In this article we will discuss about:- 1. Meaning of Bacteria 2. Reproduction of Bacteria 3. Importance.
Meaning of Bacteria:
Bacteria are the smallest living things which are visible only under very high magnification of a microscope. Many of them are positively harmful to plants and animals, as they live parasitically on the host, and cause diseases.
Some bacteria, on the other hand, are beneficial in different ways. They exist in all types of situations and can withstand extreme heat or cold and other unfavourable conditions. Bacteria are abundantly present in the air we breathe, in the food we take, in the water we drink, in the soil we inhabit, in different objects we touch and even inside our bodies.
Bacteria were first noted and described by a Dutch merchant Leeuwenhoek in the seventeenth century. In the nineteenth century famous French scientist Louis Pasteur asserted that sterilised fruit juice remained free from bacterial contamination. He really dealt the death blow to the theory of spontaneous generation.
Robert Koch in the same century discovered that bacteria are the causes of cattle-disease anthrax and tuberculosis and Asiatic Cholera. In fact, Pasteur and Koch are the builders of a new branch of biology, called bacteriology, which has advanced by rapid strides in recent years and revolutionised medical science.
Bacteria form a group of extremely small unicellular plants. Each has protoplasm which a surrounding limiting membrane which contains no cellulose. They may remain united together by forming filaments or irregular masses. Well-formed nuclei are always absent but chromatin granules remain distributed, which serve as corresponding nuclear material.
Plastids and chlorophyll are absent, though some pigments may often be noticed in them. Occasionally a large number of bacteria remain embedded in a gelatinous sheath forming a colony. They vary in size, smallest ones may even be less than 1 micron in length.
According to their forms, bacteria are of three principal types (Fig. 199), viz- spherical or coccus (pI. cocci) forms, rod-shaped or bacillus (pl bacilli) forms and spiral or spirillum (pl. spirilla) forms. Some of them are non-motile, while others are provided with cilia.
Reproduction of Bacteria:
Bacteria reproduce very’ rapidly by fission or fragmentation. They are constricted in the middle and ultimately break up into pieces of equal size. The rate of multiplication is surprisingly high. Prolific reproduction is checked by external factors like scarcity of food.
Under unfavourable conditions bacteria produce spores. Usually one spore is produced in each cell, where protoplasm contracts and is surrounded by a tough resistant wall.
Spores can stand very high temperatures, poisonous substances and other extremely unfavourable conditions. Spore-formation is regarded as a device for tiding over the unfavourable period. They are present everywhere. Under favourable conditions, each spore germinates to produce a bacterium.
Bacteria usually cannot manufacture their food and are perforce dependent on other sources. Many of them live parasitically on plants and animals including human beings. Parasitic bacteria are the causes of many diseases like cholera, tuberculosis, pneumonia and typhoid fever. They cause disease by direct attack upon the host tissue or by the liberation of toxins or by both. Disease-causing bacteria are called pathogenic.
Importance of Bacteria:
Saprophytic bacteria grow on dead rotten organic matters. They are not harmful but rather beneficial. In the soil they work as scavengers. Bacteria bring about decay of plant and animal bodies into simpler materials like water, carbon dioxide, nitrates, sulphates, phosphates, etc., which may again be used by the green plants.
Different types of bacteria work out this decay step by step by secretion of enzymes. Thus they prevent accumulation of organic matters and the essential elements are set free, which otherwise would have been permanently ‘locked up’ in dead bodies.
Bacteria considerably increase the fertility of the soil. Though nearly 80% of air is nitrogen, most plants are unable to use it, and we know that this essential element is mainly absorbed as nitrates from the soil. Common free-living bacteria Azotobacter and Clostridium can fix free nitrogen from air and convert it to organic nitrogenous compounds which are ultimately set free and broken down to nitrates.
Necessary energy is obtained for the purpose by oxidation of carbon compounds of the soil. Nodule-forming bacteria, Pseudomonas radicicola infect roots of leguminous plants and lead symbiotic life. They also fix nitrogen.
Nitrifying bacteria, Nitrosomonas and Nitrobacter can oxidize ammonia and nitrites respectively, derived from plant and animal remains of the soil, into nitrates, so that they may be absorbed by the roots of green plants. Some denitrifying bacteria of soil have the power of reducing nitrates into free nitrogen which “is lost from the soil and passes into air. They, live under anaerobic conditions.
Besides these beneficial activities of the bacteria inhabiting the soil, there are many others which are also important for different industrial processes. Sugar of milk is changed by some bacteria into lactic acid which brings about coagulation of milk-protein (casein). This is really the curdling of milk.
Bacterial actions are advantageously utilised in the manufacture of cheese, cream and butter, in the curing of tobacco leaves, tanning of hides to leather, retting of fibres of jute and flax, manufacture of vinegar and alcohol and various other industrial processes.