Question

Which of the following statements are true for homofermentative lactobacilli?
A. Exclusively ferment hexose sugars to lactic acid by EMP
B. Includes L. delbrueckii ssp. bulgaricus and L.casei
C. Ferment pentose sugars
D. Grow at a temperature higher than other 2 groups of lactobacilli
Choose the correct answer from the options given below:

• A. A and C only
• B. B and C only
• C. A and D only
• D. C and D only

Hint:

Lactobacilli Groups:
Group I (Obligate Homofermentative) = Exclusively EMP pathway (A) + CANNOT ferment pentoses + High growth temp $45^\circ\text{C}$ (D) (L. delbrueckii, L. helveticus).
Group II (Facultative Heterofermentative) = Ferment pentoses (L. casei, L. plantarum).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Kandler's physiological classification of genus Lactobacillus: Group I obligately homofermentative lactobacilli exclusively ferment hexoses via the EMP pathway without pentose fermentation and exhibit high thermophilic growth temperatures ($45^\circ ext{C}$).
Key Formula or Approach:
\[ \text{Group I (Obligate Homofermentative): } \text{Hexose} \xrightarrow{\text{EMP Glycolysis}} > 90\% \text{ Lactic Acid (NO Pentose Fermentation, Grow at } 45^\circ\text{C)} \]

Step 2: Detailed Explanation:
In the taxonomy and physiological classification of genus Lactobacillus (Kandler and Weiss):
1. Group I: Obligate Homofermentative Lactobacilli (e.g., Lactobacillus delbrueckii, L. helveticus, L. acidophilus):
- A. True: Possess fructose-1,6-bisphosphate aldolase and exclusively ferment hexose sugars to lactic acid ($> 90\%$) via the Embden-Meyerhof-Parnas (EMP) pathway without producing gas ($\text{CO}_2$).
- C. False: Lack phosphoketolase and cannot ferment pentose sugars.
- D. True: They are thermophilic and grow at higher temperatures ($45^\circ ext{C}$) than the other two groups (facultative and obligate heterofermenters).
2. (L. casei is facultatively heterofermentative [Group II]).
Thus, statements A and D only are true.

Step 3: Final Answer:
Hence, statements A and D only are true, corresponding to option (C).