Microbiology Requirements for Growth

Where do autotrophs and heteroptrophs obtain the carbon they need to build their biological macromolecules

a. Autotroph:  Inorganic carbon dioxide 

b. Heterotroph: Complex organic carbon compounds (provided by autotrophs)

Where do the following types of organisms obtain the ENERGY they need to live? 

a. Chemotroph: Obtain energy for electron transfer by breaking chemical bonds 

b. Phototroph:  Electron transfer from light 

Both chemotrophs and phototrophs obtain energy by transferring high energy electrons between molecules in two types of  chemical reactions: Oxidation reactions and reduction reactions

a. What is an oxidation reaction? 

• Is a reaction that removes electrons from donor molecules, leaving them oxidized.

b. What is a reduction reaction? 

• Is a reaction that adds electrons to acceptor molecules, leaving them reduced

5. Different organisms have different requirements and tolerances for oxygen. For some organisms, oxygen is a requirement while for others oxygen is toxic!  

a. What does it mean for an organism to REQUIRE oxygen? 

• An organism cannot survive without oxygen and will die without the presence of oxygen. 

 Different organisms have different requirements and tolerances for oxygen. For some organisms, oxygen is a requirement while for others oxygen is toxic!  

b. What does it mean for an organism to TOLERATE oxygen?

• These specific organisms do not require oxygen for survival, but will not be killed by the presence of oxygen. 

Do Obligate aerobes require and tolerate O2

yes to both

do obligate ANAerobe require and/or tolerate O2`

No to both

Do faculative Anaerobe require and/or tolerate O2

no to required

yes it tolerates

do aerotolerant anaerobe require and/or tolerate O2

no to require

yes to tolerate

Many microbes can grow only in narrow ranges of pH. Define the following terms that describe the pH ranges of growth 

a. Neutrophile: 

• Most bacteria fall in this category

• They grow optimally at a pH within one or two pH units of the neutral pH of 7

 Many microbes can grow only in narrow ranges of pH. Define the following terms that describe the pH ranges of growth

b. Acidophile: 

• Microorganisms that fall into this category grow optimally at pH less than 5.55

• Ex: Sulfolobus spp. This microorganism can survive at a pH of 2.5-3.5 

• Acidophilic microorganisms can adapt to survive very strong, acidic environments 

 Many microbes can grow only in narrow ranges of pH. Define the following terms that describe the pH ranges of growth

c. Alkaliphile: 

• Microorganisms that grow best at pH between 8.0-10.5

• Extreme alkaliphiles have adapted to their harsh environment through evolutionary modification of lipid and protein structure and compensatory mechanisms to maintain the proton motive force in an alkaline environment

Microbes cannot control their temperature, and therefore assume the ambient temperature of their surroundings. They typically  can only survive in a narrow temperature range. Define the following terms that describe the temperature range of  microorganisms: 

a. Psychrophile/Psychrotroph: 

• Cold loving 

• These microorganisms grow at 0 degrees Celsius and below

• Have an optimum growth temperature close to 15 degrees celsius and don’t survive temperatures above 20 degrees celsius (usually)

• Found usually in deep waters of ocean, or in permanently cold environments

• Psychrophile /psychrotrophs are important decomposers in cold climates

 Microbes cannot control their temperature, and therefore assume the ambient temperature of their surroundings. They typically  can only survive in a narrow temperature range. Define the following terms that describe the temperature range of  microorganisms:

b. Mesophile: 

• Organisms adapted to moderate temperatures 

• Optimal growth temperature: 20-45 degrees C

• Normal human microbiota and pathogens fall in this category

  • Normal human body temperature is 37 degrees C

Microbes cannot control their temperature, and therefore assume the ambient temperature of their surroundings. They typically  can only survive in a narrow temperature range. Define the following terms that describe the temperature range of  microorganisms: 
c. Thermophile: 

• Heat loving

• Optimum growth temperature: 50-80 degrees C

• Found in hot springs, geothermal soils, manmade environments 

Hyperthermophiles can grow in temperatures of 80-110 degrees C (some survive over 121 degrees C)

d. Explain why a human pathogen is most likely a mesophile and not a psychrotroph or thermophile. 

• A human pathogen is most likely a mesophile because it can survive only at moderate temperatures, which is the human body temperature. It will not be able to survive in extreme heat (like the thermophiles/hyperthermophiles that are heat loving and thrive in the heat) or in the cold (unlike the psychrotroph who are cold loving).

Many microbes can grow only in narrow ranges of salt concentration and pH. Define the following terms that describe the salt and/or pH ranges of growth.

a. Halophile: 

• Salt-loving microorganisms (mainly bacteria and archaea)

• Thrive in high-salinity environments 

• Ex: Dead sea or Great Salt leak 

• Will lyse/burst in fresh water 

• Their proteins and enzymes are highly acidic

 Many microbes can grow only in narrow ranges of salt concentration and pH. Define the following terms that describe the salt and/or pH ranges of growth.
b. Non-halophile: 

• Microorganisms that thrive in low-salt environments(“salt avoidant/sensitive”)

• Cannot survive in high salinity 

• High salt causes their proteins to denature 

• Ex: Escherichia coli

 Many microbes can grow only in narrow ranges of salt concentration and pH. Define the following terms that describe the salt and/or pH ranges of growth.
c. Facultative halophile

• Is a microorganism that can grow in high-salt environments 

• Does NOT REQUIRE high salinity to survive 

• Salt tolerant 

• Grow well in low and moderate salt concentrations 

• Can survive in freshwater conditions 

• Ex: Staphylococcus aureus 

What is the difference between the minimum growth temperature, the maximum growth temperature and the optimum growth temperature?

minimum: lowest temp allowing growth

max: highest allowed before metabolic failure

optimum: precise/ideal temp for fastest growth rate

Why is refrigeration a good strategy for food preservation?  For pathogen control?  

preservation:

• slows bacterial action

• inhibits enzyme reactions

• maintains freshness

pathogen control:

• inhibits microbial growth

• prevents rapid multiplication

• ensures food safety

• reduces spolage

Why does the pH influence the growth of bacteria? 

impacts protein structure

enzyme function

ability to maintain energy production