Week 1 of exam 2 Flashcards
What are solutes such as salts and sugars known to decrease in microbial environments?
The availability of water to microbes
This decrease in water availability affects the growth of all cells.
How is the availability of water expressed in microbial studies?
Water activity (aw)
Higher solute concentration leads to lower water activity.
What happens to water movement in bacterial cells when in a hypotonic environment?
Water moves into the cells
Hypotonic environments have low extracellular solute concentration, such as fresh water lakes.
What is the term for the movement of water in and out of cells based on solute concentration?
Osmosis
Osmosis is influenced by the concentration of solutes inside and outside the cell.
What characterizes an isotonic solution?
Same solute concentration in and out
In isotonic solutions, there is no net movement of water.
What occurs in a hypertonic environment?
Water moves out of the cells
Hypertonic environments have high extracellular solute concentrations, leading to low water activity.
What is a halophile?
An organism that requires high salt concentration to grow
Halophiles thrive in environments like salt lakes.
What does it mean for an organism to be osmotolerant?
It can grow over a wide range of water activity
An example is Staphylococcus, which is salt-tolerant.
What type of agar is used to select for Staphylococcus growth?
Mannitol Salt Agar
This medium is high in salt concentration to inhibit non-salt-tolerant organisms.
What is a xerophile?
An organism that grows under low water activity and dry conditions
Xerophiles are adapted to survive in arid environments.
How do microbes survive in highly concentrated environments?
By using compatible solutes
Examples include potassium chloride, betaine, certain amino acids, and sugars.
What do microbes require to obtain energy and construct new cellular components?
A supply of raw materials and nutrients
Nutrients are substances used in biosynthesis and energy release, required for growth.
What percentage of the microbial cell dry weight is made up of a few major elements?
95%
The major elements include C, O, H, N, S, P, and Fe.
What are macronutrients?
Nutrients required in large amounts
Examples include C, O, H, N, S, P, Fe.
What are micronutrients?
Nutrients required in small amounts
Examples include cobalt, copper, zinc, and manganese.
What nitrogen sources can microbes use?
Ammonia (NH3) or Nitrate (NO3)
A few microbes can use nitrogen gas (N2), which makes up 79% of Earth’s atmosphere.
What challenges do microbes face in acquiring nutrients?
Rapid growth necessitates high rates of nutrient entry across membranes in a selective fashion, often against concentration gradients.
What is passive transport?
Transport that requires no energy and moves substances from higher to lower concentrations
Includes passive diffusion and facilitated diffusion.
What is the difference between passive diffusion and facilitated diffusion?
Passive diffusion allows only small molecules and certain gases, while facilitated diffusion uses membrane carrier proteins.
What is nitrogen fixation?
The process of reducing N2 to ammonia
Examples include Rhizobium in symbiosis with plants and Azotobacter, which is free-living in soil.
What characterizes active transport?
Energy-dependent transport that moves nutrients against a concentration gradient.
What are ABC transporters?
Transporters found in all domains of life that move substances in or out of cells
Includes Uptake ABC (move nutrients in) and Export ABC (move substances out).
What are the roles of Uptake ABC and Export ABC transporters?
Uptake ABC moves nutrients into cells, while Export ABC (also called Multidrug Efflux Pumps) moves substances out.
How do bacteria become resistant to antibiotics?
By using Export ABC transporters to move antibiotics out of the cell.
