Antibiotic producers have mainly been isolated from soil, which often has led to the rediscovery of known compounds. In this study, we identified the freshwater snail Physa acuta as an unexplored source for new antibiotic producers. The bacterial diversity associated with the snail was characterized by a metagenomic approach using cultivation-independent high-throughput sequencing. Although Actinobacteria represented only 2% of the bacterial community, the focus was laid on the isolation of the genus Streptomyces due to its potential to produce antibiotics. Three Streptomyces strains (7NS1, 7NS2 and 7NS3) were isolated from P. acuta, and the antimicrobial activity of the crude extracts were tested against a selection of Gram-positive and Gram-negative bacteria and fungi. 7NS3 showed the strongest activity against Gram-positive bacteria and, thus, was selected for genome sequencing and a phylogenomic analysis. 7NS3 represents a novel Streptomyces species, which was deposited as Streptomyces sp. DSM 110735 at the Leibniz Institute-German Collection of Microorganisms and Cell Cultures (DSMZ). Bioassay-guided high-performance liquid chromatography (HPLC) and high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS) analyses of crude extract fractions resulted in the detection of four compounds, one of which matched the compound characteristics of emycin A, an angucycline-like aromatic polyketide. Genome mining studies based on the whole-genome sequence of 7NS3 resulted in the identification of a gene cluster potentially coding for emycin A biosynthesis. Our study demonstrates that freshwater snails like P. acuta can represent promising reservoirs for the isolation of new antibiotic-producing actinobacterial species.

中文翻译：

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新型链霉菌属物种的类似安古环素的芳香族聚酮化合物揭示了淡水蜗牛癣是未开发的生产抗生素放线菌的水库。

抗生素生产者主要是从土壤中分离出来的，这通常导致重新发现已知化合物。在这项研究中，我们确定了淡水蜗牛Physa acuta是新的抗生素生产商的未开发来源。与蜗牛相关的细菌多样性通过使用与培养无关的高通量测序的宏基因组学方法进行了表征。尽管放线菌仅占细菌群落的2％，但由于其具有产生抗生素的潜力，因此重点放在了链霉菌属的分离上。从铜绿假单胞菌中分离出三种链霉菌菌株（7NS1、7NS2和7NS3）。，并针对选择的革兰氏阳性和革兰氏阴性细菌和真菌测试了粗提物的抗菌活性。7NS3对革兰氏阳性细菌表现出最强的活性，因此被选择用于基因组测序和系统进化分析。7NS3代表一种新的链霉菌种，已被存放为链霉菌sp。莱布尼兹研究所-德国微生物和细胞培养物保藏中心（DSMZ）的DSM 110735。生物测定指导的高效液相色谱（HPLC）和高分辨率电喷雾电离质谱（HR-ESI-MS）分析粗提物馏分可检测出四种化合物，其中一种与艾霉素A的化合物特征相符，一种类似安古环素的芳香族聚酮化合物。基于7NS3全基因组序列的基因组挖掘研究导致鉴定了可能编码阿霉素A生物合成的基因簇。我们的研究表明，淡水蜗牛（如Acuta）可以代表有前途的水库，用于分离产生新抗生素的放线菌。