Microbrial Growth Flashcards
Is microbial growth measured as an increase cell size or cell number?
Increase in CELL NUMBER
Why is cell size NOT a method used for measuring microbial growth?
b/c changes in cell size (double during lifetimes) are INSIGNIFICANT; they are relative population sizes
What units are used to measure growth rate?
Typically as microbrial generation/ time (cell doublings)
What is a colony?
Colony: Visible mass of microbial cells arising from one cell or from a group of the same microbes
How do you determine the number of cells in a colony?
To determine number of cells in colony:
set the petri dish on a grid background and count the colonies once in each grid cell, moving in methodical pattern through all of the cells
REVIEW THIS
Describe the physical and chemical requirements for Microbrial Growth
Growth Requirements
Physical Requirements:
-Temperature
-pH
-Osmotic pressure
Chemical requirements
-Carbon
-Nitrogen, sulfur, phosphorus
-Trace elements
-Oxygen
-Organic growth factors
Describe the different temperatures for Microbrial growth . When do growth rates drop?
Temperature:
Each bacteria has Minimum, Optimum, and Maximum temperatures for microbes to grow (approximately 30 degree celsius window)
-Growth rate Drops rapidly from Optimum to Maximum temperatures
(Max temp will be 30 degrees celsius, before microbe growth drops)
Describe the growth rates vs temperature for different microbes
What does “Philes” and “trophic” indicate?
Growth Rates vs Temperature for Different microbes
- Psychotrophiles- short growth rate, temp between -5 and 15 degrees celsius
Psychotrophs; longer growth rate than Strict psychotriles; but still one of shorter rates; temperature: - 10 degrees and 25 degrees C
Mesophiles: longer growth rate than psychotrophs/triles; temperature between 20 and 45 degrees
Thermophiles; Highest growth rate (temperature between 50 degrees and 65 degrees C)
Hyperthermophiles : second highest growth rate; temperature is between 75 degrees and 105 degrees C) Can live in very HOT environments
“Philes” = Loving
“trophic” = pertaining to food or nutrition
What are the temperatures for room temperature, boiling water, Hot water, Refrigerator, and freezer in Celsius
Refrigerator: 4 degrees C
Freezer: -20 degrees C
Room temperature; 20 degrees C
Boiling water: 100 degrees C
Hot water; 50 degrees C
Differentiate between psychrophiles and Psychotrophs. Discuss their optimal growth temperatures and features. Which of the two are more common and will most likely cause low-temp food spoilage
Psychrophiles and Psychotrophs
-Psychrophiles: initially classified as organisms able to grow at 0 degrees Celsius. Can also be split into two groups that can both grow at 0 degrees C
Strict Psychrophile
-Optimal growth around 15 degrees C
-Some can grow as low as -20 degrees C (since water freezes at O degrees; some organisms can grow in the snow or at lower temperatures at which water freezes)
-They are found in arctic soils, glaciers and deep ocean envrionments
-seldom cause food preservation problems (because oranges are Not around the environment where humans are)
(a species of Deinococcus; -12 to -17 C)
Psychotroph: grow Best around 25 degrees Celsius
-Much MORE COMMON
-Most likely to cause Low-temp food spoilage
Describe the food preservation temperatures. Also include the temperate at which destroys microbes, slow bacterial growth, rapid growth of bacteria, and where many bacteria survive and may grow.
-What two microbes can grow in the refrigerator?
Food Preservaation Temperatures:
- Temperatures in rage of 60-135 degrees C (or 140-260 F) DESTROY most microbes (although lower temperatures may take more time)
-Very slow bacterial growth at 50-60 degrees C (or 120-140 F)
-Rapid growth of bacteria (some may produce toxins): 15-50 degrees C (or 60-120 F)
-Many bacteria can survive (some may grow) at 5-10 degrees C (or 40-60 F)
-Refrigerator temperatures; may allow slow growth of spoilage bacteria (few pathogens) at 0-5 degrees C (or 30-40 F)
- Microbes that may grow in refrigerator: Listeria monocytogenes and Clostridium botulin
NO SIGNIFICANT growth below freezing at -30 to 0 degrees C (or -20 to 30 degrees F)
Explain why a properly set refrigerator will greatly slow the growth of most spoilage organisms of al but a few Pathogenic organisms?
