(Editor’s Note: Willow Yang is a frequent letter-writer/contributor to the Post-Geek Singularity and the Robservations live-stream. Her commentary on STAR TREK: THE ORIGINAL SERIES episodes have become a fan favorite. As a result, we’ve decided to publish them as part of our TREK TALK series under the title: “Willow Talk”.) Willow is back again, this time with an in-depth review of ST:TOS’s episode: The Immunity Syndrome (spoiler alert: she’s not a big fan of giant space amoebas).
Forewarning: this is going to be an extremely long and potentially very tedious letter. I’m writing my report on the Immunity Syndrome. This time around, instead of doing a regular review of the episode, I wanted to focus more on the science of the amoeba. Before delving into a discussion on single-celled organisms and cellular size limits however, I will just say right off the top that I thoroughly enjoyed the episode. The Immunity Syndrome provided a fantastic exhibition of the interpersonal relationships between the Holy Trinity of Kirk, Spock, and McCoy. I enjoyed all of the character interactions and rapport: the continuous exchange between Kirk and Spock as the former grows increasingly frustrated with the latter’s inability to provide answers to the strange events they were experiencing; the Sophie’s choice that Kirk had to make over which one of his friends to send out on a deadly mission; the love-hate relationship between Spock and McCoy. I personally like to interpret McCoy as being secretly infatuated with Spock and hiding his feelings behind a veneer of antagonism towards the latter, but that’s just me. Additionally, the episode provided interesting insights into Vulcan psychology and their shortcomings: the crew of the Intrepid were apparently blinded by their logic and unable to comprehend what was happening to them as they were being destroyed. The scene of Spock sensing the destruction of the aforementioned starship was uncannily similar to Obi-Wan sensing the destruction of Alderaan; I do wonder if George Lucas did this on purpose.
The first half of The Immunity Syndrome was quite eerie; the episode did a commendable job of creating an atmosphere of suspense and foreboding in the leadup to the amoeba’s reveal. There were definitely some horror elements to the plot: a Vulcan starship and an entire solar system of billions of lives were suddenly and inexplicably extinguished. The Enterprise encounters a mysterious dark void that begins draining not only the energy from the ship, but the very life of the crew; attempts of sending out probes yielded nothing but horrible, ear-splitting sounds; there’s a frightening moment when the stars abruptly vanish as the ship enters the dark zone. And then the source of all of this supernatural phenomenon finally shows itself and it’s…a gigantic space amoeba? Well, I’ve got some thoughts.
Before discussing the feasibility of a planet-sized amoeba, I will first provide a little background information on cellular classification and structure. There are three major domains of life: Bacteria, Archaea, and Eukarya. Eukarya is distinct from the other two domains in that the cells possess organelles, which are various membrane-bound structures with specialized functions (analogous to organs in the body), the most notable of which is the nucleus, an organelle that contains the cell’s genomic DNA. Amoebas belong to the Eukarya domain, and as a matter of fact, so do we and most other multicellular organisms on Earth. The term “amoeba”, however, is actually a little misleading because amoebas aren’t a single species of organisms. In fact, amoebas can be found in all the major kingdoms of Eukarya, including fungi, plants, and animals. The most commonly known amoebas, and probably the ones that The Immunity Syndrome are based on, are from the taxon Amoebozoa, which belongs to the Protista family. While amoebas are very diverse in size and morphology, the one key feature that they all share is this so-called “amoeboid movement”, which involves part of the cellular membrane forming a temporary appendage called a “pseudopodia” (Latin for “false foot”). The backend of the amoeba then contracts, pushing the rest of the cellular contents forward into the pseudopodia (you actually see this happening in the brief clip of the Earth amoeba that McCoy was playing). This type of movement normally requires some sort of surface for the amoeba’s pseudopodia to adhere to; I don’t know how such a mechanism would work in outer space.
Can a free-living cell that size exist? Why is it that, at least on Earth, we don’t see any large single-celled organisms? Well, according to high school biology textbooks, cells are dependent on the flux of materials across their membrane. The transport of these materials is often achieved via passive forces like diffusion, which is the natural tendency for particles to flow from an area of higher concentration to one of lower concentration. The rate of diffusion in a cell is, in turn, dependent on its size, specifically its surface area to volume ratio. Smaller cells have a larger ratio, enabling them to be able to exchange with the environment more rapidly than larger cells; once a cell surpasses a certain size, the rate of exchange becomes too inefficient for it to be able to sustain itself. I’m dissatisfied with this explanation however; there are examples of unicellular organisms on Earth that appear to have found methods to circumvent such issues. Moreover, the amoeba is floating in outer space, which contains a very low density of particles that wouldn’t allow efficient exchange to begin with. What I’m more concerned about is how a cell that size will be able to control its cellular processes. The nucleus is frequently referred to as the “brain” of the cell; it contains all the information necessary for a cell to be able to respond to its environment and maintain life-sustaining functions. Nuclei (the plural form of nucleus) have a finite capacity, however; each nucleus can only effectively control a limited cellular volume. The algae Caulerpa is one of the largest unicellular organisms on Earth, measuring up to a whooping 30 centimeters (12 inches) in length. In order to be able to keep up with its metabolic demands, the cells possess an enormous number of nuclei so that the genome to cell volume ratio is roughly equal to that of much smaller cells. It is baffling to me that the amoeba appears to possess only a single nucleus; in my opinion, there’s just no way it will be able to control all of its cellular processes. Realistically, something that size will require an astronomical number of nuclei to be able to sustain itself.
From an evolutionary perspective, I suspect that it’s probably disadvantageous for a cell to grow too large. Size can impose a fitness cost, with fitness here being defined as the number of progeny that an individual leaves behind. Cells that are larger will take longer to replicate, and may get outcompeted by smaller, faster dividing cells. This is particularly prominent in bacteria, where the insertion of even a small amount of foreign DNA into a cell can result in a significant reduction in growth rate. Personally, I’m not overly concerned about the amoeba reproducing: it’ll probably take a number of years for a cell that size to accurately duplicate all of its DNA and organelles. In fact, I’m dubious as to whether the cell can even divide at all: I don’t know if microtubules, protein fibres that partition the duplicated genome by pulling each copy towards the opposite poles of a dividing cell, are capable of extending thousands of miles (as opposed to a few micrometers in regular-sized cells). There is probably a decent chance that the amoeba will end up mis-segregating its contents, and both copies of the daughter cells will perish as a result.
I’ll end this extremely long letter with a few examples of real life researches that various scientists are conducting on amoebas. One of my PI’s former colleagues in Japan grew a coculture of amoebas and E coli together for a number of years. Towards the end of the experiment the two species had evolved to become so interdependent that they can no longer be cultured separately; one cannot survive without the other. Similarly, a graduate student I encountered during my recent conference in Boston is also coculturing amoebas with bacteria to study the evolutionary process of endosymbiosis. This phenomenon occurs when an amoeba engulfs a bacterium, but instead of the bacterium being digested, it continues to survive inside the host with which it forms a symbiotic relationship. Finally, another researcher who gave a talk at the same conference studies Legionella, a parasitic strain of bacteria that specializes in infecting amoebas. These bacteria have viral-like properties in that they actually enter and replicate inside of a host cell, depleting it of iron and other nutrients in the process. Thus, if I were travelling in outer space, I’d keep a storage of bacteria on hand: they might come in handy if I encounter any giant space amoebas or other hostile lifeforms that need to be stopped.