Smeulders Marjan J, Peeters Stijn H, van Alen Theo, de Bruijckere Daan, Nuijten Guylaine H L, Op den Camp Huub J M, Jetten Mike S M, van Niftrik Laura
Department of Microbiology, Institute for Water and Wetland Research, Faculty of Science, Radboud University Nijmegen, Nijmegen, Netherlands.
Front Microbiol. 2020 Aug 13;11:1959. doi: 10.3389/fmicb.2020.01959. eCollection 2020.
Anaerobic ammonium-oxidizing (anammox) bacteria, members of the " Brocadiaceae" family, play an important role in the nitrogen cycle and are estimated to be responsible for about half of the oceanic nitrogen loss to the atmosphere. Anammox bacteria combine ammonium with nitrite and produce dinitrogen gas via the intermediates nitric oxide and hydrazine (anammox reaction) while nitrate is formed as a by-product. These reactions take place in a specialized, membrane-enclosed compartment called the anammoxosome. Therefore, the substrates ammonium, nitrite and product nitrate have to cross the outer-, cytoplasmic-, and anammoxosome membranes to enter or exit the anammoxosome. The genomes of all anammox species harbor multiple copies of ammonium-, nitrite-, and nitrate transporter genes. Here we investigated how the distinct genes for ammonium-, nitrite-, and nitrate- transport were expressed during substrate limitation in membrane bioreactors. Transcriptome analysis of planktonic cells showed that four of the seven ammonium transporter homologs and two of the nine nitrite transporter homologs were significantly upregulated during ammonium-limited growth, while another ammonium transporter- and four nitrite transporter homologs were upregulated in nitrite limited growth conditions. The two nitrate transporters were expressed to similar levels in both conditions. In addition, genes encoding enzymes involved in the anammox reaction were differentially expressed, with those using nitrite as a substrate being upregulated under nitrite limited growth and those using ammonium as a substrate being upregulated during ammonium limitation. Taken together, these results give a first insight in the potential role of the multiple nutrient transporters in regulating transport of substrates and products in and out of the compartmentalized anammox cell.
厌氧氨氧化（anammox）细菌属于“布罗卡德氏菌科”，在氮循环中发挥着重要作用，据估计，海洋中约一半的氮损失到大气中都由其负责。厌氧氨氧化细菌将铵与亚硝酸盐结合，并通过一氧化氮和肼等中间体产生氮气（厌氧氨氧化反应），同时形成硝酸盐作为副产物。这些反应发生在一个特殊的、被膜包围的隔室中，称为厌氧氨氧化体。因此，底物铵、亚硝酸盐和产物硝酸盐必须穿过外膜、细胞质膜和厌氧氨氧化体膜才能进出厌氧氨氧化体。所有厌氧氨氧化物种的基因组都含有多个铵、亚硝酸盐和硝酸盐转运蛋白基因的拷贝。在这里，我们研究了在膜生物反应器中底物受限期间，铵、亚硝酸盐和硝酸盐转运的不同基因是如何表达的。对浮游细胞的转录组分析表明，在铵受限生长期间，七个铵转运蛋白同源物中的四个和九个亚硝酸盐转运蛋白同源物中的两个显著上调，而在亚硝酸盐受限生长条件下，另一个铵转运蛋白和四个亚硝酸盐转运蛋白同源物上调。两种硝酸盐转运蛋白在两种条件下的表达水平相似。此外，参与厌氧氨氧化反应的酶的编码基因也有差异表达，以亚硝酸盐为底物的那些基因在亚硝酸盐受限生长时上调，以铵为底物的那些基因在铵受限期间上调。综上所述，这些结果首次揭示了多种营养物质转运蛋白在调节底物和产物进出分隔的厌氧氨氧化细胞的运输中的潜在作用。
