Q.18 Which microorganism produces dextran?
- Clostridium acetobutylicum
- Leuconostoc mesenteroides
- Bacillus subtilis
- Enterobacter aerogenes
Leuconostoc mesenteroides Produces Dextran: Correct Microorganism Identified
Leuconostoc mesenteroides is the key bacterium that synthesizes dextran, an extracellular polysaccharide from sucrose, via dextransucrase enzyme. Other options produce different metabolites, making this the precise answer for microbiology exams.
Introduction
The microorganism produces dextran, Leuconostoc mesenteroides, stands out in industrial microbiology for its high-yield production. This lactic acid bacterium converts sucrose to α-1,6-glucan dextran, vital for food, pharma applications. This guide breaks down all options for exam mastery.
Option Analysis
Dextran: branched glucose polymer used in plasma expanders, stabilizers. Produced extracellularly by specific bacteria.
-
Clostridium acetobutylicum: Incorrect. Anaerobic, produces solvents via ABE fermentation (acetone, butanol, ethanol); no dextran synthesis. Focus: biofuels, not polysaccharides.
-
Leuconostoc mesenteroides: Correct. Lactic acid bacterium; dextransucrase polymerizes sucrose to dextran (up to 23 g/L optimized). Strains like B-512F yield clinical-grade dextran; common in sucrose-rich media (sugarcane, agave).
-
Bacillus subtilis: Incorrect. Gram-positive; produces subtilisin, biosurfactants, bacillusan (different EPS), not dextran. Used in nattō, enzymes.
-
Enterobacter aerogenes (now Klebsiella aerogenes): Incorrect. Aerobic; ferments to 2,3-butanediol, ethanol, gases; produces capsule (colanic acid), not dextran.
Production Mechanism
L. mesenteroides grows on sucrose; enzyme: sucrose + (glucose)n → dextran + n fructose.
Optimal: 25-30°C, pH 6.5-7, 10-15% sucrose, 24h aerobic.
-
Structure: 95-97% α-1,6; branches α-1,2/3/4.
-
Yield: Strain-dependent; industrial via submerged fermentation.
Applications
-
Medical: Blood plasma substitute (low antigenicity).
-
Food: Thickener (salads, candies); prevents ice crystals.
-
Industry: Chromatography matrices, drug delivery.
Exam Relevance
GATE Microbiology: Link Leuconostoc to dextran (vs. xanthan by Xanthomonas). Mnemonic: “Leuconostoc Loves Dextran from Sucrose.” Visualize slimy colonies on sucrose agar.
-
