm. On the other hand, if Yersinia were incubated at 37 ºC (98.6 ºF) (or another stressful environment like high salt), the basal body acted as a “cannon,” producing a harsh toxin. (Its technical name is a Type III secretion system. It is described in more detail in chapter 9, “The Origin of Infectious Disease”). In observing cells from the gastrointestinal tract, it was observed to avoid engulfment by macrophages. In its own defense, Yersinia produced a missile to avoid being eaten by human body defenses. The utility of a design model (instead of a Darwinian one) not only produced good science, but also has practical implications for medical microbiology and clinical medicine. Here we see evidence that design models accurately predict biological outcomes. Thinking God’s thoughts after Him and openness to the idea that the Creator has made biological structures with purpose is the key to success in biological study. Evidence, not evolution. Creation, not chance. Design theory works. The bacterial flagellum is truly one of Providence’s prokaryotic wonders!

Yersinia enterocolitica: Biological Rotary Motor

The sensory and motor mechanism of the E. coli bacterium consists of a number of receptors, which initially detect the concentrations of a variety of chemicals. Secondary components extract information from these sensors that in turn is used as input to a gradient sensing mechanism. The output of this mechanism is used to drive a set of constant torque proton-powered reversible rotary motors, which transfer their energy through a microscopic drive train and propel helical flagella from 30,000 to 100,000 rpm. This highly integrated system allows the bacterium to migrate at the rate of approximately ten body lengths per second.

How fast do bacteria move with their flagella? Some have been “clocked” at up to 100 µm per second, or the equivalent of 50 body lengths per second. By comparison, bacteria move twice as fast as the cheetah, the fastest known animal. Cheetahs, which run up to 70 mph, go a mere 25 body lengths per second. Generally, bacteria with polar flagella move faster than those with peritrichous (many) flagella.

The complexity of the bacterial flagellum is direct evidence against neo-Darwinian evolution. All the interwoven parts of the body point to an intelligent Creator. In the early 1990s, Dr. Michael Behe argued for the intelligent design of the human body. His argument is called the principle of irreducible complexity. To illustrate the complex nature of this principle, one needs to look at the design in driving.

Driving by Design—E. coli Swimming Lessons

The sensory and motor mechanism of the E. coli illustration

Microbiology is fun to study because the behavior of E. coli is increasingly being shown to be complex. Recent observation takes the argument of microbes by design to the next level by describing how new research has provided insight into how E. coli “drive” more orderly than some people. Harvard researchers have recently discovered that E. coli swim on the right side. The motion of E. coli is not random; it is directed, ordered, and reminds one of car traffic patterns (or even ant traffic patterns). When cells are confined to microchannels with soft agar floors made of hydrogels, they preferentially swim on the right hand side and closer to the floor of the gels. Bacteria are known to have clockwise, circular trajectories along surfaces; yet in free solution, they swim in random walk trajectories. All of these features seem to shout “design”!

In human terms, driving properly to avoid accidents takes driver’s education school, intelligence, and practice. It is certainly not by random chance, nor accidental. A recent article shows E. coli driving on the right side, meaning that when placed in narrow forked tubes, they are more likely to swim up the right-hand fork, due to the anticlockwise direction in which the flagella rotate. This is more than just “fascinating fact” information; it may have clinical implications for urinary tract infections. E. coli can also cooperatively move over surfaces, called swimming. It is more than just congregating. During extended periods of migration, bacteria cells move better on gel surfaces than a solid surface. This observation, combined with the ability of directed traffic, may allow new explorations of behavior studies of factors that contribute to bacterial pathogenicity.