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Aspergillus niger and Citric Acid Production

Biology · Microbes in Human Welfare · NEET

Aspergillus niger is a fungus used for the industrial production of citric acid. In one line for NEET: "niger makes it bigger" — think of the black mould Aspergillus niger filling a tank with citric acid, the acid found in lemons. This one exact pair (Aspergillus niger to citric acid) is asked again and again in NEET matching questions, so memorise it firmly.
Aspergillus niger to Citric AcidAspergillus niger(a fungus)industrialfermentorCitricAcidacid of citrus(lemon) fruits
Aspergillus niger, a fungus, is grown in industrial fermentors to produce citric acid — the same acid present in lemons and other citrus fruits. Remember: fungus, industrial, citric acid.

Your doubts, answered

Is Aspergillus niger a bacterium or a fungus?

Aspergillus niger is a fungus, not a bacterium. NCERT clearly writes 'Aspergillus niger (a fungus) of citric acid'. This matters because in the same NCERT list the acid producers Acetobacter aceti, Clostridium butylicum and Lactobacillus are all bacteria — only Aspergillus is the fungus. NEET often adds '(a fungus)' or '(a bacterium)' tags in options to test if you know the microbe type.

Which microbe produces citric acid for NEET?

The answer is Aspergillus niger. It is the industrial producer of citric acid. Do not confuse it with Acetobacter aceti (acetic acid), Clostridium butylicum (butyric acid), or Lactobacillus (lactic acid). Aspergillus niger to citric acid is the single most repeated pair in this chapter.

What is the difference between the microbes for citric acid and acetic acid?

Citric acid is made by Aspergillus niger, which is a fungus. Acetic acid is made by Acetobacter aceti, which is a bacterium. Students mix these two because both are 'acids' and their names look a little similar. Memory link: Acetobacter makes ACETic acid (both start with 'acet'); Aspergillus makes citric acid (think of Aspergillus in a citrus-acid tank).

Why is Aspergillus niger NOT counted as a household-product microbe?

Household products in NCERT means things you make at home like curd, dough, bread and cheese, using Lactobacillus, Saccharomyces cerevisiae, and Propionibacterium. Aspergillus niger is used for INDUSTRIAL (commercial) production of citric acid in fermentors, not at home. NEET 2025 asked exactly this — Aspergillus niger was the correct 'NOT a household microbe' choice.

Does Aspergillus niger produce cyclosporin A or citric acid?

Aspergillus niger produces citric acid only. Cyclosporin A (the immunosuppressant) is produced by a different fungus, Trichoderma polysporum. NEET frequently uses Aspergillus niger as a decoy option in cyclosporin A questions, so keep them separate: Aspergillus = citric acid, Trichoderma = cyclosporin A.

⚠️ The NEET trap
✗ Aspergillus niger is a bacterium that produces citric acid and is used in making household products.
✓ Aspergillus niger is a fungus that produces citric acid on an industrial (commercial) scale; it is not a household-product microbe.
🧠 NTA loves two traps here: calling Aspergillus a 'bacterium' (it is a fungus) and listing it under 'household products' (it is industrial). Remember: fungus + industrial + citric acid.

Real NEET questions

NEET 2019

Match the following organisms with the products they produce: (a) Lactobacillus (b) Saccharomyces cerevisiae (c) Aspergillus niger (d) Acetobacter aceti with (i) Cheese (ii) Curd (iii) Citric Acid (iv) Bread (v) Acetic acid. Choose the correct option.

A · (a)-(ii), (b)-(iv), (c)-(v), (d)-(iii)
B · (a)-(ii), (b)-(iv), (c)-(iii), (d)-(v) ✓
C · (a)-(iii), (b)-(iv), (c)-(v), (d)-(i)
D · (a)-(ii), (b)-(i), (c)-(iii), (d)-(v)
Solution: Lactobacillus makes curd, Saccharomyces cerevisiae ferments dough for bread, Aspergillus niger produces citric acid, and Acetobacter aceti produces acetic acid. So (a)-(ii), (b)-(iv), (c)-(iii), (d)-(v). The key pair tested here is Aspergillus niger to citric acid.
NEET 2021

Match List I (Microorganism) with List II (Product): (a) Aspergillus niger (b) Acetobacter aceti (c) Clostridium butylicum (d) Lactobacillus with (i) Acetic Acid (ii) Lactic Acid (iii) Citric Acid (iv) Butyric Acid.

A · (a)-(ii); (b)-(iii); (c)-(i); (d)-(iv)
B · (a)-(iv); (b)-(ii); (c)-(i); (d)-(iii)
C · (a)-(iii); (b)-(i); (c)-(iv); (d)-(ii) ✓
D · (a)-(i); (b)-(ii); (c)-(iii); (d)-(iv)
Solution: From the NCERT list of organic-acid producers: Aspergillus niger yields citric acid, Acetobacter aceti yields acetic acid, Clostridium butylicum yields butyric acid, and Lactobacillus yields lactic acid. This gives (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii).
NEET 2016 Phase 2

Match Column-I with Column-II: a. Citric acid b. Cyclosporin A c. Statins d. Butyric acid with (i) Trichoderma (ii) Clostridium (iii) Aspergillus (iv) Monascus.

A · a-(iii), b-(i), c-(ii), d-(iv)
B · a-(iii), b-(i), c-(iv), d-(ii) ✓
C · a-(i), b-(iv), c-(ii), d-(iii)
D · a-(iii), b-(iv), c-(i), d-(ii)
Solution: Citric acid is from Aspergillus (iii), Cyclosporin A from Trichoderma (i), Statins from Monascus (iv), and Butyric acid from Clostridium (ii). So the answer is a-(iii), b-(i), c-(iv), d-(ii). Note Aspergillus is firmly linked to citric acid, not to cyclosporin A.

Solved Microbes in Human Welfare NEET PYQs

Try the real previous-year questions from this chapter — each with the answer and a full solution.

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Frequently asked

What does Aspergillus niger produce?

Aspergillus niger produces citric acid, the acid found in lemons and other citrus fruits. It is used for the commercial/industrial production of citric acid.

Is Aspergillus niger a bacterium or a fungus?

It is a fungus. NCERT states 'Aspergillus niger (a fungus) of citric acid'. This is a common NEET trap where it is wrongly called a bacterium.

Is citric acid production a household or industrial process in NCERT?

It is an industrial (commercial) process, carried out in fermentors, not a household product like curd or bread. NEET 2025 tested exactly this point.

How to avoid confusing Aspergillus niger with Acetobacter aceti?

Acetobacter aceti makes ACETic acid (both share 'acet'), while Aspergillus niger makes citric acid. Acetobacter is a bacterium; Aspergillus is a fungus.

Which chapter and class is this topic from?

It is from Class 12 Biology, Chapter 'Microbes in Human Welfare' (NCERT Ch 8/10 depending on edition), under microbes in industrial products.

Related concepts:
Microbes That Produce Organic Acids (Citric, Acetic, Butyric, Lactic)Industrially Useful Microbial Enzymes: Lipases, Pectinase, StreptokinaseBioactive Molecules: Microbe-to-Product Matching TableMicrobes in Industrial Products and FermentorsStatins: Blood Cholesterol Lowering Agent from Monascus purpureus
Practise Biology for NEET:
Biology MCQs (free, chapter-wise)Microbes in Human Welfare PYQs