Osman Omneya Ahmed, Beier Sara, Grabherr Manfred, Bertilsson Stefan
Department of Ecology and Genetics, Limnology, and Science for Life Laboratory, Uppsala University, Uppsala, Sweden
Leibniz Institute for Baltic Sea Research, Warnemünde, Germany.
Appl Environ Microbiol. 2017 Mar 17;83(7). doi: 10.1128/AEM.02634-16. Print 2017 Apr 1.
Cyanobacterial and algal mass development, or blooms, have severe effects on freshwater and marine systems around the world. Many of these phototrophs produce a variety of potent toxins, contribute to oxygen depletion, and affect water quality in several ways. Coexisting antagonists, such as cyanolytic bacteria, hold the potential to suppress, or even terminate, such blooms, yet the nature of this interaction is not well studied. We isolated 31 cyanolytic bacteria affiliated with the genera , , , and from three eutrophic freshwater lakes in Sweden and selected four phylogenetically diverse bacterial strains with strong-to-moderate lytic activity. To characterize their functional responses to the presence of cyanobacteria, we performed RNA sequencing (RNA-Seq) experiments on coculture incubations, with an initial predator-prey ratio of 1:1. Genes involved in central cellular pathways, stress-related heat or cold shock proteins, and antitoxin genes were highly expressed in both heterotrophs and cyanobacteria. Heterotrophs in coculture expressed genes involved in cell motility, signal transduction, and putative lytic activity. l,d-Transpeptidase was the only significantly upregulated lytic gene in EK20. Heterotrophs also shifted their central metabolism from the tricarboxylic acid cycle to the glyoxylate shunt. Concurrently, cyanobacteria clearly show contrasting antagonistic interactions with the four tested heterotrophic strains, which is also reflected in the physical attachment to their cells. In conclusion, antagonistic interactions with cyanobacteria were initiated within 24 h, and expression profiles suggest varied responses for the different cyanobacteria and studied cyanolytes. Here, we present how gene expression profiles can be used to reveal interactions between bloom-forming freshwater cyanobacteria and antagonistic heterotrophic bacteria. Species-specific responses in both heterotrophs and cyanobacteria were identified. The study contributes to a better understanding of the interspecies cellular interactions underpinning the persistence and collapse of cyanobacterial blooms.
蓝藻和藻类大量繁殖，即水华，对世界各地的淡水和海洋系统产生了严重影响。许多这类光合生物会产生多种强效毒素，导致氧气消耗，并在多个方面影响水质。共存的拮抗生物，如噬藻细菌，有可能抑制甚至终止此类水华，但这种相互作用的本质尚未得到充分研究。我们从瑞典的三个富营养化淡水湖中分离出31株隶属于、、和属的噬藻细菌，并挑选了四株具有强至中度裂解活性的系统发育多样的细菌菌株。为了表征它们对蓝藻存在的功能反应，我们对共培养物进行了RNA测序（RNA-Seq）实验，初始捕食者与猎物比例为1:1。参与细胞核心途径、应激相关的热或冷休克蛋白以及抗毒素基因在异养生物和蓝藻中均高表达。共培养中的异养生物表达了参与细胞运动、信号转导和假定裂解活性的基因。l,d-转肽酶是EK20中唯一显著上调的裂解基因。异养生物还将其核心代谢从三羧酸循环转变为乙醛酸循环。同时，蓝藻与四种测试的异养菌株明显表现出相反的拮抗相互作用，这也反映在它们与细胞的物理附着上。总之，与蓝藻的拮抗相互作用在24小时内就已开始，表达谱表明不同的蓝藻和所研究的噬藻体有不同的反应。在这里，我们展示了基因表达谱如何用于揭示形成水华的淡水蓝藻与拮抗异养细菌之间的相互作用。鉴定了异养生物和蓝藻中的物种特异性反应。该研究有助于更好地理解支撑蓝藻水华持续和崩溃的种间细胞相互作用。
