Exam 2 Material (Chap. 5) Flashcards
(79 cards)
1
Q
Growth
A
increase in the number of cells
2
Q
Binary Fission
A
cell division following enlargement
- Division strategy for Bacteria and Archaea
- Haploid ONLY
- all cells must replicate and segregate genome prior to division
3
Q
Generation Time
A
time required for microbial cells to double in number
4
Q
Microbial Growth and Cell Division
A
- Increase in mass and cell numbers
- Mitosis in most eukaryotes
- Budding in yeasts
- Fragmentation in filamentous fungi
- Binary fission in bacteria
5
Q
Steps in Binary Fission
A
- Chromosome Replication
- Chromosome attachment to cell membrane
- Chromosomal segregation
- Septum formation
~ inward movement of cell wall and cell membrane dividing daughter cells - Wall Elongation
6
Q
Fts Proteins
A
Involved in Binary Fission/Cell division
- Fts (filamentous temperature sensitive) Proteins are essential for cell division in ALL prokaryotes
- Found in bacteria, archaea, chloroplasts, and mitochondria
- Interact to form division apparatus (Divisome)
- Consists of 3 subunits: FtsZ, FtsA, and ZipA
7
Q
FtsZ
A
Subunit of Fts Protein
- attaches at center of cell and forms ring
- Becomes cell division plane (tubulin-like)
8
Q
FtsA
A
Subunit of Fts Protein
-connects FtsZ ring to membrane and recruits other divisome proteins (actin-like)
9
Q
ZipA
A
Subunit of Fts Protein
-anchor protein attaches FtsZ ring to cytoplasmic membrane
10
Q
MreB
A
Major shape-determining factor in prokaryotes
- forms simple cytoskeleton in Bacteria and probably Archaea that forms spiral-shaped bands around inside of cell, underneath the cytoplasmic membrane
- NOT found in coccus-shaped bacteria
- Localizes synthesis of new peptidoglycan and other cell wall components to specific locations along cylinder of rod-shaped cell
11
Q
Peptidoglycan Synthesis
A
-Production of new cell wall material
-Major feature of cell division
~in cocci, cell walls grow in opposite directions outward from FtsZ ring
~in rod-shaped cells, growth occurs at several points along cell
12
Q
Peptidoglycan Synthesis: Before Cell Division
A
- Before cell division can occur, cell wall synthesis must occur
- Preexisting peptidoglycan needs to be severed to allow newly synthesized peptidoglycan to form
13
Q
Peptidoglycan Synthesis and Cell Division
A
- Beginning at FtsZ ring, small openings in wall are created by autolysins
- New cell wall material added across openings
- Wall band, NAM, NAG, and tetra peptide units linked to existing peptidoglycan
14
Q
Wall band
A
junction between new and old peptidoglycan
15
Q
Peptidoglycan Growth
A
- In cytoplasm uridine diphosphate attaches to NAM and NAG
- NAM-UDP attached to NAG and bacterprenol transports molecules
- Autolysins degrade peptidoglycan and new units added
16
Q
Bactoprenol
A
Lipid carrier molecule that plays major role in insertion of peptidoglycan precursors such as C55 alcohol and bonds to N-acetylglucosamine/N-acetylmuramic acid/pentapeptide peptidoglycan precursos
17
Q
Glycolases
A
Enzymes that interact with bactoprenol to:
- insert cell wall precursors into growing points of cell wall
- catalyze glycosidic bond formation
18
Q
Transpeptidation
A
Final step in cell wall synthesis
- Forms the peptide cross-links between muramic acid residues in adjacent glycan chains
- Inhibited by the antibiotic penicillin
19
Q
On which bacterial population would Penicillin work best? a) a healthy actively growing population b) a population of cells that are in decline c) a population of cells that are in a stasis state
A
A) A healthy actively growing population because penicillin inhibits transpeptidation which occurs when population is growing and cells are dividing
20
Q
Generation Time of bacteria
A
- shorter than eukaryotic microbes
- dependent on growth medium and incubation conditions
- when one cell divides to form two, one generation has occurred
21
Q
Growth of a colony
A
continues until one of these things occurs:
- Nutrients depleted
- Water depleted
- Space no longer available
- Waste products build up and poison cells
22
Q
Growth curve
A
plotted by:
- Growing one species in broth at set temperature
- Measuring number of bacteria at different time points
- Plotting number of bacteria on logarithmic scale over time
23
Q
Math of Exponential Growth
A
Relationship exists between initial number of cells present in culture and number present after period of exponential growth
-final cell # = initial cell number x2^(# of generations during period of exponential growth)
24
Q
Batch Culture
A
closed-system microbial culture of fixed volume
25
4 phases of closed system growth
1. Lag phase
2. Exponential phase
3. Stationary phase
4. Death phase
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Exponential Phase
pattern of population increase, # of cells doubles during each generation time
-rate of increase in cell # slow initially but increases at ever faster rate
**Time of maximum growth
also known as logarithmic growth phase
-cells exhibit balanced growth meaning the cellular constituents are manufactured at constant rates relative to one another
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Lag Phase
- Microbes absorb nutrients, synthesize enzymes, and prepare for cell division
- beginning of growth cycle
28
Stationary Phase
- occurs when # of microbes dying equals # of microbes dividing
- may be due to nutrients or oxygen being depleted or waste product build up altering pH
- entry into this phase activates survival strategies such as morphological changes (ex. endospore formation), decrease in size, protoplast shrinkage, and nucleoid condensation
