Kiel Plant Center

Kirstin Gutekunst - carbon and hydrogen metabolism

Kirstin Gutekunst is junior group leader of the Bioenergetics in Photoautotrophs group at the Botanical Institute at the University of Kiel. She uses cyanobacteria to study the hydrogen metabolism of cyanobacteria and the central carbon metabolism of cyanobacteria and plants. Here she explains why cyanobacteria make useful model organisms and what her research has revealed about the hydrogen and carbon metabolism in plants so far.

Scientist in lab with cyanobacteria columns
Junior Research Group Leader Kirstin Gutekunst in the lab at Kiel University. Copyright: K.Gutekunst

What is so special about cyanobacteria?

Cyanobacteria are photoautotrophs that rely on photosynthesis. It’s thanks to cyanobacteria that enough oxygen accumulated in the atmosphere so life could exist in its present form on our planet. They are also actually the ancestors of chloroplasts - the parts of the plant cell that carry out photosynthesis to capture the energy of sunlight. Cyanobacteria were incorporated into a precursor plant cell some 540 million years ago thereby introducing thousands of genes both to the plant and chloroplast genome. Due to their joint evolutionary history the carbon metabolism, respiration and photosynthesis in plants and cyanobacteria are very similar. However, cyanobacteria are much easier to manipulate than plants which makes them really nice model organisms for studying questions of plant physiology in the lab. They grow much quicker than plants and we can create mutants by knocking out genes in only two months. Thereby we can approach questions of plant physiology a lot faster than if we were exclusively using plant models in the lab. I find it highly awarding to combine studies on cyanobacteria and plants and to check if those findings that we gain in cyanobacteria are valid in plants as well.

What principles are you using cyanobacteria to study?

I am interested in the bioenergetics of photoautotrophs, so how energy flows through these organisms. In particular I am looking at the hydrogen metabolism in cyanobacteria and the carbon metabolism in cyanobacteria and plants.

How exactly are you doing this?

For example, we knock out selected enzymes of the central carbon metabolism in cyanobacteria and study the resultant mutants concerning for example their growth, photosynthetic performance, respiration and CO2-fixation. This helps us build up a detailed understanding of this network in cyanobacteria and to formulate hypotheses for plants as well. In addition we are looking for overarching principles that are valid for both cyanobacteria and plants. We do this by, for example, analysing the subcellular localization of glycolytic enzymes in plants and characterizing the deletion mutants. I find it very exciting that the regulatory principles that we find in cyanobacteria seem to be partly reflected in the subcellular organisation of the central carbon metabolism in plants. It is exciting to find similarities between cyanobacteria and plants but sometimes it is even more exciting to find the differences! By combining studies on both organisms we therefore get a deeper understanding of the processes in plants and can even add on an evolutionary perspective.

cyanobacteria grow in columns in the lab
Cyanobacteria growing in the lab. Copyright: K. Gutekunst

Recently, we were also successful in creating a cyanobacterial mutant that produces increased amounts of hydrogen. For this purpose, we fused an enzyme called hydrogenase to the photosystem I protein assembly used in photosynthesis. The hydrogenase is an enzyme that can use electrons from either the oxidation of glucose or photosynthesis to produce hydrogen.

What was special about this achievement?

Other groups have already managed to fuse the hydrogenase and photosystem I outside living cells in in vitro systems. Here the fusion has to be repeated for every experiment. Our achievement was to transfer such a fusion into a living cyanobacterial cell. Since our mutants are genetically engineered, the fusion is there every time the cells divide and replicate. The mutant produces hydrogen photosynthetically for several days, which is great. Excitingly, at about the same time a group from the US achieved the same in algae. We are in contact with this group and it is exciting to compare the physiological consequences in both organisms.

How long did it take you to get to this stage?

Usually we only need a few months to create mutants, but this was a bit more complicated. The cell was unlikely to just accept a hydrogenase fused to its photosystem I, because this results in less growth. So we deleted the hydrogenase and part of photosystem I first. We had to grow these mutants on glucose so that they would not starve. We then offered these cells the fusion construct of the photosystem I subunit and hydrogenase. The mutant was interested in getting its photosystem I back so it can perform photosynthesis again, and accepted it, even though the hydrogenase was attached. It was at that moment better than nothing. Including the design of the fusion this all took several years to achieve and to get these mutants took about a year.

What implications does this have for novel green energy technologies?

Obviously, a technological process that produces photosynthetic hydrogen based on the energy of sunlight with no carbon dioxide output is very attractive! That would be a fantastic and a great win for our energy needs. Indeed, the Christian-Albrechts-University now has a patent on our method.

What are your main findings concerning the central carbon metabolism in cyanobacteria and plants so far?

The so-called Entner-Doudoroff pathway is a glycolytic route by which glucose can be broken down. It has actually been studied in detail in archaea here in Kiel by Prof. Schönheit who recently retired. We found that the Entner-Doudoroff pathway had been overlooked as an important glycolytic route in cyanobacteria. When we checked if it also exists in other photoautotrophs as well, we found that it is indeed widespread in the whole plant lineage – so in moss, fern, algae and plants! This finding calls for a complete revision of the central carbon metabolism in cyanobacteria and plants. One central question is: why is this glycolytic pathway absent in animals but present in plants? It seems that we are about in getting answers to this question which I find very exciting.

plants in the lab
Kirstin looks for similarities and differences between pathways in cyanobacteria and plants. Copyright: K.Gutekunst

What are your future research plans?

I am fascinated by the significance of opposing processes for the regulation of metabolism: respiration and photosynthesis, carbohydrate break down via glycolytic routes and carbohydrate synthesis via the Calvin Benson cycle. Hydrogen production is a regulatory player in this network as well. I would like to understand this bioenergetic network in detail and to study how this regulation was manifested in the course of evolution and might therefore be reflected in the cellular organization of plants.

 

 

Visit Bioenergetics in Photoautotrophs group webpage

Read also more about Kirstin's latest research:

04.05.2020: Hydrogen comes alive 
Light-driven production of hydrogen by coupling natural photosystems or photosensitizers with hydrogen-producing catalysts has been achieved in numerous in vitro systems. Now, a recombinant in vivo system is described that generates hydrogen using a hydrogenase enzyme directly coupled to a cyanobacterial photosystem. /fs-botanik/kps/en/news/04-05-2020-hydrogen-comes-alive
04.05.2020: Energy of the future: photosynthetic hydrogen from bacteria 
Kiel research team investigates how cyanobacteria can be transformed into hydrogen factories /fs-botanik/kps/en/news/05-04-2020-energy-of-the-future-photosynthetic-hydrogen-from-bacteria