Oxygen Use and Tolerance Flashcards
SOD (superoxide dismutase)
Superoxide dismutase (SOD) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide (O2−) radical into either ordinary molecular oxygen (O2) or hydrogen peroxide (H2O2). Superoxide is produced as a by-product of oxygen metabolism and, if not regulated, causes many types of cell damage.
Aerobic and anaerobic bacteria can be identified by growing them in test tubes of ________________.
- thioglycollate broth
Microaerophiles
- test tube #4
- need oxygen because they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen. They gather in the upper part of the test tube but not the very top.
- A microaerophile is a microorganism that requires oxygen to survive, but requires environments containing lower levels of oxygen than are present in the atmosphere (i.e. <21% O2; typically 2-10% O2).[1][2] Many microaerophiles are also capnophiles, requiring an elevated concentration of carbon dioxide (e.g. 10% CO2 in the case of Campylobacter spp.).
Obligate Anaerobes
- tube #2
- are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest.
- Obligate anaerobes are microorganisms killed by normal atmosphericconcentrations of oxygen (20.95% O2).[1][2] Oxygen tolerance varies between species, some capable of surviving in up to 8% oxygen, others losing viability unless the oxygen concentration is less than 0.5%.[3] An important distinction needs to be made here between the obligate anaerobes and the microaerophiles. Microaerophiles, like the obligate anaerobes, are damaged by normal atmospheric concentrations of oxygen. However, microaerophiles metabolise energy aerobically, and obligate anaerobes metabolise energy anaerobically. Microaerophiles therefore require oxygen (typically 2-10% O2) for growth. Obligate anaerobes do not.[1][3][4]
Bacteria and other organisms, such as humans, which utilize ___________ pathways also produce ________________to protect themselves against the production of different ___________________such as _______________, _______________, ______________.
- aerobic respiration
- molecules or enzymes
- oxidative (or toxic) states of oxygen
- hydrogen peroxide (H2O2)
- oxygen radicals
- singlet oxygen
Aerotolerant Anaerobes
- Test tube #5
- do not require oxygen as they metabolise energy anaerobically. Unlike obligate anaerobes however, they are not poisoned by oxygen. They can be found evenly spread throughout the test tube.
______________ and __________________are examples of protective enzymes against oxidative states of oxygen.
- Catalase
- Superoxide Dismutase (SOD)
Gas Pak jars
- These jars are used to establish a completely anaerobic environment.
- Chemicals are added to generate H2 and carbon dioxide.
- Palladium tablets in the jar remove oxygen, which combines with H2, resulting in the production of water within the jar.
- The set up should also include the use of an indicator that indicates the presence or absence of oxygen within the jar.
Candle Jars
- When a candle burns in a sealed container, the oxygen is depleted to very low levels while carbon dioxide levels increase. These conditions favor the growth of microaerophiles.
Obligate Areobes
- Tube #1
- need oxygen because they cannot ferment or respire anaerobically. They gather at the top of the tube where the oxygen concentration is highest.
- An obligate aerobe is an organism that requires oxygen to grow.[1]Through cellular respiration, these organisms use oxygen to metabolise substances, like sugars or fats, to obtain energy. In this type of respiration, oxygen serves as the terminal electron acceptor for the electron transport chain.[1] Aerobic respiration has the advantage of yielding more energy (adenosine triphosphate or ATP) than fermentation or anaerobic respiration,[2] but obligate aerobes are subject to high levels of oxidative stress.[3]
Facultative Anaerobes
- test tube #3
- an grow with or without oxygen because they can metabolise energy aerobically or anaerobically. They gather mostly at the top because aerobic respiration generates more ATP than either fermentation or anaerobic respiration.
- A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentationor anaerobic respiration if oxygen is absent.[1] An obligate aerobe, by contrast, cannot make ATP in the absence of oxygen, and obligate anaerobes die in the presence of oxygen.[2]
Thioglycollate Medium
- This medium will support the growth of almost all types of bacteria.
- The medium is stored in test tubes with screw caps, and is stored in dark cabinets rather than on the shelves with other broth or slanted media.
- The medium contains glucose, cysteine, and sodium thioglycollate, a chemical which reduces the oxygen in the broth media. It also contains reazurin, which is an indicator that turns pink in the presence of oxygen, but is colorless in the absence of oxygen.
- After inoculation, the screw caps should be tight to prevent the exchange of the air trapped in the tube with the atmospheric air.
- Due to the trapped air in the tube, some oxygen will always be present in the top of the medium and will support the growth of aerobes and microaerophiles.
- Facultative anaerobes will grow anywhere throughout the medium, while anaerobes will only grow in portions that lack oxygen. As a result, the distribution of the growth within the medium is used as an indicator of the oxygen requirements of the bacterium used to inoculate the medium.
Catalase
Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals). It catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS).
