Abstract: Nitrogen-fixing Pseudomonas stutzeri A1501 can grow with nitrate/nitrite as the sole nitrogen source under aerobic conditions, suggesting that the strain has a nitrate/nitrite system in addition to nitrogen fixation and denitrification. In order to further clarify the metabolic mechanism of nitrate assimilation, bioinformatics method was used to analyze the composition and distribution of genes related to nitrate assimilation, and the pathway-specific control of nitrate assimilation was preliminarily studied. The results indicated that there were two nitrate assimilation gene clusters, nasST-nasA-nirBDnasBcobA and nasR-nasFED, distributed in different parts of the genome. In the first gene cluster, nasS-nasT encoded two-component regulatory system based on nitrate/nitrite sensing and transcription anti-termination, nasA encoded NarK/NasA family nitrate transporter, nirBD encoded nitrite reductase, nasB encoded assimilatory nitrate reductase, and cobA encodes uroporphyrin-Ⅲ C-methyltransferase involved in the synthesis of sirohaem. In the second gene cluster, nasR encoded a single-component transcription anti-terminator and nasFED encoded an ATP-dependent nitrate/nitrite transporter. Nitrate/nitrite reductase gene transcription was regulated by NasS-NasT, and nitrate/nitrite transporter gene transcription was regulated by NasR.

Key words: Pseudomonas stutzeri A1501, nitrate assimilation, gene cluster, Pathway-specific control

摘要： 固氮施氏假单胞菌（Pseudomonas stutzeri）A1501在有氧条件下能够利用硝酸盐/亚硝酸盐为唯一氮源生长，表明该菌除了具有固氮和反硝化等氮循环系统外还有同化硝酸盐/亚硝酸盐系统。为进一步阐明该菌同化硝酸盐的代谢机制，利用生物信息学手段分析了硝酸盐同化相关基因的组成及分布情况，并初步研究了同化硝酸盐途径特异性调控关系。结果表明， P. stutzeri A1501中存在两个硝酸盐同化基因簇nasST-nasA-nirBDnasBcobA和nasR-nasFED,分布于基因组不同部位。第一个基因簇中nasS-nasT编码二元抗转录终止因子，nasA编码NarK/NasA家族硝酸盐转运蛋白，nirBD编码亚硝酸盐还原酶，nasB编码同化硝酸盐还原酶，cobA编码参与西罗血红素合成的尿卟啉-Ⅲ C-甲基转移酶；第二个基因簇中nasR编码单一组分抗转录终止因子，nasFED编码ABC型（ATP依赖）硝酸盐/亚硝酸盐转运蛋白。NasS-NasT双组分蛋白调控硝酸盐/亚硝酸盐还原酶基因的转录，NasR调控硝酸盐/亚硝酸盐转运蛋白基因的转录。

关键词: 施氏假单胞菌A1501, 硝酸盐同化, 基因簇, 途径特异性控制