I’m using this blog post as an excuse to take a detour from my usual research and explore the tantalizing world of protists. Studying nothing but microbes and chemical compounds for the past year has given me an excitement for small aquatic critters of all kinds. You are officially about to become a sounding board to the army of thoughts and large confusing taxonomic names that are assaulting my brain. Bear with me and you might find yourself similarly enthralled!

It started with reading a paper on the ecology of Labyrinthulomycetes (Raghukumar 2002) as I was studying the topic of disease in eelgrass. Recently, I have been doing a lot of research on seagrass for classwork and personal interest (“NERD!”). I find seagrass meadows particularly fascinating since they are the most common coastal ecosystem on the planet, sequester 12x more carbon than terrestrial forests, provide habitat for thousands of species, and filter contaminated water in temperate AND tropical coastal/estuarine ecosystems. I think of seagrass meadows as “unsexy” coral reefs (“NERD!”).

Common eelgrass (Zostera marina) is a type of seagrass that often suffers from the parasitic disease called Eelgrass Wasting Disease. Labyrinthula zosterae is a marine protist that causes this disease by destroying the photosynthetic ability of eelgrass leaves through lesion formation. The L. zosterae protist is actually symbiotic if the host is unstressed. As soon as the host becomes stressed (due to any number of factors, such as salinity, temperature, light, etc.) L. zosterae quickly turns pathogenic and produces lesions on the plant. Labyrinthulomycota is the marine protist group under which L. zosterae is found, hence the interest in the Raghukumar paper.

Before we move on, let’s define protists. Protists are any eukaryotic organisms that are not plants, animals, or fungi – they are typically microscopic unicellular organisms. There are four groups that comprise protists: protozoa, slime molds, water molds, and algae. Labyrinthulomycetes are marine slime molds that produce a network of filaments or tubes (“ectoplasmic net”) which they use for movement or nutrient absorption. Interestingly, they are actually more closely related to algae (i.e. diatoms, other phytoplankton, and kelp) than they are to other slime molds.

Enter the chaos. Labyrinthulomycota comprises two groups of marine protists: labyrinthulids (e.g. L. zosterae) and thraustochytrids. Labyrinthulids are typically endobionts (organisms that live within another organism), while thraustochytrids are epibionts (organisms that live on the surface of another organism). My current research is interested in the effects of pharmaceutical contaminants on phytoplankton, so I started thinking about effects of contaminants on other non-algae protists as a trigger for diseases, such as Eelgrass Wasting Disease. My lab-mate, Lyle, who is also an awesomely passionate scientist, is culturing and studying chytrid parasites on phytoplankton. I thought, “Fantastic! A possible chance to study the effects of contaminants on a Labyrinthulomycete! Both chytrids and thraustochytrids are small circular epibionts that have “chytrids” in their name so they must be related… right?”. WRONG.

After a furious onslaught of text messages with [a very patient] Lyle arguing the difference between these two seemingly similar groups of organisms, I finally realized that chytrids are fungi, while thraustochytrids are protists. Now you may be thinking, “Protists and fungi… wait… aren’t those on opposite ends of the tree of life? Why are they both using the word “chytrid” in their names!?”. That’s a question that only taxonomists can answer, but one explanation is that thraustochytrids and labyrinthulids were variously placed under the fungi and protozoa groups before being consolidated into the Labyrinthulomycota protist group. Labyrinthulids look very similar to protozoa and thraustochytrids look very similar to fungi (e.g. chytrids). Similar morphology in combination with a seriously lacking fossil record makes it easy to see how taxonomists could have originally mistaken thraustochytrids for chytrids. It sure fooled me!

(above) Chytrids (left) vs. thraustochytrids (right)
(below) Protozoa (left) vs. labyrinthulids (right)
They look totally different… right?

Now that I understand that Lyle is NOT studying Labyrinthulomycetes, can I still explore the toxicology of protists in my lab? Actually… yes! Even though chytrids are fungi and thraustochytrids are protists, they employ similar life strategies (epibionts) and can be found simultaneously in the environment. For instance, chytrids and thraustochytrids colonize mangrove ecosystems by breaking down pollen spores and fallen leaves (Phuphumirat et al 2016). If they can be found co-occurring in the environment, and if they are hard to tell apart via microscopy, does that mean that Lyle might be unknowingly growing thraustochytrids as well as chytrids in his cultures? This is definitely a possibility, since he often spikes his cultures with actual material from the Columbia River Estuary.

If we have a successful thraustochytrid culture in my lab, I can perform similar toxicology tests as with my phytoplankton. Effects of contaminants on thraustochytrids will give us insight into possible effects of contaminants on other Labyrinthulomycetes, such as Labyrinthulids, which could have ramifications for outbreaks of Eelgrass Wasting Disease. Of course, labyrinthulids are endobionts so their exposure to contaminants would be different. Nevertheless, disease ecology is a wonderful excuse to expand my research interests and enter through the gateway of non-algae protists. The world of Labyrinthulomycete toxicology awaits!

On a closing note, non-algae protists are particularly neglected in the world of microbial research. I can’t help but think that part of the reason scientists bypass these organisms is due to confusing taxonomy and terminology. But don’t let that deter you – all it takes is a few text messages to your scientist friends to start understanding protists in relation to other plants, animals, and fungi. In the meantime, oh, the possibilities that this negligence affords! This could be the beginning of a beautiful project for those of us who know…

References

Raghukumar S. (2002). Ecology of marine protists, the Labyrinthulomycetes (Thraustochytrids and Labyrinthulids). European Journal of Protistology 38: 127-145.

Phuphumirat W., Ferguson D. K., Gleason F. H. (2016). The colonization of palynomorphs by chytrids and thraustochytrids during pre–depositional taphonomic processes in tropical mangrove ecosystems. Fungal Ecol. 23: 11–19. 10.1016/j.funeco.2016.05.006