The aim of this thesis is to enhance the extracellular electron transfer rates (exoelectrogenesis) in cyanobacteria, to be utilised for photo-bioelectricity generation in biophotovoltaics (electrochemical cell). An initial cross comparison of the cyanobacterium Synechococcus elongatus PCC7942 against other exoelectrogenic cultures showed a hindered exoelectrogenic capacity. Nonetheless, in mediatorless biophotovoltaics, it outperformed the microalgae Chlorella vulgaris. Furthermore, the performance of S. elongatus PCC7942 was improved by constructing a more efficient design (lower internal resistance), which was fabricated with carbon fibres and nitrocellulose membrane, both inexpensive materials. To strategically obtain higher exoelectrogenic rates, S. elongatus PCC7942 was conditioned by iron limitation and CO2 enrichment. Both strategies are novel in improving cyanobacteria exoelectrogenesis. Iron limitation induced unprecedented rates of extracellular ferricyanide reduction (24-fold), with the reaction occurring favourably around neutral pH, different to the cultural alkaline pH. Iron limited cultures grown in 5% and 20% CO2 showed increased exoelectrogenic rates in an earlier stage of growth in comparison to air grown cultures. Conveniently, the cultural pH under enriched CO2 was around neutral pH. Enhanced photo-bioelectricity generation in ferricyanide mediated biophotovoltaics was demonstrated. Power generation was six times higher with iron limited cultures at neutral pH than with iron sufficient cultures at alkaline pH. The enhanced performance was also observed in mediatorless biophotovoltaics, especially in the dark phase. Exoelectrogenesis was mainly driven by photosynthetic activity. However, rates in the dark were also improved and in the long term it appeared that the exoelectrogenic activity under illumination tended to that seen in the dark. Proteins participating in iron uptake by an alleged reductive mechanism were overexpressed (2-fold). However, oxidoreductases in the outer membrane remain to be identified. Furthermore, electroactive regions in biofilms of S. elongatus PCC7942 were established using cyclic voltammetry. Double step potential chronoamperometry was also successfully tested in the biofilms. Thus, the electrochemical characterisation of S. elongatus PCC7942 was demonstrated, implying that the strategies presented in this thesis could be used to screen for cyanobacteria and/or electrode materials to further develop systems for photo-bioelectricity generation.

abstract: Microbial electrochemical cells (MXCs) offer an alternative to methane production in anaerobic water treatment and the recapture of energy in waste waters. MXCs use anode respiring bacteria (ARB) to oxidize organic compounds and generate electrical current. In both anaerobic digestion and MXCs, an anaerobic food web connects the metabolisms of different microorganisms, using hydrolysis, fermentation and either methanogenesis or anode respiration to break down organic compounds, convert them to acetate and hydrogen, and then convert those intermediates into either methane or current. In this dissertation, understanding and managing the interactions among fermenters, methanogens, and ARB were critical to making developments in MXCs. Deep sequencing technologies were used in order to identify key community members, understand their role in the community, and identify selective pressures that drove the structure of microbial communities. This work goes from developing ARB communities by finding and using the best partners to managing ARB communities with undesirable partners. First, the foundation of MXCs, namely the ARB they rely on, was expanded by identifying novel ARB, the genus Geoalkalibacter, and demonstrating the presence of ARB in 7 out of 13 different environmental samples. Second, a new microbial community which converted butyrate to electricity at ~70% Coulombic efficiency was assembled and demonstrated that mixed communities can be used to assemble efficient ARB communities. Third, varying the concentrations of sugars and ethanol fed to methanogenic communities showed how increasing ED concentration drove decreases in methane production and increases in both fatty acids and the propionate producing genera Bacteroides and Clostridium. Finally, methanogenic batch cultures, fed glucose and sucrose, and exposed to 0.15 – 6 g N-NH4+ L-1 showed that increased NH4+ inhibited methane production, drove fatty acid and lactate production, and enriched Lactobacillales (up to 40% abundance) above 4 g N-NH4+ L-1. Further, 4 g N-NH4+ L-1 improved Coulombic efficiencies in MXCs fed with glucose and sucrose, and showed that MXC communities, especially the biofilm, are more resilient to high NH4+ than comparable methanogenic communities. These developments offer new opportunities for MXC applications, guidance for efficient operation of MXCs, and insights into fermentative microbial communities. / Dissertation/Thesis / Doctoral Dissertation Biological Design 2015

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