アイテム詳細

要旨

In our recently published genomes of Blepharisma stoltei (Seah et al. 2023; Singh et al. 2023), we found a gene pair with a high sequence identity to the reference genome of the alphaproteobacterium Caedimonas varicaedens (Suzuki et al. 2015). This obligate intracellular bacterium is known for conferring the “killer trait” to host paramecia (Preer et al. 1974) but has not been described in Blepharisma before and is absent from our lab cultures. A strain of C. varicaedens has, however, been described in a Euplotes species (Boscaro et al. 2019), showing a potential for wider distribution across the ciliate tree. The genes we found are transcribed and poly(A)-tailed like conventional eukaryotic genes, and are also encoded on long reads containing an internally eliminated sequence characteristic of Blepharisma germline DNA. So, it appears they are present in the Blepharisma genome, rather than an artefact from contamination or misassembly, and are therefore a product of a relatively recent horizontal gene transfer. Of the two genes, only one (lpxC), homologous to a key enzyme in the production of endotoxin A in gram negative bacteria, is full length and might therefore still be functional. Aside from an lpxB homolog independently acquired earlier in its evolutionary history, Blepharisma lacks the remaining enzymes of the pathway and thus would be incapable of producing the toxin. We are currently exploring whether exposure to infected Paramecium biaurelia cultures can lead to infection of Blepharisma with Caedimonas.