Industrial Biotechnology: Microbial Metabolites, Biotransformations, and Biomass Production

Vocabulary practice flashcards covering the production of microbial metabolites (organic acids, amino acids, antibiotics, vitamins), industrial biotransformations (vinegar, gluconic acid, steroids), and single cell / mycelial biomass protein production.

Organic Acids

Organic compounds characterized by the presence of at least one carboxyl group ($-\text{COOH}$) attached to a carbon chain, produced via microbial fermentation for widespread use as food additives and chemical feedstocks.

Citric Acid

A tricarboxylic acid chemically designated as 2-hydroxy-propane-1,2,3-tricarboxylic acid that serves as the primary industrial acidulant in foods and beverages, as well as a metal cleaning agent, descaler, and blood anticoagulant.

Aspergillus niger

The filamentous fungus used industrially since 1923 for high-yield commercial citric acid and gluconic acid production due to its uniform biochemical traits, ease of cultivation, and low oxalic acid byproduct formation.

Surface Fermentation (Citric Acid)

A production method where Aspergillus niger spores are inoculated onto the surface of stationary liquid media in shallow corrosion-resistant pans ($1\text{--}3\text{ cm}$ depth) at $26\text{--}28\text{ }^{\circ}\text{C}$ and pH $3.4\text{--}3.5$ for $7\text{--}10\text{ days}$, yielding $60\text{--}80\text{ g}$ of anhydrous citric acid per $100\text{ g}$ of sugar.

Submerged Fermentation (Citric Acid)

An industrial fermentation process where Aspergillus niger is grown in a dispersed mycelial state inside large, aerated, agitated bioreactors using pretreated beet molasses and inorganic salts under high aeration.

Itaconic Acid

A dicarboxylic acid also known as methylenesuccinic acid, biosynthesized from citric acid via the TCA cycle and used primarily as a co-monomer in producing acrylonitrile-butadiene-styrene (ABS) and acrylate latexes.

Aspergillus terreus

The fungal species used for commercial itaconic acid production, using high-yield mutant strains such as ATCC 10020, ATCC 10029, and NRRL 265.

Aconitate Decarboxylase (CadA)

The key pathway enzyme that decarboxylates cis-aconitic acid into itaconic acid in the cytosol following the dehydration of citric acid by aconitate hydratase.

Gluconic Acid

A polyhydroxycarboxylic acid chemically named 2,3,4,5,6-pentahydroxycaproic acid, produced by Aspergillus niger submerged fermentation or Gluconobacter species, whose anion chelates metal ions ($\text{Ca}^{2+}$, $\text{Fe}^{3+}$, $\text{Al}^{3+}$) and serves in food acidity regulation, alkaline cleaning, and pharmaceuticals.

Calcium Gluconate

A therapeutic pharmaceutical salt formulated as a gel to treat hydrofluoric acid chemical burns.

Quinine Gluconate

A pharmaceutical salt formulation of gluconic acid administered intramuscularly for the treatment of malaria.

Lactic Acid Bacteria (LAB)

A group of bacteria—including Lactobacillus bulgaricus, L. delbrueckii, L. casei, and Leuconostoc mesenteroides—that ferment glucose, sucrose, or crude starches into lactic acid at an optimal pH of $5.5\text{--}5.6$ neutralized with calcium hydroxide slurry.

Poly-L-lactic Acid (PLLA)

A biodegradable polymer synthesized from plastic-grade L-lactic acid having a high molecular weight of $M_w \ge 100{,}000$.

Essential Amino Acids

The group of nine amino acids—L-valine, L-leucine, L-isoleucine, L-lysine, L-threonine, L-methionine, L-histidine, L-phenylalanine, and L-tryptophan—that cannot be synthesized de novo by animals or humans and must be supplied nutritionally.

