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Chapter 28

Chapter 28 Notes - Bacteria and Archaea

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Department
Biology
Course
BIO153H5
Professor
Christoph Richter
Semester
Winter

Description
Notes From Reading CHAPTER 28:B ACTERIA AND ARCHAEA Key Points  Bacteria and archaea have a profound impact on humans and global ecosystems. A few bacteria cause important infectious diseases; some bacterial and archaea species are effective at cleaning up pollution; photosynthetic bacteria were responsible for the evolution of the oxygen atmosphere; bacteria and archaea cycle nutrients through every terrestrial and paquatic environment  Bacteria and archaea have been evolving for billion of years and are extremely sophisticated organisms. Although they are small and relatively simple morphologically, they live in virtually every habitat know and use remarkable diverse types of compounds in cellular respiration and fermentation 28.0 Introduction  Biologists study bacteria and bacteria and archaea for many reasons  The ubiquity and abundance of bacteria make them exceptionally important in both human and natural economies  Bacteria have a unique compound called peptidoglycan in their cell walls  Archaea have unique phospholipids – compounds containing hydrocarbons called isoprenes in their tails – in their plasma membranes  Microbes – microscopic organism are bacteria or archaea, and virtually all are unnamed and undescribed  Microbiology – the study of organisms that can be seen only with the aid of a microscope 28.1 Why Do Biologists Study Bacteria and Archaea?  Biologists study bacteria and archaea for many reasons  The ubiquity and abundance of bacteria make them exceptionally important in both human and natural economies Some Bacteria Cause Disease  No archaea are known to cause disease in humans  Bacteria that cause disease are said to be pathogenic  Pathogenic – literally means “disease-producing” o Have been responsible for some of the most devastating epidemics in human history  An Infectious Disease is one spread by being passed from an infected individual to an uninfected individual  Koch’s experiments became the basis for the germ theory of disease, which holds that infectious diseases are caused by bacteria and viruses  Koch’s postulates are used to confirm a causative link between a specific infectious disease and an infectious microbe: o The microbe must be present in individuals suffering from the disease and absent from healthy individuals Notes From Reading CHAPTER 28:B ACTERIA ANDA RCHAEA o The organism must be isolated and grown in a pure culture away from the host organism o If organisms from the pure culture are injected into organisms a healthy experimental animal, the disease symptoms should appear o The organism should be isolated from the diseased experimental animal, again grown in pure culture and demonstrated by its size, shape and color to be the same as the original organism  Antibiotics – are molecules that kill bacteria Bacteria Can Clean Up Pollution  Some of the most serious pollutants in soils, rivers, and ponds consist of organic compounds that were originally used as solvents or fuels but leaked or were spilled into the environment  These pollutants do not dissolve in water and accumulate in sediments  Bioremediation – is the use of bacteria and archaea to degrade pollutant  This is often based on complementary strategies: o Fertilizing contaminated sites to encourage the growth of existing bacteria and archaea that degrade toxic compounds o Adding specific species of bacteria and archaea to contaminated sites Extremophiles  Bacteria or archaea that live in high-salt, high-temperature, low-temperature, or high-pressure habitats are called extremophiles  Archaea are abundant forms of life in environments such as hot springs at the bottom of the ocean, where water as hot as 300 degrees C emerges and mixes with 4 degree C seawater  Understanding extremophiles may help explain how life on Earth began  Astrobiologists – use extremophiles as model organisms in the search for extraterrestrial life How Do Small Cells Affect Global Change?  Bacteria and archaea can live in extreme environments and use toxic compounds as food because they produce extremely sophisticated enzymes  The complex chemistry and abundance of bacteria and archaea make them potent forces for global change The Oxygen Revolution  No free molecular oxygen existed for the first 2.3 billion years of Earth’s history  Cyanobacteria – are a lineage of photosynthetic bacteria o Were the first organisms to perform oxygenic (oxygen-producing) photosynthesis  Cyanobacteria were responsible for a fundamental change in Earth’s atmosphere to one with a high concentration oxygen  Once oxygen was common in the oceans, aerobic respiration became possible  Prior to this, only anaerobic respiration was possible and cells had to use compounds other than oxygen as the final electron acceptor Notes From Reading CHAPTER 28:B ACTERIA ANDA RCHAEA  Oxygen is an efficient electron acceptor and much more energy is released with oxygen as the ultimate electron acceptor rather than other substances  Cyanobacteria were responsible for a fundamental change in Earth’s atmosphere – to one with a high concentration of oxygen The Nitrogen Cycle  Although molecular nitrogen (N2) is extremely abundant in the atmosphere, most organisms cannot use it  All eukaryotes and many bacteria and archaea must obtain their N in a form such as ammonia (NH3) or nitrate (NO3)  The only organisms capable of converting molecular nitrogen to ammonia are bacteria  The steps in nitrogen fixation are complex and highly endergonic redox reactions  Certain species of cyanobacteria in water can fix nitrogen  On land, nitrogen-fixing bacteria live in close association with plants – often taking up residence in nodules Nitrate Pollution  The widespread use of ammonia fertilizers is causing serious pollution problems  When ammonia is added to the soil, much of it is used by bacteria and nitrite (NO2-) or nitrate (NO3-) is released  Nitrates cause pollution in aquatic environments  In an aquatic ecosystem, nitrates can decrease the oxygen content, causing anaerobic “dead zone” to develop 28.2 How do Biologists Study Bacteria and Archaea?  Our understanding of the bacteria and archaea domains is advancing more rapidly now than at any time during the past 100 years – perhaps faster than our understanding of any other lineages on the tree of life Using Enrichment Cultures  Enrichment Cultures – are based on establishing a specific set of growing conditions – temperature, lighting, substrate, types of available food, etc.  Cells that thrive under the specified conditions will increase in numbers enough to be isolated and studied in detail Direct Sequencing  Direct Sequencing – is a strategy for documenting the presence of bacteria and archaea that cannot be grown in pure culture  Direct sequencing allows biologists to identify and characterize organisms that have never been seen  It is based on identifyin
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