Question 1

Industrial microbiology — Which species of Acetobacter (now Komagataeibacter) is well known for producing extracellular cellulosic strands (bacterial cellulose) that hold cells in a lime-like layer or pellicle?

Accepted Answer

Introduction / Context: Bacterial cellulose is a high-purity, nanofibrillar material produced by certain acetic acid bacteria. Recognizing the classic producing organism is important for questions on biomaterials, fermentation technology, and biofilms at air–liquid interfaces. Given Data / Assumptions: Several Acetobacter (now Komagataeibacter) species are involved in vinegar fermentation and biofilm formation. Bacterial cellulose forms visible pellicles/strands that can hold cells in a cohesive layer at the surface. The item asks for the best-known cellulose producer. Concept / Approach: Acetobacter xylinum (more precisely Komagataeibacter xylinus) is the textbook bacterium for cellulose pellicle formation in static cultures, yielding “nata de coco” and other biomaterial applications. Other listed species are not the archetypal cellulose producers in teaching literature. Step-by-Step Solution: Recall the canonical producer: A. xylinum / K. xylinus.Exclude alternatives lacking strong association with cellulose pellicle formation.Select Acetobacter xylinum. Verification / Alternative check: Industrial and academic sources repeatedly cite K. xylinus as a major source of bacterial cellulose with unique physicochemical properties. Why Other Options Are Wrong: A. curvum, A. schuetzenbachii: acetic acid bacteria without the classic cellulose hallmark. “Accetobacter orleanense”: spelling inconsistent and not the standard cellulose model organism. Common Pitfalls: Confusing vinegar producers broadly with the specific cellulose-producing strains; only certain lineages form robust pellicles. Final Answer: Acetobacter xylinum

Question 2

Molasses-based fermentations — For efficient ethanol and related industrial fermentations, the initial sugar concentration of molasses feed is typically maintained in which range?

Accepted Answer

Introduction / Context: Molasses is a common carbon source in industrial fermentations (e.g., ethanol). The starting sugar concentration must balance osmotic stress, viscosity, and yeast performance to maximize yield and prevent stuck fermentations or contamination. Given Data / Assumptions: Higher sugar raises osmotic pressure and inhibits yeast; too low sugar wastes reactor volume and reduces productivity. Molasses composition varies; process targets accommodate practical yeast tolerance and mass transfer. We seek the typical recommended range for initial fermentable sugar in molasses mashes. Concept / Approach: Industrial practice often sets initial fermentable sugar around 12–16% (w/w), falling within a broader safe window of approximately 10–18% to keep osmotic stress manageable while achieving good ethanol titers. Values above ~20% frequently impair yeast performance without fed-batch strategies. Step-by-Step Solution: Consider yeast tolerance to osmotic pressure and ethanol.Target a range that starts high enough for yield but below inhibitory levels.Select the option that reflects 10–18% as the practical window used widely in batch operations. Verification / Alternative check: Process manuals for distilleries and bioethanol plants commonly cite ~12–16% sugars for robust fermentations with Saccharomyces strains. Why Other Options Are Wrong: 20–30% and 30–38%: typically too high for batch without controlled feeding; risk of inhibition. 4–5%: too dilute for economical production. Common Pitfalls: Assuming “more sugar = faster fermentation.” Excessive sugar slows or stalls yeast due to osmotic and ethanol stress. Final Answer: 10-18%

Question 3

Biosensors — In bioelectronic sensor design, which biological recognition elements are commonly coupled to electronic circuits to detect analytes?