Monosodium Glutamate (MSG)

The sodium salt of (S)-glutamic acid, identified in 1908 by Kikunae Ikeda from Laminaria japonica (kombu) as the umami flavor principle, produced commercially on a large scale by Corynebacterium glutamicum fermentation.

Corynebacterium glutamicum

A high-yielding industrial bacterium capable of excreting large amounts of (S)-glutamic acid with yields up to $60\%$ and concentrations reaching $80\text{--}100\text{ g/L}$ in $200{,}000\text{-liter}$ main fermenters.

Biotin Limitation

A fermentation control strategy in glutamate production where keeping biotin levels low alters the cell membrane to allow glutamate excretion; excess biotin makes the bacterial membrane impermeable to glutamate.

Homoserine Auxotrophs (HSD- Mutants)

Corynebacterium glutamicum mutant strains that lack homoserine dehydrogenase activity, preventing the synthesis of threonine, methionine, and isoleucine to eliminate concerted feedback inhibition of aspartokinase (AK) and enable hyperproduction of L-lysine.

HSD-Leaky Mutants

Corynebacterium glutamicum strains producing a partially defective homoserine dehydrogenase that restricts intracellular threonine accumulation below inhibitory thresholds for aspartokinase, allowing L-lysine overproduction without supplemental amino acids.

α-Amino-β-hydroxyvaleric Acid (AHV)

A toxic structural analogue of threonine used to select for feedback-resistant mutants whose aspartokinase I (AKI) is insensitive to threonine inhibition, facilitating high L-threonine production.

Aspartate Ammonia Lyase (Aspartase)

The enzyme expressed in immobilized Escherichia coli cells that catalyzes the asymmetric conversion of ammonium fumarate into L-aspartate at pH $8.5$ and $37\text{ }^{\circ}\text{C}$, maintaining operational stability for over $600\text{ days}$.

Aspartate β-Carboxylase

A pyridoxal phosphate-dependent enzyme in immobilized Pseudomonas dacunhae cells that decarboxylates L-aspartate to produce L-alanine, industrialized in Japan in 1982.

6-Aminopenicillanic Acid (6-APA)

The core chemical nucleus of penicillins, comprising a four-membered β-lactam ring fused to a five-membered thiazolidine ring, obtained commercially by enzymatic cleavage of penicillins using immobilized penicillin amidase.

Penicillin

A β-lactam antibiotic biosynthesized by Penicillium chrysogenum in submerged culture using corn steep liquor ($4\text{--}5\%$ dry weight) that kills Gram-positive bacteria by inhibiting cell wall synthesis, isolated downstream via solvent extraction at pH $< 3$ and $< 10\text{ }^{\circ}\text{C}$.

Streptomycin

The first clinical aminoglycoside antibiotic, isolated from Streptomyces griseus to treat tuberculosis by binding the 30S bacterial ribosomal subunit to block protein synthesis; its biosynthesis is inhibited by excess glucose, ammonia, and phosphate.

Tetracycline

A broad-spectrum antibiotic containing a fused four-ring naphthacene nucleus produced by Streptomyces aureofaciens and S. rimosus that inhibits protein synthesis by blocking aminoacyl-tRNA attachment to the ribosomal A site.

Griseofulvin

An antifungal antibiotic produced by Penicillium patulum that accumulates intracellularly within fungal mycelia and must be extracted using acetone.

Reichstein-Grussner Synthesis

The classic industrial route for Vitamin C (L-ascorbic acid) synthesis wherein chemical hydrogenation converts D-glucose to D-sorbitol, followed by microbial biotransformation to L-sorbose by Acetobacter xylinum or A. suboxydans, followed by chemical conversion steps.

Vitamin B12 (Cobalamin)

A water-soluble organometallic cobalt complex synthesized by submerged fermentation using Propionibacterium freudenreichii or Pseudomonas denitrificans in beet molasses media supplemented with cobalt chloride, released from cells by heating to $80\text{--}120\text{ }^{\circ}\text{C}$ at pH $6.5\text{--}8.5$.

