Poolman lectures 3 and 4: microbial growth Flashcards
Which elements make up the bulk of the cell’s dry weight?
Carbon, oxygen, nitrogen, hydrogen, phosphorus and sulfur account for about 96% of a cell’s dry weight.
What are the stages of biofilm formation?
- Attachment of planktonic cells to a surface
- Colonization: microbes begin to grow and produce extracellular polysaccharides (EPS)
- Development: cells in the biofilm begin to change their metabolism
- Dispersal of cells from a mature biofilm, usually triggered by nutrient limitations or other forms of stress.
Why is Pseudomonas aeruginosa a relevant model organism for studying biofilms?
Because P. aeruginosa forms biofilms in the lungs of humans in the disease cystic fibrosis.
Why do biofilms tend to make bacteria resistant to drugs?
Because biofilms form a penetration barrier and promote metabolic differentiation.
What are four mechanisms of growth that produce unequal products?
Name some examples of organisms for each method.
- Simple budding: Pirellula, Blastobacter
- Budding from hyphae: hyphomicrobium, rhodomicrobium, pedomicrobium
- Cell division of stalked organism: Caulobacter
- Polar growth without differentiation of cell size: rhodopseudomonas, nitrobacter, methylosinus
What are cardinal temperatures?
Cardinal temperatures are three temperatures that describe growth of a mircoorganism.
1. Minimum: no growth is possible below the minimum (due to membrane gelling, for example)
2. Optimum: growth is at its maximum rate
3. Maximum: above this temperature, growth is not possible due to protein denaturation, for example
What are the four classes of microorganisms in relation to their temperature optima?
- psychrophiles: low temperature optima
- mesophiles: midrange temperature optima
- thermophiles: high temperature optima
- hyperthermophiles: very high temperature optima
What are the cardinal temperatures for E.coli?
Minimum: 8 degrees celcius, optimum: 39 degrees, maximum: 48 degrees
What is the difference between a psychrophile and a psychrotolerant organism?
A psychrophile is a microbe with an optimal growth temperature
of 15°C or lower, a maximum growth temperature below 20°C, and
a minimum growth temperature of 0°C or lower. By contrast,
microbes that grow at 0°C but have optima of 20–40°C are called
psychrotolerant.
Which bacterium has the lowest growth temperature ever documented at -15 celcius?
Planococcus halocryophilus
What are two structural adaptations of enzymes that enable them to stay flexible and functional under cold conditions?
- They have more alpha helix than beta sheet. This is because alpha helices are more flexible and less rigid than beta sheets
- Cold-active enzymes also tend to have greater
polar and lesser hydrophobic amino acid content and lower numbers of weak bonds, such as hydrogen and ionic bonds.
What adaptations do psychrophiles have in their membranes that enables them to function in the cold?
Cytoplasmic membranes from psychrophiles tend to have a higher content of unsaturated and shorter-chain fatty acids, and this helps the membrane remain in a semifluid state at low temperatures to carry out important transport and bioenergetic functions.
They also have polyunsaturated fatty acids in their membranes, which stay flexible at cold temperatures.
What are other molecular protectants that psychrophiles have? (So, besides enzyme and membrane adaptations)
- Cold-shock proteins: A type of molecular chaperone that maintains cold-sensitive proteins in an active form, or binding specific mRNAs and facilitating their translation under cold conditions.
- Cryoprotectants: include dedicated antifreeze proteins or specific solutes (such as glycerol or certain sugars) that prevent the formation of ice crystals. (These can puncture the cytoplasmic membrane)
What adaptations do emzymes of hyperthermophiles have to enable them to function at high temperatures?
- Subtle changes in amino acid sequence that affect protein structure and function to resist heat denaturation.
- Increased ionic bonding between between basic and acidic amino acids and have highly hydrophobic interiors, factors that also prevent unfolding.
- Solutes such as
di-inositol phosphate, diglycerol phosphate, and mannosylglycerate
are produced at high levels in certain hyperthermophiles, and these are thought to help stabilize their proteins against thermal
denaturation.
