Bacteria have a nasty reputation because of their association with some of the illness that afflict people. Yet without them nature would not persist to produce the rich variety of life on which we all depend. Bacteria are
microscopic in size and multiply rapidly, one producing as many as 16 million others in a single day.
Under the microscope, bacteria are seen to be transparent cells usually without colour. They consist of a mass of protoplasm encircled by a wall which is somewhat different from the cell wall of higher plants. Bacterial cells do not seem to include an organised nucleus. The cells hold food reserves, grow rapidly and divide almost immediately they have reached their full size. After división, they may split, cling together in chains or irregular masses or form a series of branches. In extremes of temperature, bacteria form thick-walled spores called endospores which remain until conditions for growth again become propitious.
Bacteria live in or on animals or plants. They secrete enzymes, lifeless substances made out of living matter, which help to break down the tissues of their hosts to feed bacterial growth. When bacteria live as parasites, they harm the host plant or animal and sometimes kill it. In the soil, they extract nitrogen from the air and convert it into nitrates which help to feed plants. When bacteria are thus beneficial to their hosts, they are said to be symbiotic, which means living in partnership. Bacteria that live on and decompose the waste matter of plants and animals are saprophytes.
Among the things for which bacteria are useful to man are separating the fibres of such plants as flax, jute and hemp for making cloth and rope, turning animal dung into nitrate-rich manure, converting wine into vinegar and milk into cream for butter, in the curing of tobacco, and the tanning of leather.
