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Questions and Answers
At what pH value can the chemoautotrophic bacteria found in drainage water from coal mines survive?
In what type of environment did Professor Thomas D. Brock make his discovery of extremophiles in Yellowstone National Park?
Where can microorganisms be found growing at temperatures as high as 120 degrees?
Which type of bacteria oxidize sulfur to form sulfuric acid and can survive at a pH value of 1.39?
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What was Professor Thomas D. Brock's amazing discovery in Yellowstone National Park in 1966?
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Where did most pathogenic bacteria exhibit a relatively narrow range of pH over which they will grow?
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Which type of microorganism requires oxygen for growth?
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Which environmental factor can affect microbial growth in nature or in the laboratory?
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Where is the growth seen in a tube containing obligate anaerobes?
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What is the role of oxygen for obligate anaerobes?
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Which environmental factor affects the ability of microbial cells to use nutrients efficiently?
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Which type of microorganism does not need or use oxygen for growth?
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Which group of microorganisms requires the highest concentration of NaCl for growth?
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What is the term for the amount of water available for a cell to utilize?
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Which of the following does NOT affect the water activity of a substance?
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Which of the following microorganisms is best adapted to grow in environments high in sugar?
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What is the primary solvent in which the molecules of life are dissolved?
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Which of the following is NOT a factor that affects the availability of water for a cell?
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Which type of microorganism can grow at 70°C?
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Which type of bacteria is best suited for growth at temperatures near 37°C?
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Which type of microorganism is considered a cold-loving organism?
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Which type of microorganism is capable of growing in a refrigerated environment?
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What temperature range is best for the growth of fungi?
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Which microorganism is an example of an extreme thermophile?
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Which type of bacteria lives by fermentation alone, regardless of the presence of oxygen?
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Which type of bacteria grows in the presence of oxygen and can also grow in its absence by relying on fermentation or anaerobic respiration?
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Which bacteria requires a specific oxygen level for growth, not too much and not too little?
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Which type of bacteria can switch between aerobic and anaerobic types of metabolism?
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Which bacteria can live by fermentation, anaerobic respiration, bacterial photosynthesis, or methanogenesis?
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Which bacteria is a common example of aerotolerant anaerobes and is used in the production of many acidic fermented foods?
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Study Notes
Environmental Factors for Microbial Growth
- A bacterium requires an energy source, a source of carbon, and other required nutrients to grow.
- Suitable environmental conditions, such as oxygen concentration, pH, temperature, moisture, and salt concentration, are necessary for microbial growth.
The Effect of Oxygen on Growth
- Oxygen is a universal component of cells and is provided to microorganisms in large amounts by H2O.
- Microorganisms display a wide range of responses to molecular oxygen:
- Obligate aerobes: require O2 for growth, use O2 as a final electron acceptor (e.g., Pseudomonas, Bacillus subtilis).
- Obligate anaerobes: do not need or use O2 as a nutrient, obtain oxygen from H2O, and are inhibited or killed by O2 (e.g., Clostridium).
- Facultative anaerobes: thrive in the presence of oxygen but also grow in its absence by relying on fermentation or anaerobic respiration (e.g., E. coli).
- Aerotolerant anaerobes: indifferent to the presence of oxygen, have an exclusively anaerobic (fermentative) type of metabolism (e.g., Lactobacillus).
- Microaerophiles: require a minimum level of oxygen for growth, about 1-10% (e.g., Helicobacter pylori).
The Effect of pH on Growth
- Most pathogenic bacteria exhibit a relatively narrow range of pH over which they will grow.
- Diagnostic media for the growth and identification of human pathogens typically have a pH near 7.
- Some bacteria can survive at extremely low pH values, such as chemoautotrophic bacteria that oxidize sulfur to form sulfuric acid.
The Effect of Temperature on Growth
- Microorganisms can grow in almost every environment where there is liquid water, regardless of its temperature.
- Microorganisms can be found in extreme temperatures, such as:
- High temperatures: black smokers, hydrothermal vents, and hot springs (up to 120°C).
- Low temperatures: icy waters of the Antarctic and household refrigerators (near 0°C).
- Thermophilic bacteria, archaea, and other "extremophiles" can grow in extreme temperatures.
The Physical Effects of Water
- Water is the solvent in which the molecules of life are dissolved.
- The availability of water for a cell depends on its presence in the atmosphere (relative humidity) or in solution or a substance (water activity).
Effect of Salts on Growth of Bacteria
- Microorganisms that require some NaCl for growth are halophiles.
- Halophiles are classified into mild halophiles (1-6% salt), moderate halophiles (6-15% salt), and extreme halophiles (15-30% NaCl).
- Bacteria that can grow at moderate salt concentrations, even though they grow best in the absence of NaCl, are called halotolerant.
Temperature Ranges for Microorganism Growth
- The temperature range at which a particular microorganism can grow is defined by three cardinal points: minimal, optimal, and maximal temperatures.
- Examples of microorganisms and their optimal temperatures:
- Mesophilic bacteria: 10-42°C (e.g., Streptococcus pyogenes, E. coli).
- Thermophilic bacteria: 45°C, but can grow at 70°C (e.g., Thermus aquaticus).
- Psychrophilic bacteria: 0°C (e.g., Vibrio marinus).
- Fungi: optimal temperatures vary depending on the species.
Food Spoilage in Refrigerators
- Psychrotrophs, which grow at 0°C, can spoil food in refrigerators.
- Psychrotrophs are brought in from their mesophilic habitats and continue to grow in the refrigerated environment, spoiling food.
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Description
Explore the importance of environmental factors for microbial growth and survival, including oxygen concentration, pH, temperature, moisture, and surface tension. Learn how these factors influence the metabolic reactions and efficiency of microbial cells.
