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BIOL 385 Chapter 5

Terms in this set (106)

Growth
An increase in the number of cells
Binary fission
Cell division following enlargement/elongation of a cell to twice its minimum size
Septum
Partition between dividing cells, pinches off between daughter cells
Generation time- 20 minutes for E.coli
Time for microbial cells to double in number
Nutrition, genetic factors, and temperature
What does generation time depend on?
1. Chromosome gets copied
2. Cell elongates
3. Cell divides into two
What are the 3 steps to binary fission?
Budding division
Results from unequal cell growth and forms a new daughter cell
Planktonic growth
Growth in suspension
Sessile growth- attached polysaccharide matrix with embedded bacteria
Growth attached to a surface that can form biofilms
Planktonic cells attach and a sticky matrix forms
Biofilms form in stages....
Microbial mats
Multilayered sheets with different organisms in each layer (hot springs and intertidal areas)
-They prevent harsh chemicals, such as antibiotics from penetrating
-They prevent protists from grazing
- They prevent washing away of cells
What purpose do biofilms serve?
They can block water distribution systems and fuel storage tanks, where the fuel can now be contaminated. They can also form from implanted devices, which can cause hard to treat infections
How do biofilms affect humans?
Exponential growth- N = No2^n
Growth of a microbial population in which cell numbers double within a specific time interval
- Log= straight line
- Arith= backwards L-shape
Logarithmic vs Arithmetic plot
g= t/n
What is the generation time of an exponentially growing population?
Batch culture
A closed-system microbial culture of fixed volume
1. Lag phase
2. Exponential (log)
3. Stationary
4. Death
4 stages of growth for bacterial cells in a closed
Lag phase
-Bacterial growth stage in which bacteria switch their metabolic machinery from the dormant state to an actively growing state; making new enzymes
- Number of new cells= number of dying cells
Log phase
Bacterial growth stage in which the bacteria are actively undergoing binary fission; cells are in their healthiest stae
Stationary
Bacterial growth stage in which the number of new cells is equal to the number of dying cells because nutrients have started to deplete
Death phase
-Bacterial growth stage where a large number of cells are dying because nutrients have been depleted and waste build up is too great
-Exponential rate
Continuous culture
An open system microbial culture of fixed volume
Chemostat
Most common type of continuous culture device
-Dilution rate
-Concentration of a limiting nutrient
Both growth rate and population density of a culture can be controlled independently and simultaneously depending on....
F/V, where F= flow rate of adding fresh medium and removing spent medium, and V= culture volume
What is the dilution rate?
Steady state
Cell density and substrate concentration do not change over time
- Can maintain exponential growth phase for weeks/months
- Used to study physiology, microbial ecology and evolution, enrichment and isolation of bacteria from nature
- Growth rate controlled by dilution rate
What are experimental uses of continuous cultures?
Culture media
Nutrient solutions used to grow microbes in a laboratory and are typically sterilized in an autoclave
1. Defined media
2. Complex media
What are the 2 broad classes of culture media?
Defined media
Exact chemical composition of the media is known
Complex media
Media composed of digests of microbial, animal, or plant products
Enriched media
-A type of media that contains complex media plus highly nutritious materials (serum or blood)
-Used to culture fastidious (nutritionally demanding) microbes
Selective media
Media that contains compounds that selectively inhibit growth of some microbes but not others
Differential media
Media that contains an indicator, usually a dye, that detects particular metabolic reactions during growth
By adding the gelling agent agar to liquid media- cells form isolated masses (colonies) when grown on solid media
How are solid media formed?
Microscopic cell count- dried on slide or liquid samples
Total cell count that involves observing and enumerating cells present
Counting chambers with squares are etched onto the slide for liquid samples- 16 squares within one square. Multiply the number of cells in 1 square by 25 large squares.
How does a microscopic cell count work?
1. Cannot distinguish between live and dead cells without special stains
2. Small cells can be overlooked
3. Cell suspensions of low density of are hard to count (<10^6 cells/ml)
4. Motile cells need to be immobilized
5. Debris in sample can be mistaken for cells
Limitations to microscopic cell counts?