Accepted Answer

Introduction / Context: Biosensors integrate a biological recognition element with a physicochemical transducer to generate measurable electronic signals. In industrial microbiology and environmental monitoring, both whole cells and purified enzymes are widely used as the biorecognition component. Given Data / Assumptions: Whole-cell biosensors exploit cellular metabolism or regulatory circuits. Enzyme-based biosensors rely on specific catalytic reactions to detect substrates or products. Transducers (electrochemical, optical, piezoelectric) convert biological events into signals. Concept / Approach: Because both microorganisms and their enzymes can be immobilized on electrodes or membranes and interfaced with electronics, the best answer includes both. Examples range from glucose oxidase electrodes to microbial BOD sensors and bioluminescent reporter strains. Step-by-Step Solution: Recognize enzyme biosensors (e.g., glucose oxidase for glucose meters).Recognize whole-cell biosensors (e.g., respiration-based toxicity sensors).Select the inclusive option acknowledging both approaches. Verification / Alternative check: Commercial and research biosensors use oxidoreductases, hydrolases, and living cells for diverse targets (glucose, lactate, pollutants). Why Other Options Are Wrong: Microorganisms only or enzymes only: each is too restrictive. Neither: contradicts extensive biosensor literature and products. Common Pitfalls: Assuming only enzymes are used because they are simpler; whole-cell systems provide broader, pathway-level detection. Final Answer: Either microorganisms or microbially derived enzymes

Question 4

Amino acid biotechnology — Which microorganism is utilized in industrial processes for producing D- or DL-alanine?

Accepted Answer

Introduction / Context: Industrial amino acid production relies on carefully selected microbes and enzymes. Alanine (particularly D- or DL-alanine) is important in pharmaceuticals and as a building block in chemical synthesis, and specific strains are exploited for efficient production and racemization. Given Data / Assumptions: Several coryneform and related bacteria are used in amino acid fermentations. Microbacterium ammoniaphilum has been reported for D/L-alanine processes via dehydrogenases/alanine racemase systems. Other listed organisms are associated with different amino acids (e.g., Brevibacterium, Corynebacterium glutamicum for L-lysine, glutamate). Concept / Approach: Match each organism to its classic industrial product. While multiple platforms exist, the teaching-key association pairs D-/DL-alanine with Microbacterium ammoniaphilum, distinguishing it from lysine/glutamate producers. Step-by-Step Solution: Recall canonical associations: C. glutamicum → glutamate and many L-amino acids; Brevibacterium flavum → L-lysine.Identify Microbacterium ammoniaphilum as linked to D-/DL-alanine production.Exclude Arthrobacter paraffineus which is not the standard alanine workhorse. Verification / Alternative check: Bioprocess literature describes D-/DL-alanine production using enzyme systems or microbes like Microbacterium species due to robust racemase/dehydrogenase activity. Why Other Options Are Wrong: Brevibacterium flavum: historically famous for L-lysine, not D-/DL-alanine. C. glutamicum: widely used for glutamate and many L-amino acids. Arthrobacter paraffineus: not the classical choice for alanine production. Common Pitfalls: Assuming all coryneforms produce all amino acids; strain specialization matters greatly. Final Answer: Microbacterium ammoniaphilum

Question 5

Antibiotic production by Brevibacillus (Bacillus) brevis — This organism is exploited commercially to produce which of the following peptide antibiotics?

Accepted Answer

Introduction / Context: Bacillus brevis (now Brevibacillus brevis) is historically important in antibiotic discovery. It produces several membrane-active peptides used as topical agents and research tools. Recognizing these products aids in linking microbial taxonomy to natural product chemistry. Given Data / Assumptions: Tyrothricin is a mixture of tyrocidines and gramicidins. Gramicidin A and tyrocidin are classic products from B. brevis. The question asks whether one or all apply. Concept / Approach: Since B. brevis produces both gramicidin (notably gramicidin A) and tyrocidin, and tyrothricin refers to the combined preparation, the most inclusive correct choice is “all of the above.” Step-by-Step Solution: Identify gramicidin A as a linear peptide ionophore from B. brevis.Recognize tyrocidin as a cyclic decapeptide from the same organism.Recall tyrothricin is a mixture (gramicidin + tyrocidin), historically obtained from B. brevis. Verification / Alternative check: Classic antibiotic catalogs and microbiology texts attribute these peptides to B. brevis. Why Other Options Are Wrong: They are not wrong individually, but each is incomplete relative to the full set the organism produces. Common Pitfalls: Confusing tyrothricin with bacitracin; bacitracin is from B. subtilis group, whereas tyrothricin is the B. brevis mixture of tyrocidin and gramicidin. Final Answer: all of the above

Question 6

Substrate utilization for lactic fermentation — Which organism is used industrially to ferment pentose sugars from sulfite waste liquor to lactic acid?

