WAR  of  the  MICROWORLDS  

How do I kill Thee?   Let me count the Ways!   (# 40)   click here for full list

40: Drechslerella species:  Haptoglossa (click here) has the most complex and sophisticated attack cell (gun cell) but the constricting ring found in Drechslerella is the most sophisticated trapping device used by fungi to capture and consume live prey.    A lateral branch forms a three-celled ring  that, when activated, snaps shut in the blink of an eye (1/10th sec) and holds the nematode fast.   The victim is then penetrated, colonized and digested.

The two-celled spore (extreme right) of Drechslerella anchonia has germinated and will produce a short hypha bearing up to five three-celled constricting rings.   In this micrograph a nematode has been captured.    Usually, the nematode is captured by a single ring cell but in its violent struggles to escape it often sticks its head or tail into a second loop and is held helpless until invaded and subsequently consumed by the assimilative hyphae of the predator.    Ring cells are activated mehanically by touching the inside of the ring cells.   Mechanical stimulation or heat can cause the consricting ring to trigger.   Violent struggles of the victim have triggered another of the CRs (extreme left) to close. 

SEM of Nematode crushed by constring rings.

Nematode 'captured' by the Constricting Ring of Drechslerella -  Click here to find out how the constricting ring works.

  Under suitable conditions, the conidia of Drechslerella dactyloides and D. brochopaga can germinate directly to produce constricting ring trapping devices.    These are are often referred to as 'conidial traps'.   Here,  a ring from such a conidial trap has constricted around the body of a nematode that has entered the ring.   Two of the ring cells have germinated, penetrated through the cuticle of the nematode and germ tubes are invading the body of the victim.   These initiate the assimilative hyphal system that  digests and absorbs the contents of the host.   The generic name Drechslerella is now favoured for all the predatory Hyphomycetes that capture nematodes using the constricting ring device. Previously this fungus was classified as an Arthrobotrys species (Arthrobotrys dactyloides) based on its two-celled conidium.

Images copyright MycoAlbum CD by George Barron

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