Tuesday, 15 April 2014

Bacteria, zombies and individuality

Are bacteria observable? Or are they theoretical constructs, like electrons. Who ever actually saw a bacterium?
You can see their waste products when they form big enough colonies. You can see wavy tic tac shaped things crawling around under a laser microscope. And with an electron microscope you can see their little tails, their furry grappling hooks, even what they had for dinner. But is this really observing them? I certainly had to be taught how to 'see' the little things under the microscope, it ain't obvious.

Robert Koch defined disease-causing pathogens, including bacteria, in terms of whats isolable - what can be grown in pure (monogenomic) culture in the laboratory. This constitutes a massive abstraction from their normal, multispecies, complicated ecological context. The lab bacteriologist has to use all sorts of tricks to keep bacteria in this idealised, pure unicellular state. They grow microbes inside special incubators that shake constantly to keep the cells from clumping together and switching into their preferred, colonial state. They keep the strains in the freezer to slow down their metabolism to stop them evolving new traits. But then its pretty much taken that inferences from colonies of these domesticated lab-bugs to conclusions about the properties of wild bacterial cells are okay. We calculate how much of an enzyme a particular cell pumps out, for example, by measuring how much of the enzyme is produced by a culture of 100 millions cells.....then dividing the answer by 100 million. But how do we know there were 100 million cells in the culture?

To work that out, we can measure the density of the culture by shining a light through the test tube. We compare that to the amount of light that shines through a very dilute culture. Then we take a tiny drop of the very dilute culture, and drop it onto a petri dish filled with agar and food. We spread the drop out very thinly by putting little round beads into the dish and shaking it with the lid on. Then we remove the beads and leave the dish overnight. The next day the dish will be filled with little spots, and we get a pen out and count them. The reasoning is that each spot is a colony, founded by a single cell. So counting a colony tells us how many cells there were in our tiny drop of very dilute culture yesterday. Then we just need to do some maths to find out how many cells there were in our enzyme-pumping colony.

Zombies are usually said to be a Haitian idea, but John Carey wrote (here) that the ancient cultural roots of zombies lie in our fear of bacteria (see also here). Not bacteria exactly, but any sort of invisible entity that infects people in huge numbers, possibly making their flesh fall off, possibly making them froth at the mouth and try to bite people. Our pre-romantic ancestors had a very rational and very deep seated loathing of nature in general, Carey claimed. Of its slow but ultimately unstoppable defeat of everything in its path. Like the weeds and vines that crawl and cover the ruins of ancient civilisations, nature will always get its horrible way in the end.

Classical zombies were slow, stupid and not particularly scary in singular form. One zombie could always be pushed aside. The problem was they always come in endless tides, which slowly sweep over a victim and overcome him, chewing his arms gently but ceaslessly. Scares me just typing it.

Modern zombies aren't nearly so frightening - they mostly deliver a quick, painless death, I reckon. But the same old fear now appears in films as some sort of virus, sometimes giving people rabies/zombie-like symptoms, always spreading fast and threatening all of humanity.When I was a child books like 'The Andromeda Strain' had me fantasising about one day donning a safety suit and working in a level-four top-secret underground laboratory.

My tenuous excuse for banging on about zombies and scifi is that  in most of these films and books the day is always saved, not by destroying every single zombie, but by finding the cure - beating the type. That is, there is an implicit treatment of the infected as parts of the enemy, rather than as individuals. The same goes for the awesome army of skeletons in Jason and the Argonauts. You know that trying to bash down those critters with your sword is asking for trouble. And its not just a numbers game. They don't merely outnumber you. There is a sense that their number is infinitely replenishable. You need to find their weak spot and thus beat all of them at once, rather than hacking patiently away.

Newer zombie films have incorporated a new meme. The 28 days series, and the new Dawn of the Dead, have the feature that the zombies can learn. New tricks spread rapidly through the zombie population, so you cant rely on simple barriers to keep them out, for example.  Bacteria, too, have a horrifying ability to teach each other new tricks, and so outpace our attempts to contain them. Lateral gene transfer constitutes a mechanism by which a handy trick, such as resistance to an antibiotic, can be shared amongst all the bacteria in a population. As soon as one of them has figured out how to get past that wall, its time to find another wall.

Zombies are scary and scifi is awesome. Fact.

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