title: Nutritional stress effects under different nitrogen sources on the genes in microalga Isochrysis zhangjiangensis and the assistance of Alteromonas macleodii in releasing the stress of amino acid deficiency.
abstract: The expressions of nine nitrogen assimilation-associated genes, NRT2, NAR1, NIA2, NIR, GLN2, GLSF, GSN1, GDH, and AAT2, in the microalga Isochrysis zhangjiangensis were investigated to unveil the effects of limitations of various nitrogen sources (NaNO3 , NH4 Cl, NaNO2 , and an amino acid mixture) on the microalgae. The results demonstrated that the NRT2, NAR1, GLN2, GSN1, and AAT2 genes were highly expressed in lipid-rich microalgae under inorganic nitrogen-deficient conditions and they decreased after nitrogen resupply. Significant increases in the expressions of NAR1, GLN2, and GLSF were found in nitrate-depleted microalgae, whereas significant increases in the expressions of NRT2, NAR1, GLN2, and GSN1 were found in nitrite-depleted microalgae. Significant increases in the expressions of only NRT2 and GSN1 were found in ammonium-depleted microalgae (P < 0.05). Except for the NRT2, other genes were expressed at lower levels under amino acid-deficient conditions compared with amino acid-sufficient controls. The expression of the NIA2 gene decreased in nitrogen-depleted microalgae regardless of the initial nitrogen source. However, the results of fatty acid analyses showed that the features of fatty acid profiles followed a similar mode, in which the percentage compositions of C16:0 and C18:1Δ(9) increased in nitrogen-depleted cells and that of C16:1Δ(9) , C18:3Δ(9,12,15) , C18:4Δ(6,9,12,15) , and C18:5Δ(3,6,9,12,15) decreased, regardless of the type of nitrogen source applied. It was also found that the epiphytic bacterium Alteromonas macleodii played a particularly important role in releasing microalgae from the stress of amino acid deficiency. These findings also provide a foundation for regulating microalgal lipid production through manipulation of the nitrogen assimilation-associated genes.
authors.affiliation: Marine Bioproducts Engineering Group, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning, 116023, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Wu
authors.affiliation: Marine Bioproducts Engineering Group, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning, 116023, China.
authors.forename: Jiannan
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Marine Bioproducts Engineering Group, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning, 116023, China.
authors.forename: Yanjuan
authors.initials: Y
authors.lastname: Xin
authors.affiliation: Marine Bioproducts Engineering Group, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning, 116023, China.
authors.forename: Song
authors.initials: S
authors.lastname: Xue
keywords: Alteromonas macleodii; Isochrysis zhangjiangensis; amino acid nitrogen; epiphytic bacterium; nitrogen assimilation; nitrogen deficiency; nitrogen source indicators