They are often used in natural samples where DAPI reacts with DNA- fluorescent stains can be used to differentiate between live and dead cells. Phylogenetic stains can determine proportion of Bacteria and Archaea.
How can microbial cell counts be used in microbial ecology?
Viable cell plate count
Plate count that involves measuring living, and reproducing populations
1. Spread-plate method
2. Pour-plate method
What are the 2 ways to perform plate counts?
The sample is mixed with molten media. A limitation is that colonies can form under the surface and can be missed during counting.
What is the pour-plate method?
30-300 (significant)
Count colonies on plates with _______-___________ colonies
Diluted (Plate count x Dilution factor = CFU's per ml)
To obtain the appropriate colony number, the colony to be counted should always be.....
1. Quick and easy
2. Used in food, dairy, medical, and aquatic microbiology, and water analyses
3. Can target particular species in mixed samples
What are applications of the viable plate count method?
Direct microscopic counts of natural samples reveal far more organisms than those on recoverable plates
What is the great plate count anomaly?
Microscopic methods use dead cells, whereas viable cell counts do not. Different organisms may have vastly different requirements for growth and growth rates (a possible error is length of incubation time).
Why does the great plate count anomaly occur?
Temperature
A major environmental factor controlling microbial growth
1. Minimal
2. Optimal
3. Maximal
*Range is less than 40 degrees celcius
What are the 3 cardinal temperatures?
Membrane gelling and transport processes are so slow that growth cannot occur.
What happens at minimal temperatures for organisms?
Enzymatic reactions are occurring at maximal rates.
What happens at optimal temperatures for organisms?
Proteins denature and the cell membrane starts to collapse. There is also thermal lysis.
What happens at maximal temperatures for organisms?
1. Psychrophile- cold
2. Mesophile- normal temperatures, most studied, most pathogens
3. Thermophile- hot environments
4. Hyperthermophile- found in extremely hot environments such as hot springs and deep-sea hydrothermal vents
5. Psychrotrophs- lead to food spoilage in fridge at cool temps
What are the 5 temperature classes of organisms?
Extremophiles
Organisms that grow under extremely hot or cold conditions
Psychrophiles
Organisms with optimal growth temperatures below 15 degrees, max of 20 degrees and a minimum of 0 degrees
Psychrotolerant
-Organisms that can grow at 0 degrees celsius, but grow optimally at 20-40 degrees celsius
-More widely distributed than psychrophiles
- Isolated from soils and water in temperate climates and food at 4 degrees celsius
-Enzymes have more alpha helices than beta sheets
-More polar amino acids, less hydrophobic
-Fewer weaker bonds like hydrogen and ionic
What are molecular adaptations of enzymes to life in the cold?
-High unsaturated and shorter fatty-acid chain content
-Some polyunsaturated fatty acids that remain flexible at low temps
-Cold shock proteins (chaperones)
-Exopolysaccharide cell surface slime
-Cryoprotectants that prevent the formation of ice crystals (antifreeze proteins, glycerol or other sugars)
Molecular adaptations to life in the cold
Thermophiles
Organisms with growth temperature optima between 45 and 80 degrees
Hyperthermophiles
Organisms with optima greater than 80 degrees
Only prokaryotic cells survive but there is great diversity
Can organisms live above 65 degrees celsius?
Chemoorganotrophs and chemolithotrophs. Both bacteria and archaea are present. Generation times can be as low as one hour
What kind of species can be hyperthermophiles?
-Some subtle amino acid substitutions provide more heat-tolerant folds
-Increased ionic bonding between acidic and basic amino acids resist unfolding
-Highly hydrophobic interiors
How are enzymes and proteins able to function at extreme temperatures?
They can prolong shelf-life like the Taq polymerase from the hyperthermophile Thermus aquatic
How can enzymes be commercially useful?
They have lipids in long-chain saturated fatty acids
How do bacterial thermophiles keep flexibility in their cytoplasmic membrane?
They have C40 hydrocarbons made of repeating isoprene units bonded to glycerol phosphate and membranes form monolayers
How do archaeal thermophiles keep flexibility in their cytoplasmic membrane?
2-3 units
Each microbe has a pH range of how many units?
3-9
Most natural environments have a pH of....
