Animalcules and Their Motors

Summary

In 1674, a Dutch cloth merchant in Delft, Antoni van Leeuwenhoek, spent his free time tinkering with lenses. One day, he pressed a drop of rainwater beneath his homemade microscope and observed what he called “animalcules” darting about. Leeuwenhoek described these creatures in two letters he sent to the Royal Society in London for publication, each replete with charming descriptions:[T]he motion of most of these animalcules in the water was so swift, and so various upwards, downwards and round about that ‘twas wonderful to see: and I judged that some of these little creatures were above a thousand times smaller than the smallest ones I have ever yet seen upon the rind of cheese.Leeuwenhoek may have been the first person to see microbes in motion, but his microscopes weren’t powerful enough to see the actual machinery responsible. (Leeuwenhoek mused that his animalcules might be using “little paws” to move.) It wasn’t until the 1830s that a German naturalist, Christian Gottfried Ehrenberg, saw whisker-like appendages, later named flagella, protruding from microbes. Still, the mechanism by which they worked remained unknown until the latter half of the 20th century, when electron microscopes finally homed in on the thousands of proteins that make a flagellar motor, able to convert flowing protons into mechanical motion.A microscope crafted and used by Leeuwenhoek. Upon his death, Leeuwenhoek left behind hundreds of microscopes, only nine of which have survived to the present. Credit: Wellcome Collection/WikimediaOne of Leeuwenhoek’s earliest sketches of animalcules. Note the dotted lines, suggesting movement.Even more recently, a surge of research has revealed how evolution has finetuned the flagellum to operate in vastly different ways based on a cell’s niche. Whereas an E. coli flagellum spins around nearly 20,000 times per minute, the flagellum in a microbe called Vibrio alginolyticus spins about five times faster, or slightly more than 100,000 times per minute. (...