Biology · Microbes in Human Welfare · NEET
Aspergillus niger produces citric acid, and it is a fungus (a mould). This is the point NEET tests most, because it is the ONLY fungus among the four acid producers. The other three acid producers (Acetobacter, Clostridium, Lactobacillus) are all bacteria. So if a question asks 'which is different / which is a fungus', the answer is Aspergillus niger.
Acetobacter aceti, a bacterium, produces acetic acid. Acetic acid is the sour acid found in vinegar. Do not confuse it with lactic acid (from Lactobacillus). Acetobacter = Acetic acid is an easy name match to remember.
Clostridium butylicum, a bacterium, produces butyric acid. The species name 'butylicum' hints at 'butyric', so the name itself is the clue. Clostridium is an anaerobic bacterium, so it works without oxygen.
No. Three of the four are bacteria (Acetobacter aceti, Clostridium butylicum, Lactobacillus). Only Aspergillus niger is a fungus. NEET loves to test this odd-one-out, so remember: 3 bacteria + 1 fungus.
Lactobacillus (a bacterium) produces lactic acid and is also the microbe that turns milk into curd. Acetobacter aceti (a bacterium) produces acetic acid, the acid in vinegar. Different acids, different microbes, but both are bacteria. Lactobacillus links to curd; Acetobacter links to vinegar.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Citric acid from Aspergillus niger (fungus), acetic acid from Acetobacter aceti (bacterium), butyric acid from Clostridium butylicum (bacterium), and lactic acid from Lactobacillus (bacterium).
Because it is the only fungus among the acid producers and it makes citric acid. This odd-one-out point is frequently used in match-the-column and 'which is different' questions.
Yeast, Saccharomyces cerevisiae, is used for commercial production of ethanol. It is grouped with the industrial microbes in the same NCERT line but produces alcohol, not an organic acid.
Yes. Lactobacillus produces lactic acid, and lactic acid bacteria (LAB) are the microbes that convert milk into curd. So it appears in both the acid-producer list and the curd topic.
