Question

Enzyme chymosin (EC 3.4.4) derived, via fermentation, from a non pathogenic and non toxigenic strain of ____}

• A. Enterobactor aerognes K‐18
• B. Lactobacillus acidophilus K‐22
• C. Sacharomyces cerevisiae K 21
• D. Escherichia coli K‐12

Hint:

FPC (Fermentation-Produced Chymosin) is used in nearly $80$ to $90$% of all cheese produced today. It is "vegetarian" because no animal was killed to obtain the enzyme.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the specific genetically modified microbial host used to produce Fermentation-Produced Chymosin (FPC), which is widely used as a vegetarian rennet in the cheese industry.

Step 2: Detailed Explanation:

• Chymosin (Rennet): Traditionally, rennet is an enzyme extracted from the fourth stomach of unweaned calves. It is essential for coagulating milk to make cheese.

• FPC Development: Due to ethical concerns and limited supply, the bovine chymosin gene was cloned into microorganisms to produce the enzyme via fermentation. This was the first-ever genetically engineered food ingredient approved for use.

• The Microbe: The most famous and historically first strain approved for this purpose (by Pfizer) was a genetically modified strain of Escherichia coli K-12.

• Safety: Although some E. coli are pathogens, the K-12 strain is a well-characterized, safe lab organism (non-pathogenic and non-toxigenic). The enzyme produced is identical to the one from the calf but is "pure" as it is filtered away from the bacteria.

• Other Hosts: While yeasts like Kluyveromyces lactis are also used today, the specific reference in textbooks to the "non-pathogenic/non-toxigenic strain" often points to the landmark approval of E. coli K-12.

Step 3: Final Answer:
The fermentation-produced chymosin is derived from a modified strain of Escherichia coli K-12.