Molecular detection of protists associated with the Manila clam Ruditapes philippinarum inhabiting the Wajiro tidal flat in Hakata Bay, Fukuoka Prefecture

Abstract

Tidal flats are ecologically important as they support a large community of animals (e.g., crabs, mollusks, and polychaetes) and restore water quality. However, information regarding microbial eukaryotes, most of which are protists, associated with animals inhabiting these environments is limited. In the present study, utilizing polymerase chain reaction techniques, we detected fragments of the small subunit ribosomal RNA (SSU rRNA) gene of protists from the gill tissues of the Manila clam Ruditapes philippinarum in the Wajiro tidal flat, Hakata Bay, Japan. Based on the phylogeny of the SSU rRNA gene, the detected organisms were shown to belong to not only Perkinsozoa but also to Ciliophora, Kinetoplastida, and Haplosporidia. For the protist affiliated with Perkinsozoa, the internal transcribed spacer (ITS) of the rRNA genes was retrieved from the same gill tissue samples for precise identification at the species level. The ITS sequence obtained was identical to that of Perkinsus olseni, which is highly prevalent in Manila clam populations in Japan. Our findings suggest that protists potentially parasitic on this representative mollusk in tidal flats are phylogenetically diverse, and that the organisms detected may affect the population dynamics of the host clams.