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Death Phase
occurs when population starts decreasing due to depletion of resources or waste build up
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Continuous cultures
The Chemostat
- nutrients constantly supplied and end products flushed out
- growth rate and population density of culture controlled simultaneously
- useful for studies that need to keep cultures in constant environments for long periods
* **Possible to control population growth rate- known as steady state***
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Chemostat
common type of continuous culture device
| -consists of fresh medium entering via a flow-rate regulator and waste leaving carrying overflow of microbial cells
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Continuous culture vs. batch culture
1. precise control of cell growth rates/densities
2. able to maintain cell growth in exponential phase
3. study microbial interactions under different conditions
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4 Methods of measuring Microbial Growth
1. Microscopic counts
2. automatic cell counts
3. viable cell counts
4. Turbidimetric methods
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Microscopic counts
microbial cells are enumerated by microscopic observation
- all cells are counted in large squares: several large squares counted and numbers are averaged
- unreliable results
35
Limitations of microscopic counts
- can't distinguish between live and dead cells without staining; phase-contrast microscope required if stain not used
- small cells can be overlooked
- precision difficult to achieve
- motile cells need to be immobilized
- debris in sample can be mistaken for cells
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Automatic Cell Counts
method for enumerating cells in liquid sample using a flow cytometer, using laser beams, fluorescent dyes, and electronics
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Viable Cell Counts
plate counts
- measurement of living, reproducing population
- microbes grown on plates
- to obtain accurate colony #, sample to be counted should always be serially diluted
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Serial Dilution
Diluting sample into varying amounts of water
* done in micro lab
* for specifics view slide
39
The Great Plate Anomaly
direct microscopic counts of natural samples reveal far more organisms than those recoverable on plates, Why?
-microscopic methods count dead cells where viable methods do not and different organisms may have vastly different requirements for growth
40
Turbidimetric Methods
an indirect but very rapid and useful method of measuring microbial growth
uses light absorbed to determine density of colony
-most often measured with spectrophotometer and referred to as optical density (O.D.)
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Limitations of Turbidimetric Counts
- quick and easy to perform
- typically don't require destruction or significant disturbance of sample
- sometime problematic because microbes can form clumps or biofilms in liquid media
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Factors regulating growth
1. Nutrients
2. environmental conditions such as temperature, pH, and osmotic pressure
3. generation time
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Extremeophiles
most organisms grow in fairly moderate environmental conditions but these types of microorganisms grow under harsh conditions that would kill most other organisms
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Temperature on Microbial Growth
- microbes can't regulate their internal temperature
- enzymes have optimal temperature at which they function optimally, higher temps may inhibit enzyme functioning and can be lethal
- exhibit distinct cardinal growth temps: minimal, maximal, and optimal
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Minimal growth temperature
membrane gelling; transport processes so slow that growth can't occur
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Maximum growth temperature
protein denaturation; collapse of the cytoplasmic membrane; thermal lysis
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Temperature ranges for microbial growth
- Psychrophiles: 0-20 degrees C
- Mesophiles: 20-45 degrees C
- Thermophiles: 55-85 degrees C
- Hyperthermophiles: 85-113 degrees C
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Mesophiles
```
Organisms that have midrange temperature requirements; found in:
-warm-blooded animals
-terrestrial and aquatic environments
-temperate and tropical latitudes
20-45 degrees C
```
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Psychrophiles
organisms with cold temperature optima
| -inhabit permanently cold environments
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Psychrotolerant
organisms that can grow at 0 degrees C but have optima of 20-40 degrees C (can tolerate extreme but prefer midrange temps)
-more widely distributed in nature than psychrophiles
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Molecular Adaptations to Psychrophily
1. Productions of enzymes that function optimally in cold; more alpha-helices than beta, more polar/less hydrophobic AAs, fewer weak bonds, decreased interactions b/w protein domains
2. Transport processes function optimally at low temps; modified cytoplasmic membranes, high unsaturated fatty acid content
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End of Eukaryotic life
