Tunicates (Ascidians, sea squirts) are marine protochordates, which live sedentary or sessile in colonial or solitary forms. These invertebrates have to protect themselves against predators and invaders. A most successful strategy, to not being eaten by predators and prevent pathogenic microorganisms to settle, is the usage of chemical molecules for defence. To accomplish this, tunicates take advantage of the specialized metabolites produced by the bacteria associated with them. Therefore, the microbiome of the tunicates can be regarded as a promising bioresource for bacterial strains producing compounds with antibacterial activity. The aim of this study was to test this hypothesis by (i) isolation of tunicate-associated bacteria, (ii) analysis of the antibacterial activities of these strains, and (iii) purification and structure elucidation of an active compound derived from this bioresource. In total, 435 bacterial strains were isolated and thereof 71 (16%) showed antibacterial activity against multidrug resistant (MDR) bacteria. Therefrom, the ethyl acetate crude extracts from liquid fermentations of 25 strains showed activity against MDR Extended-Spectrum Beta-Lactamase (MDR-ESBL) Escherichia coli, MDR Bacillus cereus, Micrococcus luteus, and Bacillus megaterium. Phenotypic analysis based on 16S rDNA sequencing revealed the active strains belonging to different genera and phyla, like Bacillus, Pantoea, Pseudoalteromonas, Salinicola, Streptomyces, Vibrio and Virgibacillus. To obtain first insights into the molecules responsible for the antibacterial activities observed, strain Pseudoalteromonas rubra TKJD 22 was selected for large-scale fermentation and the active compound was isolated. This allowed the purification and structure elucidation of isatin, a compound known for its strong biological effects, thereunder inhibition of Gram-positive and Gram-negative pathogens.

中文翻译：

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被膜相关细菌显示出发现抗菌化合物的巨大潜力。

被膜（海鞘，海鞘）是海洋原生动物，以定居或单居形式生活在久坐或无柄的状态。这些无脊椎动物必须保护自己免受掠食者和入侵者的侵害。一种最成功的策略是使用化学分子进行防御，以防止被天敌捕食，并防止病原微生物沉降。为了做到这一点，被膜剂利用了由与其相关的细菌产生的专门代谢产物。因此，被膜的微生物组可以被认为是产生具有抗菌活性的化合物的细菌菌株的有前途的生物资源。这项研究的目的是通过（i）分离与被膜菌相关的细菌，（ii）分析这些菌株的抗菌活性，来检验这一假设。（iii）纯化和阐明源自该生物资源的活性化合物。总共分离出435株细菌，其中71株（16％）对多药耐药（MDR）细菌表现出抗菌活性。从中，来自25个菌株的液体发酵的乙酸乙酯粗提取物显示出对MDR超广谱β-内酰胺酶（MDR-ESBL）大肠杆菌，MDR蜡样芽孢杆菌，黄褐微球菌和巨大芽孢杆菌的活性。基于16S rDNA测序的表型分析显示了属于不同属和门的活性菌株，如芽孢杆菌，泛菌，假单胞菌，沙门氏菌，链霉菌，弧菌和病毒杆菌。为了初步了解负责观察到的抗菌活性的分子，选择菌株Pseudoalteromonas rubra TKJD 22进行大规模发酵，并分离出活性化合物。这样就可以纯化和阐明伊斯兰丁（一种以其强大的生物学效应而闻名的化合物），从而抑制了革兰氏阳性和革兰氏阴性病原体。