Microbial Growth Factors Quiz

Questions and Answers

What does optical absorbance measure in a turbidity test?

The genetic diversity of the bacteria

The temperature of the culture

The concentration of bacteria in the suspension (correct)

The pH level of the bacterial broth

Which statement best describes the concept of continuous culture?

It involves intermittent feeding of nutrients

It is a closed system with no nutrient input

Fresh media is continuously added while old broth is removed (correct)

It is a method used for long-term storage of cultures

What distinguishes a thermophilic bacterium from a thermotolerant bacterium?

Thermophilic bacteria grow at elevated temperatures, while thermotolerant bacteria can only survive at those temperatures. (correct)

Thermophilic bacteria survive at high temperatures, but thermotolerant bacteria can grow at those temperatures.

Thermophilic bacteria require a specific pH to grow, whereas thermotolerant bacteria do not.

Both types of bacteria thrive in low temperatures.

How is mean generation time related to the growth rate of bacteria?

Growth rate is the reciprocal of mean generation time Signup and view all the answers

Which of the following terms describes organisms that can survive but not grow under specific conditions?

Tolerant organisms Signup and view all the answers

In which type of culture system do cells reach a constant equilibrium level as long as the nutrient feed is maintained?

Continuous culture Signup and view all the answers

What is the primary focus of measuring turbidity in microbial growth studies?

To estimate the biomass of bacterial cells Signup and view all the answers

Which of the following best describes the suffix '-phile' as it relates to microbes?

It refers to organisms that prefer specific growth conditions Signup and view all the answers

Who is credited with the first accurate description of microorganisms?

Anton van Leeuwenhoek Signup and view all the answers

Which scientist proposed that air carried germs to the culture medium in his experimental design?

Lazarro Spallanzani Signup and view all the answers

What conclusion did John Tyndall reach regarding the growth of microbes?

Preventing dust allowed for sterile conditions. Signup and view all the answers

Which of the following assertions about spontaneous generation is true?

Spontaneous generation was universally accepted until challenged. Signup and view all the answers

What experimental improvement did Lazarro Spallanzani introduce compared to John Needham?

Heating the broth before sealing the flasks. Signup and view all the answers

Which of the following statements is consistent with Aristotle's beliefs about spontaneous generation?

Life can originate from non-living materials. Signup and view all the answers

What was one of the critical controls used by Schwann in his experiments on microbial growth?

Heated air passed through sterile wool. Signup and view all the answers

Which of the following was a misconception about the conditions for microbial growth prior to Spallanzani's findings?

Microbial growth was independent of air exposure. Signup and view all the answers

What describes an organism that can grow under sub-optimal conditions but does not require them for survival?

Facultative organism Signup and view all the answers

What is the optimal temperature range for psychrotrophs?

20 – 30 ºC Signup and view all the answers

Which type of organism requires elevated salt concentrations for growth?

Halophile Signup and view all the answers

Which of the following groups of organisms requires oxygen for their growth?

Strict aerobes Signup and view all the answers

What describes organisms that can use CO2 as their sole carbon source?

Autotrophs Signup and view all the answers

Which factors can influence microbial growth?

Temperature, pH, salt concentration, oxygen concentration Signup and view all the answers

Which term describes organisms that grow optimally at a pH below 5.5?

Acidophiles Signup and view all the answers

Which nitrogen source is primarily derived from amino acid catabolism?

Organic nitrogen Signup and view all the answers

What is the optimal pH range for neutrophiles?

5.5 – 8 Signup and view all the answers

Which group of organisms can grow equally well in the presence or absence of oxygen?

Aerotolerant anaerobes Signup and view all the answers

Study Notes

Microbial Growth Conditions

Obligate organisms need specific conditions for growth, while facultative organisms can thrive in varying conditions.
Facultative conditions typically relate to sub-optimal environments where growth is still possible.

Temperature Influences

Bacterial growth range is approximately 20 ºC, with an optimum temperature for maximum growth.
Psychrophiles: Optimal at 0-15 ºC, can grow at 0 ºC.
Psychrotrophs: Optimal at 20-30 ºC, maximum around 35 ºC; can grow at 0-10 ºC.
Mesophiles: Optimal growth around 20-45 ºC.
Moderate thermophiles: Optimal growth at 55-65 ºC.
Extreme thermophiles (hyperthermophiles): Optimal growth at 80-113 ºC.

pH Requirements

Acidophiles: Optimal growth between pH 0-5.5.
Neutrophiles: Optimal growth between pH 5.5-8.
Alkalophiles: Optimal growth between pH 8-11.5.

Salt Concentration Needs

Halophiles: Require high salt concentrations (0.2 M or more) for growth; e.g., Halobacterium.
Osmotolerant organisms: Can grow in various salt concentrations; e.g., Staphylococcus aureus.

Oxygen Concentration Types

Strict aerobes: Require ~20% oxygen for growth.
Strict anaerobes: Grow only in the absence of oxygen.
Facultative anaerobes: Prefer oxygen but can grow without it at reduced rates.
Aerotolerant anaerobes: Grow well in both oxygen-rich and oxygen-free environments.
Microaerophiles: Require reduced oxygen concentrations (~2-10%).

Nutrient Requirements

Carbon sources:
- Autotrophs utilize CO2 as their sole carbon source.
- Heterotrophs need organic carbon, cannot use CO2.
Nitrogen sources:
- Organic nitrogen from amino acids.
- Inorganic forms: nitrate (NO3-), nitrite (NO2-), and ammonium (NH4+).
- Nitrogen gas (N2) can be fixed by some bacteria.
Phosphate sources: Organic and inorganic phosphates (H2PO4- and HPO4 2-).
Sulfur sources: Organic sulfur, oxidized (sulfate SO4 2-) and reduced forms (sulfide S2- or H2S), and elemental sulfur (S0).
Special requirements include amino acids, nucleotide bases, and enzymatic cofactors or vitamins.

Measurement of Microbial Growth

Turbidity: Light diffraction by bacteria in broth cultures measured as optical absorbance; correlates with bacterial concentration.
Mean generation time: Can be derived from a log plot of bacterial concentration versus time after inoculation.

Continuous Culture

A continuous culture system (chemostat) allows fresh media to be added while removing old broth, maintaining a constant cell concentration as long as nutrient feed is sustained.

Growth vs. Tolerance

"Growth" refers to biomass acquisition leading to reproduction, whereas "tolerance" describes organisms that can survive adverse conditions without actual growth.
Thermophilic bacteria thrive at elevated temperatures, while thermotolerant bacteria survive those temperatures without growing.

Historical Concepts in Microbiology

Spontaneous generation was a widely held belief that living organisms could arise from non-living matter.
Notable figures:
- Aristotle (384-322 BC): Asserted simple organisms could arise spontaneously.
- John Needham (1713-1781): Suggested spontaneous generation after observing growth in boiled and sealed broth.
- Lazzaro Spallanzani (1729-1799): Improved Needham's method by sealing flasks before boiling, showing no growth; theorized air carried germs to cultures.

The Microscopy Era

Anton van Leeuwenhoek (1632-1723): First accurately described microorganisms, reigniting debates on spontaneous generation.
Schwann et al. (1830s): Showed that filtered air did not contaminate flasks, supporting the concept that microbes come from the air.
John Tyndall demonstrated that preventing dust entry into media flasks also resulted in no microbial growth.

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Description

Test your knowledge on facultative and obligate conditions affecting microbial growth. This quiz will cover key concepts that differentiate between organisms based on their growth requirements. Explore how different environmental factors influence microbial life.