To Symbiosis or Not To Symbiosis

I’m almost certain this is an unpopular opinion, but the terminology for symbiosis is horrible. 

 

The textbook explains symbiosis is a close and long-term biological interaction between two organisms. There are three types of symbiosis: mutualism, in which both species benefit; commensalism, in which one benefits and the influence on the other is neutral; and parasitism, in which one benefits and the other is harmed. 

 

First, let’s get rid of parasitism. I don’t mean cut the word, but let’s delete it from the lexicon of symbiosis. Most parasitism is more akin to predation, others…wait, let me get away from this line, let’s just call parasites their own thing. There is no need for layers of terminology.

 

Second, commensalism- ugh, what a horrible word. It means together (com)  and table (mensa); thus, it means shared table, WTF. Does this meaning fit commensal organisms, or, more importantly, are there any commensal organisms? I hypothesize that the answer is no.

 

The first example of commensalism that I found is with barnacles that live on whales. No, these are not commensal; they are parasites; they harm the whale, at least by slowing it down. The second example the vast internet showed me is remoras attached to sharks and rays; again, this harms the sharks, at least by slowing them down, and thus, they are parasites. The third example is epiphytes that grow on trees. Supposedly they do not harm the trees, bullshit. They will compete for the light energy. Also, if the epiphytes get too massive, they can cause the tree to break more easily; these are parasites. 

 

Okay, no more commensalism: Now we have parasites, their own thing, and symbiosis, also known as mutualism. Great, now we can get rid of mutualism. No need for two words meaning the same thing. WOOOOO.

 

Symbiosis is incredibly fascinating. I never paid much attention to it in biology classes until the endosymbiont hypothesis was explained. This hypothesis suggests that eukaryotic organisms emerged because single prokaryotic cells engulfed other prokaryotic cells without digesting them. The engulfed cells became mitochondria and chloroplasts, which are energy organelles. There is substantial evidence for this: they possess their own DNA, their DNA is circular (like that of bacteria), they replicate independently, and they have double membranes. The late Lynn Margulis was a proponent of this idea. She published a paper on it in 1967. Later, she authored several books on this theme, including Symbiosis in Cell Evolution, Acquiring Genomes: A Theory of the Origins of Species, Microcosmos: Four Billion Years of Microbial Evolution, and What is Life?

 

The first person to propose the endosymbiosis idea was Konstantin Mereschkowski, who proposed that this occurred in plants in his 1905 paper, On the Nature and Origin of Chromatophores in the Plant Kingdom. That title is translated; good luck reading the paper if you don’t read German.

 

Are there other awesome symbiosis examples? Why, yes, I‘m glad you asked.

 

Heart cockle clams, Corculum cardissa, aid the photosynthesis of algae that live inside them by transmitting sunlight through their shells. Many of the harmful UV rays are blocked, but up to 60% of other solar radiation gets through. How? The shell structure, made of aragonite (a crystalline form of calcium carbonate), acts as fiber optic cables transmitting light to the inside. The cockles gain nutrients and energy from the algae’s photosynthesis. The algae receives shelter, protection, and a stable environment. Mutualism, oh wait, I was getting rid of that term, SYMBIOSIS!

 

Deep-sea snails that live around hydrothermal vents carry on symbiosis. Previously, tubeworms and clams had been shown to do this. In 1988, researchers found that snails in the genus Alviniconcha, Mariana vent snails, house sulfur-oxidizing bacteria that perform chemosynthesis. 

 

Chemosynthesis is a whole nother ballgame in organism energy:

Briefly, the enzyme Sulfide Oxidase converts toxic hydrogen sulfide to less harmful compounds. Rhodanese then detoxifies the sulfur, and  ATP-Sulfurylase & APS-Reductase metabolizes sulfur. 

 

Chemosynthesis was discovered in 1890. If you’re looking for a nasty, long science word, here it is: It was a chemolithoautotrophic bacteria he discovered (good luck reading the Russian paper cited at the end). It wasn’t until 1977 that it was shown to be involved in hydrothermal vent organisms, first being seen in giant tubeworms (Riftia pachyptila).

One last example of symbiosis, this time a newly discovered one (2024). Similar to the endosymbiosis of mitochondria and chloroplasts, a recent finding suggests that a nitrogen-fixing organelle (nitroplasts) found in some marine algae Braarudosphaera bigelowii (pictured at the top of this essay) came about via endosymbiosis. These were once single-celled prokaryotic nitrogen-fixing cyanobacteria. These cyanobacteria are called UCYN-A.

Quick summary: 

No more commensalism.

Parasitism is not a form of symbiosis. 

No more mutualism, just symbiosis. 

And, boy, do I need to learn more languages. 

 

 

 

Sources and Further Readings:

Coale TH, Loconte V, Turk-kubo KA, Vanslembrouck B, Ma WKE, Cheung S, Ekman A, Chen J-H, Hagino K, Takano Y, Nishimura T, Adachi M, Le Gros M, Larabell C, & Zehr JP. 2024. Nitrogen-fixing organelle in a marine alga. Science 384(6692): 217–222. (Image above taken from this paper).

Margulis L. 1967. On the origin of mitosing cells. Journal of Theoretical Biology, 14(3), 225–274.

 

Margulis L. 1981. Symbiosis in Cell Evolution: Life and Its Environment on the Early Earth. W. H. Freeman & Co.

 

Margulis L, & Sagan D. 1986. Microcosmos: Four Billion Years of Microbial Evolution. Harper & Row

 

Margulis, L. 1993. Symbiosis in Cell Evolution: Microbial Communities in the Archean and Proterozoic Eons. 2nd edition. W. H. Freeman & Co.

 

Margulis, L. 2000. Symbiosis in Cell Evolution: Microbial Communities in the Archean and Proterozoic Eons. 3rd edition. W. H. Freeman & Co.

 

Margulis L, & Sagan D. 2002. Acquiring Genomes: A Theory of the Origins of Species. Basic Books.

 

McCoy DE, Burns DH, Klopfer E, Herndon LK, Ogunlade B, Dionne JA, & Johnsen S. 2024. Heart cockle shells transmit sunlight to photosymbiotic algae using bundled fiber optic cables and condensing lenses. Nature Communications, 15, 9445.

 

Mereschkowski, K. 1905. Über Natur und Ursprung der Chromatophoren im Pflanzenreiche. Biologisches Centralblatt, 25, 593–604.

 

Mereschkowski, K. 1910. Theorie der zwei Plasmaarten als Grundlage der Symbiogenesis, einer neuen Lehre von der Entstehung der Organismen. Biologisches Centralblatt, 30, 278–288, 289–303.

 

Stein JL, Gary SC, Hessler RR, Ohta S, Vetter RD, Childress JJ, & Felbeck H. 1988.Chemoautotrophic symbiosis in a hydrothermal vent gastropod. Biological Bulletin, 174(3), 373–378.

 

Winogradsky S. 1890. Recherches sur les organismes de la nitrification. Annales de l'Institut Pasteur, 4, 213–231.