Microbial Metabolism Flashcards
Define metabolism
All chemical reactions in an organism
Define catabolism
Breakdown of larger molecules into smaller ones
Define anabolism
Synthesis of larger molecules from smaller molecules
What are the results of oxidation in cellular respiration? (2)
- CO₂
- Water
What is the result of oxidation in fermentation?
Organic waste products
Which is more efficient at extracting energy from organic molecules – cellular respiration or fermentation?
Cellular respiration
When does fermentation occur?
When cells lack a terminal electron acceptor and cannot carry out cellular respiration
The synthesis of ATP without the electron transport chain is known as ______
Substrate-level phosphorylation
The synthesis of ATP using a proton motive force generated via electron transport chain is known as ______
Oxidative phosphorylation
34 molecules of ATP are oxidatively phosphorylated via ______
Chemiosmosis
How is the bulk of ATP (34 out of 38 per molecule of glucose) generated via respiration? (3)
- Glycolysis - 2 NADH (6 ATP)
- Synthesis of acetyl-coA - 2 NADH (6 ATP)
- Krebs cycle - 6 NADH (18 ATP) and 2 FADH₂ (4 ATP)
What is the essential function of fermentation in terms of making glycolysis possible?
Regeneration of NAD+
NADH reduces pyruvic acid in which type of fermentation?
Lactic acid fermentation
Pyruvic acid undergoes decarboxylation to form ethanol in which type of fermentation?
Alcoholic fermentation
What is decarboxylation?
CO₂ is given off
What microbe is responsible for alcoholic fermentation?
Saccharomyces cerevisiae
Describe how alcoholic fermentation serves as a means of preservation
End products prevent growth of spoilage microbes
What 3 ingredients or conditions are necessary to make wine?
- Sugar
- Yeast
- Anaerobic conditions
Describe how lactic acid fermentation serves as a means of preservation
Regulates pH and prevents growth of microbes
What microbes are responsible for lactic acid fermentation? (2)
- Streptococcus
- Lactobacillus
In practice, what is the difference between the “O” and “F” tubes?
- O tube = aerobic
- F tube = anaerobic oil overlay
Indicate the carbohydrate used in the oxidative / fermentative catabolism test
Glucose
What is the pH indicator in the oxidative / fermentative catabolism test?
Bromothymol blue
Describe the expected color changes at a basic pH in the oxidative / fermentative catabolism test
Green
Describe the expected color changes at an acidic pH in the oxidative / fermentative catabolism test
Yellow
______ acidify the O/F glucose medium
Fermenters
Indicate the 3 different carbohydrates used in the Durhman sugar tube test
- Glucose
- Lactose
- Sucrose
What is the pH indicator in the Durham sugar tube test?
Phenol red
Describe the expected color changes at a basic pH in the Durham sugar tube test
Red
Describe the expected color changes at an acidic pH in the Durham sugar tube test
Yellow
What are the expected results of gas production for the Durham sugar tube test?
Bubbles
Indicate the carbohydrate used in the methyl red (MR) test
Glucose
What type of fermentation is detected by the methyl red (MR) test?
Mixed-acid fermentation
What is the pH indicator in the methyl red (MR) test?
Methyl red
What color would be associated with a positive methyl red (MR) test?
Red
What color would be associated with a negative methyl red (MR) test?
Yellow
What type of fermentation is detected by the Voges-Proskauer (VP) test?
Butanediol fermentation
Place the following in the correct order according to the 2,3-butanediol fermentation pathway: 2,3-butanediol, acetoin, glucose
- Glucose
- Acetoin
- 2,3-butanediol
Place the following in the correct order according to the color development: diacetyl, acetion, red color
- Acetoin
- Diacetyl
- Red color
Hydrogen peroxide (H₂O₂) is a ______ in aerobic respiration
Highly reactive oxidizing agent
How does the enzyme catalase ‘detoxify’ H₂O₂ (what is the actual chemical reaction)?
H₂O₂ → H₂O + O₂
What causes the formation of bubbles due to catalase activity in the catalase test?
Hydrogen peroxide
Cytochrome c oxidase is an enzyme in the ______
Electron transport chain
What specific role does cytochrome c oxidase play in aerobic respiration?
Transfers electrons to O₂
What role does molecular oxygen (O₂) play in aerobic respiration?
Terminal electron acceptor
What is the role of tetramethyl-p-phenyl-edediamine?
Artificial electron donor
When electrons are transferred from reduced tetramethyl-p-phenyl-edediamine to cytochrome C, the sample turns ______
Blue
How are anaerobic respiration and the reduction of nitrate (NO3-) to nitrite (NO2-) (or other reduced forms of nitrate) related?
Some bacteria use nitrate as a terminal electron acceptor during anaerobic respiration
What is the role of “nitrate reductase” in anaerobic respiration?
