Botryococcus braunii carbon/nitrogen metabolism as affected by ammonia addition

Carbon metabolism in photosynthesizing and respiring cells of Botryococcus braunii was radically changed by the presence of 1 mM NH₄Cl in the medium, when the so-called resting state previously had been subjected to a nitrogen-deficient medium. Ammonia addition to the algae photosynthesizing with ¹⁴C-labelled HCO ₃ ^- almost completely inhibited the synthesis of ¹⁴C-labelled botryococcenes and other hexane-extractable compounds, and also inhibited the formation of insoluble compounds; however, it resulted in a large increase in the synthesis of alanine, glutamine, other amino acids, and especially of 5-aminolevulinic acid. Total CO₂ fixation decreased about 60% and O₂ evolution decreased more than 50%.CO₂ fixation in the dark with ammonia present led to labelled products derived from phosphoenolpyruvate carboxylation, such as glutamine, glutamate, and malate. Respiratory uptake of O₂ increased by about 70%.The inhibition of terpenoid synthesis and increased synthesis of C₅ amino acids by Botryococcus upon ammonia addition indicates 1) a diversion of acetyl coenzyme A from synthetic pathways leading to terpenoids and 2) increased operation of pathways leading to the synthesis of amino acids, especially 5-aminolevulinic acid, a precursor to chlorophyll biosynthesis.This work was supported in part by the Office of Energy Research, Office of Basic Energy Sciences, Biological Energy Research Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098, in part by a grant from SOHIO, and, in part, by a grant from the Japan-U.S. Cooperative Science Program (The Japan Society for the Promotion of Science, National Science Foundation, Division of International Programs)