Analysis Of Growth Characteristics And Transcriptome Of Nitzschia Palea In Response To Ammonium Nitrogen In Danjiangkou Reservoir

Danjiangkou Reservoir as the water source for the Middle Route of the South-to-North Water Diversion Project,it is a first-class water source protection area and a national ecological civilization demonstration area.The concentration of ammonia nitrogen in water is an important indicator of water quality evaluation,the change of concentration can directly affect the growth of phytoplankton in water.In this study,a strain of diatom was isolated from phytoplankton in Danjiangkou reservoir using dilution separation and small droplet separation methods.Based on observe the morphological characteristics and homologous analysis of 18S rDNA,SSU rDNA,and rbcL sequences,the strain of diatom obtained from Danjiangkou reservoir was identified as Nitzschia palea.Ammonium nitrogen was selected as nitrogen source to study its effect on the growth of N.palea,the results showed that the maximum growth rate and the cell density were0.2920 d^-1 and 189×10⁴ cells/mL,respectively,when N.palea was supplied with 350μmol/L of ammonium chloride.In the range of 60～700μmol/L,chlorophyll a content of N.palea cultured on the 14th day,with the increase of ammonium nitrogen concentration,it first increased and then decreased.The results suggested that high concentration of ammonium as nitrogen source inhibited the growth of N.palea.N.palea treated with different concentrations of ammonium were used as materials for transcriptome analysis on Illumina HiSeq sequencing platform.Totally,88.53 Gb clean data and 603,376,612 clean reads were obtained and then assembled into 60,001unigenes,of which 19,538 different expression genes（DEGs）were identified.KEGG and GO enrichment analyses showed that many DEGs were associated with a wide range of functions,including photosynthesis,organic acid metabolic process,nitrogen metabolism,Arginine biosynthesis,et al.In addition,38 DEGs were involved in the nitrogen metabolism pathway of N.palea,including glutamine synthetase,nitrate reductase and glutamate synthetase.This study provided not only a basis for mechanism of nitrogen utilization and nitrogen metabolism of diatom in response to nitrogen in fresh water column but also foundation for water quality protection and ecosystem management in Danjiangkou reservoir.