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  Evolution and biochemistry of photosynthesis - electron transfer reactions, renewable energy production, biotechnology, and chloroplast genomes

   Department of Biochemistry

  Prof C J Howe  Applications accepted all year round  Awaiting Funding Decision/Possible External Funding

About the Project

The common theme of our work is the biochemistry and evolution of photosynthesis.

Although we have a good understanding of the ‘Z-scheme’ of photosynthesis, it is increasingly clear that there are many side-reactions that help protect the photosynthetic machinery against damage from excessive or rapidly fluctuating light. Some years ago, we discovered a novel protein, cytochrome c6A, which is related to the well-characterized cytochrome c6 that can transfer electrons from the cytochrome bf complex to Photosystem I in some algae. However, cytochrome c6A is unable to carry out this function because (among other reasons) its redox potential is unsuitable (1, 2). Having discovered this protein, we want to find out what it does – it is highly conserved, suggesting an important function, and we think it may be involved in a photoprotection response.

We and others have shown that algae and photosynthetic bacteria emit electrons both in the dark and (more so) in the light. These electrons can be collected by an anode, and form the basis of ‘biophotovoltaic’ systems, which we have shown can be used to power small electronic devices such as environmental sensors. Although the power densities achieved at present are lower than for conventional solar cells, biophotovoltaics should be cheaper to produce (and decommission!) and may be useful for power production in remote areas, perhaps in developing countries, or environmentally sensitive locations. We aim to understand how electrons are released from photosynthetic microorganisms, and how we might be able to increase electron output (3, 4). As well as their practical applications, biophotovoltaic systems may also be a useful tool for studying the electron transfer pathways of photosynthetic microorganisms.

There is increasing interest in the possibility of using purple anoxygenic photosynthetic bacteria, such as Rhodopseudomonas palustris, as a biotechnology chassis. We think it will be particularly valuable for waste treatment, as it is metabolically versatile, and resilient to many toxic materials (5). The combination of waste processing with production of useful molecules (‘waste valorisation’) is particularly attractive, and we are developing systems to do this using R. palustris.

We are also interested in the evolution of the chloroplast genome in eukaryotic algae. We are particualrly interested in the dinoflagellate chloroplast genome, wich is highly unusual in its organisation (6). Dinoflagellates are very eimportant as symbionts of corals, and the breakdown if the symbiosis results in coral bleaching. We have established a dinoflagellate chloroplast transformation system, and can now apply this to studies on bleaching (7).

Biological Sciences (4)


1) Molina-Heredia FP, Wastl J, Navarro JA, Bendall DS, Hervas M, Howe CJ, De La Rosa MA (2003) "A new function for an old cytochrome" Nature 424:33-34

2) *Slater B, *Kosmützky D, Nisbet RER, Howe CJ (2021“The evolution of the cytochrome c6 family of photosynthetic electron transfer proteins” Genome Biology & Evolution, 13:8 evab146

3) Bombelli P, Savanth A, Scarampi A, Rowden SJL, Green DH, Erbe A, Årstøl E, Jevremovic I, Hohmann-Marriott MF, Trasatti P, Ozer E, Howe CJ (2022) “Powering a Microprocessor by Photosynthesis” Energy & Environmental Science 15:2529-2536
4) Saar KL, Bombelli P, Lea-Smith DJ, Call T, Aro E-M, Mueller T, Howe CJ, Knowles TPJ (2018) “Enhancing power density of biophotovoltaics by decoupling storage and delivery” Nature Energy 3:75-81

4) McCormick AJ, Bombelli P, Bradley RW, Thorne R, Wenzel T, Howe CJ (2015) “Biophotovoltaics: oxygenic photosynthetic organisms in the world of bioelectrochemical systems” Energy & Environmental Science 8:1092-1109.

5) Pott RWM, Howe CJ, Dennis JS (2014) “The purification of crude glycerol derived from biodiesel manufacture and its use as a substrate by Rhodopseudomonas palustris to produce hydrogen” Bioresource Technology 152:464-470.

6) Dorrell RG, Howe CJ (2015) “Integration of plastids with their hosts: Lessons learned from dinoflagellates” Proc Natl Acad Sci USA 112:10247-10254.

7) Nimmo IC, Barbrook AC, Lassadi I, Chen JE, Geisler K, Smith AG, Aranda M, Purton S, Waller RF, Nisbet RER, Howe CJ. “Genetic transformation of the dinoflagellate chloroplast” eLife (2019) 8:e45292

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