Lecture 6 Flashcards
Which of the following uses sunlight for energy and CO2 for a carbon source ?
Photoautotrophs
What species differentiates into fruiting bodies ?
Myxococcus xanthas
INTRODUCTION
Microbes have both the fastest and slowest growth rates of known organisms
- Some hot springs bacteria double in as little as 10 min
* Some deep-sea sediment microbes take as long as 100 years
What determines the differences in growth rate?
- Nutrition
- Temperature
- pH
- Osmolarity
ENVIRONMENTAL LIMITS ON GROWTH
What are “normal” growth conditions?
From our human frame of reference “normal” is defined as: sea level, 20-40C, near neutral pH, salt concentration 0.9%, and ample nutrients
Any ecological niche outside this window is labeled “extreme” and organisms inhabiting them are called ____
Extremophiles. (Like temp. & pressure)
• Extremophiles may evolve to survive multiple extreme environments
• Extremophiles may provide insight into the workings of extraterrestrial microbes we may one day encounter (astrobiology)
MICROBES ARE COMMONLY CLASSIFIED BY THIER ENVIRONMENTAL NICHE
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GROWTH AND TEMPERATURE
Every organism has an optimum temperature at which it grows most quickly
Also, minimum and maximum temperatures that define the limits of growth
Fastest growth rate occurs at temp where all proteins work most efficiently as a ______
Group
*as it starts
Optimum —-> normal
Rising temperatures cause critical enzymes or cell structures (e.g. cell membrane) to ____
Fail
At _______ temperatures enzymatic processes become too sluggish and the cell membrane becomes too rigid
Cold
*move a lot slower
The relationship between growth rate constant and temperature obeys ______ equation
Arrhenius
k= Ae ^ Ea/RT
General result – growth rate roughly ____ every 10C rise in temperature
Doubles
______ breaks down at upper and lower limits of growth
Arrhenius
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The typical temperature growth range spans the organisms optimal growth temperature by ____
30 - 40 C
* Some organisms have a smaller range
_______ principles limit a cell’s growth to a
narrow temperature range
Thermodynamic
• Heat increases molecular movement with proteins
• Too much or too little movement will interfere with enzymatic reactions
MICROBES ARE CLASSIFIED BY GROWTH TEMPERATURE
Mesophiles :
~15-45 C, typical lab strains
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PSYCHROPHILES (0-20 C)
(Grow in extreme cold temps)
Optimum growth
~15 C
Proteins are more ____
Flexible
Require less ____ (heat) to function
Energy
Membranes are more ____
Fluid
Have antifreeze proteins and other ____ That depress the freezing point
Cryoprotectants
THERMOPHILES (40-80 C)
Hyperthermophiles
65-121 C
Enzymes are more stable – don’t unfold as easily
Low amounts of glycine
Chaperone
proteins that help refold other proteins
undergoing denaturation
DNA binding proteins that ____ DNA
Stabilize
Membranes are more ____
Rigid.
(So they can withstand the higher temps)
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GROWTH AND PRESSURE
Barophiles or piezophiles –
organisms adapted to grow at high pressures
• Up to 1,000 atm (110 MPa, 15,000 psi)
• Sea level – 1 atm
Barotolerant
grow well over 1-50 MPa but their growth falls off thereafter
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Many_______ are also psychrophiles or hyperthermophiles
Barophiles
How bacteria survive extreme pressures is still a mystery
• Increased hydrostatic pressure and cold temperatures reduce membrane fluidity
• Specially designed membranes and protein structures are needed
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OSMOLARITY
Water activity (aw)
is a measure of how much water is available for use
Osmolarity
is a measure of the number of solute molecules in a solution and is inversely related to aw
• The more particles in a solution the greater the osmolarity and the lower the water activity
• Hypertonic – external osmolarity is higher
• Hypotonic – internal osmolarity is higher
• Water will move across the semi permeable membrane in an attempt to equalize osmolarity across the membrane
OSMOLARITY
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Aquaporins
are membrane-channel proteins that allow water to traverse the membrane much faster than by diffusion
• Help protect the cell from osmotic stress
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PROTECTION AGAINST OSMOTIC STRESS
When in a ________, bacteria try to protect their internal water from leaving by synthesizing or importing more solutes (proline, glutamic acid, potassium, betaine)
Hypertonic solution
Cells contain _________ (mechanosensitive) channels that can be used to leak solutes out of the cell
Pressure sensitive
• Activated by rising internal pressures
HALOPHILES
Require high _____ concentrations to grow
Salt (NaCl)
• 2-4 M (20-30%)
• Compared to sea water ~3.5% NaCl
Use special ion pumps to excrete ____ and replace it with other cations
Sodium
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PH
