In­ter­plan­e­tary Bio­min­ing

by Elio

We are not short of ev­i­dence that mi­crobes can sur­vive in space for ex­ten­sive times. A fa­vored way to find out is to carry out of­ten multi­na­tional stud­ies by plac­ing sam­ple or­gan­isms on the sur­face of the In­ter­na­tional Space Sta­tion. Such ex­per­i­ments have sug­gested that small rock ejecta just a few cen­time­ters in di­am­e­ter could pro­tect ra­di­a­tion-re­sis­tant bac­te­ria or bac­te­r­ial spores against the in­tense ra­di­a­tion in space. Porous rocks may pro­vide nooks and cran­nies for mi­crobes to hide and be shielded from the vi­cis­si­tudes of space travel. How­ever, mi­cron-sized grains may not af­ford suf­fi­cient pro­tec­tion.

Fig­ure 1. a. Top-down im­age of one Ex­per­i­men­tal Con­tainer (EC) con­tain­ing one EU (Ex­per­i­men­tal Unit) show­ing both cul­ture cham­bers in­flated with medium. b. Si­deways cross sec­tion through cul­ture cham­ber show­ing lo­ca­tion of basalt slide at the back of the cham­ber and prin­ci­ple of medium in­jec­tion and in­ver­sion of mem­brane (shown here in yel­low; left side closed, right side in­flated with medium). c. Im­age of basalt slide in a Petri dish sub­merged in 50% R2A in a ground ex­per­i­ment. d. Eu­ro­pean Space Agency (ESA) as­tro­naut Luca Parmi­ta­no in­serts an EC into a KUBIK in­cu­ba­tor on board the In­ter­na­tional Space Sta­tion (im­age credit to ESA) Source. Fron­tispiece: The bac­te­r­ial ex­po­sure experi­ment took place from 2015 to 2018 us­ing the Ex­posed Fa­cil­ity lo­cated on the ex­te­rior of Kibo, the Japan­ese Ex­perimental Mod­ule of the In­ter­na­tional Space Sta­tion. Credit: JAXA/NASA. Source

In later ex­per­i­ments, cells of the ra­di­a­tion tol­er­ant bac­terium, Deinococ­cus ge­ot­her­malis sur­vived for about two years out­side the sta­tion, both as dried plank­tonic cells and, even bet­ter, as biofilms. They lost vi­a­bil­ity but re­tained such key prop­er­ties as mem­brane in­tegrity, ATP con­tent, and es­terase ac­tiv­ity. An­other set of ex­per­i­ments, us­ing a dif­fer­ent Deinococ­cus species, D. ra­dio­du­rans also placed out­side the In­ter­na­tional Space Sta­tion, re­vealed that cells in pel­lets 500 mi­crons thick stayed alive af­ter 3 years in space. Once cul­ti­vated, they re­paired their dam­aged DNA via the prod­ucts of uvrA gene (nu­cleotide ex­ci­sion re­pair) and uvdE gene (UV-dam­age ex­ci­sion re­pair). For yet more de­tailed data with yet an­other Deinococ­cus, see here and for a movie of re­cent ac­tiv­i­ties of this sort, click here. But what about grav­ity? Pre­vi­ous ex­per­i­ments (plus some even ear­lier ones by our friend Con­rad Woldringh) showed that re­duced grav­ity had lit­tle ef­fect on the growth of E. coli. So, di­min­ished grav­ity may not mat­ter much for bac­te­ria in space.

All this may well be rel­e­vant to long-term ex­trater­res­trial col­o­niza­tion. Why? Among many other rea­sons, be­cause bac­te­ria can be used for min­ing needed min­er­als. That's true here on Earth and may be true else­where. Mod­ern tech­nol­ogy re­lies cru­cially on the use of rare earth el­e­ments (REEs), such as yt­trium, scan­dium, and the lan­thanides. They are used for mak­ing lasers, al­loys, mag­nets used in cell phones, com­puter screens, and elec­tric cars. But these min­er­als are not only hard to mine by con­ven­tional meth­ods, but they need to be con­stantly re­placed. How to en­sure a good sup­ply in space? En­ter some species of bac­te­ria that are able to ex­tract min­er­als, a process called bio­min­ing. In fact, on Earth, some 10–20 % of all cop­per and about 5% of all gold is bio­mined (and that's prob­a­bly just a start). Now for space. Pro­longed stay on an­other planet or in space it­self would re­quire a way to re­plen­ish these es­sen­tial com­po­nents. Easy! Send up ap­pro­pri­ate bac­te­r­ial min­ers and let them do the work.

Fig­ure 2. Ef­fects of mi­croor­gan­isms on rare earth ele­ment leach­ing. a. Rel­a­tive (%) dif­fer­ence in mean con­centration of leached REEs in the bulk fluid be­tween bi­o­log­i­cal ex­per­i­ments and non-bi­o­log­i­cal con­trols show­ing mi­cro­grav­ity, sim­u­lated Mars and Earth grav­i­ties on the In­ter­na­tional Space Sta­tion for the three mi­croor­gan­isms. b. Ground (true Earth grav­ity con­trol) ex­per­i­ment for the three mi­croor­gan­isms. Source

The ques­tion then arises, do mi­cro­bio­min­ers work in re­duced grav­ity? Does bio­min­ing work un­der such con­di­tions? An ex­ten­sive piece of work by Charles Cock­ell and some 30 col­lab­o­ra­tors from a half dozen coun­tries set out to find out. They also used the In­ter­na­tional Space Sta­tion as their lab, send­ing up slices of basaltic rock (sim­i­lar to what is found on the moon and on Mars) and three dif­fer­ent bac­te­r­ial species, Sphin­gomonas des­ic­ca­bilis, Bacil­lus sub­tilis, and Cupri­avidus met­al­lidu­rans. Us­ing a set-up called the BioRock re­ac­tor, they in­cu­bated sam­ples un­der var­i­ous grav­ity con­di­tions, from none to those sim­u­lat­ing that on Mars and Earth (this can be done by us­ing a cen­trifuge on board). Af­ter 21 days in­cu­ba­tion, the sam­ples were sent back to Earth for analy­sis. Of the three bac­te­ria, only S. des­ic­ca­bilis showed a sig­nif­i­cant amount of min­eral leach­ing, about a fac­tor of two in­crease, thus re­veal­ing that some bac­te­ria are bet­ter min­ers than oth­ers. In­ter­est­ingly, with this or­gan­ism there were no de­tectable dif­fer­ences at the var­i­ous grav­ity con­di­tions. Why is this unan­tic­i­pated? The se­nior au­thor of the pa­per, Charles Cock­ell, said in an in­ter­view: "That sur­prised us, be­cause with­out grav­ity, there is no con­vec­tion that usu­ally car­ries away waste from the bac­te­ria and re­plen­ishes nu­tri­ents around the cells." And then, "One might then hy­poth­e­size that mi­cro­grav­ity would stop the mi­crobes from do­ing bio­min­ing or it would stress them to the point where they weren't do­ing bio­min­ing," he said. "In fact, we saw no ef­fect at all."

Space mi­cro­bi­ol­ogy? Surely this is a branch of our sci­ence that is here to stay. See a pre­vi­ous post in these pages. Who knows where this will end up?  Will train­ing in space tech­nol­ogy be in­cluded in mi­cro­bi­ol­ogy grad­u­ate pro­grams? Soon maybe? I would not bet against it.

 

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