Mechanisms of ammonium assimilation by chlorella vulgaris F1068: Isotope fractionation and proteomic approaches

Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) Removal of ammonium (NH₄⁺-N) by microalgae has evoked interest in wastewater treatment, however, the detailed mechanisms of ammonium assimilation remain mysterious. This study investigated the effects of NH₄⁺-N concentration on the removal and biotransformation efficiency by Chlorella vulgaris F1068, and explored the mechanisms by ¹⁵N isotope fractionation and proteome approaches. The results showed NH₄⁺-N was efficiently removed (84.8%) by F1068 at 10 mg L⁻¹ of NH₄⁺-N. The isotope enrichment factor (ε=-2.37±0.08‰) of 15N isotope fractionation revealed 47.6% biotransformation at above condition, while 7.0% biotransformation at 4 mg L⁻¹ of NH₄⁺-N (ε=-1.63±0.06‰). This was due to the different expression of glutamine synthetase, a key enzyme in ammonium assimilation, which was up-regulated 6.4-fold at proteome level and 18.0-fold at transcription level. The results will provide a better mechanistic understanding of ammonium assimilation by microalgae and this green technology is expected to reduce the burden of NH₄⁺-N removal for municipal sewage treatment plants. Copyright © 2015 Published by Elsevier Ltd.