Riboflavin (Vitamin B2)

A water-soluble vitamin consisting of 6,7-dimethylisoalloxazine linked to D-ribitol, synthesized commercially via submerged aerated fermentation of Ashbya gossypii or Eremothecium ashbyii supplemented with lipids such as corn oil.

Biotransformation (Bioconversion)

The enzymatic conversion of defined organic compounds into structurally related, chirally pure, or value-added target molecules using whole living cells (microbes, plants, animals) or isolated enzymes under moderate reaction conditions.

Xenobiotic Biotransformation

The biocatalytic modification of a foreign chemical substrate not naturally present in the organism's regular metabolic pathways, typically proceeding through one or two enzymatic steps catalyzed by enzymes possessing broad substrate specificity.

Biosynthetically Directed Biotransformation

A bioconversion where the supplied precursor closely mimics an endogenous metabolic intermediate, exploiting the flexibility of natural biosynthetic enzymes to create modified products.

Glucose Isomerase

An industrial enzyme utilized in massive large-scale continuous bioconversions (approximately $10{,}000{,}000\text{ tons/year}$) to convert glucose into high-fructose corn syrup.

Mother of Vinegar

A cellulosic, biofilm-like microbial mat composed of acetic acid bacteria that develops on the surface of alcoholic liquids during traditional acetification, first recognized as a living entity by Herman Boerhaave in 1732.

Orleans Method (Surface Culture)

The standardized traditional vinegar manufacturing method in which wooden barrels are filled to two-thirds capacity and ventilated through side bung holes, allowing acetic acid bacteria to form a film at the liquid-air interface.

Schützenbach System

A semi-rapid vinegar generation technique where alcoholic mash trickles downward through a vessel packed with beechwood shavings supporting immobilized acetic acid bacteria, completing acetification in approximately one week.

Trickle Bed Bioreactor

An industrial bioreactor design using acetic acid bacteria immobilized on wood chips through which alcoholic substrate trickles against countercurrent airflow, enabling rapid $24\text{-hour}$ cycles and high acidity levels of $23\text{--}25\%$ acetic acid.

Acetic Acid Bacteria (AAB)

Gram-negative or Gram-variable obligately aerobic rods or ellipsoids (such as Komagataeibacter, Acetobacter, and Gluconobacter) that incompletely oxidize ethanol to acetic acid via membrane-bound dehydrogenases.

Komagataeibacter europaeus

A robust, acid-tolerant species of acetic acid bacteria (formerly classified under Gluconacetobacter) that dominates industrial vinegar fermentations when acetic acid concentrations exceed $5\%$.

5-Keto-D-Gluconate (5-KGA)

An oxidized organic acid intermediate produced by genetically engineered Gluconobacter oxydans overexpressing the gluconate:NADP-5 oxidoreductase (gno) gene, serving as a chemical precursor for L-(+)-tartaric acid.

Aureobasidium pullulans

A yeast-like fungus utilized in continuous-culture immobilized cell systems for high-yield gluconic acid production, capable of metabolizing high starting concentrations of glucose without cell stability loss.

Steroid Nucleus

The core cyclopentanoperhydrophenanthrene framework consisting of four fused rings designated A, B, C, and D, with numbered carbon positions 1 through 17.

11α-Hydroxylation

A regio- and stereospecific microbial biotransformation carried out by Rhizopus nigricans or Aspergillus species that introduces an alpha-hydroxyl group at position C11 of progesterone with approximately $85\%$ yield, eliminating difficult multi-step chemical synthesis of cortisone.

11β-Hydroxylation

The microbial addition of a beta-hydroxyl group at position C11 of 11-deoxycortisol to produce cortisol, carried out by Cunninghamella blakesleeana or Curvularia lunata.

Steroid Dehydrogenation

The microbial oxidation of steroid secondary alcohols or the introduction of a double bond between C1 and C2 of the steroid A-ring, catalyzed by Arthrobacter or Septomyxa species without clearing the core side chain.

