Chapter 5 cont. - Chapter 5 cont Tuesday 11:01 AM Begin...

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Chapter 5 cont Tuesday, February 03, 2009 11:01 AM     Begin Exam 2   pH pH- relative hydrogen ion concentration in a solution Scale is from 0 to 14 7 is neutral, < 7 is acidic, > 7 is basic  Most bacteria grow at pH of 6-8  Bacteria can be found to exist at almost any pH  Most cells internal pH remains near 7 regardless of pH of their environment    Most organisms have a pH range at which they can grow of 2-3 pH units  Acidity or alkalinity of an environment can greatly affect microbial growth  Weak acids can pass through membranes  Ex: Good food preservatives   Classification based on optimal pH Some organisms have evolved to grow best at low or high pH, but most organisms  grow best between pH 6 & 8 and are called  neutralophiles (neutrophiles)    Acidophiles- grow best at low pH Stability of CM is critical since increases in pH can cause lysis  Ex. Many fungi,  Thiobacillus  produces sulfuric acid, volcanic thermal soil  archaea  Picrophilus oshimae  grows optimally at pH 0.7     Alkalophiles- grow best at high pH found in soda lakes &  high carbonate soil Many species of  Bacillus  live in very alkaline soils  Bacillus firmus  has a pH range of  7.5-11 Proteases and lipases made by alkaliphiles are mass produced & used in  household detergents.   Oxygen
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Microorganisms vary in their need or tolerance of oxygen (O 2 ) & can be grouped based  on their requirements for O 2 . oxic environment- O2 is present anoxic environment- no O2 present   Aerobes- use O2 to generate energy by respiration Facultative aerobes use O in respiration but can also grow in anoxic  environments  Ex.  Streptococcus mutans  on teeth  ; E. coli  in large intestine  Obligate aerobe- use O
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