Kirstin Gutekunst | Glycolytic shunts replenish the Calvin cycle as anaplerotic reactions
Channel: CyanoWorld
Date: 2021-03-05

Kirstin Gutekunst - Christian Albrechts University Kiel & University of Kassel, Germany

Homepage: https://www.biotechnologie.uni-kiel.de/en/copy_of_research/junior-research-group-bioenergetics-in-photoautotrophs-dr-kirstin-gutekunst
Research Gate: https://www.researchgate.net/profile/Kirstin-Gutekunst-2

Glycolytic shunts replenish the Calvin-Benson-Bassham cycle as anaplerotic reactions in transition states in the cyanobacteria Synechocystis sp. PCC 6803

The discovery of the Entner-Doudoroff (ED) pathway as a third glycolytic route beside Embden-Meyerhof-Parnas (EMP) and oxidative pentose phosphate (OPP) pathway in cyanobacteria and plants calls for a revision of their central carbohydrate metabolism (Chen et al., 2016). We observed that deletion of the ED pathway alone, and even more pronounced in combination with other glycolytic routes, diminished growth under photoautotrophic conditions under continuous illumination in the cyanobacterium Synechocystis sp. PCC 6803 (Makowka et al., 2020). Furthermore, we found that the ED pathway is required for optimal glycogen catabolism in parallel to an operating Calvin-Benson-Bassham (CBB) cycle. It is counter-intuitive that glycolytic routes, which operate in reverse to the CBB cycle and do not provide any additional biosynthetic intermediates, are important under photoautotrophic conditions. However, a closer look at the relative light-intensity distributions in our cultures, depending on optical density revealed highly heterogenous light regimes. In line with this, we observed that the ability to reactivate an arrested CBB cycle depends on glycolytic shunts that tap the cellular carbohydrate reservoir to replenish the cycle. Our results suggest that the classical view of the CBB cycle as an autocatalytic, completely autonomous cycle that exclusively relies on its own enzymes and CO2 fixation to regenerate ribulose-1,5-bisphosphate for Rubisco is an oversimplification. We propose that in common with other known autocatalytic cycles, the CBB cycle likewise relies on anaplerotic reactions to compensate for the depletion of intermediates, particularly in transition states that are common in nature. Glycolytic routes might thus have a dual function: they either operate at their full length or alternatively form shunts to support CO2 fixation. The delicate interplay and interdependence of anabolic and catabolic processes will be discussed (Gutekunst, 2018). 

This talk is part of the CyanoWorld online seminar series, hosted by Nicolas Schmelling and Ilka Axmann, and was held on Zoom on February 25th, 2021.

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