Moselio Schaechter


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June 03, 2013

Terraforming Mars With Microbes

by Ben Auch

Using new advances in synthetic biology and our updated understanding of Martian geochemical conditions, we should be able to inoculate the planet Mars with specially designed extremophilic microbes in an attempt to start (or re-start) life on its surface. This could be the largest and most audacious scientific experiment ever undertaken, aimed at one of the greatest puzzles in biology: how does life evolve on a planet? In so doing, the microbial pioneers we launch could pave the way for future human colonization of Mars and beyond.

A Biosphere is Born

Figure1
Fig. 1. Source: Jackson Moore.

Four billion years ago the Earth was entirely hostile to the life we find on it today. Our home-to-be was harsh and unrecognizable, with high volcanic activity, asteroid impacts, 1000-foot tides, and a toxic, anaerobic atmosphere. But then something amazing and maybe unique happened: through some mechanism life appeared. No, it did more than that: it exploded, and it changed the planet forever. How this happened is far from clear. The first microbes may well have been chemoautotrophs, using widely available sulfur and iron as a substrate for growth. These early anaerobes were largely supplanted by the photosynthetic cyanobacteria, which released large amounts of toxic oxygen into the atmosphere, killing their predecessors and causing Earth’s longest ice age. When the dust settled, a new Earth was born, rich in oxygen and a protective ozone layer, and eventually permissive to the aptly named Cambrian explosion, the root of most eukaryotic domain of life. Said another way, the initial genesis of life was the spark that unlocked a vast array of biochemical reactions on a global scale, creating an environment and atmosphere capable of supporting the vast diversity of life we see, study, and even represent today. This was the evolution of a biosphere.

Life Out There

Figure2
Fig. 2. A self-portrait of Curiosity on Mars. Source: NASA

Exactly how this extraordinary transformation proceeded, and whether it has occurred elsewhere in our universe, continues to puzzle us all, scientists and non-scientists alike. While the Earth’s biosphere remains a dynamic and fascinating system, we cannot go back to see it evolve. We rely instead on samples in deep rock layers and fossilized remains. To add more to our understanding of how a biosphere evolves, we might try moving beyond n=1. We could then ask: what do diverse biospheres have in common, and in what ways do they differ? NASA’s Kepler spacecraft has been searching the skies for exoplanets that might be capable of supporting life, and it has found over 100 of them. As many as 1 in 6 stars may harbor Earth-like planets. So perhaps the Earth isn’t so special. While many of these planets lie light-years (and many, many life-times) away, another potentially Earth-like planet is situated a mere 225 million km from us.

Was there, and is there now, life on Mars? Most of our scientific efforts on that planet have focused on these questions. Water is required for all life as we know it, and 2008’s Phoenix lander mission confirmed that water-ice is present on Mars, including in the Martian soil. The Mars Science Laboratory (Curiosity) has recently found evidence of liquid water flowing in very large quantities on an ancient Mars. In terms of direct evidence of life, however, we’ve come up short - the high UV irradiance and presence of oxidizing compounds may have destroyed all traces of surface life. Further robotic lander missions may bring us closer to an answer, but we may never know.

A Grand Experiment

Instead of mere observation, perhaps we should shift our focus to experiments that use Mars as our “petri dish.” The idea of terraforming (making planets Earth-like) has long been on the minds of science as well as science fiction writers, the aim being to industrially induce planets to support human colonies. There may come a time when humanity desires (or is required) to expand beyond the boundaries of its own home.

What would it take to make Mars into a planet capable of supporting human life? Humanity hasn’t even sent a manned mission to Mars, or any planet beyond our gravity well. What can we do to move human colonization of Mars forward? What I discuss here is to approach terraforming by stimulating the evolution of a new biosphere: planetary ecopoiesis.

Figure3
Fig.3. A candidate for terraforming? Growth of permafrost isolate WN1359 on TSBYS at 0 °C and Earth atmosphere and pressure (circles); simulated Mars atmosphere and Earth pressure (triangles); and simulated Mars atmosphere and pressure (squares). Source.

