Xinpeng Fan | Search PubMed

PubMed2026

Detection of endocytobionts inhabiting the macronucleus of Frontonia paramagna (Ciliophora, Peniculida).

Bacterial endosymbionts of Frontonia, a widely distributed ciliate genus, remain poorly characterized. Here, we investigated the endosymbiotic microbiota of a Shanghai population of Frontonia paramagna using an integrated morphological and molecular approach. Fluorescence in situ hybridization (FISH) targeting the 16S rRNA gene, coupled with V3-V4 high-throughput sequencing, consistently identified Caedimonas as the bacterial symbiont, specifically localized within the host macronucleus. FISH and transmission electron microscopy confirmed this intramacronuclear colonization with high prevalence and revealed that the symbionts lack flagella and R-bodies. Phylogenetic analysis of full-length 16S rRNA gene sequences placed the F. paramagna symbionts within a well-supported clade containing Caedimonas from divergent hosts. Comparative analysis of the 16S rRNA internal excised element (IEE) showed substantial sequence and secondary structural divergence between the Frontonia-associated lineage and other Caedimonas strains from different ciliates. We conservatively designate this lineage as Caedimonas varicaedens Fpa. These distinct molecular features suggest that the diversity and host distribution of Caedimonas are far from fully described, and genomic approaches will be necessary to evaluate species delimitation within the genus and the possible presence, distribution, and horizontal transfer of R-body genetic determinants.

16S rRNA gene↗

PubMed2026

Biocontrol potential and molecular basis of predation in a marine raptorial ciliate.

Predator-prey interactions are widespread across organisms and are key drivers of morphological and behavioral evolution. Despite this, predation remains poorly understood among microbial eukaryotes, mostly due to the absence of a tractable experimental system that allows quantitative, reproducible investigation. This study establishes the marine raptorial ciliate Chaenea vorax as a highly efficient predator, with Rosenzweig-MacArthur model simulations based on predation data showing that only a few dozen individuals can eliminate the vast majority of the facultatively pathogenic ciliate Uronema marinum within 1-2 days, providing a quantitative basis for developing predator-based biocontrol strategies in aquaculture. Genomic analysis shows that C. vorax possesses a highly fragmented macronuclear genome enriched with predation-related pathways, including calcium-mediated contractility, cellular proteolysis, toxin expulsion systems, among others. Transcriptomic profiling during predation events further demonstrates significant upregulation of genes involved in cytoskeletal remodeling, proteolytic activity, and cellular detoxification. Evolutionary analyses suggest that C. vorax has an extremely long evolutionary history, exceptionally high nucleotide diversity even among ciliates, and gene family expansions linked to predatory adaptation. Although the prey possesses certain defensive mechanisms (e.g. trichocysts), these are largely ineffective against short-term predation in closed aquatic environments. These findings provide fundamental insights into the molecular basis of predation in ciliates and suggest the potential utility of C. vorax in biocontrol applications targeting pathogenic ciliates.

Ciliophora↗