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The mesopelagic calanoid copepod Cephalophanes reflugens is characterized by its large eyes with semi-parabolic reflectors. It is hypothesized that the eyes aid in finding crustacean carcasses as food in poor deep-sea light and oligotrophic conditions. Here, the crustacean carcasses-associated luminous, chitin-degrading bacteria may play a vital role in detecting and digesting foods by the copepod. In this study, we collected adult female C. reflugens (n  = 9) from the mesopelagic layers off southwestern Japan in the Pacific Ocean and obtained a total of 47 bacterial isolates from the gut contents. None of the isolates were luminescent, but almost half of the isolates were chitinolytic. Based on the 16S rRNA gene sequences, these chitinolytic bacteria were identified as members of the genus Vibrio , Photobacterium and Pseudoalteromonas. In culture experiments at 15°C, most of the chitinolytic isolates efficiently utilized colloidal chitin as the sole carbon source and degraded the carapace strip of shrimp (Litopenaeus vannamei). Some isolates showed these chitinoclastic activities even at low temperatures (<5°C), equivalent to that of the deep-sea waters. The present results imply that chitin-degrading bacteria significantly contribute to chitin digestion in the gut of C. reflugens , whereas the involvement of luminous bacteria in the feeding mechanism remains unidentified. [ABSTRACT FROM AUTHOR]

Numerous biologically active natural products have been discovered from marine sponges, particularly from Theonella swinhoei, which is known to be a prolific source of natural products such as polyketides and peptides. Recent studies have revealed that many of these natural products are biosynthesized by Candidatus Entotheonella phylotypes, which are uncultivated symbionts within T. swinhoei. Consequently, Entotheonella is considered an untapped biochemical resource. In this study, we conducted metagenomic analyses to assess the diversity of Entotheonella in two T. swinhoei Y and two T. swinhoei W (Y and W referring to the yellow and white interior of the sponge, respectively), after separating filamentous bacteria using density gradient centrifugation. We obtained five Entotheonella metagenome-assembled genomes (MAGs) from filamentous bacteria-enriched fractions. Notably, one of these MAGs is significantly different from previously reported Entotheonella variants. Additionally, we identified closely related Entotheonella members present across different chemotypes of T. swinhoei. Thus, our metagenomic insights reveal that the diversity of Entotheonella within Theonella sponges is greater than previously recognized., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

A macrocylic dodecapeptide, cycloforskamide, was isolated from the sea slug Pleurobranchus forskalii, collected off Ishigaki Island, Japan. Its planar structure was deduced by extensive NMR analyses and was further confirmed by MS/MS fragmentation analyses. Finally, the absolute configuration was determined by total hydrolysis and chiral-phase gas chromatographic analysis. This novel dodecapeptide contains three d-amino acids and three thiazoline heterocycles and exhibits cytotoxicity against murine leukemia P388 cells, with an IC50 of 5.8 μM.

A neuraminidase inhibitor, nobiloside (1), was isolated from the marine sponge Erylus nobilis Thiele, 1903. Its structure was determined as a penasterol trisaccharide. The absolute configurations were determined by NMR and chiral GC analysis. It inhibited neuraminidase from the bacterium Clostridium perfringens with an IC50 value of 0.46 microg/mL.