‘Candidatus Mellornella promiscua’ n. gen. n. sp. (Alphaproteobacteria: Rickettsiales: Anaplasmataceae): an intracytoplasmic, hepatopancreatic, pathogen of the flatback mud crab, Eurypanopeus depressus

Jamie Bojko, Krista McCoy, April Blakeslee

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Abstract

Bacterial pathogens are a long-standing threat to the longevity and survival of crustacean hosts. Their presence and continuing emergence require close monitoring to understand their impact on fished, cultured, and wild crustacean populations. We report the presence of a new bacterial pathogen belonging to the Anaplasmataceae (Alphaproteobacteria: Rickettsiales), providing pathological, ultrastructural, phylogenetic, and genomic evidence to determine a candidate genus and species (‘Candidatus Mellornella promiscua’). This bacterium was found to infect the mud crab, Eurypanopeus depressus on the North Carolina coastline (USA) at a prevalence of 10.8%.
This bacterium is often observed in co-infection with the rhizocephalan barnacle, Loxothylacus panopaei. The bacterium infects only the hepatopancreas of the mud crab host, causing cytoplasmic hypertrophy and tubule necrosis. The bacteria form large plaques within the cytoplasm of the host cell and exhibit an abundance of sex-pili. The circular genome of the bacterium is 1,013,119bp and it encodes 939 genes in total. Phylogenetically, the new bacterium branches within the Anaplasmataceae. The genome is dissimilar from other bacteria, with 16S gene similarity observed at a maximum of 85.3% to a Wolbachia endosymbiont.
We explore this novel bacterial pathogen using genomic, phylogenetic, ultrastructural, and pathological perspectives, discussing these results in light of current bacterial taxonomy, similarity to other bacterial pathogens of Crustacea, and the potential impact upon the surrounding disease ecology of the host and benthic ecosystem.
Original languageEnglish
Article number107737
JournalJournal of Invertebrate Pathology
Volume190
Early online date2 Mar 2022
DOIs
Publication statusE-pub ahead of print - 2 Mar 2022

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