Accepted Answer

Introduction / Context: Using industrial by-products like sulfite waste liquor (rich in pentoses) improves sustainability of bioprocessing. The selection of lactic acid bacteria (LAB) depends on sugar utilization profiles, particularly the ability to metabolize pentoses efficiently. Given Data / Assumptions: Sulfite waste liquor contains pentose sugars from wood pulping. Not all LAB ferment pentoses; some specialize in hexoses. The question asks for the organism that ferments pentoses to lactic acid. Concept / Approach: Lactobacillus pentosus (name hints at pentose utilization) is known for fermenting pentose sugars to lactic acid via heterofermentative pathways. Other LAB listed (L. bulgaricus, L. casei) primarily prefer hexoses; Streptococcus lactis is now Lactococcus lactis and is also more associated with lactose/hexoses in dairy fermentations. Step-by-Step Solution: Identify the waste stream's pentose profile.Match the LAB species with pentose-fermenting capability.Select Lactobacillus pentosus as the industrial choice for this feedstock. Verification / Alternative check: Process references for lactic acid production highlight L. pentosus and related species for hemicellulose hydrolysates rich in xylose and arabinose. Why Other Options Are Wrong: Streptococcus (Lactococcus) lactis: dairy hexose/lactose fermentation. L. bulgaricus: yogurt cultures, primarily hexose fermenter. L. casei: broader substrate range but not the classic pentose specialist in this context. Common Pitfalls: Choosing based on industrial familiarity (yogurt/cheese strains) rather than matching sugar profile of the feedstock. Final Answer: Lactobacillus pentosus

Question 7

Pathways of fermentation — In many microbial fermentations, pyruvic acid can be reduced to which characteristic end-products?

Accepted Answer

Introduction / Context: Pyruvate is the pivotal branching point of central metabolism. Under anaerobic conditions, cells regenerate NAD+ by reducing pyruvate to characteristic fermentation end-products. Recognizing these products is essential for understanding industrial fermentation and food microbiology. Given Data / Assumptions: We are considering classic microbial fermentation, not aerobic respiration. Different microbes use distinct terminal steps to reoxidize NADH. The item asks for common organic end-products derived from pyruvate reduction. Concept / Approach: Two emblematic routes: alcoholic fermentation converts pyruvate to acetaldehyde and then ethanol (e.g., by Saccharomyces), and lactic fermentation reduces pyruvate directly to lactate (e.g., by Lactobacillus, Lactococcus). Glucose, fructose, starch, and cellulose are not pyruvate reduction products. Citric and isocitric acids are TCA intermediates formed in aerobic metabolism, not typical fermentative sinks for NADH regeneration. Step-by-Step Solution: Recall ethanol pathway: pyruvate → acetaldehyde → ethanol (regenerates NAD+).Recall lactate pathway: pyruvate → lactate via lactate dehydrogenase (regenerates NAD+).Select “ethyl alcohol and lactic acid” as the pair of classic fermentation end-products. Verification / Alternative check: Fermentation profiles in industrial settings (brewing, dairy fermentations) consistently show ethanol or lactate as the main reduced products of pyruvate. Why Other Options Are Wrong: Glucose/fructose: upstream glycolytic substrates, not pyruvate reduction products. Starch/cellulose: polysaccharides, biosynthesis not driven by pyruvate reduction in fermentation. Citric/isocitric acid: TCA intermediates formed aerobically, not typical fermentation endpoints. Common Pitfalls: Mixing catabolic end-products with anabolic polymers; fermentation focuses on redox balance, not polysaccharide synthesis. Final Answer: ethyl alcohol and lactic acid

Question 8

In industrial vinegar production using submerged fermentation, which special fermenter designs are employed for rapid acetification under aerated conditions?

