Extremophiles 1 and 2 (Jason) Flashcards
Distinguish between the terms extremophiles and extremotolerant
Extremophiles: Cells that grow best under extreme conditions and may not survive under normal conditions.
Extremotolerant: Cells that tolerate extremes but grow best under normal conditions.
Describe water activity and the effect it has on microbial growth
- Water availability is the fraction of water which is available and isn’t interacting with a solute.
- Pure water aw = 1
- Higher solute concentrations = lower aw
- Water moves from higher aw to lower aw.
- Many microbes cannot tolerate low aw, so reducing aw is important for food preservation.
- Microbes which can grow over a range of water activities are described xerotolerant (or osmotolerant) or xerophiles (or osmophiles).
- Many microbes respond to increases in osmolarity by accumulating compounds in their cytoplasm which protect them from dehydration. These are called compatible solutes.
What are compatible solutes
- Molecules which can accumulate inside the cell without interfering with cellular metabolism.
- They maintain shape and function of the cell in lower water activity environments.
- Examples: glycine, glutamine, and proline.
What are halophiles, how they cope, and where do we find them
- Halophiles are a class of osmophile which live in high salt environments.
- Require high levels of NaCl to grow.
- Examples: some Archaea and cyanobacteria.
- They accumulate potassium and sodium internally to adapt their internal environment to be stable when exposed to these ions. Also accumulate compatible salts.
- Found in artificial environments such as solar salterns and natural systems such as drying water bodies.
What names are given to microbes in relation to their optimal pH ranges for growth
Acidophiles - grow best between pH 0 and 5.5
Neutrophiles - grow best between pH 5.5 and 8
Alkalophiles - grow best between pH 8 and 11.5
How do pH tolerant cells cope
- Microbes which live at pH extremes try to maintain their cytoplasm around a neutral pH.
- May have pumps to keep internal proton levels just right.
- May have membranes or cell walls with altered permeability.
- May accumulate or get rid of cations such as sodium to alter the movement of protons.
- May contain proteins which cope with pH changes.
- Thermoplasma spp. live at pH 1-2 and have an acid-resistant membrane.
How does temperature affect microbes
- Microbes are poikilothermic (they can’t regulate their temperature so it changes with the environment around them).
- Low temperatures will slow enzyme catalysed reactions while high temperatures can denature enzymes.
- The effects of temperature lead to distinct cardinal growth temperatures (minimum, maximum, and optimum temperatures for growth).
Describe the microbes which grow at low temperatures, the effects of low temperatures, and how these microbes cope
- Microbes that like low temperatures for growth are called psychrophiles.
- Optimum temperature is below 15 degrees celsius.
- Common habitats include Arctic ice and snow.
- Low temperature slows the movement of molecules and makes proteins and cell membranes more rigid.
- Low temperatures reduce membrane fluidity leading to a more solid membrane which prevents transport of substances.
- To cope with membrane rigidity microbes can increase the number of short unsaturated fatty acids in their cell membranes which have fewer interactions holding them together. Unsaturated bends in the carbon chains prevents molecules packing too closely making the membrane more fluid.
- Microbes can produce anti-freeze proteins which reduce the freezing temperature of water to protect them against ice crystals. They also accumulate compatible solutes for the same reason.
What name is given to microbes which grow at relatively normal temperatures, state their optimum temperature range, and give an example microbe
Mesothermic microbes
20 to 45 degrees celsius
Includes all human pathogens
What are high temperature microbes called, state their optimum temperature for growth, and describe the problems they face and how they cope with them
- (Hyper)thermophiles
- 50 degrees celsius
- High temperatures increase the fluidity of membrane to the point that they cannot control what moves across them. To prevent this microbes increase the number of longer, saturated fatty acids in their membranes.
- Heat denatures DNA so microbes use sodium and potassium to increase the stability of nucleic acids.
- Proteins may denature under high temperature therefore more internal interactions such as disulphide bonds and the use of chaperone proteins can help hold proteins together.
How does oxygen affect microbes and state and define the different classifications in relation to oxygen dependence
- Using oxygen for energy generation can create reactive oxygen species.
- Reactive oxygen species can chemically modify molecules which they come into contact with. Examples of these species include superoxide, hydrogen peroxide, and hydroxyl radicals.
- Obligate aerobes: must have oxygen for growth.
- Facultative anaerobes: do not require oxygen for growth but grow better with it.
- Aerotolerant anaerobes: ignore oxygen and grow equally well whether it is present or not.
- Obligate anaerobes: do not tolerate oxygen and die if it is present.
- Microaerophiles: are damaged by the normal atmospheric level of oxygen but require lower levels for growth.
What are the classifications in relation to pressure, what are the challenges it presents, and how do microbes cope
- Barotolerant microbes can tolerate high pressures whereas barophilic species will grow at approximately 700 atm but not below 500 atm of pressure.
- Pressure compresses lipid membranes resulting in decreased membrane fluidity. Less saturated membranes can help address this in the same that it addresses the effects of low temperature.
- Low pressure also affects enzyme catalysed reactions by reducing enzyme flexibility.
- The blob fish lives under high pressure.
How does the bacterium Deinococcus radiodurans withstand radiation
- High dose of radiation cause double stranded DNA to break but D. radiodurans stitches the fragments back together.
- The DNA is condensed into a small volume creating a smaller target for high energy radiation to hit.
- The bundles of DNA contain a high concentration of DNA repair proteins.
- The cells are polyploid (contain many copies of their genome). These spare copies can continue functioning when another copy is damaged, or act as a template for repairing damaged DNA.