To bring life to a “dead” planet, we need a suitable seed and suitable terrain. What the lander missions have found is not encouraging to life. Although the life we humans know is unsuited to the Martian surface, I think we can address this challenge with the same tool that changed our own planet so dramatically billions of years ago: microbes. On Mars, an “inoculation” by a hardy collection of microbial species could begin the process of terraforming, improving the chances of growth for other types of life, much like a pioneer species in ecological succession. These microbial pioneers would face some hefty tasks: they must increase Mars’ atmospheric pressure and mean temperature, melt ice to create pools of liquid water, increase atmospheric greenhouse gases, and provide an atmospheric shield to UV radiation. And they must do this with what is available in situ on Mars. What would be the traits of this microbial pioneer? They would have to be highly cold tolerant, anaerobic, photoautotrophic, and UV-resistant, and able to use highly limited available substrates for growth. They would have to be able to grow on solid ice. We have examples of several candidates on Earth today, including cyanobacteria.

Chroococcidiopsis is a rock-dwelling cyanobacterium highly resistant to desiccation, hypersalinity, and temperature swings found in extremely arid environments. Carnobacterium spp. has recently been shown to grow in permafrost at very low atmospheric pressures and without oxygen. Methanogenic archaea combining carbon dioxide and hydrogen could be critical in promoting rapid greenhouse warming.  Many of these organisms function best as members of trophic and bioengineered consortia, so they should not be seeded in isolation.

A Five Year Mission?

Key advances in our understanding of Martian geochemistry, Earth-based bioprospecting, genomic sequencing, and synthetic biology make planetary ecopoesis on Mars thinkable at long last. In the next five years, we could make significant progress towards developing microbial pioneers for Mars. First, we must continue to gather data on the physicochemical conditions on Mars. Curiosity has enough power for at least 14 years of operation and has the most sophisticated suite of analytical tools ever sent to another planet. A companion mission is planned for 2020.

Second, we must further bioprospect our own planet for appropriate template organisms and identify candidates that may grow in the Martian environment. Sequencing and metagenomics are paving the way for cataloging the unique adaptations of extremophiles, and a search for microbial pioneers would add to a growing body of knowledge about microbial communities in extreme environments.

Third, we must develop the tools to genetically manipulate natural isolate organisms in order to modify them to fulfill the requirements of the parameters of the mission. Say what you will about the meaning of the term synthetic biology, but it’s clear that on the shoulders of micro, molecular, and systems biology, we are rapidly advancing our ability to modify microbes. Key to these advances has been the plummeting cost of DNA sequencing and, more recently, DNA synthesis. From parts, to modules, to systems, things are moving quickly. An important next step will be the construction of synthetic microbial consortia, key to this experiment. We can extend some of the natural abilities of our most extremophilic organisms by leveraging our new knowledge. In a sense, we can give evolution a head start. We can create rationally designed microbial consortia that are suited to living in the harsh Martian landscape, using Earth-based extremophiles as models and whose growth on a large scale could begin to tip Mars towards being supportive of less extremophilic life, such as our own. In addition to genetic changes for survival on Mars, other changes could enhance the ability of our consortium to adapt and evolve. Viruses could play a role in encouraging rearrangements of genetic information both within and between microbes, and enhanced conjugation could improve the ability of helpful mutations to propagate across the consortium. Additionally, we could send along equipment for DNA synthesis, allowing new adaptations discovered on Earth to be uploaded, synthesized, and transformed into the metagenome: genetic teleportation.

In drawing this to a close, I must leave many potential problems and pitfalls untouched, to say nothing of the ethics of seeding an entire planet with a synthetic microbial consortium. Who knows—maybe our own planet was seeded by a microbe hitching a ride on an asteroid! I can think of few experiments in the past or future as daring, and perhaps hubristic, as the creation of a new biosphere. This aside, I ask you: would it be so bad to have on hand a potential extension of our Earth-bound biological uniqueness? A handful of bugs could be our sojourners to the stars, microbial partners offering a new home and a peek back at our own origins. Maybe now isn’t the right time. We have so many problems on our own planet to take care of. But maybe, in a perhaps not unthinkable scenario, our terrestrial microbes would be our last message to the universe: amidst the collapse of our world, we load on a rocket our little bugs, bound for Mars or elsewhere to preserve for a while longer an extension of our existence. Alas, ad astra per aspera: a rough road leads to the stars. But maybe we can make it a little easier by relying on the unique talents of the microbes in our midst with whom we share this tiny dot.

