Onderwerp scriptie

CO utilization by Desulfotomaculum, Desulfosporosinus and Desulfitobacterium

Carbon monoxide (CO) is present in different environments widely spread on earth because it is naturally and industrially produced. CO is produced by burning processes, volcanoes and hydrothermal vents, plants, animals, photochemical and thermochemical degradation of organic matter in soils, marine sediments and aquatic systems. CO is a colorless and odorless gas, which is toxic for humans and animals, and also to many microorganisms. The toxicity of CO to microbes is due to its binding to metal-containing redox enzymes, which can result in the interruption of electron transport chains. Interestingly, microorganisms can use CO as a sole carbon and energy source. CO and the degradation of CO by microorganisms play an important part in the global carbon cycle, and it has an important contribution to industry, bioremediation and waste treatment. Therefore, the microbial degradation of CO is of great interest and we aim for a better understanding of CO metabolism by anaerobic microbial communities.

Anaerobic CO oxidation is catalyzed by a nickel containing carbon monoxide dehydrogenase (CODH) in a wide diversity of prokaryotes. The anaerobic CODH catalyzes the following reaction:

CO + H2O ā†’ CO2 + 2H+ + 2eāˆ’

The electrons generated by the oxidation of CO can be coupled to reduction reactions like CO2 reduction to CH4 and acetate, sulfate reduction, fumarate reduction, metal reduction, or proton reduction that results in the production of hydrogen. This leads to different end products in different microorganisms due to different CODH complexes. Acetate production from CO degradation, for example, involves the same bifunctional CODH complex also involved in the acetyl-CoA pathway [1, 2]. Moreover, in hydrogen producing CO utilizers a different CODH complex is involved. This complex contains both CODH genes and hydrogenase genes [3].

The sulfate/sulfite reducing bacteria  belonging to the Desulfotomaculum, Desulfosporosinus and Desulfitobacterium genera  show differences in their CO utilization. These differences range between no growth with CO, due to its toxicity, and growth in the presence of 100% CO. It is interesting to study which strains can grow in what concentration and  what causes the differences.

Aim:

To study the CO metabolism of Desulfotomaculum, Desulfosporosinus and Desulfitobacterium species.

Practical approach:

In order to elucidate the CO metabolism of Desulfotomaculum, Desulfosporosinus and Desulfitobacterium the MSc student will do growth studies in different growth conditions, for example variable concentrations of CO and using different electron acceptors. Additionally, CODH activity will be measured from strains from different growth conditions.

Techniques and methods that will be used:

  • Cultivation of strict anaerobic microorganisms
  • Analytical methods (like GC and HPLC measurements)
  • Protein measurements
  • Enzyme activity assays
  • SDS-PAGE
  • Genome analysis/comparison*

* depending on the time available

Supervisors will be Michael Visser, Irene Sanchez, Thomas Kruse. Please do not hesitate to contact us for further information.

References:

1. Oelgeschlager, E. and M. Rother, Carbon monoxide-dependent energy metabolism in anaerobic bacteria and archaea. Arch Microbiol, 2008. 190(3): p. 257-69.

2. Ragsdale, S.W. and M. Kumar, Nickel-containing carbon monoxide dehydrogenase/acetyl-CoA synthase. Chemical Reviews, 1996. 96(7): p. 2515-40.

3. Hedderich, R., Energy-converting [NiFe] hydrogenases from archaea and extremophiles: ancestors of complex I. J Bioenerg Biomembr, 2004. 36(1): p. 65-75.