Core Transcriptome of Hydrogen Producing Marine Vibrios Reveals Contribution of Glycolysis in Their Efficient Hydrogen Production.

Pyruvate (Pyr) is the end product of the glycolysis pathway. Pyr is also renewable and is further metabolized to produce formate, which is the precursor of H, via pyruvate formate lyase (PFL) under anaerobic conditions. The formate is excluded and re-imported via the formate channel and is then converted to H via the formate hydrogenlyase (FHL) complex. In H producing marine vibrios, such as Vibrio tritonius and Vibrio porteresiae in the Porteresiae clade of the family Vibrionaceae, apparent but inefficient H production from Pyr has been observed. To elucidate the molecular mechanism of why this inefficient H production is observed in Pry-metabolized marine vibrio cells and how glycolysis affects those H productions of marine vibrios, the "Core Transcriptome" approach to find common gene expressions of those two major H producing Vibrio species in Pyr metabolism was first applied. In the Pyr-metabolized vibrio cells, genes for the "Phosphoenolpyruvate (PEP)-Pyruvate-Oxalate (PPO)" node, due to energy saving, and PhoB-, RhaR-, and DeoR-regulons were regulated. Interestingly, a gene responsible for oxalate/formate family antiporter was up-regulated in Pyr-metabolized cells compared to those of Glc-metabolized cells, which provides new insights into the uses of alternative formate exclusion mechanics due to energy deficiencies in Pyr-metabolized marine vibrios cells. We further discuss the contribution of the Embden-Meyerhof-Parnas (EMP) pathway to efficient H production in marine vibrios.