Short introduction to current research topic:

Comparison of bacterial rhizosphere communities from plant microbial fuel cells with different current production by 454 amplicon sequencing

The novel technology we study in this project is the Plant Microbial Fuel cell. The concept involves living plants that harvest solar energy with their leaves to produce carbohydrates from carbon dioxide. These carbohydrates are transported from the production site (leaves) to the underground roots. A part of these carbohydrates and other molecules can be excreted into the surrounding soil. These so-called exudates or rhizodeposits, mainly low-molecular weight organic acids and carbohydrates, are in nature used by micro-organisms in the complex soil ecosystem (rhizosphere). Our approach is to efficiently convert in-situ the chemical energy of exudates into electrical energy using an emerging technology, the microbial fuel cell (MFC). Principally, this can be accomplished by placing the plant with its roots in the bioanode, containing electrochemically active micro-organisms, of the microbial fuel cell.
To characterize these microorganisms DNA extracted from Glyceria maxima root samples derived from the anode compartments of one plant MFC which produced high current output and one with lower current the 16S rDNA was amplified. With these samples a 454 pyrosequencing run was performed. Resulting sequences were assembled, aligned by the ARB software tool and allocated to their proper phylogenetic position.
Microbiological diversity was highest for the high current producing plant MFC roots from the top layer, while microbiological differences between high and low current producing plant MFCs were most pronounced for roots from the bottom layer. Most dominant classes were Clostridia in the high current producing plant MFCs and β-Proteobacteria in the low current system. The families of Ruminococcaceae for the high current plant MFC and Comamonadaceae for the low current producing plant MFC were the dominant groups, making up over 50% of the total 16S rDNA sequences found in the samples from the bottom part of the plant MFCs. Diversity and abundance of Archaea was much less then of Bacteria. In the low current plant MFC members of the Methanobacteriaceae family were accompanied by several genera belonging to other families, while in the high current plant MFC the genus Methanobacterium was making up over 95% of the total community.
To localize active bacteria detected with 454 sequencing of the 16S rDNA, the fluorescent in situ hybridization (FISH) technique was applied. With a Geobacter specific probe set it was possible to detect fluorescent Geobacter cells which appeared more frequently on graphite granules than root surface. With the probe specific for only three Ruminococcaceae species a small number of cells was positively identified on the surface and to a much larger extent in outer cortex layers of roots of the high current plant MFC.
The results from this study will enable a specific selection of important bacterial strains for the inoculation of plant MFCs in further trials.

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