Industrial Microbiology Practice Questions
20 free Industrial Microbiology practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
In industrial fermentation, what is the primary purpose of a 'sparger' within a stirred-tank bioreactor?
- A To introduce sterile air into the medium
- B To monitor the pH of the medium
- C To mix the nutrients uniformly
- D To regulate the temperature of the vessel
Correct answer: To introduce sterile air into the medium
A sparger is a device, often a ring with small holes, located at the bottom of the bioreactor. It breaks sterile air into tiny bubbles to maximize the oxygen transfer rate to aerobic microorganisms.
Which microorganism is most commonly used in the industrial production of ethanol from starchy or sugary substrates?
- A Saccharomyces cerevisiae
- B Aspergillus niger
- C Lactobacillus acidophilus
- D Bacillus subtilis
Correct answer: Saccharomyces cerevisiae
Saccharomyces cerevisiae, or brewer's yeast, is the workhorse of the ethanol industry. It efficiently ferments hexose sugars into ethanol and carbon dioxide under anaerobic conditions.
A 'primary metabolite' is a compound that is produced by a microorganism during which phase of the growth curve?
- A Exponential phase
- B Lag phase
- C Stationary phase
- D Death or decline phase
Correct answer: Exponential phase
Primary metabolites, such as amino acids and ethanol, are essential for the growth and reproduction of the cell. They are produced during the active exponential (log) phase of growth, often referred to as the trophophase.
Which of the following organic acids is commercially produced using the filamentous fungus Aspergillus niger through submerged fermentation?
- A Acetic acid
- B Lactic acid
- C Propionic acid
- D Citric acid
Correct answer: Citric acid
Aspergillus niger is highly efficient at overproducing citric acid when grown in media with high sugar concentrations and limiting amounts of trace metals. This process accounts for the majority of the world's citric acid supply.
What is the main advantage of using 'immobilized enzymes' in industrial bioprocessing?
- A They allow the enzyme to be recovered and reused
- B They increase the activation energy of the reaction
- C They make the enzyme more susceptible to heat
- D They remove the need for cofactors entirely
Correct answer: They allow the enzyme to be recovered and reused
Immobilization attaches enzymes to an inert, insoluble material. This allows the enzyme to be easily separated from the product stream, reused multiple times, and often increases the enzyme's stability.
The production of penicillin by Penicillium chrysogenum is considered a 'secondary metabolite' because it occurs during the:
- A Trophophase
- B Idiophase
- C Lag phase
- D Death phase
Correct answer: Idiophase
Secondary metabolites are produced during the stationary phase (idiophase) when growth is limited. These compounds are not essential for basic growth but provide ecological advantages, such as inhibiting competitors.
In the dairy industry, which pair of bacterial genera is primarily responsible for converting lactose into lactic acid to produce yogurt?
- A Streptococcus and Lactobacillus
- B Escherichia and Salmonella
- C Pseudomonas and Bacillus
- D Corynebacterium and Mycobacterium
Correct answer: Streptococcus and Lactobacillus
Starter cultures for yogurt typically include Streptococcus thermophilus and Lactobacillus bulgaricus. They ferment the sugar lactose into lactic acid, which coagulates milk proteins to create the characteristic texture.
What is the 'Scale-up' process in industrial microbiology?
- A The sterilization of large-scale equipment
- B Increasing the size of the microbial cells through genetic engineering
- C Transferring a lab-scale process to industrial fermenters
- D Measuring the weight of the final dried product
Correct answer: Transferring a lab-scale process to industrial fermenters
Scale-up involves translating the optimized conditions found in a small shake flask or lab bioreactor to large industrial fermenters. It requires complex engineering to maintain consistent oxygen transfer, mixing, and temperature.
Which of the following is a bio-plastic produced by various bacteria, such as Alcaligenes eutrophus, as an intracellular energy reserve?
- A Polystyrene (PS)
- B Polyhydroxyalkanoates (PHA)
- C Polyvinyl chloride (PVC)
- D Polyethylene terephthalate (PET)
Correct answer: Polyhydroxyalkanoates (PHA)
PHAs, like poly-beta-hydroxybutyrate (PHB), are biodegradable plastics synthesized by bacteria under nutrient-limiting conditions. They serve as carbon and energy storage granules similar to fat in humans.
Which screening method is used to identify microorganisms that produce antibiotics by looking for 'zones of inhibition'?
- A Replica plating technique
- B Crowded plate technique
- C Gram staining
- D PCR amplification
Correct answer: Crowded plate technique
The crowded plate technique involves plating soil dilutions to get a high density of colonies. One looks for colonies surrounded by a clear zone where no other bacteria can grow, indicating antibiotic secretion.