What are the adaptations to the cytoplasmic membrane of hyperthermophiles?
- Hyperthermophiles have a higher content of long-chain and saturated fatty acids. Long-chain fatty acids have a higher melting point than short-chain fatty acids, and saturated fatty acids form a storonger hydrophobic environment than unsaturated fatty acids.
- Hyperthermophiles don’t have fatty acids, instead C40 hydrocarbons
composed of repeating units of isoprene bonded by ether linkage to
glycerol phosphate. - A lot of hyperthermophiles have a lipid monolayer instead of a bilayer.
What is a halophile?
A halophile is a microorganism that grows best in an environment with high salt concentrations.
Organisms that can live in environments high in sugar are called…
Organisms that can live in very dry environments are called…
osmophiles, xerophiles
What are compatible solutes, and when and why are they needed by the cell? What is the compatible solute of
Halobacterium?
A compatible solute is a solute that is pumped into a cell in order to retain positive water balance in environments with low water availability.
The compatible solute of Halobacterium is KCl.
What is the difference between a microaerophile and an aerobe?
While aerobes grow and thrive at oxygen concentrations of the air (21%), mircoaerophiles can only use oxygen when its concentration is lower than in air, because of their limited capacity to respire, or because of some O2- sensitive molecule in their system.
What is the difference between obligate and aerotolerant anaerobes?
Obligate anaerobes are inhibited or killed by exposure to O2, while aerotolerant anaerobes can grow in the presence of O2, even though they can’t respire.
What is a reducing agent and name an example of one commonly used.
A reducing agent is a chemical agent that is added to a culture to remove traces of O2 by reducing it to H2O.
An example is thioglycolate.
What are some intermediates produced in the reduction of O2 to H2O that are toxic to cells?
- Superoxide anion (O2-)
- Hydrogen peroxide (H2O2)
- Hydroxyl radical (OH*)
Which organisms (aerobic or anaerobic) have the enzyme superoxide reductase and what does it do?
Anaerobic microorganisms make use of the enzyme superoxide reductase, which functions to remove O2- by reducing it to H2O2, WITHOUT producing O2, thus avoiding the exposure of O2 to the organism.
How would you test a microbial culture for the presence of catalase? Which reaction would be present in this culture?
Mix an amount of culture with hydrogen peroxide. If bubbles appear, this means there is catalase present:
H2O2 + H2O2 –> 2H2O + O2
What is the decimal reduction time D?
The decimal reduction time is the time required at a given temperature for the 10-fold reduction in the viability of a microbial population.
At which PH is microbial deach more rapid: acidic, or alkaline?
Microbial death is more rapid at acidid PH.
Why is ionizing radiation more effective than UV radiation for sterilization of food products?
Because ionizing radiation has way higher penetrating power than UV radiation. This means that ionizing radiation is good for killing microorganisms in bulk items such as food products or medical supplies.
Distinguish between the major types of sterilization filters
used in the microbiology laboratory.
- Depth filter: a fibrous sheet made from an array of overlapping paper or glass fibers that traps particles in the network of fibers. (example: biological safety cabinet)
- Membrane filter: high-tensile-strength polymers manufactured in such a way as to contain a large number of tiny pores. (used for liquid sterilization)
- Nucleopore filter: made from a thin polycarbonate film that is treated with radiation and then etched
with a chemical, yielding very uniform-sized holes. (used to isolate specimens for scanning electron microscopy)
Distinguish between the antimicrobial effects of -static, -cidal, and -lytic agents.
Agents that kill the microorganism are called -cidal agents.
Agents that do not kill
but only inhibit growth are called -static agents.
-lytic agents cause cell lysis.
Distinguish between a sterilant, a disinfectant, and an antiseptic.
- Sterilants destroy all microorganisms, including endospores.
- Disinfectants kill microorganisms but not nessecarily endospores and are used on surfaces.
- Anticeptics (also called germicides) are chemicals that kill or inhibit the growth of microorganisms but are sufficiently nontoxic to animals to be applied to living tissues.
