Optimizing electrogenic activity from photosynthetic bacteria in bioelectrochemical systems
Creators: name: Call, Toby Primo
Publisher: name: Apollo - University of Cambridge Repository
Year: 2018
Subjects: Microbial fuel cell
biophotovoltaic
cyanobacteria
purple bacteria
bioenergy
electrogenic
pili
photosynthesis
bioelectrochemical
system
graphene
Synechocystis
Rhodospeudomonas palustris

description: The aims of this project were to investigate a range of limitations affecting the electrical performance of bioelectrochemical systems (BES) and their use as analytical tools. The model cyanobacterium Synechocystis sp. PCC6803 was used to characterize light-driven BESs, or biophotovoltaic (BPV) devices. The phycobilisome (PBS) antenna size was altered to modify light absorption. At low to medium light intensities the optimum PBS antenna size was found to consist of one phycocyanin (PC) disc. Incorporating pulsed amplitude fluorescence (PAM) measurements into the BPV characterization allowed simultaneous comparison of photosynthetic efficiency to EET in Synechocystis. Non-photochemical quenching (NPQ) was investigated as a limiting factor in biophotovoltaic efficiency and was found to be reduced in the PBS antenna-truncated mutants. Fluorescence and electrochemical data were combined to develop a framework for quantifying the efficiency of light to bioelectricity conversion. This approach is a first step towards a more comprehensive and detailed set of analytical tools to monitor EET in direct relation to the underlying photosynthetic biology. A set of metabolic electron sinks were deleted to remove a selection of pathways that might compete with extracellular electron transfer (EET). The combined deletion of a bi-directional hydrogenase – HoxH, nitric oxide reductase – NorB, cytochrome-c oxidase – COX, bd-quinol oxidase – cyd, and the respiratory terminal oxidase – ARTO, roughly doubled light driven electron flux to EET. Deletion of nitrate reductase – NarB, and nitrite reductase – NirA, increased EET to a similar degree, but combination with the other knockouts compromised cell viability and did not increase output further. In addition to Synechocystis, the purple non-sulphur α-proteobacterium Rhodopseudomonas palustris CGA009 was used to test the effect of storage molecule synthesis knockout in a more industrially relevant organic carbon source driven BES, or microbial fuel cell (MFC). However, the removal of glycogen and poly-ß-hydroxybutyrate (PHB) did not have a significant effect on electrical output. Finally, the importance of electrode material and design for cell to anode connections in an MFC was investigated. EET from R. palustris was greatly enhanced using custom designed graphene and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) aerogels. Pristine graphene is also shown for the first time to be a viable, low cost alternative to platinum as a cathodic catalyst. Together, these results present a holistic view of major limitations on electrical output from BESs that may contribute to enhancing EET for power generation from MFCs in the long term, and optimization of BPV devices as reliable analytical tools in the short term.