Tunicate-associated bacteria show a great potential for the discovery of antimicrobial compounds

Abstract

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.

Bacterial isolates from bryozoan Pleurocodonellina sp.: Diversity and antimicrobial potential against pathogenic bacteria

“…All 12 strains of Virgibacillus-related isolates in this study were also validly marine origin bacteria. Compared to this results, the genus Virgibacillus is commonly associated in other marine organisms in Java Sea such as; corals (Kristiana et al 2017;) and ascidians (Ayuningrum et al 2019).…”

“…From what is known of other tropical regions (Almeida et al 2015;Almeida et al 2017;Almeida et al 2018), it is likely that the majority of the hard-shore and coral-associated intertidal zones of the Java Sea would have many more bryozoan species including genus Pleurocodonellina. The study of potential bacteria isolated from bryozoans is not as comprehensive as for other marine organisms such as sponges (Asagabaldan et al 2017), corals (Sibero et al 2019) and ascidians (Ayuningrum et al 2019) in the Java Sea; indeed, no information exists. Teluk Awur is located in the central Java Sea, the latter presenting a wide variety of associated rich organismal communities.…”

“…These antagonistic interactions between marine bacteria and infectious human bacteria might be an important aspect in discovering new source of pharmaceutical agents. In the previous study, Ayuningrum et al (2019) isolated similar bacteria (Virgibacillus, Pseudoalteromonas, Bacillus, and Halomonas comprising 56% of all isolates) from ascidians and tested them against different human pathogen bacteria (B. cereus, B. megaterium, E. coli, ESBL, and Micrococcus luteus). In this case, the authors discovered compound isatin that isolated from genus Pseudoalteromonas, since their best activities against all indicator organisms, which was similar to our results.…”

Antibacterial potential of nudibranch-associated bacteria from Saparua and Nusa Laut Islands, Indonesia

“…The 96 well plates were incubated overnight at 37 0 C in a shaker at 210 rpm and using MTT (4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide) methods as color-based indicators of antibacterial activity. Vancomycin was used as positive control and DMSO (Dimethyl sulfoxide) were used as a negative control (Ayuningrum et al 2019).…”

Antibiotics Development and the Potentials of Marine-Derived Compounds to Stem the Tide of Multidrug-Resistant Pathogenic Bacteria, Fungi, and Protozoa

“…The ethyl acetate crude extracts from liquid fermentation of tunicates-associated Gram-negative marine bacterium, Pseudoalteromonas rubra TKJD 22 (Indonesia) exhibited anti-MDR activity against some pathogens, including MDR E. coli and MDR-ESBL E. coli. The active compound in the fraction was identified to be a red-orange crystalline solid, isatin (Figure 3B)[69]. Streptomyces sp.…”