Exam 2 - chapter 6, 7, 8, 9
The Requirements for Growth
Physical requirements
o Temperature
o pH
o Osmotic pressure
Chemical requirements
o Carbon
o Nitrogen, sulfur, and phosphorus
o Trace elements and organic growth factors
o Oxygen
Typical Growth Rates of Different Types of Microorganisms in Response to Temperature
(graph) (Know optimal temperature)
o Psychrophiles don’t tend to be pathogens (optimal temp around 12˚C)
o Psychrotrophs overlap with psychrophiles with optimal temperature around 22˚C
(something with food spoilage)
o Mesophiles - optimal growth at 37 ˚C (same as human body temperature)
(incubators set to this temp, most common spoilage),
o Thermophiles optimal temperature around 60-65˚C (but endospores can resist
lower temp)
, o Hyperthermophiles (high amounts of pressure with high amounts of heat - 95˚C)
(archaea, up to 121 C)
Figure 6.2 Food Preservation Temperature (don’t forget the orange juice, it’ll explode :))
Figure 6.3 The effect of the amount of food on its cooling rate in a refrigerator and its
chance of spoilage
pH
o Very few at pH 4
One chemoautotroph bacteria grows at pH 1
o Most bacteria grow between pH 6.5 and 7.5
o Molds and yeast grow between pH 5 and 6
o Acidophiles grow in acidic environments
o Phosphates, peptones, amino acids act as buffers, neutralizing acids produced by
bacteria in lab
Osmotic Pressure
o Hypertonic environments (higher in solutes than inside the cell) cause plasmolysis
due to high osmotic pressure
When plasma membrane pulls away from cell wall, growth is inhibited, so
plasmolysis is used to preserve food e.g. salted fish
o Extreme or obligate halophiles require high osmotic pressure (high salt)
Organisms from dead sea usually require at least 30% salt
o facultative halophiles tolerate high osmotic pressure
can grow up to 2-15% salt
Chemical Requirements
o Carbon
Structural backbone of organic molecules
Makes up 50% weight of bacteria
Chemoheterotrophs use organic molecules as energy
Autotrophs use CO2
o Nitrogen
Component of proteins, DNA, RNA, and ATP
The Requirements for Growth
Physical requirements
o Temperature
o pH
o Osmotic pressure
Chemical requirements
o Carbon
o Nitrogen, sulfur, and phosphorus
o Trace elements and organic growth factors
o Oxygen
Typical Growth Rates of Different Types of Microorganisms in Response to Temperature
(graph) (Know optimal temperature)
o Psychrophiles don’t tend to be pathogens (optimal temp around 12˚C)
o Psychrotrophs overlap with psychrophiles with optimal temperature around 22˚C
(something with food spoilage)
o Mesophiles - optimal growth at 37 ˚C (same as human body temperature)
(incubators set to this temp, most common spoilage),
o Thermophiles optimal temperature around 60-65˚C (but endospores can resist
lower temp)
, o Hyperthermophiles (high amounts of pressure with high amounts of heat - 95˚C)
(archaea, up to 121 C)
Figure 6.2 Food Preservation Temperature (don’t forget the orange juice, it’ll explode :))
Figure 6.3 The effect of the amount of food on its cooling rate in a refrigerator and its
chance of spoilage
pH
o Very few at pH 4
One chemoautotroph bacteria grows at pH 1
o Most bacteria grow between pH 6.5 and 7.5
o Molds and yeast grow between pH 5 and 6
o Acidophiles grow in acidic environments
o Phosphates, peptones, amino acids act as buffers, neutralizing acids produced by
bacteria in lab
Osmotic Pressure
o Hypertonic environments (higher in solutes than inside the cell) cause plasmolysis
due to high osmotic pressure
When plasma membrane pulls away from cell wall, growth is inhibited, so
plasmolysis is used to preserve food e.g. salted fish
o Extreme or obligate halophiles require high osmotic pressure (high salt)
Organisms from dead sea usually require at least 30% salt
o facultative halophiles tolerate high osmotic pressure
can grow up to 2-15% salt
Chemical Requirements
o Carbon
Structural backbone of organic molecules
Makes up 50% weight of bacteria
Chemoheterotrophs use organic molecules as energy
Autotrophs use CO2
o Nitrogen
Component of proteins, DNA, RNA, and ATP
