I just read something that mentioned spirochetes and it rekindled an old question of mine.
Is there any biological reason for those bacteria to be so screwy? For example it looks like it may make reproduction by cell division complicated; so there must be an evolutionary advantage to that shape, but it completely eludes me.
Obviously, the spiral structure of a spirochete enhances reproductive success. It would appear that there are more factors in play than the increased complexity of cell division.
Spirochetes have a long set of flagella that run down their insides, and when these rotate, the entire creature rotates about its long axis. When that happens, the spiral corkscrew shape makes it move forward (or backward), much as rotating a corkscrew moves it forward or backward. So the spiral shape is key to their ability to move.
But why move this way? Why not just thrash a flagellum out the back like an outboard motor? Here we get into some subtlety about motion in water at very small distance scales. It turn out swimming in water when you are 1 micron in size is high Reynolds number motion. That is, it’s comparable to a 1m size animal swimming in glue or tar. A fast reciprocating motion is less efficient at propulsion, because the fluid “sticks” to the moving bit on the backstroke, and provides just as much backward propulsion as the forward stroke provides forward propulsion. Result, you go nowhere. The most efficient mode of swimming in high Reynolds number situations is to ooze or wriggle through the water, without any violent motion, and applying a continuous pressure on the fluid. The amoeba takes the oozing route. The spirochete takes the wriggle route. This makes it so efficient at motion through sticky thick fluid that it can even swim through fluids that are otherwise too viscous for ordinary bacteria, which gives it an advantage – it can hide out in protoplasm that is unusually full of non-water components, where immune systems rarely patrol.
I see, I had no idea they moved around in that way. Thanks!
What was let unclear was that the spirochette gets inside the host cells.
The ability to move is obviously important to the long spirochette, to ensure it gets all of itself into the cell, otherwise its tail would be out in the anti-body laden serum…
Other bacteria do enter cells. These are the most damaging ones… Some E Coli has other means to get into the cell. TB can survive inside a macro-phage, without even killing it.
Are all spirochetes parasitic?
Is my very, very thin grasp of the subject showing? 