Ring A Aromatization

A microbial reaction carried out by Nocardia restricta on 19-hydroxycholesterol involving C1 dehydrogenation and side-chain cleavage, causing spontaneous ring rearrangement to form aromatic estrone for estrogen synthesis.

Single Cell Protein (SCP)

Dried microbial biomass (bacteria, yeast, molds, or microalgae) produced in controlled aerated bioreactors containing $40\text{--}80\%$ protein by dry weight, used as an alternative dietary protein supplement for human food or animal feed.

Saccharomyces cerevisiae

An ascomycetous budding yeast cultivated aerobically on molasses to optimize vegetative biomass yields for commercial baker's and brewer's yeast preparations.

Fed-Batch Fermentation

A bioprocess operation where fresh nutrient feed (such as molasses) is supplied incrementally at a controlled rate without withdrawing broth, keeping sugar concentrations low to suppress alcoholic fermentation and maximize biomass yield.

Airlift Fermenter

A bioreactor design lacking mechanical impellers that circulates culture fluid and aerates cells using pressurized sterile gas injected at the vessel base through spargers, used in commercial baker's yeast ($200{,}000\text{ liters}$) and continuous mycoprotein production.

Nozzle-Type Disc Stack Centrifuge

A continuous mechanical separator that uses conical disc stacks to rapidly isolate and concentrate yeast cells from fermented broth into liquid yeast cream.

Cream Yeast

The liquid suspension of yeast cells harvested directly from centrifugal separation, chilled to approximately $4\text{ }^{\circ}\text{C}$ and shipped in bulk tankers to commercial wholesale bakeries.

Compressed Yeast

A high-moisture cake form of baker's yeast containing $27\text{--}32\%$ solids prepared by dewatering yeast cream on rotary vacuum filters or filter presses, accounting for approximately $85\%$ of commercial baker's yeast production.

Pruteen

A commercial bacterial single cell protein developed by Imperial Chemical Industries (ICI) in the UK by cultivating Methylophilus methylotrophus continuously on methanol.

Nucleic Acid Reduction

A required downstream processing treatment (using controlled heat shock, RNase enzymes, or alkaline extraction) applied to microbial biomass to lower RNA content and prevent elevated serum uric acid and gout in humans.

Pekilo Process

An industrial biomass production process developed in Finland that uses the filamentous microfungus Paecilomyces varioti to convert wood-pulping sulfite waste liquor into single cell protein for animal feed.

U-Loop Bioreactor

A continuous loop-shaped bioreactor designed with high mixing and mass transfer rates to cultivate methanotrophic bacteria (such as Methylococcus capsulatus) on gaseous methane and oxygen feeds.

Mycoprotein

A human food ingredient consisting of RNA-reduced, fiber-rich filamentous fungal hyphae of Fusarium venenatum (or Fusarium graminearum) commercialized under the trade name Quorn, whose interwoven hyphal network mimics meat muscle myofibrils.

Fusarium venenatum

The designated filamentous microfungal production organism utilized in continuous airlift fermenters on glucose syrup and mineral salts to manufacture Quorn mycoprotein.

RNA Reduction Heat Treatment

A precise post-fermentation thermal process where fungal biomass broth is held at $64\text{ }^{\circ}\text{C}$ for $20\text{--}30\text{ minutes}$ to inactivate proteases while allowing active endogenous RNases to degrade RNA, reducing nucleic acid levels to approximately $1\%$ of dry weight (below the WHO $2\%$ threshold).

Neurospora crassa

An edible filamentous ascomycete traditionally consumed in Indonesian oncom (fermented peanut press cake), investigated as a safe, non-toxic, and non-allergenic mycoprotein source for human food and animal feed.

Oncom

A traditional Indonesian fermented food prepared by inoculating peanut press cake with the filamentous mold Neurospora crassa.