Question

Genus of lactic acid bacteria that possess a DNA base composition with GC% 57 -65 is ____________\.

• A. Bifidobacterium
• B. Pediococcus
• C. Leuconostoc
• D. Streptococcus

Hint:

Bifidobacteria are phylogenetically distinct from other lactic acid bacteria, belonging to the high-GC Gram-positive group (Actinomycetota) with a GC content of 57% - 65%.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The molar percentage of guanine and cytosine (% GC content) in genomic DNA is a fundamental chemotaxonomic marker used to classify and differentiate bacterial genera.
Lactic acid bacteria (LAB) are historically divided into low-GC and high-GC groups.
Genera such as Lactococcus, Pediococcus, Leuconostoc, and Streptococcus are low-GC Gram-positive bacteria, typically possessing a GC content between 34% and 46%.

Step 2: Detailed Explanation:
Bifidobacterium, although often grouped with LAB due to its production of lactic acid and ecological niche, belongs to the Actinomycetota phylum and is characterized by a high GC content.
The GC content of Bifidobacterium species ranges from 57% to 65%, which is significantly higher than that of typical dairy lactic acid bacteria.
This difference is a major criterion used in molecular identification and phylogenetic analysis.
Pediococcus, Leuconostoc, and Streptococcus are low-GC genera, typically possessing a GC content of 34% to 46%.
Therefore, Bifidobacterium is the correct genus matching the 57% - 65% GC composition range.

Step 3: Final Answer
The genus of lactic acid-producing bacteria with a DNA GC content of 57% - 65% is Bifidobacterium.