Stay­ing Safe in Space

by Jen­nifer Tsang

The thought of bring­ing alien life forms to Earth or of cre­at­ing dan­ger­ous mu­tant mi­croor­gan­isms dur­ing space travel might seem straight out of a sci­ence fic­tion movie. But are these con­cerns real­ly that far fetched? As our in­ter­est in as­tro­bi­ol­ogy (the study of life in the uni­verse) grows, the con­cern for an un­in­ten­tio­nal ex­change of life be­tween Earth and other ce­les­tial bod­ies be­comes in­creas­ingly re­al­is­tic. What hap­pens if we in­tro­duce Earth's mi­crobes to other plan­ets? What if we bring alien life back to Earth? Ques­tions re­gard­ing such in­ter­plan­e­tary con­t­a­m­i­na­tion pose not on­ly prac­ti­cal is­sues but eth­i­cal ones as well.

Fig­ure 1. Artist's ren­der­ing of Eu­ropa Lan­der. Source

Mi­crobes cover every niche of our planet. The Dutch mi­cro­biologist Lourens Baas Beck­ing once said, "every­thing is every­where, but the en­vi­ron­ment se­lects." Mi­crobes ex­ist as in­vis­i­ble pas­sen­gers in­hab­it­ing all plants and ani­mals, in­clud­ing hu­mans. Mi­cro­bial life ex­ists on Earth in habi­tats rang­ing from frigid wa­ters to hy­drother­mal vents, from low to high pH, and even with or with­out oxy­gen. Clearly, mi­croor­gan­isms sur­vive and even flour­ish in near­ly any con­di­tion imag­in­able. Be­cause of this re­sil­i­ence, as­tro­bi­ol­o­gists are con­cerned that mi­cro­bial life could sur­vive the stresses of space flight and pos­si­bly con­t­a­m­i­nate other plan­ets upon ar­rival. We don't want to travel to a new planet only to "dis­cover" life that we mis­tak­enly brought from Earth, nor do we want to dis­rupt life, or its evo­lution, on other plan­ets.

Safe­guard­ing against in­ter­plan­e­tary con­t­a­m­i­na­tion

As dis­cussed at the Amer­i­can As­so­ci­a­tion for the Ad­vance­ment of Sci­ence (AAAS) meet­ing this Fe­bru­ary, NASA plans to send a space­craft to Jupiter's moon Eu­ropa in 2025 (Fig­ure 1). The mis­sion aims to search for undis­cov­ered life on Eu­ropa. As wa­ter is nec­es­sary to sus­tain life, the large salt­water ocean be­neath the icy sur­face of Eu­ropa makes it a hope­ful can­di­date for ex­trater­res­trial life (Fig­ure 2). To min­i­mize plan­e­tary con­t­a­m­i­na­tion, the Eu­ropa lan­der will be built in a clean fa­ci­li­ty. Though a clean fa­cil­ity is "clean," it is not ster­ile, and some species of bac­te­ria have been found. Any mi­crobes re­main­ing on the lan­der will be baked out at tem­per­a­tures greater than 125°C for hours to days. The lan­der will be en­cased in an alu­minum bio­bar­rier keep­ing con­ta­mi­nants at bay dur­ing its long jour­ney to Eu­ropa. As Kevin Hand, an as­tro­bi­ol­o­gist from NASA Jet Propul­sion Lab­o­ra­tory, said dur­ing the AAAS meet­ing, "we want to keep Eu­ropa for Eu­ropans."

Fig­ure 2. Cross-sec­tion of Eu­ropa. Source

In­tro­duc­ing mi­cro­bial life to other plan­ets is not the only risk. Mi­crobes could be brought back to Earth know­ingly for study or in­ad­ver­tently through con­t­a­m­i­nated equip­ment. Sam­ples must be han­dled with care to min­i­mize any un­known risk to na­tive life on Earth. The Eu­ropa lan­der mis­sion is not sched­uled to bring sam­ples back to Earth, but sam­ple-re­turn is pos­si­ble for fu­ture mis­sions. Such mis­sions may bring back any­thing from liq­uids, soil and rocks, or small amount of min­er­als that will be stud­ied us­ing in­stru­ments that could not be brought into space. To pre­vent con­t­a­m­i­na­tion of Earth, col­lected sam­ples are stud­ied us­ing the most strin­gent bio­con­tain­ment fa­cil­i­ties (BSL‑4).

You may be won­der­ing whether in­ter­plan­e­tary con­t­a­m­i­na­tion ac­tu­ally mat­ters. Af­ter all, me­teo­rites and mi­crom­e­te­orites have bom­barded plan­ets in our so­lar sys­tem for four bil­lion years. Ma­ny sci­en­tists be­lieve the trans­fer of mi­crobes be­tween plan­ets has al­ready hap­pened. Oth­ers think that we are un­nec­es­sar­ily cau­tious and should spend pre­cious re­search dol­lars else­where. How­ev­er, can we risk a War of the Worlds-style alien in­va­sion of Earth? The dilemma re­mains: we don't know if in­ter­plan­e­tary con­t­a­m­i­na­tion is a real risk, but it seems rea­son­able to take pre­cau­tions in case these risks ex­ist.
 

