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Bacteria and Viruses © Lisa Michalek Bacteria Bacteria are microscopic, unicellular (one-celled) organisms that lack a nuclear membrane. Bacteria can live on land, in water, and in the air. – They also live in and on both living and dead plants and animals. Most bacteria are heterotrophs. – Heterotrophs are organisms that cannot make their own food. Shapes of Bacteria Coccus - round shaped Bacillus – rod shaped Spirillum – spiral shaped Structure of Bacteria A bacterium is made up of a thick cell wall that encloses and protects cellular material. Bacterial Nutrition Some bacteria live separately and others remain together to form colonies. –Colonies are large groups of bacteria. Bacterial Nutrition There are bacteria that live as parasites. – A parasite absorbs food materials from other living organisms called their hosts. Others digest and absorb food materials from dead organisms. – These bacteria are called saprophytes. Beneficial Bacteria Most bacteria are beneficial (helpful) to humans. Bacteria are decomposers that cause decay. – Decomposers are organisms that break down dead organisms and return the nutrients to the soil. Beneficial Bacteria Many bacteria are used to produce food and life-saving drugs. – Bacteria are used to make cheese, pickles, yogurt, vinegar, and sauerkraut. Beneficial Bacteria By using methods of gene transplanting, bacteria have been encouraged to produce substances such as insulin. Beneficial Bacteria The human intestinal tract contains millions of bacteria. – Many of these bacteria help the digestive process and others produce vitamins. Beneficial Bacteria Bacteria are also used in the tanning of leather, the curing of tobacco, and the production of food for feeding cows. Harmful Bacteria Some bacteria are not beneficial to man. Bacteria spoil food by secreting enzymes into the food causing it to rot. – Along with enzymes, other substances produced by bacteria are released into the food. – Some of these substances are toxic, making the food poisonous to humans and other organisms. Harmful Bacteria Bacteria in large numbers can pollute (dirty) lakes, streams, and drinking water. During respiration, bacteria reduce the dissolved oxygen content in water supplies. Harmful Bacteria Many bacteria are pathogenic. – A pathogen is an organism that causes disease and/or infection. – Some bacterial diseases of humans are tuberculosis, tetanus, and strep throat. Controlling Harmful Bacteria Antiseptics, disinfectants, and antibiotics are used to control pathogenic bacteria. – An antibiotic is a chemical that can stop the growth of some bacteria. – Bacteria are able to produce types that are resistant to certain antibiotics. – When this happens, new antibiotics must be developed. Controlling Harmful Bacteria Bacteria can also be killed in foods by: – pasteurization – canning – chemical preservatives – radiation – steam/pressure – salt curing – dehydration (drying) Harmful Anaerobic Bacteria Some bacteria can live anaerobically and cause botulism (Clostridium botulinum). A dangerous type of food poisoning, in foods that have not been properly canned. Tetanus is a disease also caused by an anaerobic bacteria (Clostridium tetani) which is closely related to botulism. Tetanus is also known as lock jaw. Both Botulism and Tetanus are serious illnesses and often fatal Harmful Anaerobic Bacteria Two other anaerobic bacteria can cause venereal diseases. – Gonorrhea (causes sterility). – Syphilis (can result in death). A venereal disease is a contagious disease that a person gets through sexual contact. Both diseases can be treated successfully by antibiotics if detected early enough. Viruses A virus is not a cell. It is made up of genetic material inside a protein coat. Viruses do not carry on most metabolic activities. Viruses They can only reproduce inside a living cell called the host cell. Outside the host cell, a virus is “lifeless” and often exists as a crystal. A virus has no means of locomotion. Virus Reproduction Negative Virus Influences They cause infections in both plants and animals. Some viruses cause tumors and warts. They also destroy cells and are responsible for human diseases such as: – polio – measles – mumps – influenza – hepatitis – colds – AIDS Human Papilloma Virus - Warts Rabies Virus Influenza Virus - Flu Human Immunodeficiency Virus AIDS Positive Virus Influences Certain viruses are used in the control of insect pests. Others are used in genetic research. Scientists have been able to use viruses to biologically control caterpillars of the European pine sawfly and the gypsy moth.