Ben




Ben is a Biology graduate student at UCSD participating in the UCSD/SDSU Joint Doctoral Integrative Microbiology graduate course.


ResearchBlogging.org

Graham, J. (2004). The Biological Terraforming of Mars: Planetary Ecosynthesis as Ecological Succession on a Global Scale Astrobiology, 4 (2), 168-195 DOI: 10.1089/153110704323175133

Friedmann EI, & Ocampo-Friedmann R (1995). A primitive cyanobacterium as pioneer microorganism for terraforming Mars. Advances in space research : the official journal of the Committee on Space Research (COSPAR), 15 (3), 243-6 PMID: 11539232

Nicholson WL, Krivushin K, Gilichinsky D, & Schuerger AC (2013). Growth of Carnobacterium spp. from permafrost under low pressure, temperature, and anoxic atmosphere has implications for Earth microbes on Mars. Proceedings of the National Academy of Sciences of the United States of America, 110 (2), 666-71 PMID: 23267097

Comments

You might like my article here on my science20 blog about some of the things that could go wrong when terraforming Mars, and some of the differences between Earth and Mars which mean we need a different solution for Mars. Interested in any thoughts you have on it.

Not at all saying we shouldn't do it ever, just that, there is no hurry to start, and there are many complexities that could mean that it might easily go wrong just through some small mistake we make or something we haven't thoughth of.

It is perhaps unlikely to evolve its own terraforming cycles naturally, but instead would end up in some other state eventually, maybe back pretty much to the way it is now, but in a state that is harder to terraform a second time.

While perhaps it could be that we can engineer a long term solution for Mars that deals with its lack of continental drift, lack of magnetic field, more elliptical orbit, greater amount of axial tilt, lower gravity and mass, but whatever we end up with will be a unique solution for Mars and probably need a lot of foresight and planning to get it right.

http://www.science20.com/robert_inventor/trouble_terraforming_mars-126407

Elio replies:
I great enjoyed reading your article. It's erudite, imaginative, and gives a balanced view of this thorny subject. Thanks for sharing it.


I haven't read much on terraforming Mars, but I dont see how you will get very far towards a sustainable system without significant plate tectonics*, regardless of how hot you get it, how wet you get it, or how many designer microbes you shoot at it.

Essential elements that do not have gas phases in their biogeochemical cycles spend a great deal of their time sitting around in rocks. If we turned off our plate tectonics, these rocks would would cease to be uplifted, and erosion would decrease, yielding fewer and fewer nutrients for terrestrial habitats. Soils would become lifeless as their nutrients were all leached into ocean basins, and the terrestrial pedosphere would become relatively uninhabitable.

The oceans wouldn't fair much better. Once rivers stopped delivering phosphate, sulfate, transition metals, etc., the amount of biomass relying on these nutrients in the surface waters of the ocean would decrease since the only remaining source would be relatively inefficient diffusion or physical recirculation of the elements. Another good source of chemical nutrients for life is hydrothermal venting of ocean water at the mid-ocean ridges. This water has circulated through hot, reducing conditions and blasts all sorts of chemical goodness back into the oceans. Turn off plate tectonics and you lose those too. Combine these very rudimentary, sluggish, geochemical cycles with half the solar energy density we have here on Earth and I dont see how you could have a sustainable system much more exciting than an ocean with a few primary producers, maybe a microbial grazer if you're lucky. Thats not to say living on Mars is out of the questions, you could put up some solar panels, and maybe throw together some sort of hydroponic prochlorococcus farm (yum), but a full-scale ecosystem supporting trophic levels all the way up to humans doesn't seem possible. Our Gaia is great, but unfortunately for Mars I think her heartbeats are earthquakes.

*there was a recent paper on possible mars plate tectonics, which goes against a long history of people saying there arent any. regardless, the claim is for very low levels, so probably doesn't affect this argument much.

