Parasitic worms seem to be a topic being covered here more often as of late, but that’s likely because they are just as involved in every aspect of our lives as bacteria are. Understanding how these worms function can bring new insights into human health, agriculture, and more.
In one of our prior articles, we discussed the basics of entomopathogenic worms, that is those that prey upon insects. Nematodes in particular are well known to work with entomopathogenic bacteria and utterly destroy the bodies of insects for their own nourishment. Previous knowledge had suggested that the worms are incapable of actively killing their insect hosts and that they rely on their symbiotic relationships with bacteria in order to accomplish that task.
This does still appear to be true for some species and groups of parasitic worms, but for the previously discussed model organism of Steinernema carpocapsae and its fellow species, new research suggests otherwise. Researchers from the University of California at Riverside decided to directly test these worms in order to determine if they have their own mechanisms of killing insects.
It had already been known that S. carpocapsae secretes various substances and that these are involved in negative effects on insects, such as modulating their immune systems. It has been difficult to directly study these substances and their components, as they are complicated mixtures made up of proteins, nucleic acids, and other molecules.
Other studies have suggested though that these secreted substances do have a direct toxic effect on insects, as juvenile nematodes without a symbiotic link with bacteria are still able to kill insect hosts. Furthermore, culture media that nematodes were kept in and then removed have a toxic effect on insects when exposed to the media.
All of this implied that a direct investigation of these secretions is needed to determine just how toxic this family of nematodes are on their own and how much the bacteria is involved or not in their lethality to insects. They also wanted to test it in vivo, within insect tissue with a living nematode, to watch the effects of the secretions in action, as all the other studies thus far had tested the compounds individually in a petri dish.
Using flasks, they placed the nematodes within samples of insect tissue and measured what happened, along with collecting samples of the secretions throughout the process. What they discovered was largely expected at this point, that these secretions are incredibly toxic to multiple kinds of insects.
They also conducted a transcriptome analysis of nematodes that looked in those that had activated their secretions and those that hadn’t, in order to see which genes and RNA sequences were turned on during the process, narrowing down the involved genes. This sequencing allowed them to develop a map and profile of the nematodes for use in future experiments. This also proved that this process can be successfully studied in an in vivo and in vitro with similar results.
Lastly, they took samples of 472 venom proteins and compared them to the proteomes of other nematode species, to see why the Steinernema genus differs from the rest. What they found is that over 50% of the proteins are unique to the genus and that their gene sequences are grouped into particular clusters that are only activated during the parasitic life stage.
Another Piece Of Knowledge
The study was able to prove that this genus of nematodes are more than just passive vectors that bacteria use to attack insects. The worms themselves are actively involved in the killing of their insect hosts, even more so apparently than the bacteria. They were also able to confirm once again the usefulness of S. carpocapsae as a model organism for testing the capabilities and effects of parasitic worms in insects and other organisms, including humans.
Better understanding of the functionality of parasitic worms in general will allow scientists to combat them wherever they appear.