Lecture 7 and 8 Flashcards
What are the 5 shapes of colonies?
Circular, rhizoid, irregular, filamentous, spindle
What are the 6 possible margins of a colony?
Entire, undulate, lovate, cruled, rhizoid, filamentous
What 4 elevations can a colony have?
Flat
Raised
Convex
Umbonate
What is the smallest colony size?
Punctiform
Bacteria within a colony can be genetically identical but, they can be…
Metabolically different
Define binary fission
Division into 2 equally sized daughter cells
What happens during binary fission?
Cell elongates/replicates DNA
Cell wall/plasma mebrane constrict
Cross wall forms
Cells separate
Define generation time
Time required for cell to divide
What is generation time for E.coli in nutrient rich medium at 37?
30 minutes
What is the generation time for Mycobacterium tuberculosis?
15-20 hours
What is the advantage of using logarithmic scale over non-logarithmic scale when representing bacterial populations?
Possible to predict the number of cells that will be produced over a certain time period
Why is there a lag phase?
New cultures usually come from cultures in stationary phase/ death phase (not adjusted to new environmnet)
What phase comes after lag phase?
Log phase
What happens during log phase?
High metabolic activity: cells divide, exponential growth
What phase comes after log phase?
Stationary phase
Why stationary phase?
Cells run out of nutrients, metabolic changes pH, waste products accumulate (equilibrium)
What phase comes after the stationary phase?
Death phase
Name three indirect methods of measuring microbial growth.
Turbidity
Metabolic activity
Dry weight
Name 4 direct methods of measuring microbial growth.
Plate counts
FIltration
Microscopic count
Most probable number (MPN)
What is turbidity as an indirect method for measuring microbial growth?
The use of a spectrophotometer to measure percentage transmission in suspended cells
What is a disadvantage to turbidity?
If bacteria change morphology in growth phases, turbidity changes
Cells may aggregate
What is metabolic activity as an indirect method for measuring microbial growth?
The amount of certain metabolic products is directly proportional to number of bacteria (e.g. acid or CO2 production)
What is dry weight as an indirect method of measuring microbial growth?
Cells removed from media, filtered, dried, weighted
What is a plate count?
Serial dilution of population, the number of cells is expressed as colony forming units (CFU)
How is the amount of bacteria in the original sample calculated using plate counts?
Count colonies on plate, multiply by dilution factor
What are the two types of plate count?
Pour plate method
Spread plate method
What type of bacteria can be grown using the pour plate method?
Facultative anaerobic bacteria (problematic if bacteria are temperature sensitive)
What is the filtration method of measuring microbial growth?
Bacteria are filtered and the filter is placed on a growth medium
When is filtration used to measure microbial growth?
When quantity of bacteria is very small (e.g. samples from lakes/ streams)
How does the MPN (most probable method) measure microbial growth?
Dilute to reduce density to which no bacteria are left to grow in tubes
When is MPN useful?
When microbes will not grow on solid media
What is MPN?
The statistical estimation of number of cells
What are the two main requirement catagories for bacterial growth?
Physical requirements
Chemical requirements
What name is given to bacteria that grow between ~-10-20 degrees C?
Psychrophiles
What name is given to bacteria that grows between 0 and 30 degrees C?
Psychrotrophs
Between which temperatures do mesophiles grow?
10 and 50 degrees
Between which temperatures do thermophiles grow?
40 and 70
What name is given to bacteria that grows between 65 and 110 degrees?
Hyperthermophiles
How do psychrophiles keep their fatty acids remaining fluid?
Proeinaceous antifreeze
Name a psychrotroph that grows in fridges.
Listeria monocytogenes
Name a mesophile.
E.coli
Name a thermophile
Sulfolobus (e.g. Yellowstone national park hotsprings)
What are the red/brown bacteria in Grand pismatic spring?
Pigmented bacteria (carotenoid) gives protection from light
Name a hyperthermophile.
Thermothoga maritima (lives in hydrothermal vents)
What is the temperature growth record?
121C
What pH do acidophiles grow at?
pH below 7
What pH do moderate acidophiles grow between?
3-5
What name is given to acidophiles that grow below pH 3?
Extreme acidophiles
What bacteria grow between pH 6.5 and 7.5?
Most bacteria
Neutrophiles
What type of bacteria grows at pH 9-12?
Alkaliphiles
What does hypertonic environments cause?
Plasmolysis
What name is given to bacteria that require high external solute concentration?
Extreme/obligate halophiles
What name is given to bacteria that can tolerate high external solute concentrations?
Facultative halophiles
Why do bacteria require nitrogen?
Protein synthesis
DNA
RNA
ATP
Where do bacteria obtain nitrogen from?
Amino acids
NH4+
NO3-
Gaseous N2
Why do bacteria require sulfur?
Protein synthesis, vitamins
Where do bacteria obtain sulfur from?
Amino acids
SO4^2-
Hydrogen sulfide
Why do bacteria require phosphorus?
DNA, RNA, ATP
Where do bacteria obtain phosphorus from?
PO4^3-
What are trace elements?
Inorganic elements require in small amounts for co-factors in enzymes
Name some trace elements
Iron, copper, zinc
What are organic growth factors?
Organic compounds obtained from the environment
Name some organic growth factors
Vitamins
Amino acids
Purines
Pyrimidines
What bacteria have only aerobic growth (oxygen required)?
Obligate aerobes
What bacteria have both anaerobic and aerobic growth?
Facultative anaerobes
What bacteria only grows anaerobically?
Obligate anaerobes
What name is given to bacteria that only grows anaerobically, but continues in the presence of oxygen?
Aerotolerant anaerobes
What name is given to bacteria that only grow in aerobic conditions, but oxygen is required in low concentration?
Microaerophiles
Why can oxygen be toxic?
Singlet oxygen (O2-) Higher energy state Peroxide anion (O2^2-) contained in H2O2
What enzyme detoxifies peroixide anions?
Superoxide dismutase (SOD) turns it back to H2O2
What enzyme turns H2O2 into water and oxygen?
Catalase
What enzyme turns H2O2 into water in the presence of hydrogen?
Peroxidase
How do bacteria communicate in biofilms?
Quorum sensing
What do nutrient agar’s typically contain?
Peptone Beef extract Sodium chloride Agar Water
What is peptone? Why is it added?
Partially digested protein
Energy, carbon, nitrogen, sulfur
Why is beef extract in agar?
Vitamins, organic growth factors
What are two types of medium?
Selective medium, differential medium
What is an enrichment culture?
Similar to selective medium, but increases number of desired microbes to detectable levels
