An updated view of glucose pathways in cyanobacteria

Cyanobacteria are photosynthetic microorganisms that can generate glucose through solar energy (autotrophy) or absorb it from their environment (mixotrophy/heterotrophy) (Cohen and Gurevitz, 2006; Stebegg et al., 2023; Muñoz-Marín et al., 2024). Once produced, glucose undergoes central carbon metabolic pathways, including classical glycolysis, the Embden-Meyerhoff-Parnass pathway (EMP), and the oxidative pentose pathway (OxPP) (Flamholz et al., 2013; Lucius and Hagemann, 2024).

A third proposed pathway, the Entner-Doudoroff (ED) pathway, was thought to be used by some cyanobacteria to degrade glucose, but recent research has contradicted this claim (Evans et al., 2024). The latest study by Ojha et al. in eLife reports new insights into the glucose metabolite pathways of cyanobacteria, specifically using the Synechocystis strain.

Using a combination of experiments, biochemical characterization, and enzyme activity measurements, the researchers found that Synechocystis lacks the EDD enzyme exclusive to the ED pathway, which was previously believed to promote the pathway's existence. While Synechocystis has the EDA enzyme, it is not involved in glucose degradation but rather in the metabolism of phosphoenolpyruvate and proline.

The study concludes that the main advantage of these glucose utilization pathways is energy production rather than reducing the cost of enzyme biosynthesis. This new understanding of cyanobacterial glucose metabolism clarifies the metabolic landscape and highlights the importance of accurate biochemical characterization when studying complex metabolic pathways.