18 Questions
What is the preferred pH range for most microorganisms?
pH 7.0–7.4
Which group of microorganisms prefer a pH of >8.5?
Halophiles
What is the characteristic pH range for acidophiles?
pH 2 to 5
What is the term used for solutions with higher solute concentration outside the cell compared to inside?
Hypertonic
Which group of microorganisms can endure very cold or even freezing temperatures?
Psychrophiles
What is the preferred temperature range for psychrotrophs?
+4°C
What is the term used to describe organisms that prefer to live in salty environments?
Halophilic organisms
If a solution has the same concentration of solutes inside and outside a cell, what is it called?
Isotonic
What happens to bacteria with rigid cell walls when placed in a hypertonic solution?
They undergo plasmolysis
Which type of organism is Staphylococcus aureus classified as in terms of its preference for salty environments?
Haloduric organism
What is the process known as when a bacterial cell escapes cytoplasm due to bursting in a hypotonic solution?
Plasmoptysis
Which term describes microbes that can survive in high atmospheric pressure?
Piezophiles
What is the role of water in microbial growth?
Water is essential for carrying out normal metabolic processes.
What are halophiles?
Halophiles are microorganisms that require high salt concentrations for growth.
Why can certain microbial stages like bacterial endospores survive desiccation?
Because they enter a state of suspended animation.
At what temperature do thermophiles grow best?
High temperatures
What determines the temperature range over which an organism grows best?
The optimum temperature and pH ranges of its enzymes
What is the optimum temperature for mesophiles to grow best?
$37^{ ext{o}}$C (human body temperature)
Study Notes
Temperature
- Psychrophiles prefer cold temperatures, such as deep ocean water
- Psychrotrophs, a type of psychrophile, prefer refrigerator temperature (4°C)
- Psychroduric organisms can endure very cold or freezing temperatures, but prefer warm temperatures
pH
- Most microorganisms prefer a neutral or slightly alkaline growth medium (pH 7.0-7.4)
- Acidophiles prefer a pH of 2 to 5
- Alkaliphiles prefer a pH of >8.5
Osmotic Pressure and Salinity
- Osmotic pressure is the pressure exerted on a cell membrane by solutions both inside and outside the cell
- Osmosis is the movement of a solvent through a permeable membrane from a lower concentration of solutes to a higher concentration of solutes
- A hypertonic solution has a higher concentration of solutes outside the cell than inside the cell
- Plasmolysis occurs when a bacterial cell is placed in a hypertonic solution, causing the cell membrane and cytoplasm to shrink away from the cell wall
- A hypotonic solution has a lower concentration of solutes outside the cell than inside the cell
- Plasmoptysis occurs when a bacterial cell bursts in a hypotonic solution, causing the cytoplasm to escape
- Isotonic solutions have equal concentrations of solutes inside and outside the cell
- Halophilic organisms prefer to live in salty environments
- Haloduric organisms can survive in salty environments but do not prefer them
Barometric Pressure
- Piezophiles are microbes that can survive in high atmospheric pressure (>14.7 psi)
Nutrients and Moisture
- All living organisms require nutrients to sustain life
- Nutrients are energy sources, and organisms obtain energy by breaking chemical bonds
- Moisture is essential for life and necessary for carrying out normal metabolic processes
- Some microbial stages (e.g., bacterial endospores and protozoal cysts) can survive drying (desiccation)
Test your knowledge on the factors that affect microbial growth, encouraging the growth of microbes in vitro, and inhibiting the growth of microbes in vitro as outlined in Chapter 8 of Burton’s Microbiology for the Health Sciences.
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