Modification of cyanobacterial strains for optimised light harvesting and growth in photobioreactors

Spackman, Fred (2021) Modification of cyanobacterial strains for optimised light harvesting and growth in photobioreactors. Masters thesis, University of East Anglia.

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The cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis) has great potential for industrial biomass and chemical production, but commercialisation is dependent on improving productivity. Cyanobacterial light harvesting is not optimal for growth in photobioreactors and could potentially be improved via genetic modification including: 1) truncation of the phycobilisome, the light harvesting complex, in order to increase light penetration in dense cultures and reduce photoinhibition; 2) Expression of proteorhodopsin, a foreign light harvesting complex, to the thylakoid membrane in order to allow utilisation of green light and increase the spectrum harvested. In order to test the latter hypothesis, a necessary control strain was generated for characterisation of PsaFTSPR, a Synechocystis strain producing thylakoid membrane targeted proteorhodopsin. Preliminary growth characterisation suggests that PsaFTSPR reaches higher cell densities than wild-type when it is grown in cultures that are deep, dense, and not carbon-limited. In order to generate a Synechocystis strain with optimal light harvesting properties, a proteorhodopsin gene with a thylakoid membrane targeting sequence was inserted into the chromosomal DNA, replacing a varying number of phycobilisome antenna genes. These mutants were characterized via absorption spectroscopy and oxygen evolution experiments. Absorption spectroscopy concluded that the mutants were not absorbing considerably more green light. This may have been due to low levels of retinal, the chromophore in proteorhodopsin, during exponential phase. Using an oxygen electrode, it was found that the proteorhodopsin expressing strain with a 75% reduced phycobilisome, Olive: PsaFTSPR, demonstrated a significantly increased maximum photosynthetic rate of 33.2% compared to wild-type, and 45.4% compared to a strain with only the 75% reduced phycobilisome. This suggests that expression of proteorhodopsin may compensate for the deleterious effects of phycobilisome truncation, specifically the excess capacity for protein production. However, further experiments are required to test whether expression of proteorhodopsin had a role in improving photosynthesis in this strain.

Item Type: Thesis (Masters)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 09 Aug 2022 09:31
Last Modified: 09 Aug 2022 09:31

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