{"title":"The ammonium transporter AmtB is dispensable for the uptake of ammonium in the phototrophic diazotroph Rhodopseudomonas palustris","authors":"","doi":"10.1016/j.eti.2024.103853","DOIUrl":null,"url":null,"abstract":"<div><div>Ammonium (NH<sub>4</sub><sup>+</sup>) transport across cell membranes plays an important role in assimilation or removal of the environmental nitrogen. The membrane protein AmtB has been considered to be the NH<sub>4</sub><sup>+</sup> transporter that is responsible for the NH<sub>4</sub><sup>+</sup> uptake. The phototrophic diazotroph <em>Rhodopseudomonas palustris</em> harboring two <em>amtB</em> genes has been widely used in wastewater treatment and bioremediation. However, the role of AmtB in NH<sub>4</sub><sup>+</sup> uptake remains unclear in <em>R. palustris</em>. Here, we employed an innovative approach combining stable isotope probing (SIP) with Raman spectroscopy to determine the physiological functions of AmtB1 and AmtB2 in <em>R. palustris.</em> This powerful technique allowed us to investigate NH<sub>4</sub><sup>+</sup> uptake at the single-cell level. The generated <em>R. palustris</em> Δ<em>amtB1</em> Δ<em>amtB2</em> mutant lacking AmtB1 and AmtB2 proteins was still capable of utilizing <sup>15</sup>NH<sub>4</sub><sup>+</sup> even the <sup>15</sup>NH<sub>4</sub><sup>+</sup> concentration was as low as 5 μM. These data demonstrate that both of the AmtB proteins are not essential for <em>R. palustris</em> to take up NH<sub>4</sub><sup>+</sup> regardless of environmental NH<sub>4</sub><sup>+</sup> levels. However, both AmtB1 and AmtB2 can contribute to NH<sub>4</sub><sup>+</sup> uptake under nitrogen-limiting conditions. Given that <em>R. palustris</em> primarily expresses AmtB2 in these conditions, AmtB2 plays a more important role in NH<sub>4</sub><sup>+</sup> uptake compared to AmtB1. In addition, transcriptomic analysis showed that the deletion of the <em>amtB1</em> and <em>amtB2</em> genes resulted in the upregulation of many transporter genes, providing potential targets for future investigation of alternative NH<sub>4</sub><sup>+</sup> uptake systems.</div></div>","PeriodicalId":11725,"journal":{"name":"Environmental Technology & Innovation","volume":null,"pages":null},"PeriodicalIF":6.7000,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Environmental Technology & Innovation","FirstCategoryId":"93","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S2352186424003298","RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"BIOTECHNOLOGY & APPLIED MICROBIOLOGY","Score":null,"Total":0}
引用次数: 0
Abstract
Ammonium (NH4+) transport across cell membranes plays an important role in assimilation or removal of the environmental nitrogen. The membrane protein AmtB has been considered to be the NH4+ transporter that is responsible for the NH4+ uptake. The phototrophic diazotroph Rhodopseudomonas palustris harboring two amtB genes has been widely used in wastewater treatment and bioremediation. However, the role of AmtB in NH4+ uptake remains unclear in R. palustris. Here, we employed an innovative approach combining stable isotope probing (SIP) with Raman spectroscopy to determine the physiological functions of AmtB1 and AmtB2 in R. palustris. This powerful technique allowed us to investigate NH4+ uptake at the single-cell level. The generated R. palustris ΔamtB1 ΔamtB2 mutant lacking AmtB1 and AmtB2 proteins was still capable of utilizing 15NH4+ even the 15NH4+ concentration was as low as 5 μM. These data demonstrate that both of the AmtB proteins are not essential for R. palustris to take up NH4+ regardless of environmental NH4+ levels. However, both AmtB1 and AmtB2 can contribute to NH4+ uptake under nitrogen-limiting conditions. Given that R. palustris primarily expresses AmtB2 in these conditions, AmtB2 plays a more important role in NH4+ uptake compared to AmtB1. In addition, transcriptomic analysis showed that the deletion of the amtB1 and amtB2 genes resulted in the upregulation of many transporter genes, providing potential targets for future investigation of alternative NH4+ uptake systems.
期刊介绍:
Environmental Technology & Innovation adopts a challenge-oriented approach to solutions by integrating natural sciences to promote a sustainable future. The journal aims to foster the creation and development of innovative products, technologies, and ideas that enhance the environment, with impacts across soil, air, water, and food in rural and urban areas.
As a platform for disseminating scientific evidence for environmental protection and sustainable development, the journal emphasizes fundamental science, methodologies, tools, techniques, and policy considerations. It emphasizes the importance of science and technology in environmental benefits, including smarter, cleaner technologies for environmental protection, more efficient resource processing methods, and the evidence supporting their effectiveness.