S. carpocapsae and X. nematophila are mutualistic symbionts that parasitize, kill and use insects for reproduction. S. carpocapsae develop into non-feeding infective juveniles (IJ’s). The S. c. IJ’s serve as vectors for the X. n. The vector IJ’s then colonize at a place termed the vesicle. X. n. are released from the vesicle, via nematode defecation, into a new insect host. This process serves as a model to understand general aspects of horizontal transmission of symbionts by their hosts. It takes very few X. n. cells that are retained in the intestinal vesicle to initiate colonization of S. c.
Microbial attachment to host tissues plays an important role in the initiation of pathogenic and nonpathogenic microbe-host interactions. Besides providing a basis for hosts, specific interaction between bacterial and host molecules is important in determining the ability of some bacterial species to colonize certain hosts, but not others.
Fimbriae, nonfimbrial adhesins and polysaccharides are the general classes of bacterial outer surface structures that mediate adherence to host tissue receptors. Many of the biochemical activities for these processes still remain unknown.
A study of the morphology of the intestinal vesicle was done using differential interference contrast (DIC) light microscopy and transmission electron microscopy. The study concluded that the vesicle is a modification of the anterior nematode intestine and forms independently of bacterial colonization.
The nematode Steinernema carpocapsae and bacteria Xenorhabdus nematophila were studied in this paper. Their symbiotic relationship is formed when X. nematophila bacteria adhere to a site consisting of spherical bodies in the lumen of the nematode’s intestine termed the intravesicular structure (IVS).
The lumen is the interior of a vessel, a small central space within an artery or a vein that allows blood flow. The lumen can also refer to the inner membrane space of cellular molecules such as chloroplasts, Golgi apparatuses, and mitochondria.
The intravesicular structure (IVS) is an “untethered cluster of anucleate spherical bodies”. In laymen’s terms, the IVS consists of molecular structures that contain no nucleus.
In the case of nematodes, the lumen is the basic lining of the intestines where colocalization occurs. The colonizing bacteria continue to grow until their discharge is stimulated by insect haemolymph.
Haemolymph is defined as the circulatory fluid of certain invertebrates; it is analogous to blood in arthropods and to lymph in other invertebrates.
In this process, the insect haemolymph causes the anal release of X. nematophila that have colonized its IVS. It was also shown that in the absence of colonizing bacteria, the nematode still secretes its IVS. This process of secretion also expels the excess X. nematophila that have not attached to the vesicle.
In order for the S. carpocapsae to colonize and grow more efficiently, the presence of...