Cloning and transcription analysis of the nitrate reductase gene from Haematococcus pluvialis

Objectives To optimize the cultivation media for the growth rate of Haematococcus pluvialis and to study the transcription regulation of the algal nitrate reductase (NR), a key enzyme for nitrogen metabolism. Results The NR gene from H. pluvialis hd7 consists of 5636 nucleotides, including 14 introns. The cDNA ORF is 2718 bp, encoding a 905 aa protein with three conserved domains. The NR amino acids of H. pluvialis hd7 are hydrophilic and have similarity of 72% compared to that of Dunaliella. NR transcription increased with an increase of nitrate concentration from 0.4 to 1 g/l. A deficiency of nitrogen increased NR transcription significantly. The transcription level of NR increased at phosphorus concentrations from 0.08 to 0.2 g/l, with a maximum at 0.08 g/l. The optimum parameters of medium component for transcription of NR and growth of H. pluvialis were 0.3 g NaNO 3 /l, 0.045 g KH 2 PO 4 /l and 1.08 g sodium acetate/l. Conclusions This study provides a better understanding of nitrate regulation in H. pluvialis .