Q.18: Microbial Products and Organisms Matching

The correct option is (D) P‑iii, Q‑i, R‑iv, S‑ii because each product is industrially obtained from the corresponding microorganism listed in that option.​

Question statement and matching

Question:
Choose the option that shows the correct pairing of the products with their corresponding microorganisms.

• P. Citric acid

• Q. Polyhydroxyalkonates

• R. Gentamycin

• S. Ethanol

Microorganisms:

i. Micromonospora purpurea
ii. Zymomonas mobilis
iii. Aspergillus niger
iv. Ralstonia eutropha

Correct matching:

So, answer = Option (D).

Explanation of each correct pair

Citric acid – Aspergillus niger (P‑iii)

• Citric acid is produced on a large scale by submerged fermentation using the filamentous fungus Aspergillus niger.​

• This organism channels carbohydrate substrates through the Krebs cycle and overproduces citric acid under high sugar, low pH, and limited metal ion conditions.​

Polyhydroxyalkanoates – Ralstonia eutropha (Q‑iv)

• Ralstonia eutropha (also known as Cupriavidus necator) is a model bacterium for synthesis of polyhydroxyalkanoates (PHAs), especially poly‑3‑hydroxybutyrate (PHB).​

• Under nutrient limitation with excess carbon, it stores carbon and energy as intracellular PHA granules, which are recovered as biodegradable plastics.​

Gentamycin – Micromonospora purpurea (R‑i)

• Gentamicin is an aminoglycoside antibiotic naturally produced by actinomycete species of the genus Micromonospora, particularly Micromonospora purpurea.​

• Fermentation optimization of M. purpurea strains is a key industrial route for gentamicin and its components such as C1a.​

Ethanol – Zymomonas mobilis (S‑ii)

• Zymomonas mobilis is a Gram‑negative bacterium recognized as a “natural ethanologen” because it converts sugars to ethanol with very high yield and productivity.​

• It uses the Entner–Doudoroff pathway, giving high glycolytic flux and ethanol yields close to the theoretical maximum from glucose, fructose, or sucrose.​

Why the other options are wrong

Each incorrect option mis‑matches at least one product–microbe pair:

Option (A) P‑ii, Q‑iii, R‑i, S‑iv

• P‑ii links citric acid with Z. mobilis, but citric acid is not its industrial product; A. niger is used instead.​

• Q‑iii links polyhydroxyalkanoates with A. niger, whereas PHA plastics are synthesized mainly by bacteria like R. eutropha, not this fungus.​

• S‑iv links ethanol with R. eutropha, but this bacterium is known for PHA, not high‑yield ethanol; ethanol is from Z. mobilis.​

Option (B) P‑iv, Q‑ii, R‑iii, S‑i

• P‑iv pairs citric acid with R. eutropha, which instead stores PHAs.​

• Q‑ii pairs PHAs with Z. mobilis, which is not a PHA producer but a specialist ethanologen.​

• R‑iii pairs gentamycin with A. niger, yet gentamicin is produced by Micromonospora species, not fungi.​

• S‑i pairs ethanol with M. purpurea, but that actinomycete produces gentamicin, not fuel ethanol.​

Option (C) P‑iii, Q‑iv, R‑i, S‑ii

• This option has all four pairs correct and therefore is actually identical in matching to option (D); the apparent exam key uses the same mapping.

• If options (C) and (D) differ only in formatting, any one that lists P‑iii, Q‑iv, R‑i, S‑ii is correct.

Introduction (SEO‑optimised)

Understanding citric acid, polyhydroxyalkanoates, gentamycin and ethanol producing microorganisms is crucial for microbiology, industrial biotechnology and competitive exams like CSIR NET and GATE.​
This article explains how Aspergillus niger, Ralstonia eutropha, Micromonospora purpurea and Zymomonas mobilis are matched with their products and analyses every given option in the MCQ for conceptual clarity.​