What's Tau Ceti + Amoeba?
"Rocky has spent 46 years at Tau Ceti trying to solve the stellar problem. He has the most advanced engineering tools in the known universe, but lacks one specific scientific instrument: an external sample collector. Grace has it."
Sunskritha R Shivaprasad
7/30/20264 min read
Novel 'Taumoeba' are the Astrophage's Mew Predators.
The Art Gene
The main turning point in Project Hail Mary is the discovery of a microbe capable of stopping the Astrophage’s world-ending havoc. Andy Weir’s fictional microbe–Taumoeba–is the cosmic antidote that Grace and Rocky need. The Taumoeba is the Astrophage’s natural predator, a microbe capable of keeping the star-eater in check.
Named after the star Tau Ceti and Earth’s native amoeba, Taumoeba are microbes somewhat similar to ours. They possess arm-like extensions called pseudopodia that extend outwards towards their prey. Next, they pinch their membrane inward and create a “food vacuole " into which large particles, dead cells, or bacteria (like the Astrophages) get pulled. Later, the engulfed particles or Astrophage are digested. This is their way of obtaining nutrients and energy for survival.
An amoeba using it's pseudopodia to engulf a Paramecium.
Despite Grace’s new discovery, it’s been found that the Taumoeba cannot tolerate the high nitrogen concentrations found on Venus–where the astrophage travels to grow its population. This discovery offers a stark contrast to how amoebas thrive on Earth–they require nitrogen in some form to build proteins and DNA, which both contain nitrogen. This suggests that the Taumoeba might not be confined to the same rules that we see on Earth.
Grace's Taumoeba seen under the microscope.
A representation of the steps required for directed evolution.
To acquire Taumoeba that could thrive in nitrogen-rich environments, Grace and Rocky decide to selectively breed the Taumoeba. In real-world biology, this mirrors directed evolution.
Directed evolution is a protein engineering method that mimics natural selection in a laboratory setting, usually used to develop biomolecules or new or improved functions–in this case, being able to survive in nitrogen-rich environments. Using directed evolution, the Taumoeba are pushed to adapt using mathematics governed by the Monod equation. The Monod equation is an empirical mathematical model that explains the relationship between the concentration of a limiting nutrient (or the substrate) in a particular environment and the growth rate of the organism. By using directed evolution along with the Monod equation, the fitness of the organism can be optimized. By changing enzymes or transport proteins, directed evolution modifies kinetic parameters such as μmax and Ks, which shifts the Monod curve and causes cells to grow more quickly at lower substrate levels. It also improves an enzyme’s ability to handle new chemicals–in this case, nitrogen– shifting the organism’s fitness positively.
The Taumeoba can be compared to a real-life predatory bacterium, Bdellovibrio bacteriovorus, which invades and consumes other bacteria. This bacterium consumes a wide range of gram-negative bacteria (unlike gram-positive bacteria, they have an outer lipid membrane). Some gram-negative bacteria that B. bacteriovorus consumes are Escherichia coli (E. coli), Salmonella, Shigella, Vibrio, Yersinia, and Pseudomonas. It cannot consume gram-positive bacteria as its hunting mechanisms rely on burrowing through the outer cell membrane that gram-positive bacteria lack.
This bacterium devours its prey using two phases. First, during the attack phase, it attacks its prey by swimming at high speeds using its single flagellum. Next, it burrows itself through the outer membrane and wedges itself in the periplasmic layer. This is the growth phase. This act of invasion forces the prey to form a spherical structure called a bdelloplast. Over time, B. bacteriovorus secretes digestive enzymes that break down the prey’s inner protein and nucleic acid components. Using the energy obtained, the bacteria can eventually break through the remnants.
The Monod equation.
μ = specific growth rate
μmax = maximum specific growth rate
S = substrate concentration
Ks = half-saturation constant
This adaptation could also be a case of phenotypic plasticity. Phenotypic plasticity is the ability for an organism to alter its physical, physiological, or behavioral traits in response to environmental conditions (addition of Xenonite) without changing its underlying genetic code. This allows organisms to survive sudden changes in their environment. Over time, the new trait could also become “fixed” in the population through natural selection. And as for Rocky, who took some Taumoba onto his Xenonite ship–his ship itself was the leak.
Grace and Rocky face yet another setback when Grace discovers that there’s been a contamination on board Hail Mary. More specifically, the Taumoeba evolved to escape the Xenonite breeder tanks and began to consume the Astrophage that powered Grace’s ship. When the Taumoeba were selectively bred in the Xenonite breeder tanks designed by Rocky, some of the Taumoeba not only evolved to thrive in Nitrogen but also evolved a way to bypass the Xenonite. Rather than just building chemical resistance/tolerance to Nitrogen, the Taumoeba could have possibly adapted a mechanism that allowed it to hide between the molecular gaps of Xenonite to escape the Nitrogen itself. Through multiple generations, the Taumoeba were finally able to escape the breeder tank and make its way to the fuel tanks. This evolutionary change refers to an unintended selection, where a trait (here, Xenonite resistance) was selected, increasing fitness for the Taumoeba in this case and is a classic example of experimental evolution.
The Taumoeba were more than a cure to the dimming sun. They were an example of how ecosystems around us grow–through evolution. Selection isn’t always set in stone, and highlights the caution and gift that selective breeding imposes upon us. Project Hail Mary is a scientifically convincing fiction that mixes facts, reality, imagination and a bit of awe and inspiration.
“Amaze, amaze, amaze." 👎👎👎
An example of phenotypic plasticity in the Himalayan rabbit, where the color of it's coat changes based on the surrounding temperature.
