The amoebae drill holes (arrows) through the thick, pigmented wall of fungus spores and suck out the contents.
Left: Spore of the Parasitic Fungus Cochliobolus sativus engulfed in Soil by the Giant Amoeba Vampyrella(Micrograph by Terry Anderson).
Right: SEMs from Anderson and Patrick, Phytopathology 68:1618. 1) perforations in conidia of Cochliobolus (arrows). 2). hyphae (white arrows) and aleuriospore (black arrow) of Thielaviopsis basicola with perforations. 3). SEM of Cochliobolus conidia with tiny perforations (arrows). 4). SEM of conidia of Cochliobolus with annulations (arrows).
In 1967, Ken Old (then at University of Dundee, Scotland) reported that many spores of Cochliobolus sativus recovered from natural soil after several weeks incubation had perforations in their walls. Old worked for some years on this problem and he and Wong summarized the findings in 1976. While they were able to show that microbial agents caused the holes it was not possible to identify the causal agent. Holes ranged in diameter from 0.5 - 6.0 microns. Later, Anderson and Patrick (University of Toronto, Canada), found that both Thielaviopsis and Helminthosporium spores also developed perforations when incubated for a period in natural soils.
In 1977 both groups successfuly established the causal organisms and published their findings. Anderson and Patrick reported that one amoeba (Vampyrella sp) caused perforations 2-5 microns in diam in spores of Cochliobolus and spores and hyphae of Thielaviopsis basicola. They found a second amoeba caused perforations, one micron or less, in spores of Thielaviopsis basicola and Helminthosporium sativum. Concurrently, Old described how perforations in Cochliobolus were caused by a giant amoeba resembling Leptomyxa reticulata. Both groups have since added additional amoebae species attacking a variety of fungus spores. Anderson and Patrick showed that perforations were initiated by 'cutting' an annular depression in the spore wall. Eventually the wall was cut through and a circular perforation produced. Pseudopodia penetrated through the perforation to the interior of the spore and the amoeba absorbed the contents in a matter of hours.Corollary on Mycophagy Based on work of Charles Drechsler In 1978 I published a short addendum on this interesting topic based on the findings of the renowned Charles Drechsler published in 1936. Drechsler, always the keen observer, reported the following comments on the biology of Geococcus vulgaris, a testaceous rhizopod (= walled amoeba). " ...often the animal obtains its nourishment from objects as formidable as the oospore of Pythium ultimum, which not only exceeds it in size but is surrounded by a thick and thoroughly substantial oospore wall. Neither of the more usual methods of amoeboid ingestion is followed by G. vulgaris. Instead Geococcus applies its mouth flush to the oospore wall, caulks the zone of contact with a yellow secretion, and gradually perforates the delimited portion of the spore wall, probably by some sort of digestive action. Once communication is established with the interior of the osopore, the granular contents, now visibly degenerating, are drawn into the test of the animal; the movement of material appearing much the same as in the sucking of an egg. " In a subsequent paper Drechsler noted that Euglypha denticulata attacked the oospores of Pythium ultimum in the same way as Geococcus vulgaris. Drechsler noted that hyphae were also attacked. The rediscovery of Drechsler's findings in no way detracts from the excellent work of Anderson, Old and others. By tackling the problem from an unbiased square one, they found another remarkable method to perforate thick-walled spores. Much has still to be learned about fungus/amoeba relationships. (Note: G. vulgaris has since undergone several name changes.)