Chap 6 Flashcards
Physical requirements for microbial growth
- Temperature
- pH
- Osmotic pressure
Chemical requirements for growth
- Carbon
- N,S,P
- trace elements
- Oxygen
- Organic growth factors
Types of temperatures involved in growth
Minimum growth temperature
Optimum growth temperature
Maximum growth temperature
Psychrophiles
cold-loving
Mesophiles
Moderate temperature loving
Thermophiles
heat-loving
Psychrotrophs grow between which temperatures?
0 C and 20-30 C
Psychotrophs cause
food spoilage
Refrigerator temperatures
40 to 40 F
Many bacteria survive, some may grow
40 F to 60 F
Danger zone temp range
60 F to 130 F
Very slow bacterial growth
50-60 C
Temperatures in this range destroy most microbes, although lower temperatures take more time
above 60 C
Thermophiles optimum growth temperature
50-60C
Thermophiles are found in
hot springs and organic compost
Hyperthermophiles optimum growth temperature
above 80C
Most bacteria grow between what pH range?
6.5-7.5
Molds and yeasts grow between what pH range?
5 and 6
Acidophiles grow in what environments
acidic
What is plasmolysis?
the process of water leaving plant cells, allowing the cytoplasm and plasma membrane to shrink away from the cell wall.
What causes plasmolysis?
hypertonic environments; high osmotic pressure
Extreme or obligate halophiles require what kind of osmotic pressure?
high osmotic pressure (high salt)
Faculative halophiles tolerate what?
high osmotic pressure
Why are hyperthermophiles that grow at temperatures above 100C seemingly limited to oceanic depths?
the extreme pressure at those depths allows water to remain liquid at such high temperatures, which is necessary for their survival; essentially, the high pressure counteracts the boiling point of water, enabling them to exist in a liquid environment where they can function properly.
Other than controlling acidity, what is an advantage of using phosphate salts as buffers in growth media?
primary advantage of using phosphate salts as buffers in growth media is that they provide a readily available source of phosphorus, an essential nutrient for most bacteria, making them non-toxic and beneficial for microbial growth.
Why might primitive civilizations have used food preservation techniques that rely on osmotic pressure?
Growth of the cell is inhibited as the plasma membrane pulls away from the cell wall. The high salt or sugar concentrations draw water out of any microbial cells, thus prevent their growth.
Name each of the four elements needed in large amounts for microbial growth.
carbon, nitrogen, sulfur, and phosphorus
Identify ways in which aerobes avoid damage by toxic forms of oxygen
produce enzymes such as catalase, peroxidase and/or superoxide dismutase that break down toxic forms of oxygen and their intermediate byproducts.
Function of carbon
Structural backbone of organic molecules
Chemoheterotrophs use organic molecules as
energy
Autotrophs use
CO2
Nitrogen is a component of
proteins, DNA & ATP
Most bacteria decompose protein material for the
nitrogen source
Some bacteria use NH4+ or NO3- from
organic material
A few bacteria use what in nitrogen fixation?
N2
Sulfur is used in
- Amino acids,
- Thiamine
- Biotin
Most bacteria decompose protein for the
sulfur source
Some bacteria use SO4 2- or H2S
true
Usage of phosphorus
DNA, RNA, ATP
Phosphorus is found in
membranes
What is a source of phosphorus?
PO4 3
What are trace elements?
Inorganic elements required in small amounts
Trace elements usually function as
enzyme cofactors
Examples of trace elements
iron, copper, molybdenum, and zinc
Obligate aerobes+
require oxygen
Facultative anaerobes
grow via fermentation or anaerobic respiration when oxygen is not available
Anaerobes
unable to use oxygen and most are harmed by it
Aerotolerant anaerobes
tolerate but cannot use oxygen
Microaerophiles
Require O2 concentration lower than air
Growth of obligate aerobes
Growth on top. Growth occurs where high concentrations of oxygen have diffused into the medium
Faculative anaerobes
Growth
Growth is most concentrated on top, but some is into the medium. Growth is best where most oxygen is present, but occurs throughout the tube.
Growth of obligate anaerobes
Growth occurs only where there is no oxygen. At bottom of broth.
Aerotolerant anaerobes growth
growth occurs evenly, oxygen has no effect
Singlet Oxygen
boosted to a higher-energy state and is reactive. 1O2 -
Superoxide radicals
O2
Superoxide radicals equation
O2- + O2- + 2H+ —> H2O2 + O2
Peroxide anion
O2 2-
Peroxide Anion equation
2H2O2 —> 2H2O + O2
H2O2 + 2H+ —> 2H2O
Hydroxyl radical
OH -
OH.
Organic compounds are obtained from the
environment
Examples of organic growth factors
- Vitamins,
- amino acids,
- purines,
- pyrimidines
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?
Bacterial cells would incorporate the radioactive sulfur (35S) into amino acids, proteins, and nucleic acids in their cells
How would one determine whether a microbe is a strict anaerobe?
culture it in an oxygen-free environment and observe if it grows well; if the microbe only grows in the absence of oxygen, it is considered a strict anaerobe
Oxygen is so pervasive in the environment that it would be very difficult for a microbe to always avoid physical contact with it. What, therefore, is the most obvious way for a microbe to avoid damage?
Produce enzymes that would neutralize them from toxicity
What are biofilms?
Microbial communities
Biofilms form
slime or hydrogels that adhere to surfaces
How do bacteria in biofilms communicate?
Bacteria communicate cell-to-cell via quorum sensing
quorum sensing
a cell-to-cell communication process that allows bacteria to sense their population density and adjust their gene expression
How do bacteria use quorum sensing to communicate?
Bacteria secrete an inducer (signaling chemical) to attract other bacterial cells
In biofilms, bacteria share
nutrients
In biofilms, the bacteria can be sheltered from
harmful environmental factros
