When bacteria meet many arms: Autecological insights into Vibrio pectinicida FHCF-3 in echinoderms

Abstract Sea star wasting (SSW) has been described globally in over 25 species of asteroids. This condition is characterized by body wall lesions, loss of turgor and ray autotomy, which often results in the mortality of specimens. The cause of SSW has remained elusive. A recent report detailing a potential causative agent, Vibrio pectenicida FHCF-3 (Prentice et al., 2025), inspired an investigation into its occurrence in available genomic and transcriptomic data from 2013-2015 from wild specimens and those enrolled in experimental incubations. While Vibrio pectenicida FHCF-3 16S rRNA gene sequences were detected in abnormal body wall tissues of Pycnopodia helianthoides from public aquaria in 2013, they were not detected in grossly normal or abnormal body wall specimens of other species sampled concurrently at sites where mass mortality was observed and from public aquaria. Experimental amendment of Pisaster ochraceus with organic matter substrates led to enrichment of V. pectenicida FHCF-3 16S rRNAs at the animal-water interface, and that they surged in abundance 24h prior to body wall lesion appearance. However, in this experiment V. pectenicida FHCF-3 16S rRNAs were inconsistently detected in coelomic fluid of abnormal specimens, and their abundance at specimen surfaces was inversely related to coelomic fluid detections. Perplexingly, V. pectenicida FHCF-3 was detected in abnormal P. helianthoides treated with 0.2 µm filtrates of homogenized tissues, but absent in grossly normal heat-treated filtrate controls in prior work. Vibrio spp, are copiotrophs that experience rapid growth to dominate microbial communities in plankton and tissues when amended to seawater in a mesocosm experiment. These patterns indicate V. pectenicida FHCF-3 might cause abnormalities in P. helianthoides under certain conditions, but its growth might be a secondary rather than primary determinant of disease (i.e. it is saprobic or an opportunistic agent). It remains possible that sea star wasting abnormalities in P. helianthoides represent a generalized response to bacterial infiltration, driven by a diverse set of bacteria which includes but does not require species such as V. pectenicida FHCF-3. Finally, our data suggest that this taxon is not intimately tied to SSW abnormalities in other species. Hence, V. pectenicida FHCF-3 may be a driver of a SSW disease in P. heliathoides, but cannot be the cause of all SSW across species. Competing Interest Statement The authors have declared no competing interest.