Shen Jean Lim

1 Introduction Scuticociliates (phylum: Ciliophora, class: Oligohymenophorea, subclass: Scuticociliatia) are prevalent in marine ecosystems, where they serve important trophic roles in food webs (Pierce and Turner 1992). Some scuticociliates cause scuticociliatosis in fishes (Piazzon et al. 2013; Kim et al. 2025), urchins (Hewson et al. 2023; Zirler et al. 2023; Ritchie et al. 2024; Roth et al. 2024), and other marine organisms (Small et al. 2005).

eLife Assessment This valuable study presents findings linking prophage carriage to lifestyle regulation in the marine bacterium Shewanella fidelis, with potential implications for niche occupation within a host (Ciona robusta) and mediation of host immune responses.

Abstract Lysogens, bacteria with one or more viruses (prophages) integrated into their genomes, are abundant in the gut of animals. Prophages often influence bacterial traits; however, the influence of prophages on the gut microbiota-host immune axis in animals remains poorly understood. Here, we investigate the influence of the prophage SfPat on Shewanella fidelis 3313, a persistent member of the gut microbiome of the model marine tunicate, Ciona robusta.