Accepted Answer

Introduction / Context: Vinegar is produced by Acetobacter and related acetic acid bacteria that oxidize ethanol to acetic acid. Two broad process routes exist: surface (trickling) fermentation using packed generators and submerged fermentation using specially designed, highly aerated fermenters. This question checks awareness of the correct vessel types used for submerged acetification. Given Data / Assumptions: We are focusing on submerged (not surface) vinegar fermentation. Options list different equipment names, some specific to submerged technology. Goal is to identify which designs match submerged systems. Concept / Approach: Submerged acetification requires intense aeration and efficient heat removal because the ethanol to acetic acid conversion is exothermic and oxygen-demanding. Classic submerged fermenters include the Frings acetator and the cavitator (and related designs), which maximize oxygen transfer (kLa) via turbines, air sparging, draft tubes, and sometimes mechanical foam control. Step-by-Step Solution: Recognize acetator → canonical submerged vinegar fermenter engineered for high oxygen transfer. Recognize cavitator → another submerged design leveraging intense mixing and aeration. Identify packed vinegar generator → belongs to surface/trickle processes, not submerged. Therefore, submerged fermentation employs acetator and cavitator → choose both (a) and (b). Verification / Alternative check: Textbook classifications of vinegar plants split into packed generators (Orleans/quick process) and submerged fermenters (acetator/cavitator). Industrial case studies confirm the latter for high throughput. Why Other Options Are Wrong: Packed vinegar generator: surface culture; does not represent submerged acetification. “None of these” contradicts established practice. Common Pitfalls: Confusing process types; assuming all vinegar systems use packed beds. Submerged units differ by agitation, aeration, and foam handling. Final Answer: Both (a) and (b).

Question 9

For Eremothecium ashbyii and Ashbya gossypii (riboflavin-producing fungi), why must cultures and fermentation residues be sterilized before disposal?

Accepted Answer

Introduction / Context: Eremothecium ashbyii and Ashbya gossypii are classic industrial riboflavin (vitamin B2) producers. Beyond their biotechnological value, they have ecological and plant-health implications. Proper waste treatment is a key biosafety consideration in fermentation facilities. Given Data / Assumptions: The organisms listed are filamentous ascomycetes associated with plants. Industrial processes may generate biomass and spent broth requiring safe disposal. The question asks the reason for mandatory sterilization before discard. Concept / Approach: Ashbya gossypii (syn. Eremothecium gossypii) and Eremothecium ashbyii have been described as plant-pathogenic or plant-associated fungi (e.g., affecting cotton and related hosts). Accidental release could pose phytopathological risks. Therefore, deactivation of biomass by sterilization mitigates environmental dissemination. Step-by-Step Solution: Identify the organisms’ ecological role → plant-associated with pathogenic potential. Industrial biosafety best practice → sterilize cultures/residues prior to disposal. Select the reasoning that they are plant pathogens → correct safety rationale. Verification / Alternative check: Industrial microbiology guidelines emphasize sterilization of wastes when production strains may be plant pathogens or could persist in the environment. Why Other Options Are Wrong: Human pathogens: not the primary classification for these species. Plant mutants: imprecise and irrelevant to biosafety. Bacteriophages: viruses of bacteria, unrelated here. Common Pitfalls: Assuming any production organism is harmless; pathogenicity to plants can still necessitate strict waste treatment. Final Answer: They are plant pathogens.

Question 10

In biochemistry and food science, β-carotene is more accurately described as which vitamin-related compound?

Accepted Answer

Introduction / Context: β-carotene is a carotenoid pigment widely distributed in plants and is nutritionally important for humans. Understanding its relationship to vitamin A clarifies labeling, fortification, and dietary recommendations. Given Data / Assumptions: β-carotene is a precursor to retinoids (vitamin A activity) in humans. The question distinguishes a vitamin from its provitamin form. Concept / Approach: “Vitamin A” refers to retinol, retinal, and retinyl esters of animal origin or delivered forms. β-carotene is a plant-derived carotenoid that the body can enzymatically cleave to form retinal, which is then reduced to retinol or oxidized to retinoic acid. Hence, β-carotene is properly termed provitamin A. Step-by-Step Solution: Recognize chemical nature: β-carotene → carotenoid hydrocarbon. Convertibility: intestinal dioxygenase splits β-carotene to retinal. Terminology: compounds convertible to vitamin A are “provitamin A”. Select “Provitamin A”. Verification / Alternative check: Nutrition references list retinol equivalents and consider β-carotene as a source of vitamin A after bioconversion, not vitamin A itself. Why Other Options Are Wrong: Vitamins C, D, K are unrelated. “Vitamin A” alone would imply preformed retinoids, not the precursor. Common Pitfalls: Equating dietary plant carotenoids directly with retinol; bioavailability and conversion efficiency vary. Final Answer: Provitamin A.

