Anne L. Leinbach, age 9, of Williamsport, Pa., for her question:
How do bacteria grow?
An army of 1000 bacteria could cover the point of a pencil. One bacterium is too small for our eyes to see. It is not easy to learn the secrets of these bitsy living things. Yet bacteriologists do this every day. They know how many different bacteria live and grow.
Bacteria come in many shapes and sizes, but none are big enough for our eyes to see. A row of 25,000 of them measures, about one inch, to study how they live and grow, we must shrink our minds down to the teeming world of tiny atoms. Bacteria are living cells; stuffed with molecules and molecules are bundles of assorted atoms. Very special molecules in the bacteria do the job of growing.
A new bacterium is just half the size of its parent. It appeared when its parent divided itself into a pair of twins. The magic molecules in the parent were doubled, and each twin got a full Set of them. Our twin is a busy factory filled with all the chemical workshops it needs to grow and multiply. All it needs is a steady stream of supplies from outsider.
Our bitsy twin happens to be a lactic acid bacterium. It floats in a quart of warmish milk, and food Seeps through its cell wall. Things are just right. In half an hour it will, be full sized and ready to divide into a pair of newer twins. There will be a trillion bacteria in 20 hours, and the milk will all be sour. There will be no more food for the bacteria, and unless they find themselves in more fresh milk they can grow no more.
The magic chemicals inside the living cell do this amazing miracle. Molecules of salt and sugar cannot do things by themselves. But the magic m0iecules in the living bacteria can do marvelous tricks. They take molecules of food, break them up and arrange the pieces to make different molecules.
They take sugar and other small m0iecules and build them into proteins and other big molecules. They are chemical workshops, busy using food to create all the molecules needed by the growing bacteria.
This busy chemical work also creates waste materials, which seep out through the cell wall. Our lactic acid bacterium sends out a waste material that turns the milk sour. These bacteria are put to work by dairies. They make the curdled milk, which is used to make cheese.
Different bacteria need different diets. Some need food, which would be no Use to us, such as wood. Some need ammonia, which would poison us; some need the smelling stuff that comes from rotten eggs or other items that are downright revolting to us. When things are just right, a bacterium can stuff him at a great rate. He devours enough food to equal his own weight in half an hour and this stuffing goes on day and night without stopping until all the food is gone.