Mi­croor­gan­isms pro­duce ele­mental car­bon

Re­search­ers identify a new kind of pure car­bon pro­duc­tion by mi­croor­gan­isms

Carbon occurs on the Earth in a variety of structures and forms. Elemental Carbon is usually formed under conditions of high pressure and temperature. Researchers have now, for the first time, identified microorganisms that produce elemental carbon. The team, which includes Dr. Gunter Wegener of MARUM – Center for Marine Environmental Sciences of the University of Bremen and the Max Planck Institute for Marine Microbiology in Bremen, has now published its results in the Journal Science Advances

Sampling from the hot sed­i­ments of the hy­dro­thermal seep at the Guay­mas Basin off the coast of Mex­ico. The meth­ane-ox­id­iz­ing con­sor­tia live un­der­neath the whit­ish-yel­low and or­ange-colored bac­terial mats.
Sampling from the hot sed­i­ments of the hy­dro­thermal seep at the Guay­mas Basin off the coast of Mex­ico. The meth­ane-ox­id­iz­ing con­sor­tia live un­der­neath the whit­ish-yel­low and or­ange-colored bac­terial mats [An­dreas Teske, Univ. of North Car­o­lina (USA)]

Life on the Earth is based on car­bon. Through the course of evol­u­tion, liv­ing or­gan­isms have learned to form and pro­cess large num­bers of dif­fer­ent car­bon com­pounds. Car­bon is the corner­stone of most bio­lo­gic­ally pro­duced or­ganic com­pounds such as pro­teins, car­bo­hydrates, fats and DNA. All of these com­pounds con­tain, in ad­di­tion to car­bon, many other ele­ments, in­clud­ing hy­dro­gen, ni­tro­gen and oxy­gen.

The scientists cultivated the microbial consortia in the laboratory. The black masses, for the most part, are amorphous carbon
The scientists cultivated the microbial consortia in the laboratory. The black masses, for the most part, are amorphous carbon [MARUM – Center for Marine Environmental Sciences, University of Bremen; G. Wegener]

Ele­mental car­bon is formed from or­ganic car­bon com­pounds in the Earth without bio­lo­gical in­flu­ence when high tem­per­at­ure and pres­sure con­di­tions ex­pel all of the other ele­ments such as hy­dro­gen and ni­tro­gen. For ex­ample, wood deep un­der­ground first be­comes coal un­der high tem­per­at­ures, then with in­creas­ing pres­sure and tem­per­at­ure, forms with very high car­bon con­tent like an­thra­cite and graph­ite are formed. These are crys­tal­line forms of car­bon. When wood, gas or oil is burned, soot is formed that con­sists mostly of an amorph­ous form of car­bon. It was pre­vi­ously not known that liv­ing or­gan­isms them­selves can also pro­duce ele­mental car­bon.

For more than 15 years, the Bre­men sci­ent­ist Dr. Gunter We­gener has been cul­tiv­at­ing mi­croor­gan­isms that con­sume meth­ane without oxy­gen to pro­duce the en­ergy they need. These are ar­chaea that live in sym­bi­osis with bac­terial part­ners. Not much en­ergy can be ob­tained from this pro­cess for either part­ner, so the con­sor­tia grow with doub­ling times of sev­eral months, which is a very long time for mi­croor­gan­isms. The re­search­ers no­ticed some time ago that the mi­cro­bial con­sor­tia were un­usu­ally dark, al­most black. At an early stage, a por­tion of this black mass had already been de­scribed as metal sulf­ides. These are formed from iron that is ad­ded to the cul­ture me­dium and the sulf­ide pro­duced by the part­ner bac­teria.

We­gen­er’s col­leagues, Dr. Kylie Al­len and Prof. Robert White from Vir­ginia Tech (USA), are al­ways search­ing for new bio­molecules and their func­tions. As a part of their ef­forts, they ex­trac­ted meth­ane-ox­id­iz­ing cul­tures from the spe­ci­mens in Gunter We­gen­er’s labor­at­ory us­ing or­ganic solvents. A residue of black ma­ter­ial was left be­hind that could not be dis­solved by strong acids or bases. “At first we had no idea what this black mass could be,” ex­plains Robert White. “Then we used other meth­ods to ana­lyze the ma­ter­ial as a solid phase and found that it was al­most pure car­bon. This ex­is­ted in a highly dis­ordered form known as amorph­ous car­bon.” Where did this ele­mental car­bon come from? The team ruled out the pos­sib­il­ity of a pure chem­ical ori­gin. They then fed the cul­ture with iso­top­ic­ally labeled car­bon, which can be tracked in the break­down pro­cess, and ana­lyzed the car­bon formed. “We were thus able to prove that the meth­ane-ox­id­iz­ing ar­chaea were in­deed re­spons­ible for the form­a­tion of ele­mental car­bon,” says Gunter We­gener.

