Snapshot of the Bacterial Composition of Two Invertebrates, Peltodoris atromaculata and Petrosia ficiformis, from a Shallow Hydrothermal Spring on the West Coast of Sicily

Hydrothermal springs (HTSs) are unique environments characterized by the emergence of geothermally heated groundwater that often releases large amounts of dissolved minerals. Despite the interest in HTSs, the microbial composition of these sites remains largely under-explored, particularly concerning the interactions between marine invertebrates and microorganisms. The shallow HTSs near the west coast of Sicily (Italy), with a constant temperature of 31 degrees C throughout the year, host two invertebrates: the nudibranch Peltodoris atromaculata (P. atromaculata) and the sponge Petrosia ficiformis (P. ficiformis). Using Next-Generation Sequencing (NGS) of the bacterial 16S rRNA gene marker, the bacterial communities of these invertebrates were analyzed. Microbial diversity was higher in the P. atromaculata mantle and in P. ficiformis than in the P. atromaculata gut, with notable differences in families such as Caldilineaceae, Endozoicomonadaceae, Alteromonadaceae, and Enterobacteriaceae, showing abundance variations among the samples. Unique bacterial signatures, including Mycoplasmataceae, Endozoicomonadaceae, and Alteromonadaceae in the gut and Enterobacteriaceae in the mantle of P. atromaculata, were also identified. These findings provide valuable insights into the bacterial diversity of these two marine invertebrates, which are recognized as bioindicators of environmental conditions.