Question 11

Industrial biotechnology: Which of the following is NOT a typical product made by the fungus Aspergillus niger?

Accepted Answer

Introduction / Context: Aspergillus niger is a workhorse of industrial microbiology, producing organic acids and many enzymes. Distinguishing what A. niger commonly produces helps in process selection and exam readiness. Given Data / Assumptions: Citric acid and gluconic acid are famous A. niger products. A. niger also secretes multiple hydrolases (e.g., pectinases, amylases, some β-galactosidases depending on strain). Lysine is a bulk amino acid typically produced by bacteria. Concept / Approach: Citric acid production by A. niger is one of the largest microbial processes. Gluconic acid is also made by A. niger via glucose oxidase pathways. Enzymes like pectinase are standard A. niger products for fruit juice processing. By contrast, industrial L-lysine is produced mainly by Corynebacterium glutamicum and related bacteria via amino acid fermentation. Step-by-Step Solution: Confirm A. niger primary acid products: citric and gluconic acids → true. Confirm enzyme secretions: pectinase and some galactosidases → plausible A. niger enzymes. Identify exception: lysine is not a typical A. niger industrial product. Verification / Alternative check: Industrial process surveys list A. niger for acids/enzymes, whereas lysine is catalogued under amino acid fermentations driven by Corynebacterium/Escherichia strains. Why Other Options Are Wrong: They correspond to well-known A. niger outputs: acids and hydrolases. Common Pitfalls: Assuming all commodity chemicals can be made by the same microbe; production strains are highly specialized. Final Answer: Lysine.

Question 12

Ethanol manufacture: Production from starch-rich and raw sugar feedstocks commonly employs selected strains of which microorganism?

Accepted Answer

Introduction / Context: Commercial alcohol production relies on robust ethanologens capable of high ethanol yields, osmotolerance, and inhibitor tolerance. The organism choice depends on substrate (starch vs sugars) and process conditions. Given Data / Assumptions: Feedstocks include starch-derived hydrolysates and raw sugars such as molasses. We are to identify the standard industrial organism used worldwide. Concept / Approach: Saccharomyces cerevisiae is the classic yeast for brewing and fuel ethanol. It efficiently ferments glucose, fructose, and sucrose, tolerates high ethanol, and operates over a broad pH and temperature range. Candida species have niche uses (e.g., lactose fermentation or SCP), but are not the mainstream choice for starch/sugar ethanol plants. Step-by-Step Solution: Match core industrial trait: high ethanol yield and tolerance → S. cerevisiae. Candida utilis: renowned for single-cell protein, not primary ethanol fermenter from these feedstocks. Candida pseudotropicalis: specialized lactose fermentations; less common in standard sugar/starch plants. Therefore select Saccharomyces cerevisiae. Verification / Alternative check: Distillery and fuel ethanol literature consistently cites S. cerevisiae for molasses and starch hydrolysates; Zymomonas mobilis is used in select processes but is not the default in many industrial molasses/starch operations. Why Other Options Are Wrong: They lack the broad, routine industrial deployment for these substrates or are used for different purposes. Common Pitfalls: Overgeneralizing niche organisms; industrial constraints (tolerance, contamination resistance) favor Saccharomyces. Final Answer: Saccharomyces cerevisiae.

Question 13

Food acids from microbes: Which major organic acid is widely produced by microbial fermentation and used in foods?

