While some microbes are tiny, others can be monumental.
It’s impossible to know for certain, but we’ve seen back-of-the-envelope estimates that suggest there may only be around 1,000 people in the US whose height is over 7 feet.
Although humans come in a variety of shapes and sizes, heights tend to fall into a relatively narrow band, which probably explains why we tend to notice people when they’re a lot taller than average.
But how would things look if you were an average bacterium?
Would other species appear to be around your own size?
Or might they seem a lot bigger, or smaller, than you?
Well, if you were a person of average height, who’d been scaled down to the size of an E. coli cell, the world’s largest bacterium would be a whopping 100 times larger than you.
It would be about the height of the Washington Monument, in fact, and that’s a pretty sizeable differential.
You probably wouldn’t want to pick a fight with it.
Before we investigate this mega-microbe in more detail, let’s look briefly at the unit of measurement that’s used when we need to size-up tiny organisms.
We’re talking about the micrometer, to use the American spelling, or the micrometre in other parts of the world.
Using the US form is slightly confusing, as a micrometer is also the name of the screw gauge device often used in mechanical engineering for precise measurement of small – but not microscopic – items.
The micrometer used for bacterial measurement, however, is sometimes also known as micron, and represents one millionth of a metre, or one thousandth of a millimetre.
It’s generally written using the Greek letter µ, or “mu”, the word micro coming from the Greek mikrós, which means small.
By the way, if you want to produce a µ on a computer, it’s Option-M on a Mac, or if you’re on Windows hold down the Alt key, and type 0181 on the numeric keypad.
Now we’ve pinned down our measuring unit, let’s consider the biggest and smallest in the world of microorganisms.
That E. coli cell that we’ve already referenced has a rod-shaped appearance that’s around seven micrometers in length.
One of the smallest bacterial species is actually not much tinier than this.
Haemophilus influenzae was originally, and wrongly, thought to cause influenza.
False accusations aside, it has legitimately earned itself a slot on the small end of the size scale, being between 0.5 and two micrometers long.
Interestingly, despite its tiny size, it’s around the smallest object that is visible through a light microscope. Any smaller, and you’d need an electron microscope.
What about the other end of the scale, though?
If there was a Guinness World Record for largest bacterial cell, which species would carry it off?
Well, for six years beginning in 1993, it looked as though the award would be held by a microorganism called Epulopiscium fishelsoni, which researchers discovered in the gut of the brown surgeonfish.
Epulopiscium means “guest at a banquet of fish.”
E. fishelsoni’s cells are an extraordinary 600 micrometers long – over half a millimeter, which is about the length of a hyphen in some printed texts, and definitely visible to the naked eye.
Prior to 1993, it had been hypothesized that bacteria couldn’t be this large, because as cell size increases, the ratio between size and surface area decreases.
And surface area is critical to microorganisms, since a cell absorbs vital nutrients through its surface, so in theory large organisms wouldn’t be able to get enough nutrients to enable their survival.
Luckily, E. fishelsoni has a trick up its sleeve.
Its unfeasibly wrinkled sleeve, to be precise.
Just like the surface of a brain, the outer membrane of the cell contains many folds, increasing its effective surface area.
E. fishelsoni is unusual in another in another way.
Bacteria generally reproduce through a process known as binary fission, when one cell divides into two.
E. fishelsoni, however, goes about reproduction in a totally different way.
Don’t worry, it’s SFW.
Between one and twelve daughter cells grow inside one parent cell, before the parent lyses and dies.
Despite its unique characteristics, E. fishelsoni’s reign at the top of the size spectrum didn’t last all that long after its 1993 discovery.
In 1999, a group of German, Spanish, and American scientists found a bacterium that was even larger, responsible for our earlier Human vs. Washington Monument matchup.
Thiomargarita namibiensis was discovered in sediment off the coast of Namibia.
Its name means “sulfur pearl of Namibia,” since T. namibiensis has a form similar to a string of pearls.
But what a string it is, measuring a highly visible 750 micrometers – three quarters of a millimetre.
Returning to our person the size of an E. coli cell, this string of pearls would stretch 530 feet long, the length of the 17th hole at Pebble Beach, where a well-known golfer famously hit the pin in the 1972 US Open.
This superstar golfer’s name?
Why, Jack Necklace, of course.