Entwicklung bioelektrochemischer Systeme für die Untersuchung von elektrodenabhängigen Konversionsprozessen

In the present dissertation 3 typs of bioelectrochemical systems were developed. The 1st one was a microbial fuel cell which was tested in a domestic sewage treatment plant. An electrical current was produced while organic carbon and N2-compounds were removed from the wastewater. The 2 other systems served for the characterization of electrotrophic microbes. In this context the use of an carbon cathode as the sole electron donor for a genetically modified R. sphaeroides strain was demonstrated

Proof of principle for an engineered microbial biosensor based on Shewanella oneidensis outer membrane protein complexes

Shewanella oneidensis is known for its ability to respire on extracellular electron acceptors. The spectrum of these acceptors also includes anode surfaces. Based on this activity, a versatile S. oneidensis based biosensor strain was constructed in which electricity production can be modulated. Construction started with the identification of a usable rate-limiting step of electron transfer to an anode. Thereafter, the sensor strain was genetically engineered to produce a protein complex consisting of the three proteins MtrA, MtrB and MtrF. This complex is associated to the outer membrane and most probably enables membrane spanning electron transfer. MtrF is an outer membrane cytochrome that catalyzes electron transfer reactions on the cell surface. Under anoxic conditions, wild type cells do not express MtrF but rather MtrC as electron transferring outer membrane cytochrome. Still, our analysis revealed that MtrF compared to MtrC overexpression is less toxic to the cell which gives MtrF a superior position for biosensor based applications. Transcription of mtrA, mtrB and mtrF was linked up to an inducible promoter system, which positively reacts to rising l-arabinose concentrations. Anode reduction mediated by this strain was linearly dependent on the arabinose content of the medium. This linear dependency was detectable over a wide range of arabinose concentrations. The l-arabinose biosensor presented in this study proves the principle of an outer membrane complex based sensing method which could be easily modified to different specificities by a simple change of the regulatory elements

MOESM3 of Electrode-assisted acetoin production in a metabolically engineered Escherichia coli strain

Additional file 3: Table S3. Bacterial strains used in this study

MOESM1 of Electrode-assisted acetoin production in a metabolically engineered Escherichia coli strain

Additional file 1: Table S1. Oligonucleotides used in this study

MOESM5 of Electrode-assisted acetoin production in a metabolically engineered Escherichia coli strain

Additional file 5: Table S5. Summary of growth experiments: end products

MOESM4 of Electrode-assisted acetoin production in a metabolically engineered Escherichia coli strain

Additional file 4: Table S4. Summary of growth experiments: Âľ and final optical density

MOESM2 of Electrode-assisted acetoin production in a metabolically engineered Escherichia coli strain

Additional file 2: Table S2. Plasmids used in this study

MOESM6 of Electrode-assisted acetoin production in a metabolically engineered Escherichia coli strain

Additional file 6: Table S6. Comparison of end-product yields in DH5αZ1 and JG806 expressing pMAL_alsSD with NO3 − as the electron acceptor

Unbalanced fermentation of glycerol in Escherichia coli via heterologous production of an electron transport chain and electrode interaction in microbial electrochemical cells

Microbial electrochemical cells are an emerging technology for achieving unbalanced fermentations. However, organisms that can serve as potential biocatalysts for this application are limited by their narrow substrate spectrum. This study describes the reprogramming of Escherichia coli for the efficient use of anodes as electron acceptors. Electron transfer into the periplasm was accelerated by 183% via heterologous expression of the c-type cytochromes CymA, MtrA and STC from Shewanella oneidensis. STC was identified as a target for heterologous expression via a two-stage screening approach. First, mass spectroscopic analysis revealed natively expressed cytochromes in S. oneidensis. Thereafter, the corresponding genes were cloned and expressed in E. coli to quantify periplasmic electron transfer activity using methylene blue. This redox dye was further used to expand electron transfer to carbon electrode surfaces. The results demonstrate that E. coli can be reprogrammed from glycerol fermentation to respiration upon production of the new electron transport chain