Mi­cro­bial evo­lu­tion in space

Com­ing from a planet where mi­crobes rule every niche (in­clud­ing the hu­man body), it is in­evitable that as­tro­nauts bring mi­crobes from Earth onto space mis­sions. What is un­clear though is how mi­crobial life adapts and evolves to new con­di­tions. Things get even more com­pli­cated when you throw in how the hu­man mi­cro­biome and im­mune sys­tem changes in space. With these cir­cum­stan­ces, it is likely that host-mi­crobe in­ter­ac­tions will change upon leav­ing Earth.

There is strong ev­i­dence that the im­mune sys­tem is com­pro­mised dur­ing space travel. More­over, the hu­man mi­cro­biome be­comes less di­verse af­ter time in space: sam­ples from as­tro­nauts on the Salyut and Mir or­bit­ing plat­forms showed a sig­nif­i­cant re­duc­tion in hu­man mi­cro­biota di­ver­sity even af­ter just two weeks! Op­por­tunis­tic pathogens, which rely on re­duced im­mune func­tion or al­tered host mi­cro­biota to cause dis­ease, have the po­ten­tial to wreak havoc in space. Changes in our mi­cro­biome and im­mune sys­tem go hand in hand; our mi­cro­biome, just like our im­mune sys­tem, pro­tects against pathogens.

Fig­ure 3. Scott and Mark Kelly. Source

To gain in­sight into changes in the hu­man body dur­ing space flight, NASA be­gan a study of twins. Iden­ti­cal ve­te­ran as­tro­nauts twins, Scott and Mark Kelly, pro­vide an ideal com­par­i­son for the ef­fects of long-term space mis­sions on the hu­man body (Fig­ure 3). Start­ing in March 2015 Scott spent a year on the In­ter­na­tional Space Sta­tion (ISS) while his brother Mark served as an earth­bound con­trol sub­ject. By ob­tain­ing base­line mea­sure­ments of each, sci­en­tists could pin­point bi­o­log­i­cal dif­fer­ences af­ter a year of zero grav­ity and freeze-dried food. Fred Turek, a sci­en­tist from North­west­ern Uni­ver­sity char­ac­ter­ized the mi­croor­gan­isms from the twins and found dif­fer­ences in vi­ral, bac­te­r­ial, and fun­gal mi­cro­biome be­tween them. In Scott's mi­cro­biome, the ra­tio of Fir­mi­cutes and Bac­teroidetes, two dom­i­nant bac­te­r­ial groups in the gut, was al­tered upon space travel. Upon re­turn to Earth, the ra­tio of the two bac­te­r­ial species re­turned to pre-flight lev­els.

To make mat­ters worse for as­tro­nauts, bac­te­ria be­come more vir­u­lent and more re­sis­tant to an­ti­biotics in space. These changes are due to both in­creased ra­di­a­tion lev­els and the mi­cro­grav­ity en­vi­ron­ment in space: en­vi­ron­men­tal stres­sors that se­lect for re­sis­tance. Ra­di­a­tion breaks DNA strands or dam­ages DNA bases, pre­vent­ing it from be­ing read or repli­cated cor­rectly, lead­ing to mu­ta­tions. Af­ter 40 days on Mir, mu­ta­tion rates in yeast were two to three times higher than in ground con­trols. In a study of Bacil­lus sub­tilis spores, mu­ta­tions lead­ing to ri­fampicin re­sis­tance were in­duced by 2–4 or­ders of mag­ni­tude greater than Earth con­trols. A high mu­ta­tion rate al­lows bac­te­ria to more quickly adapt to chang­ing con­di­tions.

Un­der mi­cro­grav­ity con­di­tions, growth rate, motil­ity, and metabo­lite pro­duc­tion are also al­tered. This is likely due to re­duced ex­tra­cel­lu­lar mass-trans­port, with move­ment of mol­e­cules lim­ited in low grav­ity. A team of sci­en­tists from the Uni­ver­sity of Col­orado, the Hud­son Al­pha In­sti­tute, and the Uni­ver­sity of Al­abama, de­ter­mined how mi­cro­grav­ity af­fects gene ex­pres­sion of bac­te­ria by com­par­ing the same E. coli strain grown on Earth and on the ISS. They found that cells grown on the ISS had in­creased ex­pres­sion of genes as­so­ci­ated with star­va­tion, me­tab­o­lism, and use of al­ternative en­ergy sources.

Many times, as­tro­nauts are un­able to re­turn to Earth un­til their space mis­sions end. Be­cause crewmem­bers may be­come sick or in­jured in space, it is es­sen­tial that we un­der­stand the fate of mi­cro­bial life in space. Be­tween 1989 and 1998, there were 26 doc­u­mented in­fec­tions in space for US as­tro­nauts. Stud­ies in the 1980s showed that an­tibi­otics need to be 2–4 times more con­cen­tra­ted to kill E. coli and S. au­reus in space than on the ground. In­creased an­tibi­otic re­sis­tance in bac­teria may mean that typ­i­cal treat­ments are not ef­fec­tive, and in­creased vir­u­lence may mean that the symp­toms of an in­fec­tion are more se­vere. As we ex­pand our reach into the so­lar sys­tem, we need to take pre­cau­tions to make sure we do so safely for our­selves, the Earth, and other ce­les­tial bod­ies.

 

Jen­nifer Tsang is a post­doc­toral re­search fel­low study­ing an­timi­cro­bial re­sis­tance in the lab of James Kirby at Beth Is­rael Dea­coness Med­ical Cen­ter. She blogs at The Mi­cro­bial Menagerie.