Identification and in situ Detection of Two Lineages of Bacteroidales Ectosymbionts Associated with a Termite Gut Protist, Oxymonas sp.

Bacterial attachments often cover the entire surface of flagellated protists in the guts of termites. Based on PCR-amplified 16S rRNA gene sequences, we investigated the phylogenetic positions of the rod-shaped bacteria (ectosymbionts) attached to the protist Oxymonas sp. in the termite Neotermes koshunensis. Two distinct and unique lineages of the ectosymbionts within the order Bacteroidales were identified, each belonging to a cluster exclusively comprised of the sequences from termite gut. We designed two oligonucleotide probes specific for the two lineages, and successfully detected the ectosymbionts, each of which distributed over the entire surface of Oxymonas sp. However, few cells of Oxymonas sp. simultaneously harbored both lineages of the ectosymbionts.