Which vitamin is produced commercially by fermentation using the bacteria Pseudomonas denitrificans and Propionibacterium shermanii?
- A Vitamin C (ascorbic acid)
- B Vitamin B12 (cobalamin)
- C Vitamin D (calciferol)
- D Vitamin A (retinol)
Correct answer: Vitamin B12 (cobalamin)
Vitamin B12 (cobalamin) is chemically too complex to synthesize cheaply and is produced industrially only by microbial fermentation. Pseudomonas denitrificans and Propionibacterium shermanii are the main production strains.
In downstream processing, which technique is used to rupture microbial cells to release intracellular products?
- A Lyophilization
- B Homogenization
- C Centrifugation
- D Distillation
Correct answer: Homogenization
High-pressure homogenization or sonication are physical methods used to break open (lyse) cell walls. This is necessary when the desired industrial product, such as a recombinant protein, is stored inside the cytoplasm.
The 'Crabtree effect' in yeast refers to:
- A The inhibition of yeast growth by high concentrations of dissolved salts
- B The production of ethanol despite ample oxygen at high glucose levels
- C The ability of yeast to move toward a light source
- D The process of spore formation under adverse nutrient conditions
Correct answer: The production of ethanol despite ample oxygen at high glucose levels
When glucose concentrations are high, S. cerevisiae prefers fermentation over aerobic respiration, even if oxygen is available. In industrial settings, glucose must be fed slowly to avoid unwanted ethanol production when biomass is the goal.
Which enzyme, produced industrially by microbes, is used in the 'stone-washing' of blue jeans to give them a faded look?
- A Alkaline protease
- B Alpha-amylase
- C Cellulase
- D Lipase
Correct answer: Cellulase
Cellulases break down cellulose fibers on the surface of the denim fabric. This releases the indigo dye in a controlled manner, providing a soft, worn look without the harshness of physical pumice stones.
What is fed-batch fermentation?
- A A system where nutrients are added continuously and the product is removed continuously
- B A closed system where nothing is added after inoculation
- C A system where nutrients are added periodically but nothing is removed until the end
- D A system that uses only solid substrates like bran or rice
Correct answer: A system where nutrients are added periodically but nothing is removed until the end
Fed-batch fermentation allows for the control of substrate concentration, preventing catabolite repression and extending the idiophase. It is widely used to achieve high cell densities and high product yields.
Which of the following is a characteristic of an ideal industrial microorganism?
- A It must require expensive, complex growth media
- B It should produce the desired product in low concentrations
- C It should be genetically stable and easy to manipulate
- D It must be highly pathogenic to ensure fast growth
Correct answer: It should be genetically stable and easy to manipulate
Industrial strains must be safe (non-pathogenic), stable over many generations, and capable of growing on cheap, crude substrates. They also need to be amenable to genetic engineering for yield improvement.
In the production of vinegar, Acetobacter species oxidize ethanol into:
- A Methane
- B Butyric acid
- C Lactic acid
- D Acetic acid
Correct answer: Acetic acid
Vinegar production is an aerobic process where 'mother of vinegar' (Acetobacter) converts ethanol (from wine or cider) into acetic acid. This is an incomplete oxidation of the alcohol.
What is the primary role of 'antifoam agents' in a fermentation vessel?
- A To kill contaminating bacteria
- B To provide a source of nitrogen
- C To reduce surface tension and collapse gas bubbles
- D To increase the solubility of the product in the broth
Correct answer: To reduce surface tension and collapse gas bubbles
Intense agitation and aeration often create foam, which can clog air filters and lead to contamination. Antifoams (like silicone oils) reduce surface tension to prevent foam buildup.
Which extracellular polysaccharide, produced by fermentation with a bacterial pathogen of cabbage, is used in the food industry as a thickener and stabilizer?
- A Pullulan
- B Gellan gum
- C Bacterial cellulose
- D Xanthan gum
Correct answer: Xanthan gum
Xanthan gum is an extracellular polysaccharide made by aerobic fermentation with Xanthomonas campestris, the bacterium that causes black rot of cabbage and other crucifers. It is prized for its rheological behaviour, staying stable across a wide range of temperatures and pH levels.
The use of microorganisms to remove or neutralize pollutants from a contaminated site is known as:
- A Biopharming
- B Bioprospecting
- C Bioleaching
- D Bioremediation
Correct answer: Bioremediation
Bioremediation utilizes microbial metabolism to degrade toxic chemicals (like oil spills or heavy metals) into less toxic substances. It can be done 'in situ' at the site or 'ex situ' by removing the material.