Catenaria anguillulae

Catenaria anguillulae is a member of the Chytridiomycota, the only major group of true (chitin-walled) fungi that produce motile spores, termed zoospores. This fungus can be grown easily on culture media but in nature it is often found as a facultative (non-specialised) parasite of nematodes, the eggs of liver flukes, or other small organisms. The images below were taken from videotapes, using phase-contrast microscopy, and show the behaviour of this fungus when parasitising nematodes.

B. Two zoospores crawling along the surface of a nematode; the flagella are clearly seen (arrowhead).

C. Five zoospores (the centre one is out of focus) that were attracted to a specific site on the nematode - the bulb region (heart-shaped) where an excretory pore (not seen) discharges compounds that cause zoospores to accumulate by chemotaxis. One of the zoospores recently arrived at this site and we can still see its flagellum (arrowhead); the other zoospores have encysted and withdrawn their flagella.

D. Three zoospore cysts (marked 'c') that germinated on a glass surface. Each produced a narrow outgrowth tube which swelled to form a vesicle (ves), and narrow rhizoids (rh) developed from the vesicles. Lipid bodies are seen as bright globular structures in the vesicles and some of the cysts.

E. Several zoospores were attracted to the tail region of a nematode, near the anal pore (not seen). They encysted and produced vesicles and rhizoids, many of which are inside the body of the animal. At a later stage of development, the vesicles will become sporangia: their contents will be cleaved to produce zoospores which will be released to repeat the infection cycle.

For further aspects of Catenaria zoospore biology see Chytrid zoospores

Further reading:

JW Deacon & G Saxena, 1997. Mycological Research 101, 513-522.

We do not know, but the question is worth considering because some nematodes (the eelworms, about 1 mm long) cause major damage to crop plants, and others (the roundworms) are important parasites of humans and domesticated animals.

There are several points to consider when trying to use a living organism as a control agent. Some of them are discussed below. Others can be found in the other Biocontrol Profiles:

Biological control: Bacillus popilliae
Biology and control of crown gall
Pythium oligandrum and other mycoparasites
Bacillus thuringiensis
Heterobasidion root rot
Biology and control of take-all

• The organism must be safe to use, with no adverse effects on humans, and minimal effects on 'non-target' organisms. Catenaria probably meets these requirements. Any impact that it might have on other organisms (in the environments where it would be used) could be minimised by the design of application methods. In addition, C. anguillulae is a cosmopolitan fungus, present in at least low levels in many soils.
• The organism must be consistently effective in practice. This can be a major problem for biological control agents because they are influenced by environmental factors, often beyond our control. For example, Catenaria would require relatively moist conditions because its zoospores swim in water films. But so do nematodes!
• The organism must be able to be delivered to the specific sites where it is expected to act - for example, to the roots of plants growing in soil. This can be a major problem because we cannot uniformly inoculate the soil. But zoospores can swim and, at least in theory, could locate their target hosts by chemotaxis in soil. Catenaria also might be applied to animal dung to control roundworms.
• The organism must be marketable and cost-effective. Marketing includes all the problems associated with cost-effective production, storage and distribution of the product, as well as the potential market size. Many of these factors are unknown for Catenaria. Cost-effectiveness involves the value of the product to the end-user. As a rule of thumb, many agrochemical companies aim for a cost-benefit ratio of about 1:4 for the end-user. Again, we do not know if Catenaria would achieve this; a lot of work on product development and field testing would be required.

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