Isolation and characterization of bacteria from the gut of a mesopelagic copepod Cephalophanes reflugens (Copepoda: Calanoida)

• Published in: Journal of plankton research 2024-01, Vol.46 (1), p.48-58
• Main Authors: Hirano, Katsushi, Nakai, Toshihiro, Nagai, Takahiro, Takada, Kentaro, Fujii, Sotaro, Sambongi, Yoshihiro, Kondo, Yusuke, Komeda, Sota, Nakaguchi, Kazumitsu, Yamaguchi, Shuhei, Maekawa, Youichi, Nakamura, Toru, Oba, Yuichi, Ohtsuka, Susumu
• Format: Article
• Language: English
• ISSN: 0142-7873; 1464-3774
• DOI: 10.1093/plankt/fbad049

Abstract 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 (