Read the following passage carefully and answer the given questions.

We use microbes and microbially derived products almost every day. Bacteria called lactic acid bacteria (LAB) grow in milk to convert it into curd. The dough, which is used to make bread, is fermented by yeast called Saccharomyces cerevisiae. Microbes are used to produce industrial products like lactic acid, acetic acid and alcohol, which are used in a variety of processes in the industry. However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with $CO_2$ and $H_2$. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment. Microbes are also used for commercial and industrial production of certain chemicals like organic acids, alcohols and enzymes. Examples of acid producers are Aspergillus niger (a fungus) of citric acid. You are familiar with the commonly used antibiotic Penicillin. Do you know that Penicillin was the first antibiotic to be discovered, and it was a chance discovery? Statins produced by the yeast Monascus purpureus have been commercialised as blood-cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

Which of the following statements is not true with respect to microbes?

The puffed up appearance of dough is due to the production of CO gas by bacteria.

The correct answer is Option (3) → The puffed up appearance of dough is due to the production of CO gas by bacteria.

Wine is produced by fermentation without distillation. (Correct – Wine is made by yeast fermentation of grapes without distillation. Distillation is used for spirits like whisky, rum, etc.)

Microbes can also be used to kill harmful pests, a process called biocontrol. (Correct – e.g., Bacillus thuringiensis used as biocontrol agent.)

The puffed up appearance of dough is due to CO gas by bacteria. (Wrong – It is actually due to CO₂ gas produced by yeast (Saccharomyces cerevisiae) during fermentation, not bacteria.)

Methanogens are anaerobic bacteria. (Correct – e.g., Methanobacterium, produce methane in biogas plants.)

So, the not true statement = “The puffed up appearance of dough is due to the production of CO gas by bacteria.”