Heterolobosea I: Eruptive amoebae, a preview

So I've been challenged to write about Heterolobosea. It all began with my slightly cruel and potentially foolish challenging of our friendly neighbourhood taxonomist to write up a series of posts on Amoebozoa. I was rather confused about the Chaos chaos in the Amoebozoan kingdom, so the sensible thing to do was making someone else sort it out for me ^_~ And sort them out he did, with the following fascinating and informative posts that I urge you all to read:

General Amoebozoa: Putting the Formless in Formation.
Breviata anathema: TAFKAMI; TAFKAMI Walks.
Tubulinea: The Paragons of Amoeboids; Amoeba: Much Wierder than You Think.
Discosea: Keeping a Low Profile.
Mycetozoa: The Diversity of Slime Moulds.
Various Amoebozoa incertae sedis ('Variosea'): Amoebozoan Oddments.
Archamoebae: The Apogee (or Nadir) of Amoebozoan Evolution.

For the uninitiated, a nice intro to amoebae; keep in mind that the ones there are amoebozoans (except for page 3 - those appear to be Cercozoans). Before we set of on an amoeboid adventure, a quick clarification: the colloquial 'amoeba' refers to the blobby cell shape, which is called 'amoeboid'; amoeboid cells exist in many distantantly-related taxa, the larger and more famous of which is Amoebozoa. To make matters even more confusing, Amoeba is a genus of amoebae within Amoebozoa. In short, Amoeba != amoebozoan != amoeboid cell type. Amoeboid cells can actually be quite diverse:

(Leidy 1879 Fresh-Water Rhizopods of North America; some amoeboid diversity, mostly amoebozoans and cercozoans. Amoebae were formerly classified under Sarcodina and Rhizopoda, a dumping ground for organisms with various forms of pseudopodia.

Amoebae of the Rhizarian (incl. Cercozoa) and Amoebozoan 'kingdoms' are summarised and organised (phylogenetically) in Pawlowski & Burki (2009 JEM); we shall, however, move on to explore yet another island of amoebae in the eukaryotic kingdom: the eruptive Heterolobosea!

Heterolobosea are discicristate excavates, meaning they are members of what may be a monophyletic grouping, Excavata, with paddle-shaped mitochondrial cristae. What this means I will explain later on. They're alternatively refered to as Percolozoa, until Cavalier-Smith came along and bundled them up with the 'ciliatoid' Stephanopogon under the name Heterolobosea (Page & Blanton 1985 Protistologica), which was used before to describe the Percolozoa minus Stephanopogon... Well, sort of. Thanks to Cavalier-Smith, the story is substantially more complicated, as per usual. For our purposes, let's pretend it never happened...

Let's take another look at their phylogenetic neibourhood, and then move on to actually discussing what they are, lest I begin to look like a taxonomist =P

(Lara et al. 2006 JEM; placement of heterolobosea among the excavates and beyond. They are among discicristates, between Jakobids and Euglenozoans)

Heteroloboseans have unusual (non-canonical) Golgi bodies, as well as unique mitochondrial structure (and in some cases, hydrogenosomes), and are generally pretty weird in terms of cell structure. I will go into that in grater detail in a later post, but to clear up the confusion around 'paddle-shaped' cristae: there are several shape types for mitochondrial cristae, or folds of the inner membrane that go into the inner matrix. We opisthokonts have flattened cristae, while the dominant form seems to be tubular. The shape of the cristae seems to be fairly conserved - allowing us to categorise organisms based on that character - thus resulting in a whole group partly held together by their discoidal cristae.

So what have we got among the Heteroloboseans?

• extremophiles - both heat-loving thermophiles and salt-loving halophiles
• anaerobes- including some mostly-amitochondriate members
• an organism once considered a proto-ciliate; far from amoeboid, it has incredible structural complexity mimicking Hypotrich ciliates, to some extent.
• an amoeboflagellate that can change between amoeboid and flagellate stages (two fundamentally different cell types) within a couple of hours, with de novo centriole formation
• brain-eating amoebae
• slime moulds: aggregation, stalk, fruiting body and all.

Some sample Heteroloboseans: 1 - Stephanopogon (Wikimedia commons); 2 - Percolomonas (Wikimedia); 3,4 - Tetramitus (Robinson et al. 2006 Eur J Protistol)

And a glimpse of the family structure:

(Park et al. 2008 Protist; a Heterolobosean phylogeny. Letters represent cell types present: A - amoeboid, F - flagellate, ? - this group needs loving care and attention...)

Overall, Heterolobosea are a fairly obscure and understudied group, save for one genus that happens to be an occasional menace to humans. In which case, we suddenly start to care a lot.

So why do I insist on calling them 'eruptive'? Stay tuned for the next episode of Heterolobosea - Vahlkampfiidae: The attack of eruptive brain-eating amoebae with split personality disorder. Scary...

*Off topic, but while looking up Vampyrella, came across this neat little page, wherein we have amoebae boring holes in fungal spores and feeding on them!

References:
CAVALIER-SMITH, T., & NIKOLAEV, S. (2008). The Zooflagellates Stephanopogon and are Percolomonas a Clade (Class Percolatea: Phylum Percolozoa)
Journal of Eukaryotic Microbiology, 55 (6), 501-509 DOI: 10.1111/j.1550-7408.2008.00356.x

LARA, E., CHATZINOTAS, A., & SIMPSON, A. (2006). Andalucia (n. gen.)-the Deepest Branch Within Jakobids (Jakobida; Excavata), Based on Morphological and Molecular Study of a New Flagellate from Soil The Journal of Eukaryotic Microbiology, 53 (2), 112-120 DOI: 10.1111/j.1550-7408.2005.00081.x

NIKOLAEV, S., MYLNIKOV, A., BERNEY, C., FAHRNI, J., PAWLOWSKI, J., ALESHIN, V., & PETROV, N. (2004). Molecular Phylogenetic Analysis Places Percolomonas cosmopolites within Heterolobosea: Evolutionary Implications The Journal of Eukaryotic Microbiology, 51 (5), 575-581 DOI: 10.1111/j.1550-7408.2004.tb00294.x

Park, J., Simpson, A., Brown, S., & Cho, B. (2009). Ultrastructure and Molecular Phylogeny of two Heterolobosean Amoebae, Euplaesiobystra hypersalinica gen. et sp. nov. and Tulamoeba peronaphora gen. et sp. nov., Isolated from an Extremely Hypersaline Habitat Protist, 160 (2), 265-283 DOI: 10.1016/j.protis.2008.10.002

PAWLOWSKI, J., & BURKI, F. (2009). Untangling the Phylogeny of Amoeboid Protists Journal of Eukaryotic Microbiology, 56 (1), 16-25 DOI: 10.1111/j.1550-7408.2008.00379.x

ROBINSON, B., DEJONCKHEERE, J., & DOBSON, P. (2007). Two new Tetramitus species (Heterolobosea, Vahlkampfiidae) from cold aquatic environments European Journal of Protistology, 43 (1), 1-7 DOI: 10.1016/j.ejop.2006.08.001