Botryococcus braunii carbon/nitrogen metabolism as affected by ammonia addition

Abstract

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.