about 65 degrees C, only prokaryotic life forms exist above this temp
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Thermophiles
organisms with growth temperature optima between 45-80 degrees C
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Hyperthermophiles
organisms with optima greater than 80 degrees C
-inhabit hot environments including boiling hot springs and seafloor hydrothermal vents that can have temps in excess of 100 degrees C
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Microbial Life at high temps
- Prokaryotes are able to grow at higher temps than eukaryotes
- organisms with highest temp optima are Archaea
- nonphototropic organisms can grow at higher temps than phototropic organisms
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Molecular Adaptations to Thermophily
1. Enzyme and proteins function optimally at high temps; features that provide thermal stability include the following: critical amino acid substitutions provide more heat-tolerant folds, increased # of ionic bonds b/w basic and acidic amino acids resist unfolding, and production of solutes (di-inositol phosphate, diglycerol phosphate) help stabilize proteins
2. Modifications in cytoplasmic membranes to ensure heat stability
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Modification in cytoplasmic membrane of thermophilly bacteria
have lipids rich in saturated fatty acids
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Modification in cytoplasmic membrane of thermophilly archaea
have lipid monolayer rather than bilayer
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pH effects on microbial growth
pH=-log[H+]
- most organisms grow best between a pH of 6 and 8 (neutrophiles) while others have adapted to lower or higher pH
- most microbes maintain internal pH near neutrality: proton membrane impermeable to proton, exchange potassium ions for protons
- Acidic tolerance response: some organisms synthesize acid and heat shock proteins that protect proteins/DNA and they also pump protons out of the cell
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Acidophiles
growth optimum between pH 0 and 5.5
- membranes destroyed at neutral pH
- stability of cytoplasmic membrane critical
61
Alkaliphiles
growth optimum between pH 8.5 and 11.5
| -some have sodium motive force rather than proton motive force
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Neutrophiles
growth optimum between pH 5.5 and 7
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Barotolerant
adversely affected by increased pressure, but not as severely as non-tolerant organisms
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Barophilic (peizophilic)
- require or grow more rapidly in presence of increase pressure
- change membrane fatty acids to adapt to high pressures
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Water Activity
ratio of vapor pressure of air in equilibrium with substance or solution to the vapor pressure of pure water
- amount of water available to organisms
- reduced by interaction with solute molecules (osmotic effect)
- ***Higher solute concentrantion = lower water activity
- reduced by absorption to surfaces (matrix effect)
66
Dead Sea
- Tectonic Basin ~-423 m = lowest point on the surface of the planet
- Salinity ~350 = one of the saltiest naturally occurring bodies of water on the planet
- pH ~6
- Until 1930s believed devoid of life
- Wilkansky, 1936 showed microorganisms can inhabit (<10^5 cells/ml). Aerobic halophilic microorganisms were found.
67
Solute concentrations on orgnaisms
- cytoplasm has greater concentration than surrounding environment --> tendency for water to move into cell (cells swell and burst)
- in environment with a higher external solute concentration, water will want to flow out of the cell (cells shrink and shrivel)
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Halophiles
organisms that grow best at reduced water potential and require NaCl
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Extreme halophiles
require high levels (15-30%) NaCl
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Halotolerant
can tolerate some reduction in water activity
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Halophile Defense Mechanisms
1. increasing internal solute concentration by pumping inorganic ions into cell and synthesis of organic solutes
2. Organic In
- energetically expensive but does not require protein alteration
3. Salt In
- energetically cheap but requires protein alteration
- used by all Haloarchaea and two lineages of bacteria
72
osmophiles
organisms that live in environments high in sugar as solute
73
xerophiles
organisms that are able to grow in very dry environments
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Facultative organisms
can live with or without oxygen
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aerotolerant anaerobes
can tolerate oxygen and grow in its presence even though they cannot use it
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microaerophiles
can use oxygen only when it is present at levels reduced from that in air
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Thioglycolate Broth
complex medium that separates microbes based on oxygen requirements
-reacts with O2 so it can only penetrate the top of the tube
78
toxic forms of oxygen in cell
1. single oxygen
2. superoxide anion
3. hydrogen peroxide
4. hydroxyl radical
79
toxic oxygen enzymes
1. catalase
2. peroxidase
3. superoxide dismutase
4. superoxide dismutase/catalase combo
5. superoxide reductase
