Brock Biology of Microorganisms Chapter 4: Nutrition and Microbial Growth

Flashcards covering essential concepts from Chapter 4 of Brock Biology of Microorganisms, focusing on microbial nutrition, culture, and growth phases.

Under ideal conditions, how many cells can a single bacterium multiply to within 7 hours?

2,097,152 cells

Why is culturing bacteria important for pathogens?

To understand how quickly they respond to antibiotics or other drugs and at what concentration.

What are two major government-funded communal culture collections mentioned?

World Data Center for Microorganisms (WDCM) and ATCC (American Type Culture Collection).

What are 'macronutrients'?

Nutrients required by cells in large amounts for growth.

What are 'micronutrients'?

Nutrients required by cells in minute amounts, including trace metals and growth factors.

What six elements dominate living systems, accounting for approximately 96% of elements?

Carbon (C), oxygen (O), nitrogen (N), hydrogen (H), phosphorus (P), and sulfur (S).

What is the function of trace metals as micronutrients?

Many enzymes require a metal ion or small organic molecule as a cofactor for catalysis (e.g., iron in cellular respiration).

What is the key principle when supplying trace elements for microbial culture?

They must be supplied in the right amount, as essential metals can be lethal in high concentrations.

What is a 'defined medium'?

A culture medium where the exact chemical composition is known.

What is a 'complex medium'?

A culture medium composed of digests of microbial, animal, or plant products (e.g., yeast and meat extracts).

What is a 'selective medium'?

A culture medium that contains compounds that selectively inhibit the growth of some microbes but not others.

What is a 'differential medium'?

A culture medium that contains an indicator, usually a dye, that detects particular metabolic reactions during growth.

What is an 'axenic culture'?

A pure culture free from bacteria other than the one being studied.

What is the purpose of the streak plate technique?

To separate individual colonies of one type of bacteria by distributing inoculum along the solid surface of agar, allowing single cells to form isolated colonies.

What is 'generation (doubling) time' in prokaryotic reproduction?

The time required for microbial cells to double in number.

What defines a 'batch culture'?

A closed-system microbial culture of fixed volume where no food is added and no waste is removed.

What occurs during the 'lag phase' of bacterial growth in batch culture?

Cells are metabolically active, making enzymes and ATP, and growing slightly larger, but there is no significant increase in cell number.

What occurs during the 'log (exponential) phase' of bacterial growth in batch culture?

Cells are doubling at regular intervals, dividing at their fastest rate, resulting in exponential population growth.

What occurs during the 'stationary phase' of bacterial growth in batch culture?

The growth rate of the population is zero, as cell division decreases to equal the rate at which old cells die, resulting in a constant number of live cells.

What typically causes bacterial cultures to enter the 'stationary phase'?

Nutrients and oxygen become limiting, wastes build up, and pH often decreases due to metabolism.

What occurs during the 'decline (death) phase' of bacterial growth in batch culture?

The total number of live cells decreases at a logarithmic rate because the media no longer supports cell division due to nutrient depletion, waste accumulation, and incorrect pH.

What is a direct method for measuring microbial growth?

Microscope cell count using counting chambers or etched slides, or Most Probable Number (MPN).

How does turbidity (optical density) measure microbial growth?

Cell suspensions scatter light, so more cells result in more light scattered and a more turbid suspension, measured using a spectrophotometer.

What is reported when counting colonies from viable cell counts (serial dilutions)?

Colony-forming units (CFU), not the number of viable cells.

What is the difference between batch culture and continuous culture?

Batch culture is a closed system with fixed volume, while continuous culture is an open system where new media is continuously added and spent culture is removed, allowing the culture to be maintained in log phase.

What is a 'chemostat'?

A common type of continuous culture device where a known volume of fresh medium is added while spent medium is removed at the same rate.

What are 'acidophiles'?

Bacteria adapted to grow in acidic pH environments, typically between 0.5 and 5.4.

What are 'neutrophiles'?

Bacteria adapted to grow in neutral pH environments, typically between 5.5 and 7.9, including most human symbionts and pathogens.

What are 'obligate aerobes'?

Microbes that require oxygen for growth.

What are 'obligate anaerobes'?

Microbes that cannot grow in the presence of oxygen.

What are 'facultative anaerobes'?

Microbes that can grow with or without oxygen, possessing two sets of enzymes.

Why are most microbes not culturable?

Because their specific nutritional needs or growth conditions are not known, making it difficult to replicate their natural environment in the lab.