Chapter 5 Flashcards
“Normal” growth conditions
-Sea level atmospheric pressure
-Temperature 20oC–40oC
Neutral pH
-0.9% salt, and ample nutrients
based on one main criterion:
The tolerance of that organism’s proteins and other macromolecular structures to the physical conditions within that habitat
extremophiles
- Ecological niches far outside this window are called “extreme”
- enzymes are useful for certain scientific investigations and industrial applications
- Such as enzymes that function in extremes of temperature, salt concentrations, or pH.
- may provide insight into extraterrestrial microbes we may one day encounter.
Bioinformatic analysis
- uses the DNA sequence of a gene to predict the function of its protein product
- Allows us to study the biology of organisms that we cannot culture.
- Global approaches (all genes in a cell) used to study gene expression allow us to view how organisms respond to changes in their environment.
- Knowing which genes and proteins are expressed under different conditions reveals the microbes physiology and how they defend themselves against environmental stresses.
- It can reveal how pathogens interact with their host
Environmental Pressure- temperature
- Hyperthermophile- growth about 80oC
- Thermophile- growth between 50-80oC
- Mesophile- growth between 15-45oC
- Psychrophile- growth below 15oC
Environmental Pressure- pH
- Alkaiphile- growth above pH 9
- Include most pathogens
- Neutralophile- growth between pH 5-8
- Are often chemoautotrophs
- Acidophile- growth below pH 3
- Typically found in soda lakes
Environmental Pressure- osmolarity
halophile- growth in high slat
Environmental Pressure- oxygen
- aerobe- growth only in O2
- facultative- growth with or without O2 (E. coli)
- microaerophile- growth in small amounts of O2
- anaerobe- growth only without O2
Environmental Pressure- pressure
barophile- growth at high pressure, greater than 380 atm
-barotolerent- growth between 10 and 495 atm
Adaptation to Temperature
- Bacteria have the same temperature as their environment.
- Changes in temperature impact microbial physiology, proteins, and membranes
- Each organism has an optimum temperature, as well as minimum and maximum temperatures that define its growth limits.
- Microbes that grow at higher temperatures can typically achieve higher rates of growth
Growth Rate and Temperature
- The growth rate roughly doubles for every 10oC rise in temperature, within the range appropriate for an organism.
- The same relationship is observed for most chemical reactions.
- Bacterial organisms can typically grow within a range of 30–40 degrees around its optimal growth temperature
- But the range is not symmetric and drops off faster at high temperatures.
The Heat-Shock Response
- Temperature changes experienced during growth activates stress response genes
- Induced proteins include chaperones that maintain the shape of proteins and enzymes that change membrane lipid composition.
- Stress responses have been documented in “all” living organisms examined so far
Adaptation to Pressure
- Barophiles or piezophiles (preferred term) are organisms adapted to grow at very high pressures- Up to 1,000 atm
- Barotolerant organisms grow at moderate pressures.
- Note that many barophiles are also psychrophiles because the average temperature at the ocean floor is 2oC
Water Activity and Salt
-Water activity (aw) is a measure of how much water is available for use.
-Typically measured as the ratio of the solution’s vapor pressure -relative to that of pure water.
Most bacteria require water activity levels > 0.91
Osmolarity
is a measure of the number of solute molecules in a solution and is inversely related to aw
Aquaporins
- are membrane-channel proteins that allow water to traverse the membrane much faster than by diffusion.
- Help protect cells from certain types of osmotic stress
two mechanisms to minimize osmotic stress
- In hypertonic media, bacteria synthesize or importing compatible solutes (e.g., certain sugars, proline, or K+)
- In hypotonic media, pressure-sensitive channels can be used to leak solutes out of the cell (better than blowing up)
Adaptation to pH
- The concentration of hydrogen ions (H+)—actually, hydronium ions (H3O+)—has a direct effect on the cell’s macromolecular structures.
- Extreme concentrations of either hydronium or hydroxide ions (OH–) in a solution will limit growth.
pH Optima, Minima, and Maxima
- All enzyme activities exhibit optima, minima, and maxima with regard to pH.
- Bacteria can regulate internal pH, within limits.
- Weak acids can pass through membranes and disrupt cell pH homeostasis thus killing cells
- This phenomenon is used to preserve some foods
Oxygen and Other Electron Acceptors
- Many microorganisms can grow in the presence of molecular oxygen (O2).
- Some use oxygen as a terminal electron acceptor (TEA) in the electron transport chain.
- process is called aerobic respiration.
- Essentially the same as your mitochondria
Oxygen Benefits and Risks
- benefit to aerobes, organisms that can use oxygen as a TEA to extract energy from nutrients
- toxic to all cells that do not have enzymes capable of efficiently destroying the reactive oxygen species (ROS)—for example, anaerobes
