Question

The Photorhabdus symbiont bacterial cells are found in the entomopathogenic nematode Heterorhabditis IJs in/on the

• A. Oral cavity
• B. Intestine
• C. Receptacle
• D. Cuticle

Hint:

To remember the difference between the two main EPN genera:
- Steinernema has a specialized "receptacle" (vesicle) to carry its Xenorhabdus bacteria.
- Heterorhabditis carries its Photorhabdus bacteria directly in the "intestine."

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Entomopathogenic nematodes (EPNs) from the families Heterorhabditidae and Steinernematidae are biological control agents used to manage soil-dwelling insect pests.
These nematodes maintain an obligate mutualistic relationship with symbiotic bacteria.
The nematodes act as vectors to carry the bacteria into host insects, while the bacteria produce toxins that kill the insect and digest its tissues, providing a food source for the nematodes.

Step 2: Detailed Explanation:
The EPN genus Heterorhabditis maintains a symbiotic relationship with Gram-negative bacteria of the genus Photorhabdus (such as Photorhabdus luminescens).
During the non-feeding, soil-dwelling infective juvenile (IJ) stage, the nematode must store these bacterial cells internally to transport them to a new insect host.
In Heterorhabditis IJs, the Photorhabdus bacteria are carried in the lumen of the anterior part of the nematode's intestine.
These bacterial cells colonize the intestinal tract and are released into the host insect's hemocoel once the nematode successfully penetrates the host.
It is useful to compare this with the genus Steinernema:
- Steinernema species carry their symbiotic bacteria (Xenorhabdus) in a specialized, pocket-like structure called the intestinal vesicle or bacterial receptacle, located just behind the pharynx.
- Heterorhabditis species lack this specialized vesicle and store the bacteria directly in the anterior intestinal lumen.
Therefore, the correct location for Heterorhabditis is the intestine.

Step 3: Final Answer:
The symbiotic Photorhabdus bacteria are stored within the anterior intestine of the infective juveniles of Heterorhabditis.