by Manuel Sanchez
Figure 1. The Martian movie poster. Source
This article first appeared in the author’s blog, Curiosidades de la Microbiología and is translated with his kind permission.
Spoiler Warning: I will reveal parts of the story
The first thing that occurred to me when I heard about this film was: Will this to be about a Robinson Crusoe type Cast Away movie located on Mars? After its premiere, the social networks gradually posted positive and laudatory comments, especially regarding the scientific aspects of the story. By now I would think that almost everyone knows that this is the adaptation of an online-published novel written in 2011 by Andy Weir. Weir tried to make his story as credible as possible from the scientific point of view. Fortunately, the director, Ridley Scott kept to this intent in the screen adaptation and did not create a "Prometheus," with a crew of unreliable rogue-scientists looking for the first traces of alien life for humanity.
Figure 2. Loading hydrazine into the spacecraft Messenger. The operator wears a high-safety chemical suit. Source
Below you'll find a few of the numerous websites that have scrutinized the science of this movie. In general, the comments are quite positive, a testament to NASA following its stupendous public relations campaign since the movie "Interstellar." Most of the criticism focuses on the impossibility to have a storm like the one shown in the film due to the thin Martian atmosphere. The other major criticism is the problem of lack of protection against radiation. And finally, we’re left with the issue of hydrazine and water. We now know that there is likely to be subsurface water on Mars, so it would have been easy for Matt Damon to heat up a chunk of Martian soil, than to decompose the hydrazine. However, at the time Weir wrote his novel it was thought that Mars was a very dry place.
Anyway, let me stick to the subject of hydrazine, because it has a lot to do with Microbiology. Hydrazine is used as rocket fuel, but has a small drawback: it is super-toxic. In fact, it was wise for Matt Damon to handle it with helmet and gloves. Hydrazine is a liquid, but in the movie it is represented as a kind of crystals (perhaps it is some kind of adsorbent material, like what makes nitroglycerin into dynamite?). Here, hydrazine is reacted in order to obtain hydrogen gas, which then reacts with oxygen to get water to grow potatoes. A little farfetched but valid.
It turns out that, toxic as it is, hydrazine is synthesized by certain microbes. These are those known as anammox oxidizers because they are capable of anaerobic ammonia oxidation. Basically, they perform the following reaction:
NH4+ + NO2- → N2 + 2 H2O + Energy
Figure 3. The internal structure of Brocadia anammoxidans. The nucleoid is the dark mass, the anammoxosome is in the center of the cell. Source
This may seem very simple, but had an environmental microbiologist suggested that some kind of microbe could conduct anaerobic ammonium oxidation, he would have been laughed in the face. However in 1990 the Dutch lab of Gijs Kuenen presented conclusive evidence for such a reaction and in 1999 isolated the first bacteria capable of doing it: Brocadia anammoxidans. But surprises had just begun. When B. anammoxidans was looked at under the microscope, the researchers found that it had a totally unusual morphology: the cells contained a membranous organelle within. On analysis, it was found that the membrane was a lipid bilayer all right, but the lipid was a laderane (from "ladder"). When analyzed biochemically, the anammox reaction was seen to take place within this organelle, hence it became called the anammoxosome. But the final fireworks were that one of the intermediates of the reaction was hydrazine. As it happens, the last piece was the one that solved the whole puzzle. As we said before, hydrazine is highly toxic, so if you have to have you must make it under highly controlled conditions. A laderane bilayer is virtually impermeable, so hydrazine never leaves the inside. It is in the membrane where enzymes perform the anammox reaction. These enzymes form a multimeric complex whose three-dimensional structure has been recently determined. So maybe in the future and with the help of genetic engineering, hydrazine may be entirely biological in origin.
Figure 4. Anammoxosome structure and function. This membrane is a lipid bilayer vesicle composed of laderanes (top right). Embedded in the membrane are the enzymes responsible for the process. Hydrazine (N2H4) is an intermediate that accumulates inside the anammoxosome. Source
Now, the chief role of microbes in this movie is their enabling to grow healthy and beautiful potatoes. Matt Damon puts into practice what microbiologist Martinus Beijerinck said: "Everything is everywhere," which his colleague Lourens Baas Becking extended to include "but the environment selects." In principle, human feces contain microbes able to interact with plants and colonize the rhizosphere. Furthermore, in 2014 an article appeared in PLoS showing growth of various plants planted in simulated Martian soil. These plants grew for at least 50 days before needing some kind of nutrient. So in principle, the idea of using manure as fertilizer on Mars is not at all far-fetched, but it may have been better to compost it first. Where I have to express my criticism it is in something that will happen later. At one point there is a breach in the greenhouse structure, it undergoes a sudden decompression and it suddenly freezes. In the film we are told this means that supply of potatoes has run out, not because the plants could not be replenished, but because the microbes froze and died.
Really? Did the microbes die by being suddenly frozen? So what on Earth are we doing in our labs, keeping our strains in -80°C freezers? Additionally, it contradicts what was shown earlier in the movie. Recall that Matt Damon keeps dried droppings in sealed bags that are stored outdoors of the Martian base. At this point I think that the writers lost their keenness (by the way, in the novel, the microbes don’t die).
In conclusion, I think this is a fine and entertaining film with a good scientific background.
Links to other relevant sites
Astronautas y microbios
How scientifically accurate is The Martian?
Qué es realista y qué no en The Martian
Science fiction: Crusoe on Mars
The science behind "The Martian" and its partnership with NASA
What ‘The Martian’ gets right — and wrong — about life on Mars
This article was entered in the "Li Carnival de la Quimica," in the blog Scientia, dedicated to science on the small and the big screens.
