Effects of Oxygen on Growth

Peroxides

Act as oxidizing agents, which can strip electrons off of other molecules

Free oxygen radicals

Have unpaired electrons and are highly reactive

Peroxides and Free oxygen radicals

Two types of oxidative stress

Free oxygen radicals

Tend to attack double bonds and can cause permanent damage to DNA

Catalase

Enzyme that breaks down H2O2 before it can cause oxidative stress

Catalase

Usually used to counteract products of cellular respiration

Superoxide Dismutase

Enzyme that breaks down superoxide radical (O2-) into O2 and H2O2

Superoxide Dismutase

H2O2 can be broken down further by catalase

Obligate Aerobes

Only aerobic growth; oxygen required

Facultative Anaerobes

Both aerobic and anaerobic growth; greater growth in presence of oxygen

Obligate Anaerobes

Only anaerobic growth; ceases in presence of oxygen

Aerotolerant Anaerobes

Only anaerobic growth; but continues in presence of oxygen

Microaerophiles

Only aerobic growth; oxygen required in low concentration

Fluid Thioglycolate Medium

Method for O2 requirements that includes:

• Glucose

• Cysteine

• Sodium Thioglycolate

• Resazurin

Sodium Thioglycollate

Lowers oxidative/reduction potential

Resazurin

O2 indicator: redox sensitive dye that turns red in the presence of O2

Fluid Thioglycollate Medium

Purpose: Creates an oxygen gradient that differentiates aerotolerance

Brewer’s Anaerobic Jar

An O2 determining method that includes:

• Catalyst chamber

• Gas generator envelope

• Rubber gasket seal

• Anaerobic indicator strip

Catalyst chamber

Contains palladium pellets

Gas generator envelope

Water is added to chemicals in envelope to generate H2 and CO2. Carbon dioxide promotes more rapid growth of microorganisms

Rubber gasket seal

Oxygen is removed from chamber by combining with hydrogen to from water. This reaction is catalyzed by the palladium pellets

Anaerobic indicator strip

Methylene blue becomes colorless in absence of O2

Candle Jar

Used for capnophiles

Capnophiles

CO2 loving

Candle Jar

Hi CO2 levels and lower oxygen levels created by burning of candle

Obligate Aerobes

Facultative Anaerobes

Obligate Anaerobes

Aerotolerant Anaerobes

Microaerophiles

Brewer’s Anaerobic Jar and Candle Jar

Two methods of determining O2 requirements

Alcaligenes faecalis

Which bacteria is an obligate aerobe? (Alcaligenes faecalis, Escherichia coli, Clostridium sporogeneses)

Escherichia coli

Which bacteria is a faculative anaerobe? (Alcaligenes faecalis, Escherichia coli, Clostridium sporogeneses)

Clostridium sporogenes

Which bacteria is an obligate anaerobe? (Alcaligenes faecalis, Escherichia coli, Clostridium sporogeneses)