Correlation between fixation of high-concentration CO2 and glutamate accumulation in Sulfurovum lithotrophicum 42BKTT

Abstract

Glutamate was identified as a compatible solute for Sulfurovum lithotrophicum 42BKTT, which is a marine chemolithoautotrophic bacterium and performs CO2 fixation through the reductive tricarboxylic acid (TCA) cycle. In a medium of 20g/L or higher concentration of NaCl, sufficient to induce osmotic stress, the intracellular level of glutamate rapidly increased on exposure to high levels of NaHCO3. Correlation of the glutamate accumulation with the level of NaHCO3 was determined and compared to that with the level of NaCl. Glutamate synthesis driven by NaHCO3 was measured at 1.29mg Glu/mg protein/(Osmol/L), and 18.4 times higher than that driven by NaCl (0.07mg Glu/mg protein/(Osmol/L)). Thus, the synthesis of glutamate from 2-oxoglutarate, which is the first product of CO2 assimilation in the reductive TCA cycle, was triggered at the exposure to the high level of NaHCO3 and appeared to support S. lithotrophicum 42BKTT via resistance to osmotic stress and CO2 toxicity.