WAR of the MICROWORLDS
How do I kill Thee? Let me count the Ways! (# 6) click here for full list
' Harposporium anguillulae, DEUTEROMYCOTA: conidium (spore) of fungus has a sharply pointed apex. The ends are out of alignment so that the spore forms part of a slow helix. As the spore is pumped down the oesophagus it spirals and screws into the muscle fibres thus lodging in the oesophagus of nematode host (hypothesis!?).'
Micrograph above shows the spores (conidia) of Harposporium anguillulae (an endoparasite of nematodes) have lodged in the oesophageal muscle fibres of the host and are beginning to germinate and invade the body cavity.
The conidia are more or les crescent shaped, with a very sharp tough point at the apex. Also, the crescent is part of a slow helix such that when the conidia are pumped down the oesophagus they rotate and lodge between the fibres of the oesophageal muscle tissue. You can see germ tubes arising from some of the lodged conidia. Spores do not germinate in the environment but lie around until swallowed by a nematode as a potential food source. There is some evidence ot indicated that the spores are baited with a chemical compound that makes them attractive to the victims.
Harposporium anguillulae - reproductive apparatus arising from a dead nematode
The conidiogenous cells are spherical to subspherical phialides, each borne on a short stalk and scattered or in clusteres along the length of an erect conidiophore arising from the body of the dead host. Phialides have a very narrow neck through which a succession of conidia is produced. All the assimilative (feeder) hyphae of this fungus are inside the host, and only reproductive hyphae are produced outside the host. Therefore, this fungus is classified as an endoparasite.
Fig. 3 Fig 4
In Harposporium anguillulae, and some other Harposporium species, when the nutrient content of the nematode is nearly depleted the fungus channels the remaining energy to produce a series of thick-walled resting spores (chlamydospores) by modifying pre-existing cells inside the body (click on Figs.3,4).
Harposporium anguillulae is an endoparasite. In Endoparasites the vegetative hyphae of the fungus are contained within the body of the host as assimilative hyphae. The only structures outside the body are associated with reproduction i.e. conidiophores, conidiogenous cells and conidia (click on Figs 2, 4). Assimilative hyphae secrete enzymes that break down the contents of the nematode that are then absorbed by the fungus for growth and reproduction.
Conidia of Harposporium crassum
All images copyright George Barron from 'The Nematode-Destroying Fungi'