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
What are the toxic intermediates produced in the reduction of O2 to H2O? What are they known as?
Reactive oxygen species (ROS)
- Superoxide (O2-)
- Hydrogen peroxide (H2O2)
- Hydroxyl radical (OH•)
What causes production of ROS? (3)
- Leakage of electrions from the main path of the ETC and directly reduce O2 to O2-
- Some are necessary intermediates in enzymatic reactions
- Ionizing radiation
How does ionizing radiation generate ROS?
Splites water into H+ and OH-
What is singlet oxygen (1O2)?
An extremely reactive form of molecular oxygen in which one of the electrons jumps to a higher orbital following energy absorption
*In an excited state, NOT a free radical
How is singlet oxygen produced?
Byproduct of photosynthesis
What enzyme catalyzes the following reaction:
O2- + O2- + 2 H+ → H2O2 + O2
Superoxide dismutase
Which reaction is catalyzed by catalase and which is catalyzed by peroxidase?
- H2O2 + 2 H+ → 2 H2O
- 2 H2O2 → 2 H2O + O2
- Peroxidase
- Catalase
True or false, a bacteria can switch back and forth between using catalase vs. peroxidase depending on the conditions.
False. A bacteria only has the gene for one or the other, not both
Which type of microbe(s) utilizes superoxide disumuase and catalase?
Obligate aerobe
Facultative anaerobe
What type of microbe(s) do not have any enzymes to eliminate ROS?
Obligate anaerobes
Which type of microbe(s) utilizes superoxide dismutase and peroxidase?
Aerotolerant anaerobes
Which type of microbe(s) utilizes superoxide dismutase and sometimes catalase?
Microaerophiles
What are organic growth factors?
Essential organic compounds an organism can’t synthesize and must be obtained from the environment
Ex: vitamins, amino acides, purines, pyrimidines
Why are hyperthermophiles that grow at temperatures above 100 ℃ seemingly limited to oceanic depths?
More shallow water will evaporate at that temperature. Increased pressure at the ocean floor allows the temperature to increase without boiling (like an autoclave)
What is quorum sensing?
The ability of bacteria to coordinate gene expression with other bacteria via signaling molecules
Respond to local population density
What are the functions of a biofilm?
- Anchoring surface for microbes
- Facilitate transfer of genetic information
- Shelter bacteria from harmful factors (dessication, antibiotics, immune system)
What are some strategies used to prevent biofilm formation?
- Incorporate antimicrobials (i.e. heavy metals) into surfaces biofilms might form
- Block quorum sensing (ongoing research)
- Lactoferrin used to deplete iron to stimulate surface motility and prevent biofilm formation
What is agar?
A complex polysaccharide extracted from algae/seaweed that is combined with liquid media (broth) to creat a solid culture media
What concentration of agar will produce a completely solid medium?
1.5-2%
What concentration of agar will produce a soft agar medium?
<1%
What important properties make agar ideal for culturing microbes?
- Melts between 80-90 ℃
- Once melted, it doesn’t solidify until 40 ℃
- Cannot be degraded by most bacteria
How would you test the motility of a microbe in culture?
Inject culture into soft agar in a test tube and see how far they travel
What is a chemically defined media?
A nutrient material for culture media whose exact chemical composition is known down to moles
What is a fastidious organism? Example?
One that hsa a complex nutritional requirements (i.e. many growth factors)
Ex: gonorrhea
What is a complex media?
Nutrient material whose exact chemical composition is not known
When would you use a complex media over a chemically defined media?
When culturing heterotrophic bacteria and fungi?
What are complex medias derived from?
Made from protein hydrolysates or meat/yeast extracts
How do you remove oxygen for an anaerobic culture?
- Liquid media can be heated/autoclaved to drive-off dissolved O2 then tightly sealed
- Reducing media (sodium thiogycolate, cysteine, or glutathione) to reduce O2 to water
What methods can be used to incubate plates oxygen free?
- Anaerobic jar with palladium catalyst to reduce O2 to water
- Oxyplates
- Anaerobic chamber
How does an anaerobic jar work?
A bag container with CO2 and H2 gasses react with a palladium catalyst to reduce O2 to H2O
How does an oxyplate create an oxygen-free environment?
Culture medium contains oxyrase which catalyzes the following reaction
Lactic acid + O2 → H2O + Pyruvate
What gases are present in an anaerobic chamber?
90% N2
5+ H2
+/- 5% CO2
Mycobacterium leprae (leprosy) cannot be grown in artificial media. it is instead propagated in ______
Armadillos (natural reservoir)
Nonpathogenic strains of Treponema pallidum (syphilis) can be grown in synthetic media. The pathogenic strains can only be grown in ____
Rabbit testicles
What are Capnophiles?
Bacteria that grow best at high CO2 concentrations
What is significant about Saboraud’s Dextrose Agar?
It has a pH of 5.6 that discourages bacterial growth and can be used to isolate fungi
What is blood agar?
A differential media used to distinguish bacteria that destroy red blood cells (hemolysis)
What type of media would you use to culture Streptacoccus pyogenes?
Blood agar
What is mannitol salt agar?
A differential and selective media used to distinguish Staphylococcus aureus
What is MacConkey agar
A differential and selective media used to distinguish and select gram-negative cells that ferment lactose
What is a bismuth sulfite agar? How does it work?
A highly selective medium used to isolate Salmonella species (specifically S. typhi)
Inhibits most gram-positive and most gram-negative commensal bacteria except for Salmonella
What is an enrichment culture used for?
Preliminary isolation that favors the growth of a particular organism to bring them up to detectable levels.
What is the most common method used to isolate an individual organism in a culture (pure culture)?
Streak plating (dilutes cells)
What two methods are used for long term storage of bacterial cultures?
- Deep freezing to -80 ℃
- Lyophilization (freeze-drying) and then vacuum sealed in an ampule
What are the alternative methods for bacterial division aside from binary fission?
Budding
Conidiospores
Fragmentation
In what phyla of organisms is budding observed?
Planctomycetes
Cyanobacteria
Firmicutes
What type of bacteria produce conidiospores?
Filamentous bacteria
How often do E. coli divide?
Every 20 minutes
How often do most bacteria divide?
Every 1-3 hours
You start with 2x105 cells/mL. How many cells will there be after 5 doublings?
6.4 x 106
What are the 4 phases of bacterial growth?
- Lag phase
- Log phase
- Stationary phase
- Death or decline phase
Direct microscopic counts are measured in units of ____
Number of cells counter / volume of area counted
