Nematodes
Terms
By Melissa Nelson and Sue Choo
nematode: Nematodes are structurally simple organisms, also called roundworms. They are colorless, un-segmented and have no appendages. They feed on just about anything. Nematodes are one of the simplest animal groups to have a complete digestive system. They have a body plan that is referred to as “tube within a tube.” The “tube” inside their bodies is the digestive tube, while the outer “tube” is the outer body of the worm. Between the outer body tube and the inner digestive tube is most often a fluid-filled cavity. Nematodes are one of the most common phyla of animals, containing over 20,000 different species. Most of these species are parasitic, though there are also free-living and predaceous species. The type species of interest in this paper are the parasitic species, more specifically, entomopathogenic nematodes.
entomopathogenic nematode: The term entomopathogenic comes from the Greek entomon, meaning insect and pathogenic, meaning disease. Quite literally, an entomopathogenic nematode is a lethal parasite to insects… more specifically, soil- inhabiting insects. soil-inhabiting, lethal insect parasites that belong to the phylum Nematoda, commonly called roundworms.
Steinernema carpocapsae: The most studied readily available and versatile species of entomopathogenic nematodes. They are “ambushers.” They sit and wait in an upright position near the surface of the soil waiting for passing hosts. The only insect-parasitic nematodes possessing an optimal balance of biological control attributes are entomopathogenic or insecticidal nematodes in the genera Steinernema and Heterorhabditis.
Heterorhabditis bacteriophora: One of the most important entomopathogenic nematodes. H. bacteriophora are also versatile, but this species is a “cruiser” species. Instead of sitting and waiting like S. carpocapsae they move through the soil in search of hosts.
infective juvenile development: This is the third juvenile stage of the nematode. Nematodes of both Steinernema spp. and Heterorhabditis spp. have a life cycle which consists of egg, four juvenile stages, and adult. It is in the third stage that these nematodes attack insects.
insect haemolymph: Haemolymph is simply the “blood” of insects. Insect blood flows freely around inside their bodies. It is not used for transmission of oxygen to its cells like the blood in our bodies, so it is not red. It is usually green, though in some species it is colored. Insect haemolymph is rich in nutrients and flows around inside the body, so the insect’s organs can get the nutrients they need. The organs also dump their waste into the haemolymph.
lectins: Lectins are sugar-binding (carbohydrate) protein that agglutinate or firmly join cells
aggregate: As a verb, aggregate means to gather together. As a noun, it is the gathered together unit. formed by the conjunction or collection of particulars into a whole mass or sum; total; combined
mutualistic symbiont: Symbiosis basically means “living together.” It is a close association between two biological species. The larger of the two members is usually called the “host,” while the smaller of the two is called the “symbiont.” A mutualistic symbiont is a symbiont of “mutualistic symbiosis,” which is symbiosis where both partners obtain an advantage.
Xenorhabdus nematophila: X. nematophila is an entomopathogenic bacterium, and insect-killing species of bacteria. the gram-negative bacterial symbiont of Steinernema carpocapsae nematodes. These nematodes reproduce inside the cadavers of larval insects of the order Lepidoptera. Specifically, the nematode infects an insect host and releases the X. nematophila bacterium into the insect’s blood system. X. nematophila is then primarily responsible for killing the insect host, allowing the bacteria and the nematode to feed and multiply.
progeny: Progeny is another word for offspring.
horizontal transmission: Horizontal transmission is the transmission of a pathogen from an infected individual to individuals of the same species
host or tissue tropisms: A tropism is a biological phenomenon which involves the turning or bending movement of an organism or part toward or away from external stimuli, such as light or heat.
fimbriae: Fimbriae are appendages in many bacteria. They can be up to several micrometers long and are used by bacteria to adhere to each other and to animal cells. A single bacterium can have as many as 1,000 fimbriae!
adhesins: Adhesins are appendages of bacteria that make adhesion to other cells possible. Most fimbriae act as adhesions, but it is usually proteins found at the tip of fimbriae that are the actual adhesions.
periplasmic space: This is the space between the plasma membrane and the outer membrane in bacteria.
microvilli: Cells that are specialized for absorption and secretion, such as epithelial cells, have folds in the plasma membrane, creating tiny hair-like projections, called microvilli. Their effect is to immensely increase the surface area of the cell, facilitating higher levels of absorption and secretion.
phenotype: The phenotype of an organism is the observable physical characteristics determined by its genetic makeup.
concomitant: Concomitant is essentially another word for “accompanying.”
parasitic: Pertaining to, of the nature of or caused by a parasite.
Parasite: An organism which obtains food and shelter from another organism (for example Giardia).
morphology: the branch of biology dealing with the form and structure of organisms. The form and structure of an organism considered as a whole.
lumen: The inner open space or cavity of a tubular organ, as of a blood vessel or an intestine.
disgorged: to eject, yield, or discharge something
epithelium: Membranous tissue composed of one or more layers of cells separated by very little intercellular substance and forming the covering of most internal and external surfaces of the body and its organs.
morphogenic: Formation of the structure of an organism or part; differentiation and growth of tissues and organs during development.
C. elegans: Caenorhabditis elegans is a free-living nematode (roundworm), about 1 mm in length, which lives in temperate soil environments.
tropism: an orientation of an organism to an external stimulus, as light, esp. by growth rather than by movement. The turning or bending movement of an organism or a part toward or away from an external stimulus, such as light, heat, or gravity.
levamisole: An antihelminthic drug that has been tried experimentally in rheumatic disorders where it apparently restores the immune response by increasing macrophage chemotaxis and t-lymphocyte function. Paradoxically, this immune enhancement appears to be beneficial in rheumatoid arthritis where dermatitis, leukopenia, and thrombocytopenia, and nausea and vomiting have been reported as side effects.
anucleate: having no nucleus
monoclonal: Of, forming, or derived from a single clone
progenitor: an ancestor of an individual in a direct line of descent along which some or all of the ancestral genes could theoretically have passed
apoptosis: a genetically determined process of cell self-destruction that is marked by the fragmentation of nuclear DNA, is activated either by the presence of a stimulus or by the removal of a stimulus or suppressing agent, is a normal physiological process eliminating DNA-damaged, superfluous, or unwanted cells (as immune cells targeted against the self in the development of self-tolerance or larval cells in amphibians undergoing metamorphosis), and when halted (as by genetic mutation) may result in uncontrolled cell growth and tumor formationcalled also programmed cell death
endothelium: an epithelium of mesoblastic origin composed of a single layer of thin flattened cells that lines internal body cavities (as the serous cavities or the interior of the heart)
haemolymph: Circulatory fluid of those molluscs and insects that have an ‘open’ circulatory system. Haemolymph contains water, amino acids, sugars, salts, and white cells like those of blood. Circulated by a pulsating heart, its main functions are to transport digestive and excretory products around the body. In molluscs, it also transports oxygen and carbon dioxide.
vibrio fischeri: Vibrio fischeri is found in several niches in the marine environment and exists naturally either in a free-living planktonic state or as a symbiont of certain luminescent fish or squid. It is perhaps best known as the specific symbiont in the light-emitting organs of certain species of squids and fishes.
aberrant: Deviating from the usual course, as certain ducts, vessels, or nerves. Deviating from the normal; untrue to type.
nascent: Coming into existence; emerging. Of or relating to the state of a chemical element at the moment it is set free from one of its compounds.
corroborates: To strengthen or support with other evidence; make more certain.
spatial: of or pertaining to space. Existing or occurring in space; having extension in space
cholinergic- Activated by or capable of liberating acetylcholine, especially in the parasympathetic nervous system.