Accepted Answer

Introduction / Context: Organic acids contribute flavor, preservation, and pH control in food systems. Several are produced at scale by microbes, with one being a global benchmark for volume and applications. Given Data / Assumptions: We are choosing the acid most famously produced via fermentation and utilized in foods. Industrial organism: often Aspergillus niger. Concept / Approach: Citric acid is manufactured in multi-million-ton quantities using Aspergillus niger under controlled conditions (carbon source, trace metals, pH). It serves as an acidulant, chelator, and flavor modifier in beverages and foods. Other listed acids are either not produced microbially for food use at scale (sulfuric, uric) or are much less prominent (oxalic poses safety concerns). Step-by-Step Solution: Identify the dominant fermentation acid in foods → citric acid. Exclude strong mineral acids (sulfuric) and non-food metabolites (uric). Recognize oxalic acid’s limited and safety-constrained role. Choose citric acid. Verification / Alternative check: Food ingredient compendia and industrial microbiology texts identify citric acid as the top microbial food acid, with gluconic, lactic, and acetic following in other contexts. Why Other Options Are Wrong: They are either not typical food acids from fermentation or are not broadly used. Common Pitfalls: Confusing chemical synthesis with fermentation routes; for citric acid, fermentation dominates. Final Answer: Citric acid.

Question 14

Nomenclature check: Penicillin G is correctly known by which chemical name?

Accepted Answer

Introduction / Context: Drug nomenclature can be confusing because common names, chemical descriptors, and letter suffixes coexist. Penicillin G and penicillin V are frequently contrasted in exams. Given Data / Assumptions: Penicillin G vs penicillin V: different side chains and acid stability. We must select the proper synonym for penicillin G. Concept / Approach: Penicillin G is benzyl penicillin. Penicillin V is phenoxymethyl penicillin, more acid-stable and suitable for oral dosing. Recognizing these helps with therapeutic choices and historical context. Step-by-Step Solution: Match: Penicillin G → benzyl side chain → benzyl penicillin. Exclude: phenoxymethyl penicillin → penicillin V. Other descriptors do not correspond to standard nomenclature. Select “Benzyl penicillin”. Verification / Alternative check: Pharmacopoeias and formularies list penicillin G as benzylpenicillin; penicillin V as phenoxymethylpenicillin. Why Other Options Are Wrong: They either name penicillin V or are not accepted names for penicillin G. Common Pitfalls: Mixing up G and V; remember V = phenoxymethyl, better oral stability. Final Answer: Benzyl penicillin.

Question 15

In lactic acid fermentations neutralized with calcium carbonate, why is a high initial sugar concentration avoided in the medium?

Accepted Answer

Introduction / Context: During industrial lactic acid production, neutralization is often done with calcium carbonate to maintain pH and to avoid acid inhibition. Process performance depends on sugar levels, by-product solubility, and mass transfer in viscous broths. Given Data / Assumptions: Calcium lactate is the neutralized product formed in situ. High sugar concentrations raise ionic strength and solids, altering solubility. We aim to identify the main operational reason to avoid high sugar. Concept / Approach: At elevated concentrations, calcium lactate can crystallize, increasing slurry viscosity and impeding mixing, aeration (if used), and heat removal. Crystallization can also trap cells/nutrients, slowing metabolic rates and complicating downstream processing. Step-by-Step Solution: Assess option a: incorrect—calcium lactate is indeed produced under neutralization. Consider option b: correct—excessive calcium lactate crystallization hampers fermentation kinetics. Option c: sugar crystallization is not the central issue under normal fermentation temperatures. Choose option b as the practical process limitation. Verification / Alternative check: Process descriptions recommend fed-batch sugar addition to keep concentrations moderate, precisely to avoid salt precipitation and viscosity spikes. Why Other Options Are Wrong: They misstate chemistry or emphasize phenomena not primary to performance loss. Common Pitfalls: Assuming “more sugar, faster fermentation”; osmotic stress and salt precipitation can slow or stall cultures. Final Answer: Calcium lactate may crystallize from the broth and slow fermentation.

Question 16

Trace metals in vitamin B12 fermentations: Which element, at proper concentration, stimulates Ascomycete production of vitamin B12 and can counteract iron toxicity in Candida species?