REVIEW
Describe the features of mesophiles, including optimal temperatures. What is the optimal temperature for most pathogens?
Mesophiles
-OPTIMUM growth temperate- 25-40 degrees C
-Most COMMON type of microbe
-include most of the spoilage and disease organisms (outside refrigerator)
-Optimum temperature for most pathogens is close to that of their hosts (37 degrees C)
What are the features of thermophiles? What is their optimum growth temp and why are they important?
Thermophiles
-Optimum growth temperature of 50-60 degrees C
-Many can’t grow below 45 degrees C
-Important in ORGANIC compost piles (that get hot during the summer)
-Heat-resistant endospores can survive canning to germinate and spoil food stored at elevated temperatures (not considered public health problem)
What are the features of hyper/Extreme thermophiles? discuss their optimal growth temperature and where they are found
Hyper/Extreme Thermophiles
-Optimum growth temperature 80 degrees C
-Most live in HOT SPRINGS and SULFUR is Important for growth
-Record temperature is 121 degrees C near Deep-sea thermal vents
-Most are members of ARCHAEA
Why are Hyperthermophiles comercially important? What is the optimal growth temp for Thermus aquatics?
REVIEW
Hyperthermophiles are commercially important for INDUSTRIAL PROCESSES, that require high temperatures ( and clothes in washer to remove stains
-Thermus aquaticus (source of Taq enzyme) has an optimum growth temperature of 70-75 degrees C
Describe the different pH ranges that bacteria grow in. What pH do Mold and yeast grow? Which molecules can acts a buffers?
-Most bacteria grow between pH of 6.5 and 7.5
-Some bacteria grow in acidic environments (Acidophiles) or Alkaline environments (alkalophiles)
-Molds and Yeasts grow between pH 5 and 6
-When present in media, peptones, amino acids, and phosphate salts can acts as BUFFERS
(extreme acidophiles pH 0.5-2; acidophiles pH 2.5-5; neutrophiles pH 6-8; alkalophiles pH 9-11; Extreme alkalophiles 12-13)
Describe how osmotic pressure plays a role in microbrial growth. What kind of environment do most bacteria exist in (hypotonic, hypertonic or isotonic) ? How do they survive in this environment?
Osmotic pressure
-Microorganism obtain all their nutrients in solution from surrounding water
Most bacteria exist in a HYPOTONIC solution (concentration of solute outside cell lis LOWER than inside cell
Bacteria are able to survive this type of environment due to their STRONG CELL WALL
Describe what happens in Hypertonic environments and how cells are affected. Give examples of foods that are affected.
Hypertonic environments - more solute is on Outside of cell.
-an increase in salt or sugar causes (PLASMOLYSIS), causing cell to shrink
-Cells are inhibited (or killed) as water is drawn out
-Food preservation strategy:
salted fish, honey, jelly, sweetened condensed milk
(preserve food by packing it in a hypertonic solution of salt or sugar; killing bacteria or limiting their ability to reproduce)
What are the features of halophiles? What kind of microbes are Halophiles? What domain do extreme halophiles belong to? Differentiate between obligate halophiles and facultative halophiles
Halophiles
-Halophile means “salt loving” in Greek
-While most OCEAN microbes are SLIGHT halophiles (3-5%), moderate and extreme halophiles are generally more Specialized microbes
-Most of the Extreme halophiles belong to domain ARCHAEA
Obligate Halophiles; REQUIRE high salt (up to 30%; Dead sea)
Facultative halophiles tolerate High salt (2% or more) These halophiles can also do fine without salt
**2 % salt INHIBITS most bacteria
What are the chemical requirements for Growth?
