Question

The interaction between propionibacteria and lactobacilli in Swiss cheese changes from ______\to ______\when lactic acid is accumulated and lactobacilli starts to benefit from its removal by propionibacteria.

• A. Commensalism to Mutualism
• B. Mutualism to Commensalism
• C. Amensalism to Competition
• D. Competetion to Amensalism

Hint:

Initially, only propionibacteria benefit from lactic acid (Commensalism). When lactic acid accumulation threatens lactobacilli, the removal of this acid benefits them too, making the relationship mutually beneficial (Mutualism).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Swiss cheese manufacture involves a complex succession of microorganisms, primarily thermophilic lactobacilli and propionibacteria.
In the early stages of cheese making and ripening, lactobacilli ferment lactose to lactic acid, creating an acidic environment.
Propionibacteria, which grow slower, utilize this accumulated lactic acid as their primary energy source, converting it into propionic acid, acetic acid, carbon dioxide, and water.

Step 2: Detailed Explanation:
Initially, this interaction is a classic example of commensalism, as the propionibacteria benefit from the lactic acid produced by the lactobacilli, while the lactobacilli are unaffected.
However, as fermentation progresses, the accumulation of lactic acid becomes inhibitory to the lactobacilli due to the drop in pH.
By consuming the lactic acid, propionibacteria prevent this inhibition, allowing the lactobacilli to continue metabolizing.
Thus, the relationship shifts from commensalism to mutualism, where both species benefit from the presence of each other.
The removal of a metabolic waste product (lactic acid) is mutually beneficial: propionibacteria obtain energy, and lactobacilli escape acid-induced inhibition.
Therefore, the transition is from commensalism to mutualism.

Step 3: Final Answer
The microbial interaction changes from Commensalism to Mutualism.