The consortia under the microscope.
The consortia under the microscope [Gunter Wegener/Benedikt Geier, MPI Bremen]

Next, the re­search­ers in­vest­ig­ated the meth­ane-form­ing, or meth­ano­genic ar­chaea, which are closely re­lated to the meth­ane ox­id­izers. “Al­though not to the same de­gree, many of these groups also pro­duced ele­mental car­bon,” says Robert White.

The study, however, is now gen­er­at­ing more ques­tions than an­swers. For ex­ample, how is this car­bon formed? The form­a­tion of ele­mental car­bon nor­mally re­quires high pres­sures and tem­per­at­ures. Both were ab­sent in the cul­tures. “This kind of form­a­tion of ele­mental car­bon by or­gan­isms is com­pletely new to sci­ence. There must be re­ac­tions go­ing on in ar­chaea that were pre­vi­ously com­pletely un­known,” ex­plains Kylie Al­len, the prin­cipal au­thor of the study. “We still do not know at all what bio­chem­ical re­ac­tions and en­zymes are at work here.”

The ques­tion of ‘why’ has also not yet been ex­plained. “Ele­mental car­bon is a good elec­trical con­ductor. Car­bon may be the key to the sym­bi­osis between the ar­chaea and their part­ners,” spec­u­lates Gunter We­gener. Elec­trical charges could be trans­por­ted op­tim­ally via car­bon-based com­pounds. It is also com­pletely un­known how much ele­mental car­bon is formed by mi­croor­gan­isms in nature. “Be­cause the car­bon is de­pos­ited in sed­i­ments and re­mains there over very long time frames, our res­ults could also im­ply a here­to­fore un­known nat­ural car­bon sink.” The team will now be­gin to tackle the un­answered ques­tions, in part within the frame­work of the Cluster of Ex­cel­lence “The Ocean Floor – Earth’s Un­charted In­ter­face”, which is housed at MARUM.

Original publication

Kylie D. Al­len, Gunter We­gener, D. Mat­thew Sub­lett Jr, Robert J. Bod­nar, Xu Feng, Jenny Wendt, Robert H. White: Bio­genic form­a­tion of amorph­ous car­bon by an­aer­obic meth­an­o­trophs and se­lect meth­ano­gens. Sci­ence Ad­vances 2021. DOI: 10.1126/sciadv.abg9739.

About MARUM

MARUM pro­duces fun­da­mental sci­entific know­ledge about the role of the ocean and the sea­floor in the total Earth sys­tem. The dy­nam­ics of the oceans and the seabed sig­ni­fic­antly im­pact the en­tire Earth sys­tem through the in­ter­ac­tion of geo­lo­gical, phys­ical, bio­lo­gical and chem­ical pro­cesses. These in­flu­ence both the cli­mate and the global car­bon cycle, res­ult­ing in the cre­ation of unique bio­lo­gical sys­tems. MARUM is com­mit­ted to fun­da­mental and un­biased re­search in the in­terests of so­ci­ety, the mar­ine en­vir­on­ment, and in ac­cord­ance with the sus­tain­ab­il­ity goals of the United Na­tions. It pub­lishes its qual­ity-as­sured sci­entific data to make it pub­licly avail­able. MARUM in­forms the pub­lic about new dis­cov­er­ies in the mar­ine en­vir­on­ment and provides prac­tical know­ledge through its dia­logue with so­ci­ety. MARUM co­oper­a­tion with com­pan­ies and in­dus­trial part­ners is car­ried out in ac­cord­ance with its goal of pro­tect­ing the mar­ine en­vir­on­ment.

Source

MARUM, press release, 2021-10-27.

Supplier

MARUM – Center for Marine Environmental Sciences of the University of Bremen
Max Planck Institute for Marine Microbiology
Science Advances Journal

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