sp. nov., a novel isolated from a tropical fish (bushymouth catfish).

The is a family of strict, intracellular bacteria which include human and animal pathogens such as and . Following the death of multiple fish (bushymouth catfish) in a tropical aquarium, the specimens were examined for a potential infectious agent. To do so, McCoy cells (ATCC CRL-1696) were inoculated with samples isolated from the specimens and became infected by an intracellular bacterium. The entire genome of the infectious agent was sequenced (study accession PRJEB69484) and, based on nine taxonomic markers, was classified as a novel species belonging to the genus (DSMZ no. 117479, CSUR no. QA1836). We propose the name sp. nov., in memory of the late Professor Lloyd Vaughan. has the largest genome (1.3 Mbp) of the genus. This appears to be a consequence of multiple duplications in genes encoding putative adhesins. Like other pathogenic , it can infect mammalian cells, but it cannot infect either insect or amoeba cells. It additionally can grow in Epithelioma papulosum cyprinis (EPC) cells (fathead minnow, ATCC CRL-2872) but only when cultivated at 30 °C. We developed a -specific quantitative PCR which amplifies the gene and analysed several samples from the aquarium. was retrieved from all deceased fish, but not from any other sample in the aquarium, suggesting that it indeed originated from the fish and was not a contaminant. is the first isolated from fish.