Lessons from Nature's motors

How does the machine that enables bacteria to swim actually work?

Matt Baker of Oxford's Department of Physics and colleagues are investigating this machine: known as the bacterial flagellar motor.

Matt recently became a NOISEmaker and is helping to explain the wonders of  thrashing bacteria, as well as spoken word poetry, MCing and fencing, to school students (read his NOISE blog for more). I asked him about Nature's motors and his first taste of science communication:

OxSciBlog: How does the bacterial flagellar motor compare to manmade motors?
Matt: Baker: The Bacterial Flagellar Motor (BFM) is only 40 nanometres (nm) across, approximately one-thousand times smaller than the smallest speck of dust, and can rotate at up to 40,000 revolutions per minute (rpm). By comparison, Formula One engines are metres in size and are can operate at 20,000 rpm, and some jet engines rotate at 150,000 rpm.

The BFM can not only rotate very fast, it can also change direction of rotation in thousandths of a second, and it is this ability to switch the direction of rotation which enables bacteria to navigate their environment, moving in alternating ‘runs’ and ‘tumbles’ toward areas of high nutrient.

We aren’t able to make a motor anything like the BFM at the moment, in terms of size and structure, speed and function, and yet this motor assembles itself in the cell membrane and is responsible for one of the oldest sources of motility on the planet.

OSB: What are you hoping your investigations will reveal about it?
MB: Our group work on resolving the discrete steps that constitute this rotation. Rather than spinning smoothly, the rotation of the BFM is made up of tiny 14 degree steps, which, when the motor is moving fast, appear continuous.

Personally I have built a temperature controller to explore the motor’s rotation at high and low temperatures, to investigate how the speed and energy source change with temperature, and in the future to explore how the frequency, size, and distribution of steps may change.

OSB: How do we think the environment affects the motor's behaviour?
MB: The motor is powered by an ion gradient, that is, protons or sodium ions, depending on the type of bacteria, flowing from outside the cell, at high concentration, to inside the cell, at low concentration.

So the environment and the concentration of salt or the pH of the solution, affect the amount of energy available to the motor. In different environments it has different amounts of energy available and will rotate at different speeds, driving different loads.

OSB: How might what you find inform the creation of new technologies/devices?
MB: Motor proteins convert chemical energy into mechanical force, and this is the basis of movement, which is essential to life. They are found in myriad places such as muscles (myosins), inside cells (kinesins/dyneins) and in the rotary motor of bacteria.

Currently we aren’t able to build dynamic motors that are only 40nm in diameter, or composed of 45 different types of self assembling proteins, that can convert chemical energy into a mechanical rotation. Part of learning to develop these motors is understanding how these biological motors function, how they have evolved, and then adapting these learned lessons.

One approach is to use components of these motors to make new motors, such as the chimeric motor used by our group that is powered by sodium ions, or to use cobbled together parts of other rotary motors to build synthetic swimmers. Investigations like this allow us to begin to dream about the day where we might be able to build a protein motor for a specific task.

OSB: What's been the highlight of being a NOISEmaker so far?
MB: Being a NOISEmaker has introduced me to a great group of people that are doing interesting science, that is relevant to the community, and are excellent at communicating and explaining their research. It’s also taught me a lot about how to present your research to the public and to the media. It’s been a great window into the world of public relations, with which I had no familiarity, and also it has helped me meet some interesting people that I hope to work with in the future.

The highlight, so far, has been an introductory day where we brainstormed some ideas for novel ways of bringing science into the public, and then being able to try some of these ideas out at a festival called Underage where we presented different aspects of science to 15 year-olds.

Ecoli showing bacterial flagellar motor in action, image: National Science Foundation. Video taken by Mostyn Brown, Department of Physics.