Understanding carbon metabolism in hydrogen production by PNS bacteria

Doğan, Ezgi Melis
In biological hydrogen production systems using purple non-sulfur bacteria (PNS bacteria), a thorough understanding of the metabolism of these microorganisms plays a vital role in assessing and improving efficiency and productivity. This metabolism is very complex, and the result of the interplay of several systems and components such as the photosystems, carbon flow and enzymatic reactions. Mathematical models are sought to represent the complex metabolism of these bacteria, which in turn can be used to interpret and enhance the phenomenological equations obtained from experiment, and ultimately aid the design of large-scale bioreactors. The aim of this study is to analyze the metabolism of PNS bacteria using contemporary tools and techniques (Flux Balance Analysis), with emphasis on carbon flow. The thesis mainly concerns the modeling of the metabolism of PNS bacteria, focusing on Rhodopseudomonas palustris which utilizes sucrose as a carbon source and glutamate vi as a nitrogen source in a growth medium with a low N/C ratio. For this purpose, the metabolic model in the present work was verified with the experimental results which were previously performed based on the same conditions considered by the model. Two objective functions, namely, the maximal growth rate of biomass and maximum hydrogen production rate were investigated in particular. The distribution of fluxes in R. palustris showed s linear increase in the specific growth rate of biomass with increasing glutamate uptake rate. The biomass growth was found constant when initial sucrose concentration was changed and a strong function of glutamate uptake rate. A decrease in H2 production was observed at higher photon fluxes and PHB was antagonistically produced to H2 production. Acetic acid and formic acid were found the most and least effective organic acid for H2 production, respectively. The distribution of modeled fluxes will help explain the capability of the hydrogen production and growth on sucrose of R. palustris.


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Citation Formats
E. M. Doğan, “Understanding carbon metabolism in hydrogen production by PNS bacteria,” M.S. - Master of Science, Middle East Technical University, 2016.