Question 1

Citric acid fermentation (Aspergillus niger): To favor high yields, the production medium is formulated to be deficient in which micronutrient (critical limiter)?

Accepted Answer

Introduction / Context: Citric acid is a flagship organic acid produced by Aspergillus niger. Media composition strongly influences metabolic routing toward citrate accumulation rather than biomass or byproducts. This question probes the key micronutrient limitation used to bias metabolism toward citric acid. Given Data / Assumptions: Organism: Aspergillus niger. Industrial objective: maximize citrate yield and productivity. Medium tuning: trace metals and nutrients are tightly controlled. Concept / Approach: Manganese limitation is well known to promote citric acid accumulation by reducing certain enzyme activities and morphologies associated with excessive growth, thereby steering carbon flux toward citrate overflow. While iron and phosphate levels are also managed, the most classically emphasized deficiency for high-yield citrate production is manganese. Step-by-Step Solution: Identify the hallmark lever: trace manganese concentration kept extremely low.Link low Mn to morphological/enzymatic states favoring citrate secretion.Select “manganese” as the single, most critical deficiency. Verification / Alternative check: Fermentation manuals specify Mn in the microgram-per-liter range; inadvertent Mn contamination (e.g., from equipment) can depress titers. Why Other Options Are Wrong: Iron and phosphate are controlled but are not the principal “deficiency lever” in foundational teaching; “all of these” overstates the requirement. Common Pitfalls: Assuming any trace metal limitation will work; manganese is uniquely sensitive in this process. Final Answer: manganese

Question 2

Breaking the ethanol–water azeotrope: What distillation method is used to obtain ethanol concentrations greater than about 95 percent by volume?

Accepted Answer

Introduction / Context: Conventional distillation of fermented beer or mash is limited by the ethanol–water azeotrope near 95–96% v/v at atmospheric pressure. Exceeding this concentration is necessary for fuel-grade ethanol and some industrial uses. This question targets the unit operation needed to surpass the azeotrope. Given Data / Assumptions: Azeotropes behave as single pseudo-components in distillation. Standard column operation cannot enrich ethanol beyond the azeotropic composition. Special techniques are required to shift or break the azeotrope. Concept / Approach: Azeotropic distillation introduces a third component (entrainer) or exploits pressure-swing to alter relative volatilities and break the ethanol–water azeotrope, allowing purification above 95%. Common industrial alternatives include molecular sieves (adsorption) and pervaporation, but in the context of “distillation” methods, azeotropic distillation is the canonical answer. Step-by-Step Solution: Recognize the 95% v/v limit from ordinary fractional distillation.Identify the need for an azeotrope-breaking technique.Select “azeotropic distillation” as the appropriate method among the options. Verification / Alternative check: Industrial flowsheets often apply rectification to 92–95% followed by azeotropic distillation or dehydration (e.g., cyclohexane entrainer or newer dehydration technologies). Why Other Options Are Wrong: Fractional distillation alone cannot exceed the azeotrope; flash or mere “successive” distillations do not change the azeotropic limit. Common Pitfalls: Confusing post-distillation dehydration methods (molecular sieves) with “distillation” per se; nonetheless, among distillation choices, azeotropic distillation is correct. Final Answer: azeotropic distillation

Question 3

Downstream processing of citric acid: In classic lime–sulfuric acid recovery, citric acid is first precipitated from the fermentation broth as which salt?

Accepted Answer

Introduction / Context: Citric acid produced by Aspergillus niger must be recovered and purified. A classical downstream sequence uses lime treatment and acidification to isolate and release citric acid. Recognizing the intermediate salt is a standard question in biochemical engineering and industrial microbiology. Given Data / Assumptions: Broth contains citric acid along with cells and impurities. Calcium hydroxide (lime) is added to precipitate a sparingly soluble salt. Subsequent sulfuric acid treatment liberates citric acid and forms gypsum (calcium sulfate) as a byproduct. Concept / Approach: Adding lime converts citric acid to calcium citrate, which precipitates and can be filtered. Acidifying with sulfuric acid regenerates citric acid in solution and yields gypsum. This route is robust, economical, and widely documented historically. Step-by-Step Solution: Recall the “lime–sulfuric” sequence used in classical citric acid recovery.Identify the precipitated intermediate as calcium citrate.Choose “calcium citrate” as the correct option. Verification / Alternative check: Many process descriptions explicitly list calcium citrate precipitation followed by sulfuric acid treatment. Why Other Options Are Wrong: Magnesium or zinc salts are not the standard precipitated intermediates in the conventional industrial route; “none of these” is thus incorrect. Common Pitfalls: Confusing the precipitation step with newer solvent extraction or ion-exchange routes; the question specifically targets the classical process. Final Answer: calcium citrate

Question 4

Standardization of antibiotic potency: In the 1944 definition, one “International Unit” (IU) of penicillin activity is equivalent to what mass of crystalline penicillin G (approximately 98% purity)?

