Ch6_Microbial Nutrition and Growth

Ch6_Microbial Nutrition and Growth - MICROBIAL NUTRITION...

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MICROBIAL NUTRITION AND GROWTH *Organisms are classified into one of four groups bases upon their source of carbon and energy *Phototrophs get their energy from light *Chemotrophs get their energy from chemical compounds *Autotrophs get their carbon from inorganic carbon, CO 2 *Heterotrophs get their carbon from organic chemicals like sugar
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OXYGEN REQUIREMENTS *Some bacteria use oxygen as the final electron acceptor in the electron transport chain during oxidative respiration *Other bacteria use a different electron acceptor and cannot tolerate oxygen *Some forms of oxygen are toxic to all bacteria, these forms of oxygen are highly reactive and cause a chain of destructive reactions *Gaseous molecular oxygen and oxygen in organic compounds are not toxic
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TOXIC FORMS OF OXYGEN Toxic Forms: 1) Singlet Oxygen – 1 O 2 , have electrons in a higher energy state as a result of metabolism. Very reactive oxidizing agent. Some cells have pigment which remove the excess energy and prevent toxicity. 2) Superoxide Radicals – O 2 - formed during metabolism, incomplete reduction of oxygen. Aerobic bacteria have the enzyme Superoxide Dismutase which detoxyfies the radical 3) Peroxide Anion or hydrogen peroxide – H 2 O 2 , some bacteria have the enzymes Peroxidase and/or Catalase , to convert hydrogen peroxide to water and oxygen. 4) Hydroxyl Radical OH - , from hydrogen peroxide but does not accumulate because the latter is eliminated.
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Oxygen Detoxification Reactions 2O - 2 + 2H + == O 2 + H 2 O 2 Superoxide Dismutase H 2 O 2 + NADH + H + == 2H 2 O + NAD + Peroxidase 2H 2 O 2 == 2H 2 O + O 2 Catalase Obligate aerobes and facultatives usually possess the enzymes superoxide dismutase and either peroxidase or catalase. Aerotolerants may lack catalase but always have dismutase. All obligate anaerobes lack all these enzymes or have them in very low concentrations and therefore cannot tolerate oxygen.
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OXYGEN CLASSIFICATION OF MICROBES 1) Obligate Aerobes: Require oxygen for growth, uses it as the final electron acceptor in respiration 2) Obligate Anaerobes: Cannot survive in the presence of oxygen and use a different electron acceptor, lack oxygen detoxyifying enzymes 3) Facultatives: Can grow in the presence or absence of oxygen, although the grow more efficiently with oxygen – WHY? 4) Aerotolerant anaerobes: Grow equally well in the absence or presence of oxygen 5) Microaerophiles: Require reduced levels of oxygen, are damaged by normal atmospheric levels of oxygen 6) Capnophiles: Grow best in high levels of carbon dioxide in addition to reduced levels of oxygen
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NITROGEN REQUIREMENTS *Nitrogen is in all amino and nucleic acids *Thus a source of nitrogen is required by all living organisms *Nitrogen is a growth-limiting factor for many microbes *Nitrogen is acquired either from organic or inorganic sources *Nitrogen constitutes approx. 80% of the atmosphere but this nitrogen is not usable by most microbes *A few microbes are able to fix atmospheric nitrogen into ammonia, called nitrogen fixation
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Ch6_Microbial Nutrition and Growth - MICROBIAL NUTRITION...

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