This post made me think of Lynn Margulis. I am not sure, but I guess she would have smiled, in recognition, at the audacity of the ideas proposed. In “Welcome to the Machine” she (and Dorion Sagan) wrote : ”Imagine the successful colonisation of Mars, which will require not only fueled rockets with heat-resistant reentry tiles, sealed metallic containers, and human astronauts but also many kinds of food plants, protists, funghi, bacteria, and other animals as makers, keepers and recyclers of the enivronment. This mental exercise demonstrates the future propsects for current technology – to perpetuate all kinds of biospheric life, not just urbanized machine-humans and our consumables.” That is a fine, and not all too obvious point: we are hybrid organisms, dependent in innumerable ways upon innumerable other hybrid organisms. It is sometimes said that it takes a village to raise a child. It is also true that it will take a biosphere to raise a space colony of humans.

But is there time? What in hindsight may seem like an explosion could in real time be a process so slow that it would make the word ”glacial” on par with a bolt of ligthning. Remember the ”boring billion”! And also, Mars is not quite a petri dish, a miniature and reduced world which we can control every aspect of. Inoculation is a tempting but a bit misleading word for this Grand Experiment. Maybe infection would be less misleading, although it is not quite clear what, if anything, is infected.

I can imagine some reactions to this project. Should we introduce earth organisms (synthetic or not) to Mars before we have investigated thoroughly the present state of the planet and tried to reconstruct its history? The advocates of bold ideas often see only benefits and few costs, while the opponents see only costs and few benefits. Reality is often much more messy and confused than either of these opposite positions admit. We must not let strong intuitions and feelings cloud our judgements. So would it be bad then, “to have on hand a potential extension of our Earth-bound biological uniqueness?” I would say “no, a Martian biosphere sounds truly marvellous, but please leave the confused great ape behind. It will only mess it all up.”

Thanks Ben for a wonderful and visionary post.

Thanks to all the for the comments thus far.

Indeed the idea of terraforming on Mars is not novel. I recently had the pleasure to attend the kickoff symposium for UCSD's new Arthur C. Clarke Center for Human Imagination (http://imagination.ucsd.edu/starship/). It was an inspiring event, attended by some great scientists and science-fiction authors (and many who play both roles). The role of biotechnology in humanity's exploration (and expansion) into our solar system and beyond was emphasized, especially by the likes of Paul Davies and Freeman Dyson. I had the opportunity to speak briefly with Freeman Dyson and he expressed his excitement about the future of biology in space, an excitement I obviously share.

As for life on Mars, I remain excitedly agnostic. I'm certainly open to the possibility that life did or does exist on Mars, and even to the myriad of panspermia hypotheses. And I believe we have ways of determining the validity of these hypotheses, provided the sufficient motivation, technology, and funding. The mounds of data streaming in from Curiosity are extraordinary, and the Kepler mission, though it seems to have now reached the end of its data collection, provides the opportunity for a new look at the Drake equation. Certainly there is a bright future for astrobiology.

I was unaware of the 2010 iGEM team's project on yeast but look forward to perusing their work in the near future.

Terraforming of Mars using synthetic microbes (iGEM Valencia 2010):
http://2010.igem.org/Team:Valencia

Oh, how I loved this post, and I write that as a committed and long standing Propeller Beanie kind of guy. Bravo!

Science changes quickly, and our fiction with it... Why, in 1985, James Lovelock (he of the "Gaia Hypothesis") co-wrote a book about using CFCs to terraform Mars: http://www.goodreads.com/book/show/2179542.The_Greening_of_Mars. I have to say that it would be a wonderful thing to bring life to a lifeless world, given our history as a species. If terraforming is something we do, microbes (as always) will lead the way.

But I continue to think that life already does exist on Mars. After all, every environment with liquid water that I know of (Elio and others, are there any exceptions?) has at least microbial life. Why would Mars be different? In fact, I think that life evolved first on Mars, and was transported here via meteorite. This is something other scientists have considered long ago, of course: http://www.scientificamerican.com/article.cfm?id=could-life-have-evolved-on

Let's have a toast to Martyn Fogg, friends.

http://en.wikipedia.org/wiki/Martyn_J._Fogg

And may our microbial friends lead the way to making the universe habitable by humans...

I have few doubts that the bugs would do their job on mars, even more so as a consortium. and given the problems we have on our home planet we could easily allow them a couple of centuries before we check for the result. So i will never know, too bad.

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