Accepted Answer

Introduction / Context: International Units (IU) provide a standardized measure of biological activity, ensuring consistency across batches and laboratories. For penicillin, potency depends on antimicrobial activity rather than mass alone, and the IU anchors that activity to a reference substance of defined purity. Given Data / Assumptions: The reference is penicillin G (benzylpenicillin), the archetypal penicillin used in early standards. Purity of the reference crystal is approximately 98%. The historical IU definition is widely reproduced in pharmacopeias and microbiology texts. Concept / Approach: The 1944 standard equated 1 IU of penicillin activity to 0.6 micrograms of highly pure penicillin G. This mass-to-activity mapping allows dosing and quality control by bioassay or equivalently calibrated physicochemical methods, bridging biological potency with manufacturing specifications. Step-by-Step Solution: Identify the active reference: crystalline penicillin G.Recall the canonical conversion: 1 IU ≈ 0.6 micrograms at ~98% purity.Select the exact matching option and rule out alternatives with different masses, purities, or penicillin types. Verification / Alternative check: Pharmacopeial monographs and historical standards list the 0.6 microgram equivalence for penicillin G activity. Why Other Options Are Wrong: Options that specify penicillin F or different mass/purity do not match the official historical definition. Lower purity alters mass-to-IU equivalence and is therefore incorrect. Common Pitfalls: Confusing milligrams and micrograms; overlooking that purity is part of the definition. Final Answer: 0.6 micrograms of crystalline penicillin G of about 98% purity

Question 5

In clinical biotechnology and therapeutic enzymology, microbially produced streptokinase is administered for which primary medical purpose?

Accepted Answer

Introduction / Context: Streptokinase is a bacterial protein used as a thrombolytic (clot-dissolving) drug in emergency medicine, especially for acute myocardial infarction and certain cases of pulmonary embolism or deep vein thrombosis. Understanding its clinical role distinguishes medical biotechnology applications from industrial enzyme uses in food or detergents. Given Data / Assumptions: The enzyme named is streptokinase, produced by Streptococcus species. Context implies therapeutic use in humans. Options include non-medical uses to test conceptual clarity. Concept / Approach: Streptokinase forms a complex with plasminogen, converting it to plasmin, a broad-spectrum protease that degrades fibrin within clots. By promoting fibrinolysis, streptokinase reopens occluded coronary arteries, restoring perfusion and limiting myocardial damage. This mechanism is distinct from enzymes used in juice clarification (e.g., pectinases) or laundry (e.g., proteases, lipases), and from amylases used to hydrolyze starch in food processing. Step-by-Step Solution: Identify streptokinase as a thrombolytic agent derived from bacteria.Recall its mechanism: streptokinase + plasminogen → plasmin → fibrin degradation.Match mechanism to clinical indication: dissolving intravascular thrombi in coronary arteries.Exclude industrial enzyme applications unrelated to clot lysis.Select the option describing dissolution of blood clots in coronary blockages. Verification / Alternative check: Thrombolytic guidelines list streptokinase (along with alteplase, reteplase, tenecteplase) for early reperfusion therapy. Adverse effects like bleeding and antigenicity also align with its proteolytic, non-human origin. Why Other Options Are Wrong: Remove spots from laundry products: Detergents use bacterial proteases, not streptokinase for fibrinolysis.Clarify fruit juice: Pectinases and cellulases are typical; streptokinase is not used.Break down starch: Amylases hydrolyze starch; streptokinase targets fibrin via plasmin generation. Common Pitfalls: Confusing “enzyme” as a generic term for all industrial uses; medical thrombolytics are distinct, with strict dosing and indications. Do not conflate streptokinase with tissue plasminogen activator (tPA), which directly activates plasminogen and is human or recombinant in origin. Final Answer: Dissolve blood clots in patients with coronary artery blockages

Industrially Useful Microbial Processes Questions