Chemical requirements for Growth:
-Carbon
-Nitrogen, sulfur and phosphorous
-Oxygen
-Potassium, Magnesium, Calcium
-Trace elements
-Organic growth factors
What are the main six elements in living organisms ? How do you obtain the unique one of these elements?
Six elements in Living organisms :
carbon
nitrogen
sulfur
phosphorus
oxygen
HYDROGEN - you get H from water, organic compounds (Hydrogen consists of 8% dry weight of E coli)
Why is Carbon important and how do organisms get their carbon? How much of cell is made of carbon?
Carbon
-Needed for all organic compounds that make up the cell
-heterotrophs derive carbon from organic carbon sources
-Autotrophs derive carbon from CO2
-50% dry weight of a typical cell is carbon.
Where is Nitrogen found in cells, and how do bacteria obtain it?
Nitrogen
-found in Amino Acids and Bases (14% dry weight)
-sources for bacteria
Most Decomposed proteins, others use NH4+ (ammonia) or NO3 (nitrate)
A few fix N2 (free-living and symbiotic (legumes) )
Where is Phosphorous found in cells and how do bacteria obtain it?
Phosphorous
-found in DNA, RNA, ATP and membranes
-DECOMPOSITION of organic sources or Po4^3- serves as sources of Phosphorous for bacteria
Where is Sulfur seen in cells and how do bacteria obtain it? What percent dry weight is sulfur and phosphorus together?
Sulfur
-in Amino Acids (like Methionine and Cysteine), Thiamine and Biotin
-Some bacteria use SO4^2- or H2S to obtain sulfur
(combined sulfur and phosphorous represent 4% dry weight)
Describe the effect of Oxygen on Growth of different microbes. How does O2 affect Obligate aerobes, facultative and obligate anaerobes, aerotolernat anaerobes and microaerophiiles?
What percent of dry weight does O2 contain in E coli bacterium?
The Effect of O2 on Growth
-Obligate Aerobes (require O2 for growth, and will only grow at TOP of tube; hence particles are only diffused at top)
-Facultative anaerobes: prefer to use O2, but can also survive WITHOUT O2. hence more Growth will be at TOP of tube, and less growth at BOTTOM (hence high [ ] of particles at top and a few particles scattered to bottom.
-Obligate Anaerobes - DO NOT USE O2; and microbes will grow only at the BOTTOM of tube
-Aerotolerant anaerobes; They do NOT use O2, but grow EQUALLY throughout the tubes
Microaerophiles: Require O2, but can only tolerate a Small amount of O2. (if there is too much or too little O2, it will NOT grow) . Hence most growth is MIDDLE of tube
It is not That O2 is toxic, but rather the reactive species derived from O2.
**Oxygen constitutes 20% of the dry weight of bacterium E.coli
What occurs in Oxygen Reduction and what products are formed?