Logarithmic
What kind of scale is the ph scale?
Below 4
Very few bacteria live in what pH?
Neutral conditions
What pH does E.coli live in?
Picrophilus oshimae
An acidophile that forms from the runoff of mines and lives in a pH range of 1
Neutrophile
Organisms that grow optimally between pH of 5.5-7.9
Acidophiles
-Organisms that grow best at a pH less than 5.5
-Some can be obligate where membranes are destroyed at neutral pH
Alkaliphiles
-Organisms that grow best at a pH greater than 8
-Found in soda lakes and high carbonate soils
-Used commercially (secreted proteases and lipases used in laundry detergents
-Some have a sodium motive force rather than a proton motive force
True
T or F: The intracellular pH must stay relatively close to neutral (5-9) even if the external pH is acidic or basic
Through the use of buffers
How do microbial media maintain pH?
Osmosis
Water diffused from high to low concentrations
The tendency is for water to move into the cell since the cytoplasm has a higher solute concentration than the surroundings
What is the positive water balance?
Halophiles
-Organisms that grow best at a water activity of 0.98 (seawater)
-Have a specific requirement of NaCl
Halotolerant
Organisms that can tolerate some additional dissolved solutes but generally grow best in the absence of the added solute
Extreme halophiles
Organisms that require very high levels (15% to 30%) of NaCl and are often unable to to grow at lower conc.
E. coli
Example of a nonhalophile
Staphylococcus aureus
Example of a halotolerant organism
Aliivibrio fischeri
Example of a halophile
Halobacterium salinarium
Example of an extreme halophile
Aerobes (can be obligate)- micrococcus luteus
Require oxygen and grow at full oxygen tension (21%)
Microaerophiles- Spirillum volutans
Can use oxygen only when it is present at levels reduced from that in air due to limited respiration or oxygen sensitivity
Faculative organisms- E. coli
Organisms that can live with or without oxygen
Anaerobes
Organisms that cannot respire oxygen
Aerotolerant anaerobes- Streptococcus pyogenes
Organisms that tolerate oxygen and grow in its presence even though they cannot respire
Obligate anaerobes (C.tetani)- sewage sludge, anoxic lake sediments
Inhibited or killed by oxygen
Molecular oxygen is not toxic, but oxygen byproducts can be toxic (superoxide anion O2-, hydrogen peroxide, oxygen radical
Why is oxygen toxic?
Catalase and peroxidase
Enzymes that convert hydrogen peroxide to oxygen and water
Superoxide dismutase
Converts superoxide anion to hydrogen peroxide and oxygen
Superoxide reductase
An enzyme found in some strict anaerobes that converts O2- to hydrogen peroxide without producing oxygen
Antimicrobial agents (-cidal= kills, -static= inhibits growth)
Chemicals that kill or inhibit growth
Bacteriostatic agents (log cell number vs time gives a straight line when added to an exponentially growing population for both TCC and VCC)
Agents that inhibit biochemical processes such as protein synthesis and bind weakly
Bacteriocidal agents (TCC goes straight, VCC dives down)
Agents that bind tightly and kill the cell
Bacteriolytic (Both TCC and VCC dive down)
Agents that kill by lysis, such as detergents
Minimum inhibitory concentration (MIC)
Smallest amount of an agent needed to inhibit growth of a microorganism
An antimicrobial agent is added to a filter paper disc, which diffuses among the agar solid media. MIC is reached at some distance
How is the MIC analyzed?
Zone of inhibition
Area of no growth around disc
-Sterilants: destroy all microorganisms, including endospores
-Disinfectants: used on surfaces to kill microorganisms but not endospores
-Sanitizers: reduce microbial numbers but do not sterilize
-Antiseptics (germicides): kill or inhibit microbial growth but are nontoxic enough to be applied to living tissues
What are used to prevent growth on inanimate surfaces and external body surfaces
-Alcohol (60-85% ethanol or isopropanol in water)
-Phenol-containing compounds: hexachlorophene, triclosan, chloroxylenol, chlorhexidine
-Ocetenidine
-Iodophors (Betadine)
-Hydrogen peroxide (3%)
-Cationic detergents (Benzalkonium chloride)
Examples of antiseptics
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