PhD defence 31 July 2015 by Alice Jara de Porcellini – University of Copenhagen

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29 July 2015

PhD defence 31 July 2015 by Alice Jara de Porcellini


Manipulation of carbon metabolism in cyanobacteria for enhancing production of valuable compounds

Alice Jara de Porcellini from Section for Molecular Plant Biology at University of Copenhagen is employed as Research Assistant by the Plant Power project. She will defend her PhD thesis at 1:00 pm on the 31st of July. 

All are welcome


The consumption of fossil reserves for the production of commodities and fuels together with the constantly raising population require the establishment of new sustainable technologies to produce carbon-derived molecules without compromising food production. Moreover the utilization of carbon fossil fuels as primary energy and chemical sources has led to a constant increment of CO2 level in the atmosphere.

Exploitation of photosynthesis is a growing technology, which allows contemporary production of compounds of interest and capturing CO2 from the atmosphere. In this context photoautotrophic microorganisms, such as cyanobacteria, constitute an attractive option due to their ability of growth utilizing exclusively water, CO2 and light as energy source, without competing for arable land like plants. Chemical production in cyanobacteria is a promising technology and metabolic engineering has already enabled the production of several compounds, although in limited amounts.

Improvement of the yield can be achieved by enhancement of the photosynthetic capacity of the organism since the limits impose by its efficiency have so far contained the production. Therefore increased understanding of the physiology of these organisms and the regulatory mechanisms involved in the control of light harvesting, carbon fixation and carbon partitioning are a priority in order to develop improved sustainable biofactories.

This thesis work focus in the understanding of the mechanisms regulating carbon metabolism in cyanobacteria, being this an interesting target for biotechnological modification since it is involved in the construction of the metabolic building blocks.

In the first part of the project the work has focused in the understanding of a new mechanism involved in the regulation of carbon metabolism in Synechocystis sp. PCC 6803. Transcriptomic and physiological characterization of the pmgA deletion mutant, known to be impaired in light reactions of photosynthesis and sensitive to glucose, has led to the identification of a new genetic regulatory mechanism involving a non-coding RNA, namely Ncr0700, in glucose metabolism.

Another approach has been taken in the second part of the project. Key enzymes of the Calvin-Benson-Bassham cycle have been over express with the aim of increasing CO2 fixation. For this study, the fast growing cyanobacterium, Synechococcus sp. PCC 7002 has been chosen because of its potential robust capacity as a production host. Bifunctional fructose-1,6-bisphosphatase/ sedoheptulose-1,7-bisphosphatase (BiBP) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) have been over expressed and the phenotypes have been analyzed. Interestingly BiBP overexpressor strain showed increased photosynthesis and faster growth rate. Finally, preliminary results were presented regarding the analysis of heterologous production of ethylene based on the increase in carbon fixation obtained. The BiBP over expression mutant has been combined with an ethylene production pathway in both Synecocystis sp. PCC 6803 and Synechococcus sp. PCC 7002 and the impact on the production level has been evaluated.

The results presented in this thesis showed how diverse and complex the regulation of carbon metabolism is in cyanobacteria, and underlined the presence of different levels of regulation involving non coding RNAs and metabolites. Although a more detailed characterization is needed, these newly identified mechanisms could be manipulated to increase carbon fixation or partitioning towards enhanced production of compounds of interest.