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UW-Milwaukee BIOSCI 152 - Symbiosis

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BIO SCI 152 1st Edition Lecture 5SymbiosisMicroorganisms interact with macroorganisms in many ways. ‘Symbiosis’ is the term used to describe any two organisms that live together. We usually use this term to describe mutually beneficial symbioses, but the term is really more inclusiveTypes of symbiotic interactions include:Mutualism: Both organisms benefit Parasitism: One organism benefits and other is harmed Mutualistic interactions ExamplesMembers of the Gram negative bacterial genus Rhizobium that interact with roots of legumes to form nodules. The bacterial cells fix nitrogen (convert N2 into NH4) for the plant. Cellulose utilizing bacteria, archaea and protists in cows and in termites. These microorganisms digest cellulose and, resulting in fermentation end products that are the primary energy source of the animal. Hydrothermal vent tubeworms and bacteria. Bacteria will oxidize hydrogen sulfide and fix CO2, thus providing food for the animalsII. Parasitic InteractionsA relatively small number of microorganisms interact with their hosts in a more harmful manner and cause disease. These ‘pathogens’ include some bacteria, some protists, and some fungi. Perhaps surprisingly, no archaea are known to cause disease.A. Agrobacterium: Plant disease and Genetic engineering of plantsAn interesting example of disease in plants is the formation of crown gall or tumor by Agrobacterium species. These Gram-negative bacteria are closely related to the genus Rhizobium. Agrobacterium cells transfer part of their plasmid DNA into plant cells and cause tumors to form.Overview of Agrobacterium tumefaciens and crown gallA. tumefaciens cells swim toward a wound on a plant Transfers T DNA (small piece of a plasmid in Agrobacterium) into plant cell T DNA integrates into plant chromosomal DNA4. T DNA results in production of plant hormones (leading to plant cell growth) and production of ‘opines’ (unusual amino acids that serve as carbon and energy source for A.tumefaciens).Use of Agrobacterium in genetic engineering of plants:Examples of modifications introduced to plants:Plants that are resistance to insectsPlants with added vitamins for extra nutritional valueB. Diseases of animals and humansIn the late 1800s, R. Koch proved that bacteria can cause disease in animals. The following are the steps he took to identify pathogen causing disease:observed bacteria in a diseased animals tissues isolated bacteria from diseased animals and grew them in pure culture reintroduced the bacteria into healthy animals and observed the same disease reisolated the same bacterium from the new sick animal. Others have followed these steps (Koch’s postulates) or modified versions of them to identify many pathogensMycobacterium tuberculosis (causes tuberculosis)Treponema pallidum (a spirochete that causes the sexually transmitted disease syphilis) Staphylococcus aureus (common cause of food poisoning and many types of infections)Shigella dysenteriae- causes dysentery (diarrhea with mucus and blood), hijacks actin in eukaryotic cells to move inside cell and spread to other cells.C. Bacterial ‘parasites’Bdellovibrio species- flagellated bacterium that attacks Gram-negative bacteria and growsin their


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