[katieHaylor (OP)]

Kevin says

I was watching a YouTube video about the largest unicellular organisms and I started wondering, are there any unicellular organisms that regularly consume multicellular organisms as food?

What do you think?

[chiralSPO]

I guess this depends on how you define "prey on"...

Many types of bacteria (unicellular) consume multicellular organisms. For instance the "flesh eating bacteria" like MRSA that causes necrotizing fasciitis (don't look it up if you're at all squeamish!!!)

But this is an example of colonies of bacteria living on or in the multicellular organism (host), where each bacterium exudes digesting enzymes into the host, and then absorbs whatever comes out and eats it. This is a far cry from chasing something down, ripping it apart and ingesting it (which is what I visualize predation).

Actually, a web search revealed this article: http://onlinelibrary.wiley.com/doi/10.1111/1462-2920.12949/abstract which reports groups of unicellular protists (amoebae) "pack hunting" nematodes (a few thousand cells)

Pack hunting by a common soil amoeba on nematodes
...Protists are generally considered 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...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 considerable importance of the hitherto neglected trophic link ‘nematophagous protists’ in soil food webs.

[chris]

Yes, indeed, and @chiralSPO got there first: bacteria and fungi "eat" multicellular organisms all the time, although usually not in one mouthful. Their approach is mainly one of chemical decomposition whereby factors are released that lyse or break apart cells, and the microbes then soak up the nutrients that are released, iron foremost among them.

We talked recently about how the tuberculosis (MTB) bacterium kills and consumes host macrophages in an episode of the eLife Podcast.

[RulerK]

Hmmm… interesting. I am really talking about actual predation rather than simple "eating." I don't think the "flesh-eating" bacteria would count for that. I am thinking of anything from tentacle-like pseudopods capturing plankton-like creatures to actual amoebaesque ambushes of multicellular organisms. I think the article about amoebas pack-hunting is incredible. Does anyone know of any other examples like that which fit my criteria?