Microbial Growth and Physiology: Chapter 6 Study Guidance

Q1. How could you determine whether a microbe is a strict anaerobe?

Background

Topic: Oxygen Requirements of Microbes

This question tests your understanding of how microbes respond to oxygen and how to experimentally determine their oxygen requirements.

Key Terms:

• Strict anaerobe: An organism that cannot survive in the presence of oxygen.

• Aerobic/anaerobic growth: Growth patterns in the presence or absence of oxygen.

• Thioglycollate broth: A medium used to test oxygen requirements.

Step-by-Step Guidance

1. Prepare a series of test tubes containing thioglycollate broth, which creates an oxygen gradient from top (high O2) to bottom (low O2).

2. Inoculate each tube with the microbe and incubate under standard conditions.

3. Observe the location of microbial growth in the tube after incubation. Growth only at the bottom suggests strict anaerobe.

4. Compare the growth pattern to controls (known aerobes and facultative anaerobes) to confirm the result.

Try solving on your own before revealing the answer!

Final Answer:

A strict anaerobe will grow only at the bottom of the thioglycollate tube, where oxygen concentration is lowest. This is because strict anaerobes cannot tolerate oxygen and will not grow in its presence.

Q2. If bacterial cells were given radioactive phosphorus (P-32) in their culture media, where would you find the P-32 in the cells? Radioactive nitrogen (N-15)?

Background

Topic: Macromolecular Composition of Cells

This question tests your knowledge of where key elements are incorporated in cellular structures.

Key Terms:

• Phosphorus (P): Found in nucleic acids (DNA, RNA), phospholipids, ATP.

• Nitrogen (N): Found in proteins (amino acids), nucleic acids, and other cellular molecules.

• Radioisotope labeling: Technique to trace element incorporation.

Step-by-Step Guidance

1. Recall the major macromolecules in cells: proteins, nucleic acids, lipids, carbohydrates.

2. Identify which macromolecules contain phosphorus: DNA, RNA, ATP, phospholipids.

3. Identify which macromolecules contain nitrogen: proteins (amino acids), DNA, RNA.

4. Consider how radioactive isotopes are incorporated during biosynthesis.

Try solving on your own before revealing the answer!

Final Answer:

P-32 would be found in the DNA, RNA, ATP, and phospholipids of the cell, while N-15 would be found in proteins (amino acids) and nucleic acids (DNA and RNA).

Q3. Describe the term “biofilm” and explain how/where it is formed.

Background

Topic: Microbial Communities and Biofilms

This question tests your understanding of biofilm formation and its significance in microbiology.

Key Terms:

• Biofilm: A complex community of microorganisms adhering to a surface, embedded in a self-produced matrix.

• Extracellular polymeric substances (EPS): Matrix material produced by microbes.

• Planktonic: Free-floating microbial cells.

Step-by-Step Guidance

1. Define biofilm and its basic characteristics.

2. Describe the initial attachment of planktonic cells to a surface.

3. Explain the production of EPS and the development of a multi-layered structure.

4. Discuss common locations where biofilms form (e.g., medical devices, water pipes, teeth).

Try solving on your own before revealing the answer!

Final Answer:

A biofilm is a structured community of microbial cells attached to a surface and embedded in a self-produced matrix of EPS. Biofilms form on surfaces such as teeth, medical devices, and water systems, starting with attachment and followed by growth and matrix production.

Q4. What BSL is the laboratory we work in?

Background

Topic: Biosafety Levels (BSL)

This question tests your understanding of laboratory safety and risk assessment in microbiology.

Key Terms:

• Biosafety Level (BSL): Classification of labs based on the risk posed by the microbes handled.

• BSL-1 to BSL-4: Increasing levels of containment and safety.

Step-by-Step Guidance

1. Review the characteristics of each BSL (1-4).

2. Consider the types of organisms and procedures used in your lab.

3. Match your lab's practices to the appropriate BSL description.

Try solving on your own before revealing the answer!

Final Answer:

Most college teaching labs operate at BSL-1 or BSL-2, depending on the organisms used. BSL-1 is for non-pathogenic microbes, while BSL-2 is for moderate-risk organisms.

Q5. What is the problem with psychrotrophs?

Background

Topic: Microbial Growth Temperatures

This question tests your understanding of how temperature affects microbial growth and food safety.

Key Terms:

• Psychrotrophs: Microbes that grow well at refrigerator temperatures (0–7°C) and can spoil food.

• Food spoilage: Growth of microbes in food leading to decay and potential health risks.

Step-by-Step Guidance

1. Define psychrotrophs and their optimal growth temperature range.

2. Explain why refrigeration slows but does not prevent their growth.

3. Discuss the implications for food storage and spoilage.

Try solving on your own before revealing the answer!

Final Answer:

Psychrotrophs can grow at refrigerator temperatures, leading to food spoilage even when food is refrigerated. This is why food can still go bad in the fridge.