Accepted Answer

Introduction / Context: Vitamin B12 (cobalamin) contains a central corrin ring with a cobalt ion. Trace metal management is crucial in fermentations because micronutrients influence enzyme activity, cofactor biosynthesis, and metal toxicity balance. Given Data / Assumptions: Organisms include Ascomycetes and Candida species involved in vitamin-related fermentations. Iron can be toxic at excess; some metals mitigate adverse effects. We seek the trace metal that stimulates B12 formation and alleviates iron toxicity. Concept / Approach: Cobalt is essential to the cobalamin structure; providing controlled cobalt supports corrinoid biosynthesis. Additionally, balanced cobalt supply can offset negative impacts of iron by influencing metal uptake/competition and cofactor assembly. Step-by-Step Solution: Identify the metal core of vitamin B12 → cobalt (Co). Relate metabolic need: supplying Co stimulates corrinoid pathway enzymes. Note side benefit: appropriate Co levels can counteract iron toxicity in some yeasts. Select Co. Verification / Alternative check: Biochemical pathways of cobalamin synthesis explicitly require cobalt; process media list Co salts as key supplements. Why Other Options Are Wrong: Ni, Zn, Ca, Mg play other roles but are not the defining metal of cobalamin or the primary countermeasure cited for iron stress in this context. Common Pitfalls: Confusing cobalt's essentiality with general metal supplementation; overdosing cobalt can also be inhibitory—dosage matters. Final Answer: Co.

Question 17

Heterofermentative lactic acid bacteria: Which statement best describes their product profile and industrial use?

Accepted Answer

Introduction / Context: Lactic acid bacteria (LAB) are categorized by fermentation end products: homofermentative strains mainly yield lactic acid, while heterofermentative strains yield mixed products. This classification affects flavor, gas production, and suitability for bulk lactic acid manufacture. Given Data / Assumptions: We must characterize heterofermenters. Industrial lactic acid production favors yield and simplicity of downstream processing. Concept / Approach: Heterofermentative LAB metabolize sugars via the phosphoketolase pathway, producing lactic acid plus CO2 and either ethanol or acetic acid, with additional minor products. Homofermenters (Embden–Meyerhof pathway) produce lactic acid predominantly and are usually chosen for commercial lactic acid due to higher yields and fewer by-products. Step-by-Step Solution: Assess option a: describes homofermenters, not heterofermenters. Assess option b: matches heterofermentative profile (lactic acid + CO2 + ethanol/acetic acid). Assess option c: incorrect—industry prefers homofermenters for lactic acid mass production. Therefore choose option b. Verification / Alternative check: Fermentation textbooks show stoichiometries for both LAB groups; product distributions confirm gas and mixed acids for heterofermenters. Why Other Options Are Wrong: They either describe the wrong LAB group or make incorrect claims about industrial preference. Common Pitfalls: Assuming all LAB behave identically; end-product profiles determine both flavor in foods and process economics. Final Answer: They produce lactic acid along with carbon dioxide, ethanol or acetic acid, and traces of other products.

Question 18

Industrial microbiology — amino acid fermentation: Brevibacterium flavum (now Corynebacterium glutamicum) strains are widely engineered for amino acid production. Which amino acid listed below is classically produced using B. flavum in industrial fe…

Accepted Answer

Introduction / Context: Amino acid fermentations are a cornerstone of industrial microbiology. Strains of Brevibacterium flavum (taxonomically aligned with Corynebacterium glutamicum) have been intensively optimized to overproduce specific amino acids used as feed additives, nutraceuticals, and flavor enhancers. Given Data / Assumptions: Organism: Brevibacterium flavum. Process goal: overproduction of a defined amino acid at commercial scale. Options include several amino acids; only one fits classical, well-documented production with B. flavum without further qualifiers. Concept / Approach: B. flavum/C. glutamicum has been developed to produce multiple amino acids, most famously L-lysine and L-threonine through mutation/selection, pathway deregulation (feedback-resistant aspartokinase and homoserine dehydrogenase), and improved carbon flux. Among the options, L-threonine is a canonical product of B. flavum lines used industrially and frequently cited in classical process texts alongside L-lysine. Step-by-Step Solution: Identify the organism: B. flavum, renowned for aspartate-pathway amino acids.Map options to pathways: threonine derives from the aspartate family (aspartate → aspartyl-P → homoserine → threonine).Recall industrial precedence: B. flavum strains producing L-threonine are standard in large-scale operations.Choose the single best-supported classical answer: L-Threonine. Verification / Alternative check: Process literature and patent families on B. flavum/C. glutamicum repeatedly highlight lysine and threonine as flagship products; other amino acids require different hosts or more complex engineering. Why Other Options Are Wrong: L-Proline: Typically associated with other hosts or specific engineered routes, not the classical B. flavum product. L-Isoleucine and L-Histidine: Possible in engineered microbes, but not the textbook association for B. flavum. All of the above/L-Arginine: Overly broad; not supported as the single standard association. Common Pitfalls: Assuming a single chassis efficiently produces all amino acids; pathway regulation and redox demands vary widely. Final Answer: L-Threonine.

