Mike Margonie, age 11, of Tucson, Arizona for his question:
How many kinds of bacteria are there?
Several thousand have been identified, but nobody knows the exact number of different bacteria. When you know about them and the mini realm in which they live, you understand why this is so. For one thing, a bacterium strain is subject to change without notice. If we counted them all today, tomorrow the number would be different.
In the world of science, there are a few counting games that boggle the mind. When counting separate atoms, we run out of zeros, though most of them have been sorted into a hundred or so different kinds. Counting the stars in the universe runs into astronomical figures, naturally. Most of them can be sorted into classes, though new types keep appearing. These are counts of cosmic items.
On the planet Earth, there is an uncountable number of bitsy bacteria, much too small for human eyes to see. A few thousand types have made themselves known, either as friends or enemies. These have been identi¬fied, but others are being discovered all the time.
The types that affect our lives are but a small percentage of the teeming bacteria populations. The best that scientists can do is estimate and they admit that their most educated guesses may be far, far from the facts. For example, way back in the 1940s, a playful scientist had a go at estimating the total bacteria population of the continental United States. The fanciful figure was approximately 30 plus a string of 24 zeros. Nowadays, most experts would consider this number to be much, much too small.
Another major problem is size. Bacteria are measured in microns and their shapes are viewed with electron microscopes. There are 25,000 microns in one inch and a crowded colony of about 10,000 bacteria is just about big enough for the human eye to see. Different types come in a wide assortment of shapes. Their lengths range from one to eight microns and their widths from one half to two microns.
Countless zillions of assorted types live in every patch of soil, in every pond and stream. They teem throughout the plant world, crowding on the surface of every leaf. They swarm in the atmosphere, from ground level to miles above the surface. Their populations are crowded on every animal and on every surface we touch. The soapiest scrubbing removes only 90 per cent or so of the bacteria from your hands.
And these tiny micro organisms can multiply at astounding rates. Under thriving conditions, one bacterium can become a billion bacteria in six hours. If this continued for 24 hours, the weight of the colony would reach one billion tons. Meantime, many individuals would change and produce new strains, different from the original bacterium.
The secrets of bacteria are concealed in small sizes and large numbers. They play a zillion roles in the balance of nature and life on earth could not survive without them. A few strains are harmful to plants, animals or people. It is estimated that about three per cent of the known types can cause diseases in humans and scientists know how to cope with most of these enemy bacteria.