I recently shared some photos I found while decluttering my paper files. Here are some more.

Back at the beginning of the 90s I got my first job outside of a university. It was working for MAFTech, the technology and science division of the Ministry of Agriculture, based at Flock House [See my blog Sheep milk and boletes]. The research being done there was focused on alternative to traditional New Zealand farming practices. I was there to look into using predacious or nematode destroying fungi to control intestinal worms (nematodes) in sheep and cattle. During the course of the work, I pulled a number of species out of the paddock soil.

These fungi have evolved various methods to kill their host. They either trap nematode, or their spores are eaten by the nematode, or they have motile spores that infect the nematode.

Death by strangulation. Arthrobotrys dactyloides spores germinate and grow through the soil and when nematodes are present, which is always, they produce rings at intervals along its hyphae. These rings consist of three cell and when a nematode sticks its head through the ring touch one of the cells all three instantly expand and gripping the nematode so tightly it cannot pull out. The fungus hyphae then penetrate the nematodes body filling it with hypha and digesting its content.

Caught in a net Arthrobotrys oligospora growing in the same places as Arthrobotrys dactyloides but instead of rings it produces a net covered with glue-like substance. The net is 3 dimensional but has been flattened in this photo. Again, when a grazing nematode touches the surface of the net it is instantly stuck to its surface by the glue. The funguses hypha penetrates the body and digest its content.

Sticky bulbs. Nematoctonus which is the asexual form of the mushroom genus Hohenbeuhelia, produces simple, little hourglass shaped bulbs along its hypha. These bulbs have a cap of glue-like substance. If a passing nematode touch the glue, it is instantly stuck and held fast. An as above the fungus penetrates the nematode and digests the bodies content.

Fishhooks. Harposporium species take a different approach by producing spore that are hook-shaped and these are released into the soil. They are small enough to be swallowed by a grazing nematode, but the spores shape means that they tend to get stuck in the nematode’s “throat”. The spores germinate filling the nematodes body and digesting the contents. The fungus the breakthrough the shell of the nematode producing structures on which new spore will develop and be released into the soil to catch more nematodes. There were three species at Flock House, the smaller spored Harposporium anguillulae, the larger spored Harposporium crassum, and Harposporium helicoides with a slight spiral in its spores.

Hunters 1. Catenaria anguillulae produces motile spores, that is, they can swim in the water that exists between the soil particles. Spores can also sense the chemical being released by a nematode and actively chase them down. When zoospore catch up with a nematode it will adhere to the nematodes surface and start the process of penetrating the shell and filling the nematode with hypha. When all of the content of the nematode has been digested, the hyphae are converted to “zoosporangia in which new zoo spores are produced. Each of the zoosporangia will develop a small pore to the outside of the nematode through which the zoosporangia can be released. And the hunt begins again.

Lethal injection. Haptoglossa heterospora produces zoospores that also chase down nematodes and when the have found one they change form (encyst) into a triangular-ish shaped spore. This spore has a mechanism by which it can inject or shoot its content through the shell of the nematode. Once inside the fungus grows into large sausage-shaped structures, the infection thallus, which fills the nematodes body. These sausages are eventually completely converted to new spores which are released into the soil as the nematodes shell collapse and ruptures.

Hunter 2. Myzocytium lenticulare is also a hunter. In these photos you can see that the nematodes body is filled by the flask-shaped sporangia which are roughly spherical with a neck that breaks through the nematodes shell. In the lower photos the fungus has formed a structure that looks like a string of beads. The large beads are the “female” oogonium and the small bead is the “male” antheridium. Once fertilisation occurs the oogonium will grow into a single large, thick-walled oospore. Oospores are believed to act as a survival stage during adverse conditions. The infected nematode here is the third larval stage of a parasitic nematode that probably infects horses as it was collected in a horse paddock.

Note: The majority of these phots were taken from microscope slide preparations that have been stain with either cotton blue or basic fuchsin (pink). Where the photo is of unstained specimen the phot was taken by focusing the microscope on the surface of the agar in the Petri dish. This could have been from above or from below by focusing through the bottom of the dish and agar layer.