WAR  of  the  MICROWORLDS  

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' Spirogyromyces vermicola:  The fungus spore is ingested and attaches to the inside lining of the gut.  The fungus utilizes materials pumped through the gut by the oesophageal muscles that are being digested by the nematode during feeding.  In the micrograph below, five spores have become attached to the gut wall and are now germinating to form absorptive thalli.  PHYLUM UNKNOWN

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Early stages of infection inside nematode's gut by Spirogyromyces.  One of the spores has germinated to form a young thallus and is now developing secondary coils.

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Late stage of infection inside nematode's gut by Spirogyromyces.  The original spores have attached just below the oesophageal bulb and can grow the length of the gut.  Here the linear growth has been restricted by egg production in the host ovary.

Many years ago Dr. Shean Shong Tzean was a visiting professor from National Taiwan University working in my lab in Ontario. While processing soil samples to recover nematodes we discovered a remarkable 'fungus' growing in the intestines of free living rhabditoid nematodes.  After a detailed study we eventually published a paper on its structure and biology (Tzean and Barron, 1981. CJB 59:1861).    Based on the complex coiling system of the thallus and its branches, we named this bizarre, and  newly described,  fungus Spirogyromyces vermicola. 

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The 'fungus' behaves like a microscopic tapeworm . Primary infection is by a spore that is ingested and subsequently anchors to the wall of the nematode's intestine by means of a terminal hook-like appendage (but lectin/carbohydrate bonding can't be ruled out).     Each spore then germinates to form an elongate, septate, coiling thallus inside the nematode's gut.   A lateral branch grows from just below the septum of each cell and these also formed septate, spiral growths.   Tertiary spirals developed from these secondary spirals until a complex helicoid thallus is formed.    At maturity  the terminal branchlets form spores.

At first sparse, the coiled mass eventually fills the lumen of the intestine and stretches from just behind the oesophageal bulb to the anus. There is no ramification of the fungus outside the gut into the body cavity and the 'fungus' appears to receive all of its nutrient requirements from 'flow through' materials passing through the gut.  Activities of the nematode can cause the spores or sometimes even branches to break free.   These are then defecated through the anus to the exterior.   Spores, after release, are apparently attractive to nematodes and are subsequently consumed as a potential food source by a later generation of nematodes to begin the cycle again.

We didn't know then where to place this 'fungus' in the classification system, and I still have no idea yet but I expect there are a number of similar species around and, hopefully molecular analysis will tell us where it belongs.  Only one species of Spirogyromyces is known.  It surely wouldn't be difficult to find some more!  P.S.  I don't really think this is a fungus; so there is another publication  for someone; but first you have to find it!

Images copyright George Barron from MycoAlbum CD

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