Thioglycolate tube cultures allow labs to distinguish the oxygen requirements for microorganisms. the oxygen begins diffusing at the top of the test tube, but because the Thioglycolate medium in the tube has strong reducing properties not many oxygen molecules reach the bottom. The microbes will grow densest in the areas of optimum oxygen concentration.

Thioglycolate Tube Cultures

Reactive oxidative species are molecules that contain oxygen that has been partially reduced, typically as a byproduct of aerobic respiration, and therefore contains a highly unstable oxygen ion. ROS are very damaging to structures they come in contact with. Some examples of ROS are peroxides, hydroxyl radical, and hypochlorite ion (household bleach).

Reactive Oxygen Species (ROS)

Different organisms require various levels of oxygen for their metabolic processes, including some who are found in completely anaerobic ecosystems where no molecular oxygen is present. 

- Temperature 
- pH
- Osmotic Pressure
- Barometric Pressure
- Light 
- Oxygen (environmental)

Physical Factors Influencing Microbial Growth

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

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pH is a scale of acidity based on the concentration of hydrogen ions. pH of 7 is considered neutral, below 7 is acidic, and above 7 is basic or alkaline. pH influences the structure of DNA via hydrogen bonds, lipid structure, and production of ATP due to hydrogen ion gradient.

Osmotic pressure is the pressure created across a membrane due to differences in solute concentrations.

Osmotic Pressure

Barometric pressure is also known as the Earth's atmospheric pressure. 

Barometric Pressure

Environmental Oxygen Requirements for Microbial Growth

Some microbes require light for their metabolic processes and therefore to survive and grow.

Light as a Physical Requirement for Growth

The optimum growth temperature is where a population experiences its highest growth rates. The minimum growth temperature is the lowest temperature at which a population can grow and the maximum growth temperature is the highest. 

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