The king scallop Pecten maximus L. is the fastest growing fishery in the UK
and currently the second most valuable. Mass mortality events in scallops have
been reported associated with rickettsia-like organisms (RLOs) world-wide,
however the causative agents were uncharacterised. In May 2013 and 2014 two
mass mortality events affecting king scallops were recorded in the Lyme Bay
Marine Protected Area (MPA) South West England. Histopathological examination
showed gill epithelial tissue infected with RLO at varying intensity.
Ultrastructural examination confirmed the intracellular location in affected
epithelial cells. Partial 16S rDNA sequences of a putative RLO obtained from
infected king scallop gill samples collected from both mortality events were
identical and had 99.4% identity to 16S rDNA sequences obtained from
Candidatus endonucleobacter bathymodioli and 95% with Endozoicomonas spp. In
situ hybridisation assays using 16S rDNA probes confirmed the presence of the
sequenced RLO gene in the gill tissues. Additional DNA sequences of the
bacterium were obtained using high-throughput (Illumina) sequencing and
bioinformatic analysis identified over 1000 genes with high similarity,
ranging from 77-87% identity, to genes from Endozoicomonas spp.
