Swimming Bacteria Knit Hat

My latest science knit shows rod shaped bacteria swimming around the brim of the hat. The pattern for this hat can be found here on Ravelry or purchased directly here. 

These bacteria could be Escherichia coli or Bacillus subtilis or any other rod-shaped bacteria that have flagella over their body. 

Flagella behavior during tumbling and swimming

The flagella on these bacteria are peritrichous, which mean they surround the cell. The flagella are controlled by a molecular motor and the motor can either spin clockwise or counterclockwise. When all of the flagella on the cell spin counterclockwise, the flagella can propel the cell, as shown on this hat. When the flagella spin clockwise, they spread out and thus have no net force so cannot propel the cell anywhere. Instead of going in a direction, these cells “tumble” and basically somersault in the same place to change direction so when the flagella spin the other way again, they can set out in a different direction. These periods of “running and tumbling” allow the bacterium to explore its environment. During this exploration, when a bacterium is swimming toward nutrients, it can adjust the durations of running and tumbling so it is running for longer periods and tumbling less, thus biasing the movement toward the nutrients, in a process that is called “chemotaxis.” The bacteria on my hat are all swimming, although I considered making a version of the hat with tumbling cells as well. 

See the movie below for a video that I took of my favorite bacterium Bacillus subtilis. Some cells are stationary as they are stuck between an agar pad and a glass coverslip while others are in an area that is a bit wetter and they can swim around. This is best viewed fullscreen to better see the little organisms. It is a very short video, so you may have to hit replay to catch the action.

Full disclosure: this video was the result of an experiment that did not work. I didn't let the microscope slide dry enough before imaging and my bacteria were still swimming around. I made the most of the situation and filmed my swimming bacteria for this blog post (and I repeated the experiment to get the information I was looking for). Experiments often do not work or give inconclusive results - we as researchers learn to deal with failure very well and just keep plugging along and listening to the data to learn about the world around us. It is fascinating!