Question

Lactic acid bacteria that can grow in the presence of 18% sodium chloride are

• A. Micrococcus
• B. Pediococcus
• C. Lactococcus
• D. Tetragenococcus

Hint:

Tetragenococcus is the only extremely halophilic genus among the lactic acid bacteria, thriving in high-salt environments (up to 18%-24% NaCl) such as soy sauce fermentations.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Sodium chloride (NaCl) is widely used in food preservation because it exerts high osmotic pressure, drawing water out of microbial cells and inhibiting their growth.
Most lactic acid bacteria (LAB) are sensitive to salt and cannot survive or grow in salt concentrations exceeding 5% to 8%.
However, certain specialized halophilic lactic acid bacteria have evolved adaptive mechanisms that allow them to grow under extreme salinity conditions.

Step 2: Detailed Explanation:
The genus Tetragenococcus consists of Gram-positive, homofermentative, halophilic lactic acid bacteria.
Formerly classified within the genus Pediococcus as Pediococcus halophilus, these bacteria were reclassified due to their distinct phylogenetic and phenotypic traits.
Tetragenococcus halophilus is extremely halophilic and is capable of growing in environments containing up to 18% to 24% sodium chloride.
These bacteria survive in high-salt environments by accumulating compatible solutes (such as glycine betaine and carnitine) to balance osmotic pressure without disrupting cellular enzymes.
They are highly active in high-salt fermentations such as soy sauce, fish sauce, and salted anchovies.
In contrast, Lactococcus and Pediococcus are typical dairy LAB that are inhibited at much lower salt concentrations (5% or less).
Micrococcus species can tolerate high salt but are not classified as classical lactic acid bacteria.

Step 3: Final Answer
The lactic acid bacterium that can grow in the presence of 18% sodium chloride is Tetragenococcus.