Understanding Hepatopancreas-Associated Microbiota in the Supralittoral Tylos ponticus (Crustacea, Isopoda, Oniscidea): Insights from Next-Generation Sequencing Approaches

Tylos isopods, which are found exclusively in supralittoral beaches, play an important ecological role in the harsh sea-land interface contributing significantly to lignocellulose degradation. Herein, we investigated the hepatopancreatic microbiota in the oniscidean isopod Tylos ponticus Grebnitzky, 1874 from an Italian supralittoral zone characterized by the accumulation of beached leaves from the seagrass Posidonia oceanica. To characterize this Tylos-microbe system, we combined three Next Generation Sequencing techniques: 16S rRNA gene metabarcoding, whole-genome sequencing of cultured hepatopancreatic bacteria and shotgun metagenomic sequencing of uncultured bacterial communities. Comparative analyses revealed that some bacterial taxa were associated with the hepatopancreas of T. ponticus but were also detected in the supralittoral sandy beach where the detritivores Tylos live. However, distinct components of the microbial community may be adapted within the hepatopancreas. Moreover, the assembled and annotated genomes of hepatopancreatic bacteria allowed us to identify genes encoding lignocellulose-degrading CAZymes for a better understanding of the role of symbionts in aiding lignocellulose degradation. Finally, our shotgun sequencing data confirmed the presence of an uncultured Candidatus Hepatoplasma (Mollicutes) in the hepatopancreas of T. ponticus, with the provisional taxonomic assignment as Candidatus Hepatoplasma cf. vulgare Tp. We compared this data with recently reported metagenome-assembled genomes of uncultured Hepatoplasmataceae members from isopods, including Candidatus Tyloplasma litorale identified from the semiterrestrial isopod Tylos granuliferus, Candidatus Hepatoplasma vulgare from the terrestrial isopod Armadillidium vulgare, and Candidatus Hepatoplasma scabrum from the terrestrial isopod Porcellio scaber. In such a scenario, a deeper understanding of halophilic bacteria in the supralittoral zone also has broad relevance to applied research, particularly to the biotechnological sector related to marine biomass conversion and plastic degradation.