Organismic Interactions, Interfaculty Institute of Microbiology and Infection Medicine, Eberhard Karls University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
FEMS Microbiol Lett. 2020 Aug 1;367(15). doi: 10.1093/femsle/fnaa108.
Acid stress is an environmental problem for plants and fresh water cyanobacteria like the filamentous, heterocyst forming species Anabaena sp. PCC 7120 (hereafter Anabaena sp.). Heterocyst differentiation, cell-cell communication and nitrogen fixation has been deeply studied in this model organism, but little is known about the cellular response of Anabaena sp. to decreased pH values, causing acid stress. ATP-binding cassette (ABC) transporters are involved in acid stress response in other bacteria, by exporting proteins responsible for survival under acidification. The genome of Anabaena sp. encodes numerous ABC transporter components, whose function is not known yet. Here, we describe the function of the gene all5304 encoding a protein with homology to membrane fusion proteins of tripartite efflux pumps driven by ABC transporters like HlyBD-TolC of Escherichia coli. The all5304 mutant shows less resistance against low pH, even though the expression of the gene is independent from the pH of the medium. We compared the exoproteome of the wild type and mutant cultures and identified three proteins-candidate substrates of the putative transporter. Including the in silico analysis of All5304, our results suggest that All5304 functions as part of an efflux pump, secreting of a protein necessary for acid tolerance in Anabaena sp.
酸应激是植物和淡水蓝藻（如丝状、异形胞形成物种鱼腥藻 PCC 7120（以下简称鱼腥藻））面临的环境问题。该模式生物的异形胞分化、细胞间通讯和固氮作用已得到深入研究，但对鱼腥藻应对降低 pH 值导致酸应激的细胞反应知之甚少。ATP 结合盒（ABC）转运蛋白参与其他细菌的酸应激反应，通过输出在酸化条件下生存所需的蛋白质。鱼腥藻的基因组编码了许多 ABC 转运蛋白成分，但其功能尚不清楚。在这里，我们描述了编码与 ABC 转运蛋白驱动的三部分外排泵的膜融合蛋白同源的蛋白的基因 all5304 的功能，该蛋白如大肠杆菌的 HlyBD-TolC。all5304 突变体对低 pH 的抗性较低，尽管该基因的表达与培养基的 pH 值无关。我们比较了野生型和突变体培养物的外蛋白质组，鉴定出三种候选转运蛋白的蛋白质。包括对 All5304 的计算机分析，我们的结果表明 All5304 作为外排泵的一部分发挥作用，分泌鱼腥藻耐酸所必需的蛋白质。