The concentration of ______________ has a direct effect on the cell’s macromolecular structures
Hydrogen ions (H+)
• Actually hydronium ions (H3O+)
• Extreme concentrations of hydronium or hydroxide (OH-)
ions in a solution will limit growth
Cells can tolerate a _____ range in H+ than any other substance
Greater
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PH OPTIMA, MINIMA, AND MAXIMA
Charges of \_\_\_\_\_ or \_\_\_\_\_\_ groups within a protein play a key role in protein folding and activity
Amino. Carbonyl
[H+] concentration affects the ______ of these groups
Protonation
Thus, _______ activity exhibits optima, minima, and maxima with respect to pH
Enzyme
Biological membranes are relatively _______ to protons
Impermeable
*When difference in pH is very high, protons can leak through
Weak acids can pass through membranes
Dissociate intracellularly – acidifies internal pH (limits growth)
CLASSIFICATION OF ORGANISMS ACCORDING TO OPTIMUM GROWTH PH
Neutralophiles
pH 5-8
• Include most pathogens
Acidophiles
pH 0-5
• Often chemoautotrophs
• Altered membrane lipids – high levels of tetraether lipids – decrease proton permeability
Alkaliphiles
pH 9-11 • Typically found in soda lakes • Use sodium motive force and Na+/H+ antiporters [PIC]
OXYGEN
Many microbes can grow in the presence of ____
O2
• Some use oxygen as terminal electron acceptor (TEA) in the
electron transport chain
• This process is called aerobic respiration
Oxygen and its breakdown products are _______ reactive (reactive oxygen species)
Dangerously • Can damage DNA, RNA, protein • Aerobes have enzymes that destroy ROS (Reactive oxygen species) • Species have evolved to tolerate or avoid oxygen altogether
GROWTH AND OXYGEN
Strict aerobes
only grow in oxygen
Microaerophiles
grow only at lower oxygen levels
Strict anaerobes
die in the least bit of oxygen
Facultative anaerobes
can live with or without oxygen
Aerotolerant anaerobes
Have enzymes that kill ROS
grow in oxygen while retaining anaerobic metabolism
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NUTRIENT DEPRIVATION AND STARVATION
Lack of _____ slows metabolism
Nutrients
Growth rates ___
Slow
Daughter cells become _____
Smaller
Stimulates ____ responses
Stress
Cells begin to make and store _____
Glycogen
Programmed cell death
members of population sacrifice themselves to save others – dying cells release nutrients for other cells
ANTIMICROBIAL CONTROL MEASURES
Sterilization
killing of all living organisms
Disinfection
killing or removal of pathogens from
inanimate objects
Antisepsis
killing or removal of pathogens from the surface of living tissues
Sanitation
reducing the microbial population to safe levels
CELLS TREATED WITH ANTIMICROBIAL DIES AT A LOGARITHMIC RATE
• D-value (decimal reduction time) – length of time it takes the agent to kill 90% of the population
• 2 D-values = time to kill 99% of cells
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PHYSICAL AGENTS THAT KILL MICROBES
- Temperature
- Temperature + Pressure • Irradiation
- Filtration
- Chemical agents
- Biological agents
TEMPERATURE : PASTEURIZATION
Combination of temperature and time
- LTLT (low temperature/long time): 63C for 30 min
* HTST (high temperature/short time): 72C for 15 seconds
Doesn’t kill all microbes –
will eventually spoil
UHT (ultra high temperature): 150C for 3 seconds,
immediate cooling
• Sterilizes. Milk can be stored up to 9 months
TEMPERATURE + PRESSURE : AUTOCLAVE
Boiling water (100C) kills most cells, but killing \_\_\_\_\_\_and \_\_\_\_\_\_\_ usually requires a combo of high temperature and pressure
Spores. Thermophiles
Autoclave
• 121C, 15 psi (2atm) for 20 min
• Kills all bacteria
• Kills endospores
*Clostridum botulinum
* BacillusanthracisOTHER METHODS
Cold temperature –
refrigeration
• Slows growth, does not kill all
bacteria
Freezing
.
Irradiation
- UV, X-rays, g-rays
* Doesn’t work well on viruses
Filtration
• Defined pore sizes that remove
microorganisms
• Doesn’t work on viruses
CHEMICAL AGENTS
Phenolics
- Disrupts membranes
- Denatures proteins
- Phenol, Amphyl, Lysol
Alcohols
- Won’t kill spores
- Denatures proteins
- Dissolves membrane lipids
Aldehydes
- Combines with proteins
- Used as embalming fluid
Quaternary ammonium compounds
- Disrupts membranes
- May denature proteins
- Low toxicity (antiseptics for skin and in mouthwash)
Gases
-Combine with proteins and deactivates them
-Kills spores
-Penetrates well
-For items that cant be heated
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ANTIBIOTICS
Selectively kills microbes
• May not work on all species
Has minimal effect on ______ cells
Eukaryotic
• Can be used inside patients
Interferes with ________ enzymes
Bacterial-specific
• Cell wall synthesis
• Bacterial ribosome
Bacteriostatic
inhibits growth
Bacteriocidal
kills cells
BIOLOGICAL AGENTS
Probiotics
- “Good” bacteria
- Displace disease organisms from tissues
- Competes for niche
Bacteriophges
• Phages
• Viruses that attack bacteria
• Do not harm eukaryotes
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