Bacteria, scholar

Intelligence is an idea that is hard to catch in a definition. There are a million varieties of intelligence. If solving a mathematical equation is intelligence, so is deciding which spice will suit which dish. Selecting the right move in a chess game is intelligence, and choosing the right shade of colour in a painting is intelligence too. These are all high profile varieties of intelligence. But even activities that appear very simple to us require complex calculations, so scientists have realised.

One such simple but ever present activity is moving towards the target. Pause here, give it a thought and you can see that no animal can survive without this skill. Animals have to find food, which means they have to detect food and move towards it (with the possible exception of the lucky animals who can order food at home).

Detecting food and moving towards it requires high degree of intelligence – we just don’t recognise it because we take it for granted. Take mosquitoes for instance – they find you by smell. Or take ants and bees, which have an army of food finders and use elaborate signals to tell others that they have found it. Bats use ultrasound waves to detect their food – a mechanism called Echolocation which is so complex that when you understand it you will treat the mouse like creatures hanging from a neighbourhood tree with definite respect.

But the hero of this article is an unlikely candidate – bacteria. A primitive living being, neither animal nor plant, and visible only through very powerful microscopes. Let alone a brain, it does not even have a neuron. But with the limited means at its disposal, it does a wonderful job of moving towards its food. Bacteria were the first form of life on earth, they are still around, and most probably they will be there when we humans take our exit, which means they are finding their food alright. The mechanism they use for moving towards their food is so basic, yet so fantastic!

Dip a thin glass tube in a jar of water and pass a bit of glucose through the tube. The bacteria in the water will move and reach the tube to eat the glucose. A bacteria is really really small - 1000 bacteria can sit side by side in one millimetre mark on your scale, without the slightest discomfort. So even detecting glucose one centimetre away is like you detecting a freshly fried Batatawada from ten kilometres. How do they do it? They don’t even have noses.

Glucose, like everything else, is made up of molecules. The molecules are much smaller than the bacteria. As we drop glucose in water, these molecules spread in water, some finally reach the bacteria.

What happens next is an arresting sight, if only you can zoom it by a billion times. When the glucose molecules reach the cell wall of the bacteria, they act like a key for a lock. What does the key-lock mean here?

On the cell membrane of the bacteria, there are special sites, like our airstrips, for the glucose molecules to land. But the shape of these sites is such that only some molecules can land there. This is why I called it a key-lock mechanism.

Once the key is in the lock, the membrane opens a little bit. Certain ions from the outside liquid (like calcium or sodium) enter into the cell. (Ions are electrically charged particles that are present in all solutions.)

These ions enter in style – like a bollywood hero entering a villain’s den, and create the same kind of brisk activity. The end result of this activity is moving the small hair like extensions on the wall, called cilia (search ‘Cilia bacteria’ in Google and see the images). The movement of these cilia propel the bacteria in the right direction, like a rowboat.

But how does the bacteria know where to go, where the glucose source is? The bacteria does something very clever. It moves in a zig-zag motion, which we human beings can reproduce by drinking large amount of alcohol. But the bacteria is merely sensing the number of glucose molecules in its path. The direction in which the number of molecules of glucose goes up is the direction of the source. If it finds lesser molecules as it moves, it’s wrong direction, so it comes back and tries another direction.

Isn’t it fascinating? It tells us at least two things. First, the things at small scale are as spectacular as those we can see. Second, behaviour that appears intelligent can be produced purely by chemistry.