WAR of the MICROWORLDS
How do I kill Thee? Let me count the Ways! (# 21) click here for full list
Rotiferophthora spp: Rotifers consume fungus spores as food. As a consequence of this predilection, many species of fungi have evolved as parasites and predators following ingestion of spores. Amongst these are many species of Rotiferophthora that are specialized as parasites of rotifers but have evolved from a Verticillium-like ancestor. Over the eons the fungus has developed some interesting characteristics. e.g. The fungus fruits in air never under water; the spore masses of the fungus are not readily wetted (hydrophobic); the spore ingested as a food source germinates in the gut of the animal to initiate the parasitic phase. DEUTEROMYCOTA (affinities with ASCOMYCOTA). (For more information on this species see Barron, G.L. 1991. Can. J. Bot. 69: 494).
Left Image: The photomicrograph shows the shell of a bdelloid rotifer after complete digestion of the body contents by a species of Rotiferophthora. You can see the distinctive turbinate shape of the assimilative hyphae that are tracing through the interior of the host. The conidial state forms Verticillium-like phialophores (conidiophore bearing phialide type conidiogenous cells) and phialides. Right Image: The fungus fruits in the air above the water surface and the submerged body of the host (see illistrations below). The spore masses in Rotiferophthora, unlike most spore balls on Verticillium species, etc are hydrophobic and not readily wetted. So while floating the spores can remain safe for the moment from predation by other aquatic microorganisms. The conidiophores, along with their spore masses, act as tiny sails and the whole structure (rotifer + fungus) is dispersed to other parts on the water surface by wind and currents. Eventually the spore masses break down and the spores are released to renew infections in susceptible rotifers or to be consumed as a food source by a host of non susceptible microfauna.
While browsing through some old B and W micrographs, I came upon this image that is of particular interest because it is unusual (hard to get )and illustrates the relationship between the rotifer parasitized by Rotiferophthora and the aerial conidiophores produced by the fungus. The parasitized body of the rotifer is under water (check diagram above). The conidiophores and conidial masses ar produced above the water surface and appear very dark because of air locks in the mount. The hyphal connective between the rotifer body and the base of the conidiophore is transparent because it is under water. The water line is where the dark conidiophore meets the pale hyphal connective. You often see mounts of fungi like this if air is trapped around the material during mounting. Unlike Verticillium, the conidiophores and conidia of Rotiferophthora are hydrophobic and not easily wetted. You can also see the aleuriospores developing from the submerged body of the host.
Fungi as a rule require a dispersal spore to disseminate the species and a persistent spore to survive adverse conditions. Many of the predators and parasites of microscopic animals have both types of spores spores. Micrograph above shows a terminal aleuriospore of Rotiferophthora with very thick walls, oil drops as storage, and a firm attachment to the parent hypha.