B.Sc. / M.Sc. Opportunities

The formation of pyrite (FeS2) from H2S and FeS (Wächtershäuser reaction) might have been a relevant metabolism during the origin of life. This metabolism becomes more favorable at pH values lower than 6.5 and it can be modulated by microbial activity. Río Tinto is an extreme environment characterized by it’s low pH and high concentration of heavy metals, mainly Fe. It also shows a high concentration of anions, like sulfate. Moreover, sulfate reducing activity has been previously reported in the sediments of the river. Thus, Río Tinto has all the conditions necessary for the H2S pathway of pyrite synthesis to take place. In Río Tinto, the sulfate reducing bacteria (SRB) can produce H2S which can then react with Fe leading to the formation of FeS which can then react again with the H2S finally producing pyrite. 

The aim of this project is to study sulfate reduction and pyrite formation by sulfate-reducing bacteria (SRB) in the anoxic and acidic sediments found in the origin of Río Tinto. For this project we will study mineralogical evidences of sulfate reduction as well as the microbial communities capable of conducting this metabolism both by DNA sequencing and enrichment.  

Research Plan:

1. During the Río Tinto field campaign (in September), Microbial Trapping Devices (MTDs) containing sulfate-bearing minerals (gypsum, anhydrite and/or barite) will be placed in the sediments at the origin of the river. The student will also take samples and check in situ the physico-chemical properties to characterize the sediments.
2. After one month of incubation, these MTDs will be retrieved (in mid-October) and brought back to the lab where the student will:
   1. Study the formation of secondary minerals (FeS or FeS2) derived from the reduction of the sulfate-bearing minerals by SRB.
   2. DNA/RNA extraction from the MTDs and sequencing to study the microbial communities that colonized the minerals.
   3. Try to enrich SRB in anoxic conditions from the minerals from the MTDs. If the enrichment is successful, DNA can be extracted and sequenced to study the enriched community.

Methods: study of physico-chemical parameters in situ (pH, redox potential, dissolved oxygen), quantification of sulfur species by spectrophotometric techniques, quantification of heavy metals by ICP-OES, sequential Fe extraction, electron microscopy (SEM-EDX), DNA and RNA extraction, PCR, qPCR, sequencing, anoxic cultivation, etc. 

The amount of plastic waste is increasing rapidly, and inadequate recycling systems are leading to widespread environmental contamination. One solution is chemical recycling through gasification, which converts plastic waste into synthesis gas (syngas), which is rich in H₂, CH₄, CO₂, CO, H₂S and other gases. This syngas can be stored in subsurface reservoirs for a long period until demand arises, without prior separation. Such storage could take place in empty gas reservoirs, for example in the North Sea, which have huge capacity and the ability to safely store syngas over long periods. These reservoirs are characterised by the high abundance and activity of subsurface indigenous microorganisms, as well as introduced microorganisms that entered the subsurface during fossil gas extraction. Some of these microorganisms can obtain energy for growth by coupling oxidation of H₂ and H₂S with reduction of CO and CO₂ to form CH₄. This microbially driven process, known as methanogenesis, can lead to the accumulation of CH4. The resulting bio-concentrated CH₄ can then be extracted from subsurface reservoirs and used directly for clean energy production.

Research Plan:

• WP1: Production of CH4 from syngas (CO2, CO, CH4 and H2S) in batch cultures using synthetic media.
  The main objective is to study the inhibitory effect of syngas on methanogenesis.
• WP2: Production of CH₄ from syngas in microcosm experiments using rock cuttings (maximum diameter of 10 mm) of sandstone, carbonate and calcite, as well as quartz, and crustal fluid.
  The main objective is to study the possibility of the rock matrix and the crustal fluid supporting the growth of methanogens.
• WP3: Cultivation of methanogens in diffusion cells consisting of pristine rock with syngas in the headspace.
  The main objective is to study the potential of methanogens to colonise porous rock matrices.
• WP4: Incubation of microorganisms in a high-pressure flow cell with syngas.
  The main objective is to study the resistance of methanogens to high pressure.

Methods: anoxic cultivation, gas analysis, photometry, microscopy, protein assay, DNA/RNA extraction, PCR, qPCR, etc.