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Bacterial Growth Growth Requirements Environmental Effects Bacterial Growth Characteristics Culture Media – Chemicals » Carbon » Nitrogen » Micronutrients (S, P, Fe, Mg, K, Na, etc.) – Solid or Liquid » Agar for solid support – Sterilization usually using an autoclave Bacterial Growth Characteristics Agar – Extract of seaweed (red algae) a polysaccharide of galactose and galacturonic acid – In 1881, Fannie Hesse, who was working as a technician for her husband in the laboratory of Robert Koch, suggested agar – Used as setting agent in jam making for some time – Replaced gelatin (poor temperature characteristics and supports growth) – Dissolves at 90°C and solidifies at 40°C Bacterial Growth Characteristics Culture Media – Selective and Differential Media – Complex vs. chemically defined Bacterial Growth Characteristics Selective and Differential Media – Differential - differentiates between organisms based upon colony morphology (especially color) on media – Selective - permits only certain organisms to grow (e.g. high salt or other inhibitors) Bacterial Growth Characteristics Complex vs. chemically defined – Chemically defined – each component has a know chemical formula and/or structure, e.g. minimal media (glucose, ammonium nitrate, and a defined mixture of salts) – Complex media (undefined) – components come from non defined sources, e.g. tryptone, peptone, yeast extract, oatmeal Bacterial Growth/Environmental Energy sources Carbon sources Physical influences on growth Bacterial Growth/Environmental Energy sources – Organisms acquire energy as a result of oxidation/reduction reactions – Light energy - phototroph – Chemical energy - chemotroph » organic (reduced forms of carbon) » inorganic (reduced metals) Bacterial Growth/Environmental Carbon sources – autotrophs use carbon dioxide – heterotrophs use reduced organic carbon sources: » sugars » organic acids » alcohols Bacterial Growth/Environmental Nitrogen sources – Reduced (ammonia) – Nitrates and Nitrites – Nitrogen Fixation Bacterial Growth/Environmental Nutritional Classifications - based upon energy & carbon source – photoautotroph - uses light energy and carbon dioxide as carbon source – photoheterotroph - uses light energy and an organic carbon source – chemoautotroph - uses an inorganic chemical as energy and carbon dioxide – chemoheterotroph - uses an organic chemical as energy and an organic carbon source Bacterial Growth - Physical Physical Influences on Growth – – – – – Temperature pH Osmotic pressure Oxygen availability Oxygen toxicity Bacterial Growth - Physical Temperature – psychrophillic - an organism that exhibits optimal growth at about 15 deg. C and does not grow above 20 deg. C – mesophillic - an organism that exhibits optimal growth at about 30-37 deg. C and does not grow below 10 or above 50 deg. C – thermophillic - an organism that exhibits optimal growth between 50-60 deg. C and does not grow below 40 deg. C or above 70 deg. C – Hyperthermophillic – growth between 70 and 110 deg C Bacterial Growth - Physical pH – most bacterial prefer pH 7 or slightly acidic – can tolerate to pH 4 due to production of organic acids during glucose metabolism Bacterial Growth - Physical Osmotic Pressure – ideal seems to be about 0.5% to 1.0% NaCl – some organisms tolerate much higher salt, e.g. Staphylococcus will go to 10% NaCl – halophiles - adapted to high salt concentrations many belong to Archea bacteria Bacterial Growth - Physical Toxic Oxygen - Forms – – – – Singlet oxygen Superoxide free radicals Peroxides Hydroxyl free radicals Bacterial Growth - Physical Toxic Oxygen - Neutralization – Catalase: » 2 H2O2 2 H2O + O2 – Superoxide dismutase: » 2 O2 - + 2 H+ O2 + H2O2 – Peroxidases: » H2O2 H+ + H2O Bacterial Growth - Physical Oxygen Classification – – – – Aerobic - grows in presence of oxygen Obligate aerobe - requires oxygen Anaerobic - grows in absence of oxygen Obligate anaerobe - will only grow in absence of oxygen – Facultative anaerobe - will grow both anaerobically or aerobically Bacterial Growth - Physical Oxygen Classification – Aerotolerant - only grow anaerobically but will tolerate oxygen – Microaerophillic - growth occurs only in presence of low concentrations of oxygen Bacterial Growth - Physical Catalase SOD Obligate Aerobe + + Faculatative Anaerobe + + Obligate Anaerobe - - Aerotolerant Anaerobe - + Microaerophiles - -