Question 19

Bioethanol separation — distillation limit: In continuous distillation of fermented broth, what is the maximum ethanol concentration achievable by simple distillation before reaching the ethanol–water azeotrope?

Accepted Answer

Introduction / Context: Ethanol recovery from fermentation relies on distillation. However, ethanol and water form an azeotrope that caps the achievable purity using ordinary distillation, a critical design constraint in fuel and potable alcohol industries. Given Data / Assumptions: Feed: fermentation beer (typically 7–15% ethanol by volume). Unit operation: continuous distillation without entrainers or special dehydration steps. Question: the maximum achievable product strength before the azeotrope stops further enrichment. Concept / Approach: The ethanol–water system exhibits a minimum-boiling azeotrope near 95% ethanol by volume (about 96% v/v at 1 atm). Past this point, the vapor and liquid compositions are identical; no further separation by simple distillation is possible without auxiliary techniques. Step-by-Step Solution: Recognize distillation enriches the more volatile component (ethanol) until the azeotrope is reached.Recall the azeotropic composition at atmospheric pressure ≈ 95% v/v ethanol.Conclude that simple distillation in continuous stills tops out at ≈ 95%. Verification / Alternative check: Fuel ethanol plants add molecular sieve dehydration or azeotropic/pressure-swing methods to surpass 95% and reach anhydrous (≥99%) ethanol. Why Other Options Are Wrong: 60–70% are far below the azeotrope and easily exceeded; 99% requires additional dehydration; 80% is not the limiting composition. Common Pitfalls: Confusing weight percent with volume percent; the azeotrope is commonly cited on a volume basis in industry communications. Final Answer: 95%.

Question 20

Food and dairy microbiology — heterofermentative lactic acid bacteria: Which microorganism listed is classically heterofermentative, producing lactic acid along with CO2 and ethanol/acetate from sugars?

Accepted Answer

Introduction / Context: Lactic acid bacteria (LAB) are grouped as homofermentative or heterofermentative based on their glycolytic pathways and end products. This classification affects flavor, gas production, and texture in fermented foods. Given Data / Assumptions: We must identify a heterofermentative organism. Heterofermenters generate lactic acid plus CO2 and ethanol/acetate via the phosphoketolase pathway. Homofermenters produce primarily lactic acid via the Embden–Meyerhof pathway. Concept / Approach: Leuconostoc mesenteroides is a textbook heterofermentative LAB, contributing to flavor and gas in sauerkraut and some dairy fermentations. In contrast, L. delbrueckii and L. bulgaricus are typically homofermentative, yielding mostly lactic acid and little gas. Step-by-Step Solution: List candidates and recall metabolic type from food micro references.Match heterofermentation to Leuconostoc mesenteroides.Exclude typical homofermenters used in yogurt (e.g., L. delbrueckii, L. bulgaricus). Verification / Alternative check: CO2 bubble formation and flavor notes in vegetable ferments align with Leuconostoc activity. Why Other Options Are Wrong: L. delbrueckii/L. bulgaricus: Homofermentative. Lactobacillus pentose: Likely refers to L. pentosus, often facultative heterofermentative, but the classical single best answer remains Leuconostoc mesenteroides. Streptococcus thermophilus: Primarily homofermentative. Common Pitfalls: Assuming all LAB behave similarly across substrates; pathway choice matters to product profiles. Final Answer: Leuconostoc mesenteroides.

Industrially Useful Microbial Processes Questions