Microbial Energy Conversion and Biotechnology

Prof. Dr. Jörg Simon

Research Interests

Our lab studies key reactions of the biogeochemical nitrogen and sulfur cycles at the microbial cellular level using genetically tractable model organisms. We are especially interested in the physiology and bioenergetics of relevant anaerobic or microaerobic bacteria, focusing on the enzymology of anaerobic respiration and emerging applications in a Synthetic Biology approach.

The mechanistic basis and enzymic architecture of anaerobic respiration is elucidated using a wide range of microbiological methods as well as genetic manipulation (mutant construction, site-directed mutagenesis, overproduction of affinity-tagged proteins) and methods of molecular and structural biology.

1. Molecular microbiology of the biogeochemical nitrogen cycle

The biogeochemical nitrogen cycle depends on a diverse range of microorganisms that catalyse key reactions like nitrogen fixation, nitrification, anaerobic ammonia oxidation (anammox), denitrification, as well as assimilatory and respiratory nitrate and nitrite ammonification.

We study the nitrogen metabolism of Epsilonproteobacteria, a phylogenetic group that comprises host-associated bacteria (e.g. pathogenic Campylobacter and Helicobacter species) as well as free-living terrestrial and aquatic bacteria that appear to be abundant in sulphidic environments like deep-sea vents.

Our work focuses on the enzymology and bioenergetics of anaerobic nitrate, nitrite and nitrous oxide respiration as well as nitrosative stress defence using the non-pathogenic nitrate/nitrite ammonifying bacterium Wolinella succinogenes as model Epsilonproteobacterium. This organism produces metalloprotein complexes that are part of electron transport chains in amounts sufficiently high for biochemical characterization and structure determination.

2. A novel pathway of bacterial sulphite respiration

In the periplasm of certain Proteobacteria including W. succinogenes sulphite is reduced to sulfide by the octahaem cytochrome c MccA, a representative of a new class of highly active cytochrome c sulphite reductases. We are interested in the characterization of the corresponding electron transport chain.

The high-resolution crystal structure of MccA was determined recently. It revealed an unprecedented haem c-copper active site of sulfite reduction and confirmed the presence of a haem c group bound to a CX15CH attachment site.

Electron micrograph of a W. succinogenes cell and substrate conversions catalysed by respiratory enzymes involved in nitrate ammonification, nitrous oxide and sulfite respiration as well as in nitric oxide and hydroxylamine detoxification. Dehydrogenases (yellow) and reductases (red) are connected via the menaquinone/menaquinol pool and contribute to the generation of a proton motive force (pmf) that drives ATP synthesis. Hyd, Hydrogenase; Fdh, Formate dehydrogenase; Mcc, cytochrome c sulfite reductase; Nap, periplasmic nitrate reductase; Nrf, cytochrome c nitrite reductase; Nos, nitrous oxide reductase.
Exemplary substrate conversions of a W. succinogenes cell – for more information please click on the picture

Current research topics at a glance:

  • Composition and bioenergetics of epsilonproteobacterial electron transport systems involved in anaerobic respiration with nitrate, nitrite, nitric oxide, nitrous oxide, fumarate, polysulfide, sulphite and arsenate.
  • Structure and function of quinone / quinol-reactive membrane-bound proteins and multiheme cytochromes c (MCC family). Members of the MCC family comprise cytochrome c nitrite reductase (NrfA), hydroxylamine oxidoreductase (Hao) and cytochrome c sulphite reductase (MccA).
  • Biosynthesis of methylated menaquinone derivatives and their function in low-potential electron transport chains.
  • Modular design of synthetic microbial electron transport systems. This project aims at rational energy metabolism design in biotechnological applications (Research focus: Synthetic Biology).
  • Stress responses of Epsilonproteobacteria to combat nitrosative stress and underlying regulatory networks (Research focus: Biology of Stress Response).

Group members

Research group

Recent publications

Publications (tu-biblio)
Literature is available upon request.

Open positions

We are seeking highly motivated students at the BSc, MSc and PhD level. Projects for Bachelor and Master theses for students from Biology, Biochemistry and Biomolecular Engineering are offered in the research areas described above. Please contact Jörg Simon for details on current projects.