Pack hunting by a common soil amoeba on nematodes

Soils host the most complex communities on Earth,
including the most diverse and abundant eukaryotes,
i.e. heterotrophic protists. Protists are generally con-
sidered as bacterivores, but evidence for negative
interactions with nematodes both from laboratory and
field studies exist. However, direct impacts of protists
on nematodes remain unknown. We isolated the soil-
borne testate amoeba
Cryptodifflugia operculata and
found a highly specialized and effective pack-hunting
strategy to prey on bacterivorous nematodes.
Enhanced reproduction in presence of prey nema-
todes suggests a beneficial predatory life history of
these omnivorous soil amoebae.
Cryptodifflugia
operculata appears to selectively impact the nema-
tode community composition as reductions of nema-
tode numbers were species specific. Furthermore, we
investigated 12 soil metatranscriptomes from five dis-
tinct locations throughout Europe for 18S ribosomal
RNA transcripts of C. operculata. The presence of
C. operculata transcripts in all samples, representing
up to 4% of the active protist community, indicates a
potential ecological importance of nematophagy per-
formed by
C. operculata in soil food webs. The unique
pack-hunting strategy on nematodes that was previously unknown from protists, together with molecular
evidence that these pack hunters are likely to be
abundant and widespread in soils, imply a consider-
able importance of the hitherto neglected trophic link
‘nematophagous protists’ in soil food webs