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.

Fig. 1. Source: Jack­son Moore

A Bios­phere is Born

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

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.

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.

Ref­er­ences

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), 243−246. 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. Proc Natl Acad Sci USA, 110 (2), 666−671. PMID 23267097

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