Transfer of electrons from cytochrome B to nitrate
During the reduction of nitrate to nitrite, cultures are grown in ______ with Durham tubes
Nitrate broths
What color would be associated with a positive reduction of nitrate to nitrite?
Red
Why is Simmon’s Citrate Medium a defined medium?
The amount and source of all ingredients are known
______ is the sole carbon source in Simmon’s Citrate Medium
Sodium citrate
______ is the sole nitrogen source in Simmon’s Citrate Medium
Ammonium
How do ‘citrate-positive’ organisms obtain their citrate from the environment – what is the name of the transporter?
Citrate-permease transports citrate into the cell
What occurs if a bacterium lacks citrate-permease?
The bacteria will NOT survive on the medium
What is the pH indicator in Simmon’s Citrate Medium?
Bromothymol blue
Ammonia and ammonium hydroxide are produced by citrate-positive bacteria because they …
They alkalize the medium (turn it blue)
What color would be associated with a positive Citrate Test?
Blue
What color would be associated with a negative Citrate Test?
Green
Enzymes that catalyze the removal of an amino acid’s carboxyl group are known as ______
Decarboxylases
Enzymes that catalyze the removal of an amino acid’s amine group (NH₂) are known as ______
Deaminases
Name the carbon source and specific amino acid in the Moller’s Decarboxylation Medium used in the lab
Lysine
What is the pH indicator in Moller’s lysine decarboxylase medium?
Bromocresol purple
What color would be associated with a positive Moller’s lysine decarboxylase medium?
Purple
What color would be associated with a negative Moller’s lysine decarboxylase medium?
Yellow
A mineral overlay used in the decarboxylation / deamination test to promote ______
Fermentation
In Moller’s lysine decarboxylase medium, glucose initially turns the medium ______ due to the end products of fermentation
Yellow
In Moller’s lysine decarboxylase medium, decarboxylation of lysine results in the accumulation of alkaline end products that turn the medium ______
Purple
Low pH and the presence of the specific amino acid induces ______ to produce the enzyme
Decarboxylase-positive organisms
What occurs if the organism is capable of fermenting glucose and decarboxylating lysine?
Accumulation of alkaline end products
What substrate is required for phenylalanine deaminase?
Oxygen
What are the products for phenylalanine deaminase? (2)
- Ammonia (NH₃)
- Phenylalanine acid
______ provides a rich source of phenylalanine
Phenylalanine agar
Of the 2 products of phenylalanine deaminase activity, which one reacts with ferric chloride (FeCl3)?
Phenylpyruvic acid
What happens to the sample when phenylpyruvic acid reacts with the ferric chloride?
Turns a dark green color almost immediately
Describe hydrolysis reactions
Uses water to split complex molecules
______ are required for hydrolytic reactions
Hydrolytic enzymes
What is esculin?
A vasoprotective agent that provides nutrients
Esculin is composed of ______
Glycoside
What is glycoside?
Sugar composed of glucose and esculetin
What are the hydrolysis products of esculin catabolism? (2)
- Esculin
- Glucose
What role does esculin play in the differential quality of the Bile Esculin Test?
Catabolizes into glucose
What role does bile play in the selective quality of the Bile Esculin Test?
Selective for group D streptococci and enterococci
When esculin molecules are split, esculentin reacts with ______ in the medium
Ferric citrate
A ______ is formed when esculentin reacts with ferric citrate
Phenolic iron complex
What color would be associated with a positive Bile Esculin Test?
Dark brown
Starch is a polysaccharide composed of ______
ɑ-D-glucose subunits
Differentiate between amylose and amylopectin
- Amylose - linear
- Amylopectin - branched
What kind of linkage holds linear molecules of glucose together in amylose?
1,4-ɑ-glycosidic linkages
What kind of linkage attaches side chains of amylopectin to the main chain?
1,6-ɑ-glycosidic linkages
What specific reactions do “a-amylase” and “oligo-1,6-glucosidase” enzymes catalyze?
Starch into glucose by breaking glycosidic linkages
Explain the principle of using starch agar to detect starch hydrolysis
Organisms hydrolyze the starch in the area surrounding their growth
What role does iodine play in detecting starch hydrolysis?
Reacts with starch
What kind of color reaction develops between iodine and starch?
Blue / dark brown
What color would be associated with a positive starch hydrolysis test?
Clear
What are the hydrolysis products of urea? (2)
- Ammonia (NH₃)
- Carbon dioxide (CO₂)
______ catalyzes the hydrolysis of urea into carbon dioxide and ammonia
Urease
What is the main nutritional source in Urea Broth?
Yeast extract
What is the pH indicator in the Urease Test?
Phenol red
What color would be associated with alkaline results of urea hydrolysis?
Pink
What color would be associated with neutral results of urea hydrolysis?
Red / orange
What color would be associated with acidic results of urea hydrolysis?
Yellow
What color would be associated with a positive urease organism?
Pink
