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Ancient life liked it hot, acidic, study finds

April 4, 2011
Courtesy of the Georgia Institute of Technology
and World Science staff

A re­con­struc­tion of molecules used by very prim­i­tive or­gan­isms shows that the crea­tures were best a­dapted to hot, a­cid­ic con­di­tions, sci­en­tists say.

The re­searchers stud­ied a group of an­cient en­zymes, molecules used by life forms to speed up or en­a­ble needed chem­i­cal re­ac­tions. Since the o­rig­i­nal en­zymes are lost, the sci­en­tists re­con­struct­ed what they be­lieve are close repli­cas based on mod­ern-day de­scen­dants.

Known as thiore­doxin en­zymes, the an­cient com­pounds were found to be chem­i­cally sta­ble and to show in­creased ac­tiv­i­ty under hot, acid­ic con­di­tions com­pared to those in which they oper­ate today.

They "op­er­ated in a hot, a­cid­ic en­vi­ron­ment... which sup­ports the view that the en­vi­ron­ment pro­gres­sive­ly cooled and be­came more al­ka­line [less a­cid­ic] be­tween four bil­lion and 500 mil­lion years a­go," sa­id Er­ic Gauch­er, a bi­ol­o­gist at the Geor­gia In­sti­tute of Tech­nol­o­gy. The stud­y by Gauch­er and oth­ers was pub­lished A­pril 3 in the ad­vance on­line e­di­tion of the jour­nal Na­ture Struc­tur­al & Mo­lec­u­lar Bi­ol­o­gy.

Us­ing a tech­nique called an­ces­tral se­quence re­con­struc­tion, Gaucher and Geor­gia Tech bi­ol­o­gy grad­u­ate stu­dent Zi-Ming Zhao re­con­struct­ed sev­en an­cient thiore­doxin en­zymes from the three bas­ic types of life forms ex­ist­ing to­day, called ar­chaea, bac­te­ria and eu­kary­otes. (This third group in­cludes vir­tu­al­ly eve­ry kind of organ­ism large enough to see.)

To res­ur­rect the en­zymes, found in near­ly all known mod­ern or­gan­isms and es­sen­tial for mam­mals, the re­searchers first built a fam­i­ly tree of the more than 200 ge­net­ic se­quences cod­ing for var­i­ous sub­types of thiore­doxin en­zymes. Based on this, they re­con­struct­ed the se­quences of the an­ces­tral thiore­doxin en­zymes. Fi­nal­ly, they en­gi­neered bac­te­ri­a to mint new cop­ies of them.

The re­con­struct­ed en­zymes, from the Pre­cam­bri­an pe­ri­od—which ended a­bout 542 mil­lion years a­go—were an­a­lyzed for their re­sponses and ev­o­lu­tion un­der var­i­ous con­di­tions. The three old­est thiore­doxin en­zymes, thought to have in­hab­it­ed Earth 4.2 to 3.5 bil­lion years a­go, were found to be a­ble to op­er­ate in more a­cid­ic con­di­tions than the mod­ern coun­ter­parts, and to be sta­ble at tem­per­a­tures up to 32 de­grees Cel­si­us higher.

"Our re­sults con­firm that life has the remarka­ble a­bil­i­ty to a­dapt to a wide range of his­tor­i­cal en­vi­ron­mental con­di­tions; and by ex­ten­sion, life will un­doubt­ed­ly a­dapt to fu­ture en­vi­ron­mental changes, al­be­it at some cost to man­y species," sa­id Gaucher.

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A reconstruction of ancient molecules used by primitive organisms shows that the creatures were best adapted to hot, acidic conditions, scientists say. The researchers studied a group of ancient enzymes, molecules used by life forms to speed up or enable needed chemical reactions. Since the original enzymes are lost, the scientists reconstructed what they believe are close replicas based on modern-day descendants. Known as thioredoxin enzymes, these ancient compounds were chemically stable at temperatures up to 32 degrees Celsius (58 degrees Fahrenheit), higher than modern versions, researchers say. The enzymes, which were several billion years old, also showed increased activity in more acidic conditions. They "operated in a hot, acidic environment during early life, which supports the view that the environment progressively cooled and became more alkaline [less acidic] between four billion and 500 million years ago," said Eric Gaucher, a biologist at the Georgia Institute of Technology. The study, published April 3 in the advance online edition of the journal Nature Structural & Molecular Biology, was conducted by researchers from Georgia Tech, Columbia University and the Universidad de Granada in Spain. Using a technique called ancestral sequence reconstruction, Gaucher and Georgia Tech biology graduate student Zi-Ming Zhao reconstructed seven ancient thioredoxin enzymes from the three basic types of life forms existing today, called archaea, bacteria and eukaryotes. (This third group includes virtually every kind of animal and plant big enough to see.) To resurrect the enzymes, found in nearly all known modern organisms and essential for mammals, the researchers first built a family tree of the more than 200 genetic sequences coding for various subtypes of thioredoxin enzymes. Based on this, they reconstructed the sequences of the ancestral thioredoxin enzymes. Finally, they engineered bacteria to mint new copies of the presumed ancient enzymes. The reconstructed enzymes, from the Precambrian period—which ended about 542 million years ago—were analyzed for their responses and evolution under various conditions. The three oldest thioredoxin enzymes, thought to have inhabited Earth 4.2 to 3.5 billion years ago, were found to be able to operate in more acidic conditions than the modern counterparts, and to be stable at temperatures up to 32 degrees Celsius higher. "Our results confirm that life has the remarkable ability to adapt to a wide range of historical environmental conditions; and by extension, life will undoubtedly adapt to future environmental changes, albeit at some cost to many species," said Gaucher.