Question

Which of the following genus of bacterium is not found in freshwater?

• A. Pseudomonas
• B. Flavobacterium
• C. Aeromonas
• D. Vibrio

Hint:

Remember that Vibrio species are halophilic (salt-loving) marine and brackish-water bacteria. This distinguishes them from common freshwater genera like Aeromonas and Pseudomonas.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Aquatic environments support diverse bacterial communities.
The distribution of these bacteria is influenced by salinity, temperature, and nutrient availability.
Some bacteria can tolerate a wide range of salinities, while others are restricted to either freshwater or marine environments.

Step 2: Detailed Explanation:
Let us review the environmental preferences of the listed bacterial genera:
- Pseudomonas:
A diverse genus of Gram-negative bacteria found in soil, plants, and freshwater systems.
They are common members of the natural freshwater microbiota.
- Flavobacterium:
A genus of Gram-negative, rod-shaped bacteria commonly found in soil and freshwater.
Some species, like Flavobacterium columnare, are pathogens that cause columnaris disease in freshwater fish.
- Aeromonas:
A genus of Gram-negative, facultative anaerobic bacteria abundant in freshwater, estuarine, and sewage environments.
Aeromonas hydrophila is a common freshwater pathogen that causes motile aeromonas septicemia (MAS) in carp.
- Vibrio:
Most species in this genus are halophilic, meaning they require sodium chloride (salt) to grow.
They are found in marine and brackish water environments.
Some species, like Vibrio cholerae, can survive in brackish or estuarine waters, but the genus as a whole is characteristic of saltwater environments and is not a natural component of freshwater ecosystems.

Step 3: Final Answer:
The genus Vibrio is not typically found in freshwater ecosystems due to its salt requirement.
Thus, the correct choice is (D).