No description available.

abstract: Microbial electrochemical cells (MXCs) are promising platforms for bioenergy production from renewable resources. In these systems, specialized anode-respiring bacteria (ARB) deliver electrons from oxidation of organic substrates to the anode of an MXC. While much progress has been made in understanding the microbiology, physiology, and electrochemistry of well-studied model ARB such as Geobacter and Shewanella, tremendous potential exists for MXCs as microbiological platforms for exploring novel ARB. This dissertation introduces approaches for selective enrichment and characterization of phototrophic, halophilic, and alkaliphilic ARB. An enrichment scheme based on manipulation of poised anode potential, light, and nutrient availability led to current generation that responded negatively to light. Analysis of phototrophically enriched communities suggested essential roles for green sulfur bacteria and halophilic ARB in electricity generation. Reconstruction of light-responsive current generation could be successfully achieved using cocultures of anode-respiring Geobacter and phototrophic Chlorobium isolated from the MXC enrichments. Experiments lacking exogenously supplied organic electron donors indicated that Geobacter could produce a measurable current from stored photosynthate in the dark. Community analysis of phototrophic enrichments also identified members of the novel genus Geoalkalibacter as potential ARB. Electrochemical characterization of two haloalkaliphilic, non-phototrophic Geoalkalibacter spp. showed that these bacteria were in fact capable of producing high current densities (4-8 A/m2) and using higher organic substrates under saline or alkaline conditions. The success of these selective enrichment approaches and community analyses in identifying and understanding novel ARB capabilities invites further use of MXCs as robust platforms for fundamental microbiological investigations. / Dissertation/Thesis / Ph.D. Microbiology 2013

The process of photosynthesis begins with a capture of sunlight and its quick conversion into the chemical energy. Both these primary processes take place in a specially designed photosynthetic apparatus that is present in cells of all photosynthetic organisms. In green sulfur bacteria the apparatus consists of a massive light-harvesting antenna (chlorosome), intermediate antennas (baseplate complex and FMO proteins) and of the reaction center, where the conversion into the chemical energy occurs. The energy flow through the apparatus can be monitored by time-resolved spectroscopy techniques. Coherent two-dimensional electronic spectroscopy (2DES) in one of such techniques, which combines high temporal and spectral resolution, and therefore it is especially well suited for studying multichromophoric systems such as photosynthetic apparatus. This thesis describes the principles of the 2DES technique and outlines the basic facts about the photosynthetic apparatus of green sulfur bacterium Chlorobaculum tepidum. Finally, it summarizes the investigation of the photosynthetic machinery using 2DES. Results presented in this thesis provide new insights into the exciton diffusion and vibrational coherences within chlorosomes, excitonic structure of the baseplate and the overall energy flow through the entire...