Microbial Growth #5 Flashcards
Describe the different growth phases of bacteria in batch culture and why they occur. Describe how the timing of the growth phases will differ depending on how population size is determined.
Lag phase: bacteria is producing enzyme and preparing to grow
Exponential growth: The bacteria is growing
Stationary phase: The bacteria has used up most nutrients, and is under cryptic growth (growing at the rate it is dying), secondary compound are being produced to destroy the microbes
Death phase: Now all it does is die
Measures:
Optical density: is observing mass via light diffusion, and will therefor detect the rise of enzymes. OD will have a much shorter lag phase.
Viable counts: cell # will not increase as soon. So cell # will have a longer lag phase. Cell # however will continue to increase during late log phase while mass has stopped increasing. This is because the cell replicates multiple copies of DNA at a time. Once nutrients are gone, it must still place these copies somewhere, so it divides into many small cells. This also gives the added advantage of increasing surface area to volume ratio, which is an advantage if you are going into a limited nutrient world.
Different measures and when death phase will be detected:
Optical density: Will be the first measure to drop, cells are loosing mass, consuming
1, energy stores
2, enzymes
3, RNA (at this point the cell will likely dye)
Plate counts: 2nd measure to drop. Cells will no longer be culturable.
Live-dead stain: 3rd to drop. cells are dead and lysed.
Direct microscope counts: last measure to drop. There aren’t even cells left alive in the culture anymore
Define the terms: psychrophile, mesophile, thermophile, and extreme or hyperthermophile. What special adaptations allow these organisms to exist in extreme environments? What appears to be one of the primary restrictions limiting the distribution of living organisms?
psychrophile: survives <15 C
- short unsaturated fatty acid
mesophile: 15-45 C
thermophile: 45-80C
- long saturated fatty acids
hyperthermophile: >80 C
- monolayer of fatty acids, or very long completely saturated fatty acid bilayer
The presence of liquid water.
- Describe three effects of environmental pH on microbial growth. What terms describe microorganisms capable of living at pH extremes?
1, Elemental solubility: toxicity, cl or na may be the only soluble elements, they are very toxic
2, elemental solubility: nutrient availability, is the nutrient soluble.
3, Changes the nature of outer membrane proteins
Acidophiles: < 5.5
Neutrophiles: 5.5 - 8
Alkilophiles: > 8
Provide an equation that describes the effect of substrate concentration on the growth rate constant. Be able to provide appropriate units for the Monod constants, μmax and Ks; describe, using a graph, what the constants in the equation refer to; and describe how these constants would differ between copiotrophs and oligotrophs. Give an example of a “ubiquitous” oligotroph.
monod equation
u = (u(max)*[s])/(k(s) + [s])
u & u(max) are measured in 1/h
s = mg/ml
k(s) = mg/ml the amount of substrate that will result in half of u(max) as the growth rate constant
copiotroph: are r strategists, high u(max) high k(s).
oligiotroph: are k strategists, low u(max) low k(s)
peligabacter ubique
- Provide several terms that describe microorganisms based on their oxygen requirements.
Aerobic - Obligate aerobes: - Facultative anaerobes: - Microaerophiles: Anaerobic: - Obligate: - Aerotolerant:
- Describe the free radical forms of oxygen that are toxic to some microorganisms and how particular enzymes deal with these free radicals.
O2 + e- –> O2(-) superoxide
O2- + e- –> O2(-2) || h2o2 hydrogen peroxide
O2(-2) + e- –> H20 + OH (hydroxyl, most dangerous free radical)
OH + e- –> H20 (safe)
Superoxide Dismutase 2O2- --> H202 + O2 Catalase 2H202 --> 2H20 + O2 Peroxidase H202 + NADH --> 2 H2O
- Describe two measures of water “availability” and know how the values change as water availability changes. Be able provide approximate values (and units) for pure water, blood, and seawater.
Water activity: Is the humidity above of a solution divided by the humidity above pure water (value 1 pure water –> approaching 0)
Water potential: the amount of pressure, made negative, that it would take to make the solutions water level equal to the water level of a solution of pure water which is separated from this solution by a semipermeable layer. (values 0 pure water –> negative infinity
h20 blood sea water
Water activity 1 .996 .985
Water potential 0 -.5 -2
- Describe the adverse effects of increases and decreases in water availability on microorganisms, three reasons why microbial activity is lower at low water potential.
Microbes are less effective at low water levels
1, Larger diffusion distances
2, Enzymes are less hydrated
3, Specific ion concentration: ions are rising in concentration, the organism must counteract outside water concentrations by uptake of ions and use of compatible solutes
How do microbes respond to sudden increase in water availability?
A sudden decrease?
Sudden increase:
Water is flooding into the cell. Cell makes controlled breaks in its cell wall/membrane to let water, and more importantly solutes flow out. Goal: stop plasmoptysis
Sudden decrease/non-sudden decrease: Cell is shrinking. Absorbs some ions, but must produce compatible solutes to increase ion conc. and therefor cellular water conc. Goal: stop plasmolysis
Plasmoptysis:
Plasmolysis:
Plasmoptysis: breaking of cell due to build up of water. Caused because the environment is hypotonic to the cell.
Plasmolysis: shrinking of cell due to water loss. Caused because the environment is hypertonic to the cell.
- Define the term “compatible solute” and name at least four that are found in bacteria or fungi.
Compatible solute: Pulls water into cell, so likely charged. Do not hurt the cell. 4 examples - glutamate - glycine betaine - proline - trehelose
- glutamate is a…
compatible solute.
- glycine betaine is a…
compatible solute.
- proline is a…
compatible solute.
