Ch 6: Microbial Growth Flashcards
What unites are used to measure growth rate?
Generations / unit time
(doubling)
What is the approximate temperature range for the growth of a given organism?
30 ℃
What is a strict psychrophile? Where are they typically found?
A microbe with an optimal growth temperature around 15 ℃, with some as low as -20 ℃
Typically found in arctic soils, glaciers, and deep ocean environments
Do strict psychrophiles cause food problems?
No
What is a psychrotroph?
A microbe with an optimal growth temperature around 25 ℃
Do psychrotrophs cause food spoilage?
Yes
What are some examples of psychrotrophs that commonly cause food spoilage in the fridge?
- Listeria monogenes*
- Clostridium botulinum*
What is a mesophile?
A microbe with an optimal growth temperature range of 25-40 ℃
Are mesophiles responsible for food spoilage?
Yes. Room temperature food spoilage
What is the optimum growth temperature for thermophiles?
50-60 ℃
Are thermophiles pathogenic?
Not particularly
What is the optimum growth temperature of hyper/extreme thermophiles?
>80℃
What type of microbe is Thermus aquaticus? Why is it commercially important?
Hyperthermophile
Used for its DNA polymerase (Taq polymerase) for lab use (i.e. PCR)
Most bacteria grow in what pH range?
6.5 - 7.5
Most molds and yeasts grow in what pH range?
5 - 6
In hypertonic environments, an increase in sugar causes what to happen to a cell?
Plasmolysis
Halophiles survive in what type of environment?
High salt concentrates
What salt concentration can most ocean microbes survive in?
~3.5%
Slight halophiles
Facultative halophiles can survive at what salt concentration?
2% - 15 %
Extreme or obligate halophiles require what salt concentrations to survive?
10 - 30% (dead sea)
What concentration of salt inhibits most bacteria?
2%
What are the main chemical requirements for the growth of a microbe?
Carbon
Nitrogen
Sulfur
Phosphorus
Oxygen
Potassium Magnesium
Calcium
Trace elements
Organic growth factors
About 50% of the dry weight of a typical cell is _____
carbon
8% of the dry weight of E. coli is _____
Hydrogen
14% of the dry weight of a typical cell is ____ and ____
Amino acids and bases
What are some potential nitrogen sources for microbes?
- Decomposition of proteins
- NH4+
- NO3-
- N2 (nitrogen-fixing bacteria)
What is the primary source of phosphorus in microbes?
Decomposition of organic sources of PO4-3 directly
What are the primary sources of sulfur for microbes?
- SO4-2 directly
- H2S
- Decomposed proteins (cysteine and methionine)
4% of the dry weight of a typical cell is _____
Combined sulfur and phosphorus
What type of microbe is depicted here? Explain.
Obligate aerobe
Requires O2
What type of microbe is depicted here? Explain
Facultative anaerobe
Can grow with or without O2
What type of microbe is depicted here? Explain
Obligate anaerobe
Cannot tolerate O2
What type of microbe is depicted here? Explain.
Aerotolerant anaerobe
Doesn’t require oxygen but does not care if it’s around
What type of microbe is depicted here? Explain.
Microaerophile
has a narrow range of tolerable oxygen levels
____ constitutes 20% of the dry weight of E. coli
Oxygen