One of the highlights of the British Phycological Society’s recent meeting in Plymouth was a talk by Sebastian Hess from the University of Cologne about amoebae which preyed upon microscopic algae. His presentation included several video clips, one of which featured the aptly-named Vampyrella attaching itself to the outside of an alga cell and slowly sucking out its contents. The clip drew audible gasps from the audience, none of whom had walked into a dryly-named session on “Algal interactions across the tree of life” expecting the tropes of a horror movie to be displayed before their eyes.
The link to the YouTube video below gives you some idea of the predatory nature of these organisms. They are not technically parasites but “protoplast feeders”, penetrating the cell wall of the victim and consuming the cell contents by a process known as “phagocytosis”. Although these organisms have been known for a long time (they were first described in 1865), it is only in recent years that the diversity of these organisms has become apparent. That’s because, like many unicellular organisms, it is difficult to fully appreciate the differences just by peering at them through a microscope. It has only with the advent of environmental DNA analyses that this has been understood. We now know, for example, that the species found in freshwater, soil and marine environments are all different and that each vampyrellid is fairly specific to a particular group of algae (more about Sebastian Hess’ work can be found here.
The vampyrellid amoeba Arachnomyxa cryptophaga feeding on the green alga Eudorina elegans, from the German YouTube channel “Nicht interessant”
Those of us who are interested in algae tend to go on about their importance in trapping the sun’s energy via photosynthesis but rather less time thinking about how that energy then passes from the algae through to higher trophic levels. I often see chironomid larvae feeding on algae when examining samples (see, for example, “More about very hungry chironomids”) but these tend to use the larger filamentous algae as supports while they graze on the smaller epiphytes (mostly diatoms in the streams I look at) which grow on the surface of the filaments. The vampyrellids, by contrast, have powerful enzymes that can punch holes in the though cell walls of filamentous algae so that they can suck out the contents. At the simplest level that creates a tasty meal for the vampyrellid but, from a broader ecological perspective, these amoebae are turning large unpalatable chunks of carbon that an insect larva cannot manipulate into its mouth into smaller nuggets that could, in theory, be consumed by small beasts. These small beasts, in turn, fuel the slightly larger bugs which may be prey for a fish. The vampyrellids, in other words, help keep carbon pumping through the aquatic ecosystem.
It is not just predatory amoebae that perform this function. Another talk at the Plymouth meeting by Davis Laundon of the Marine Biological Association showed that microscopic fungi may play a similar role. Again, I’ve mentioned these organisms before (see “Little bugs have littler bugs upon their backs to bite ‘em …”) but not really reflected on what role they play in an aquatic ecosystem. Davis worked in marine rather than freshwater ecosystems but the same principle seems to be at play: large chain-forming diatoms such as Chaetoceros are too big for many zooplankton grazers to feed upon but thraustochytrid fungi inadvertently convert these big indigestible hunks of carbon into bite-sized portions which then fuels the ecosystem in Plymouth Sound.
Coincidentally, my own interest in the microscopic world started when I read about amoebae in school textbooks, and my earliest natural history explorations involved trying to find amoebae in local ponds, usually without success (when I was in Nigeria, protozoans returned the favour … but that’s another story). Even now, I do not regard amoebae as particularly easy organisms to observe and have not tried to identify them. However, once your eyes (and mind) are tuned to noticing particular phenomena in nature, there is a positive feedback loop and you start to notice these phenomena more and more. I suspect I have been suffering from “amoeba blindness” for some time. Last year I wrote an essay about what we see and don’t see when peering down a microscopeand Marian Yallop, one of my co-authors, included some photographs of amoebae, reminding me of my earlier fascination with these unicellular organisms. I’ll be watching out for these as I examine samples, and trying to learn a little more about them during 2020.
A plate from showing interactions between algae and other protists from Kelly et al. (2019). A. A ciliate has consumed a variety of live pennate and centric diatoms and cyanobacterial filaments. B. Algae autofluorescing red and cyanobacterial filaments yellow within the ciliate. C. Other protists e.g. Vorticella select relatively smaller soft-bodied green algae. D. This amoeboid protist had previously consumed two relatively large diatoms E. Some reorganising of the cell contents is required to shuffle these engulfed cells to the periphery. F. Exocytosis takes place to release the partially digested cells, and the amoeba rapidly moves away. This sequence of events lasted a few minutes. Images (A-B, D-F) were taken from biofilm material from Winford Brook, North Somerset, UK by Marian Yallop; Image C was taken from the Danube at Zimmern, Baden-Württemberg, Germany by Lydia King.
Hess, S.& Melkonian, M. (2013). The Mystery of Clade X: Orciraptor gen. nov. and Viridiraptor gen. nov. are Highly Specialised, Algivorous Amoeboflagellates (Glissomonadida, Cercozoa). Protist 164: 706-747.
This week’s other highlights:
Wrote this whilst listening to: PJ Harvey
Cultural highlight: Tutankhamun: Treasures of the Golden Pharaoh at the Saatchi Gallery in London. Was looking forward to seeing Girl From The North Country, a musical based around Bob Dylan’s songs, on the same trip to London but it was cancelled 40 minutes before the start due to cast illness.
Currently reading: Nine Lives: In Search of the Sacred in Modern India by William Dalrymple
Culinary highlight: Mildreds, a vegetarian restaurant in London’s Soho. You can’t book ahead, so we had to wait for a table. We spent this time at the closest pub, which just happened to be the John Snow, featured in “A drink of water with John Snow”, a post from 2013. Mildreds was worth the wait, particularly for the desserts. I was diagnosed as lactose-intolerant last year and normally gaze miserably at dessert menus packed with dairy-rich offerings. Mildreds, however, is fully vegan throughout January, so the entire dessert menu was there for the choosing.