Exam 2 Flashcards
Give examples of man-made vs. natural extreme environments.
- Man-made thermophilic habitats
- Acid mine drainage
- Biological wastes
- Self-heating compost piles - Natural thermophilic habitats
- Geothermally heated oil
- Geothermal and volcanic areas
- Hydrothermal vents
What adaptations have thermophiles developed?
- DNA repair proteins
- Saturated lipids maintain structure
- Higher GC content encodes thermostable amino acids
What adaptations have acidophiles developed?
- DNA repair proteins
- Chaperones
- Potassium accumulation
- Highly H+ impermeable membrane
What adaptations halophiles developed?
- Osmoprotectants accumulation
- Na+ stabilizes cell wall
- Bacteriorhodopsin pigment absorbs light
- Carotenoids protect cell DNA from UV induced radicals
What adaptations for UV resistance have microbes developed?
- DNA repair proteins
- Chaperones
- Manganese accumulation
- Reduced iron levels
- Antioxidants
What adaptations have psychrophiles developed?
- Unsaturated lipids stay fluid
- Higher GC content encodes thermostable amino acids
- Cold shock proteins
- Chaperones
- Anti freeze proteins
What adaptations for xeric habitats have microbes developed?
- EPS production
- Osmoprotectants accumulation
- DNA repair proteins
- Sporulation
What are the characteristics of hydrothermal vents? What does a typical trophic food web look like here?
The chemical laden water escaping from cracks in the seafloor around the mid ocean ridges “feed” chemoautotrophic bacteria
- What do thalassohaline and athalassohaline mean?
- What type of habitats are they?
- Give examples for both.
- Thalassohaline = derived from seawater
Athalassohaline = salts derived from geology of terrestrial habitat - Hypersaline environments
- Ex. solar salterns (thalassohaline) and the Dead Sea (athalassohaline)
How would sampling be different for aquatic vs. terrestrial environments?
- Aquatic
- Easier than soil/sediments (homogeneous)
- Can get samples remotely
- May have to filter large volumes of water
- Viruses require care - Terrestrial
- Challenges: contamination, compaction, water content
- More heterogeneous (will have to homogenize first)
How would you enumerate microbes in aquatic vs. terrestrial environment?
- Aquatic (more volume-based)
- Turbidity
- Flow cytometry
- FISH (fluorescent in situ hybridization) - Terrestrial (more area-based)
- See below - Both
- Serial dilution and plating
- Direct counts
- Most probable number
- Molecular methods (PCR, sequencing)
What is the advantage of fluorescent microscopy?
- Versatility: applicable to a broad spectrum of biological research
- High sensitivity and specificity: can attach to specific biomolecules of interest
- Multiplexing capability: allows for the simultaneous detection of multiple targets within the same sample
In what cases would some environmental samples need more preparation before molecular analyses?
- Complex matrices: environmental samples like soil, sediment, or wastewater contain a high content of organic and inorganic material that can inhibit molecular reactions
- Microbial diversity: environmental samples with high microbe diversity require selective enrichment or culture-based methods to increase the abundance of specific microbes of interest
What is the basic goal of PCR?
To amplify DNA/RNA
How is PCR limited?
-
Extraction biases
- Incomplete lysis, degradation, etc. -
PCR bias
- Limitations to amplification
- Primer bias (primers not universal) - PCR is not truly quantitative
- One must return to the environment to check
Why is a plasmid the preferred vector to make more copies of DNA?
- Can be replicated independent of the bacterial genome
- Functional markers added to vectors allow you to insert things into the DNA
How might a molecular biologist use FISH (fluorescent in-situ hybridization) to answer microbial ecology driven questions about microbes and their interactions in the environment?
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- Can tag microbial populations with fluorescent probes —> visualize/ID/quantify microbes
- Can track the tagged microbes to see how they interact with each other and their environment
How are soil/sediment samples collected?
- Coring: piston corer (can get nice stratification)
- Van Veen grab
What are some issues to consider in soil/sediment sample collection?
- Contamination: hard to decontaminate such a large drill
- Compaction: a portion of sediment might clog your piston
- Water content: sometimes too much water
Why is aquatic sampling easier than soil/sediment sampling?
- More homogeneous
- Easier to get samples, even remotely
What are some difficulties in aquatic sampling?
- May have to filter/concentrate large volumes of water
-
Viruses require care
- High volumes
- Adsorption, elution, reconcentration
How are aquatic samples collected?
- Plankton net tows: to isolate microbes of different sizes
- Niskin bottle
- CTD rosette: measure physical characteristics of water
Compare and contrast crossflow filtration and direct flow filtration.
- Crossflow (aka tangential flow)
- High permeate rate - Direct flow (aka dead-end)
- Low permeate rate
What are the difficulties in the environment in enumeration?
- Small size of microbes - hard to see to count
- Hard to determine viability of samples
What is enumeration?
Determining how many microbes there are in a sample
Explain serial dilution.
How do you get the most probably number (MPN)?
- Serial dilution of a liquid sample
- Growth in successive dilutions allows estimation of numbers in original sample
How is turbidity measured?
Optical density
- Measure how much light passes through the sample
- Use the same media as your blank
What tools are used to take direct counts?
- Microscopic measures
- Counting chamber
- Gridded filters -
Epifluorescence microscopy
- Fluoresce when you hit them (natural autofluorescence, acridine orange, DAPI)
One way gene probes can be applied is in fluorescent in-situ hybridization (FISH). What is FISH?
Lab technique used to detect and locate a specific DNA sequence on a chromosome
How is FISH done?
- Cells are preserved whole
- Cells are permeabilized with chemicals
- Cells are hybridized with labeled with probes that bind to the cell’s DNA or RNA
- Upon excitation, the fluorescent probes emit light
What is the hierarchy of organization for ecology and how does it translate to microbial ecology?
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Compare and contrast the microbial ecological niches of some model organisms.
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Which species concepts is most often applied to microbes?
Genetic species concept
Explain the genetic species concept.
A genetic species is a group of genetically compatible organisms
- Focuses on genetic isolation (as opposed to reproductive isolation)
How can horizontal gene transfer result in the blurring of the distinctions between microbial species?
- Makes it hard to categorize species
- Can replace existing gene copies
- Can introduce whole new functions
Define operation taxonomic unit (OTU). How is it used?
- Clusters of organisms grouped by DNA sequence similarity of a specific taxonomic marker gene
- Used to classify organisms based on DNA sequence similarity
What is the most common OTU definition used to describe microbial species?
97% 16S rRNA sequence identity
Explain what happens in resource partitioning and utilization.
- Through time and natural selection, the two species diverge in their use of the resource
- A new species arrives, and further competition leads to a narrower range of resource use for all three species
What are fundamental vs. realized niches?
- Fundamental: full range of conditions that an organism could use
- Realized: portion of the fundamental niche actually occupied by that species
Explain the consequences of microbial competition.
- Competitive exclusion: if there is significant niche overlap and limited resources, one population will drive the other to extinction
- Intraspecific competition will cause the population to level out
Define competition.
Interaction between populations in which growth rates decrease for both
What is the shape of a logistic vs. exponential growth curve?
What is carrying capacity (K)?
Max population size the environment can sustain
What does the Lotka-Volterra model for interspecific competition tell us and what specifically are the alpha and beta in the equation?
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The Lotka-Volterra model of interspecific competition is able to generate a range of possible outcomes. What are they?
- The predictable exclusion of one species by another
- Exclusion dependent on initial densities
- Stable coexistence