High activity and stability of codon-optimized phosphoenolpyruvate carboxylase from Photobacterium profundum SS9 at low temperatures and its application for in vitro production of oxaloacetate

Efficient production and secretion of oxaloacetate from Halomonas sp. KM-1 under aerobic conditions

The alkaliphilic, halophilic bacterium Halomonas sp. KM-1 can utilize glucose for the intracellular storage of the bioplastic poly-(R)-3-hydroxybutyric acid (PHB) and extracellular secretion of pyruvate under aerobic conditions. In this study, we investigated the effects of sodium chloride concentration on PHB accumulation and pyruvate secretion in the KM-1 strain and, unexpectedly, observed that oxaloacetate, an important intermediate chemical in the TCA cycle, glycogenesis, and aspartic acid biosynthesis, was secreted. We then further analyzed oxaloacetate productivity after changing the sodium chloride additive concentration, additive time-shift, and culture temperature. In 42-h batch-cultivation experiments, we found that wild-type Halomonas sp. KM-1 secreted 39.0 g/L oxaloacetate at a rate of 0.93 g/(L h). The halophilic bacteria Halomonas has already gained attention for industrial chemical-production processes owing to its unique properties, such as contamination-free culture conditions and a tolerance for high substrate concentrations. Moreover, no commercial scale oxaloacetate production was previously reported to result from bacterial fermentation. Oxaloacetate is an important intermediate chemical in biosynthesis and is used as a health food based on its role in energy synthesis. Thus, these data provided important insights into the production of oxaloacetate and other derivative chemicals using this strain.

Characterization of Phosphoenolpyruvate Carboxylase from Oceanimonas smirnovii in Escherichia coli

In this study, phosphoenolpyruvate carboxylase (PEPC) derived from Oceanimonas smirnovii (OS) was expressed as a soluble protein in Escherichia coli BL21(DE3). We isolated OS-PEPC (a recombinant PEPC protein) by his-tag purification. The purified protein showed a single band upon analysis with SDS-PAGE, and it had an apparent molecular mass of 98 kDa. Pufied OS-PEPC showed a specific activity value of 21.8 ± 0.495 U/mg protein. Especially, OS-PEPC showed the enzymatic activity between 40 and 50 °C. It maintained enzymatic activity in basic pH conditions (pH value, 9-10). We also measured OS-PEPC PEP and HCO3 (-) saturation kinetics and confirmed the effect of divalent cation on OS-PEPC activity.