O2: Reduction Products
-O2 is capable of accepting 4 electrons, reducing it to water
- 4 electron reduction steps for O2 progressively generate Superoxide, Hydrogen Peroxide, and the Hydroxyl radical plus water
(throughout each strip you add 1 electron atom)
(O2 + 1 e- –> O2-(superoxide). Then Superoxide O2- + 1e + 2H+ –> H2O2 (hydrogen peroxide). Then H2O2 + e- + H+ –> H2O + OH* (hydrogen radical) Then OH* + e- + H+ –> H2O)
Explain the different way reactive oxygen species can be produced. Also discuss how O2 is reduced to superoxide and the roles of quinones
REVIEW
Active respiratory chains produce ROS (reactive oxygen species) (seen in citric acid cycle, ETC)
Electrons can Leak from the main path and directly REDUCE O2 to superoxide
-ROS are also produced:
1) as necessary intermediates in a variety of enzymatic reactions
2) by ionizing radiation (ionize H2O to hydroxyl radicals + H’s)
quinones: transfer electrons from Complex 1 to III and can accidentally transfer e- to oxygen
What are the oxygen species that harm organisms and how are they formed
Oxygen species that Harm organisms:
1) Singlet Oxygen 1 O2: an extremely reactive form of molecular O2 in which one of the electrons jumps to a higher orbital following energy absorption
** the Singlet Oxygen is an Excited state. NOT a free radical. Mostly a byproduct of Photosynthesis
2) Free radicals
** Superoxide; O2-
O2- + O2- + 2H SOD–> H2O2 + O2
** Peroxide anion: O2^2-
2 H2O2 Catalase—> 2 H2O + O2 (catalase test)
H2O2 + 2H+ peroxidase—–> 2 H2O
** Hydroxyl Radical (OH)
-Formed by ionizing radiation and respiration (traces), very short half life (10^-9s) and MOST reactive. Can’t be eliminated by an enzymatic
Explain why some organisms can grow in the presence of Oxygen, while others can’t. Also discuss the enzymes used by different microbes in their environment
Toxic forms of oxygen need to be NEUTRALIZED by enzymes
-Superoxidase dismutase (SOD)
-Catalase
-Peroxidase
**Cells have one or the other (catalase or perodixase ) , but NEVER both
Obligate anaerobe: SOD +Catalase
Facultative anaerobe: SOD + catalase
Obligate anaerobe; Neither (will not survive in presence of O2)
**Aerotolerant anaerobe: SOD + peroxidase
Microaerophiles: SOD +/- catalase (small amounts)
(may or may not have catalse)
What percent of dry weight is made of potassium, Magnesium and Calcium?
What are the roles of these three elements?
Potassium: 1% of dry weight
Magnesium: 0.5 % of dry weight
Calcium: 0.5% of dry weight
All three serve as inorganic cellular cations and inorganic cofactors for certain enzymatic reactions
What are trace elements? Where are they commonly found?
Trace elements: inorganic elements required in minute amounts that are generally used as Inorganic cofactors (ex: iron, copper, molybdenum, Zinc)
-Commonly found in Tap water
What are organic growth factors? Provide examples of these factors and explain one unique feature about them
Organic Growth factors: Essential organic compounds that an organism CANNOT synthesize and must be obtained from the enviroimet (ex: vitamins, amino acids, purines and pyrimidines)
Organic growth factors are SPECIES-SPECIFIC because many bacteria can synthesize compounds and do NOT require outside sources
Out of vitamins, amino acids, purines and pyrimidines, which serve as organic growth factors for humans?
Vitamins, Amino Acids are organic growth factors for humans.
(humans can make pyrimidines and purines)
Why are hyperthermophiles that grow at temperatures above 100 degrees C seemingly limited to oceanic depths?
because if you are not at OCEAN depths; you will NOT reach temps above 120 degrees Celsius
Other than controlling acidity, what is an advantage of using phosphate salts as buffers in growth media?
REVIEW (PLAY RECORDING FOR ANSWER
If bacterial cells were given a sulfur source containing radioactive sulfur (35 S) in their culture media, in what molecules would the 35 S be found in the cells? 32P?
Cysteine, Methionine, Biotin and Thiamine are molecules where the sulfur would be in.
32P?
What are biofilms? When was their structure appreciated?
What is Quorum sensing?
- Microorganism typically live in communities called BIOFILMS in which cells (either single or diverse species) are embedded within an EPS (Extracellular Polymeric substance) (informally called Slime)
-3D structure of biofilms was NOT well appreciated until the development of confocal microscopy
-Biolfilms are NOT a thick uniform monolayer (they grow in 3d structure that allow water to pass through thin layer)
Quorum sensing: the ability of bacteria to coordinate gene expression with other bacteria via signaling molecules.
they respond to local production density
Have two distinct programs (switch between high-density group growth and low-density individual growth) (biofilm development and dispersion)
