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Lab Quiz 7
| Question | Answer |
|---|---|
| What does the Methly Red test identifiy? | Bacteria that perform mixed acid fermentation, which produces stable acid end product |
| How are the end products of fermentation different for Methyl Red positive? | Positive: feremntation products are stable acids Negative: fermentation products are closer to neutral or converted to products that are closer to neutral |
| What does a positive result of a Methyl Red test look like? | Red |
| What does a negative result of a Methyl Red test look like? | Yellow/orange |
| Why would a bacterium reduce nitrate? | When nitrate is used as a final electron acceptor during anaerobic respiration |
| What can nitrate be reduced to? | Nitrite Nitrogen gas Nitrous oxide Ammonium |
| How do we test for reduction of nitrate to nitrous oxide or molevular nitroge? What do positive and negative results look like? | Look for gas bubble in Durham tube Positive: gas bubble present Negative: no gas bubble |
| How do we test to see if the original nitrate was still in the medium? What do positive and negative results look like? What would a negative result tell us? | Add zinc to medium Positive: no color change. No nitrate was remaining in the medium, so bacteria must have reduced nitrate to something we did not test for. Negative: medium turns red. Zinc will reduce any nitrate reagents |
| What does the citrate utilization test tell us? | If the microbe can transport citrate into cell and use it as its only carbon |
| What 2 enzymes are needed for bacteria to use citrate from the media to make ATP? What is the role of each of these enzymes? | Citrate permease- transports citrate into the cells Citrate lyase- converts citrat into oxaloacetate, which is then converted to pyruvate |
| What does a positive result of a citrate utilization test tell us? What specifically causes the color change? | Medium turns blue surviving bacteria convert ammonuim phosphate in the medium into the alkaline products ammonia and ammonium hydroxide. Rasing the pH and bromothymol blue turning blue. |
| What does a negative result of a citrate utilization test? | No color change- medium stays green |
| What does the PAD tell us? | If the enzyme phenylalanine deaminase is present in the bacteria |
| What is the reaction of the enzyme phenylalanine deaminase? | Amino group is removed from the amino acid phenylalanine to create phenylpyruvate and ammonia |
| What does a positive result look like? | Medium turns green after adding ferric chloride |
| What do we add after incubation to show us a positive result? What is this reagent interacting with to cause the color change? | Ferric chloride Ferric chloride interacts phenylpyruvate |
| What does a negative result of a PAD test look like? | medium remains yellowe; no color change |
| What types of bacteria can the urease test identify? | H.pylori and Proteu species |
| What is urea? | waste product from using amino acids to produce ATP |
| What is the reaction of the urease enzyme? | urea is converted to ammonia and carbon dioxide |
| Why would it be benefical for bacteria to convert urea to ammonia? | urea is not a usable form of nitrogen, but the |
| What does a positive urease test look like? What causes the apperance of the positive result? | Pink- due to basic ammonia produced from the urease reaction |
| What does a negative urease test look like? | yellow or orange |
| What does it mean if an organism is Methly red positive? | microbe performs mixed acid fermentation and end products are either more netural or acids are converted to more netural |
| What does it mean if an organism is Methyl red negative? | microbes do not perform mixed acid ferementation and end products are either more netural or acids are converted to more netural products |
| How did we test for reduction of nitrate to nitrite? What do positive and negative results look like? | Add nitrate reagents Positive: Red color develops Negative: color stays the same |
| Nitrogen is an important component of amino acids and nucleotides. Urea is a waste product created from amino acid metabolism. What is the benefit of having the urease enzyme? | Urea is not a usable form of nitrogen, but the urease enzyme converts urea into usable ammonia |
| Why would it be beneficial for bacteria to convert urea to ammonia? | it allows them to acquire an essential nitrogen source and to buffer their environment against damaging acidity. |
| f |
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