Shell bacterial community dynamics suggest that American lobster (Homarus americanus) impoundment shell disease is...

Impoundment shell disease (ISD) in the American lobster (Homarus americanus) is a distinct pathological condition from the more well-known epizootic shell disease. It is commonly observed at low prevalences in live American lobsters held overwinter in tidal pounds and significantly reduces their economic value. Impoundment shell disease was originally described in 1937; however, its etiology remains unclear. The main goal of this study was to characterize the bacterial community associated with ISD in Canadian lobsters. Lobsters were collected from a pound in southwest Nova Scotia, Canada, and the full 16S rRNA gene of bacterial communities from lesion and healthy shell areas of asymptomatic (As), moderately symptomatic (MS) and severely symptomatic (SS) animals was sequenced. Pielou evenness and Shannon diversity indexes of alpha-diversity were higher in healthy areas compared to lesion areas. Beta-diversity metrics indicate that the bacterial diversity differences are driven mainly by the relative abundance of a small number of bacteria, rather than the specific taxa present in the samples. Taxa were designated as being potentially involved with ISD based on their relative frequency, relative abundance or being core bacteriome in the lesion shell area. Among those found in this study, Tenacibaculum and Vibrio were previously described in ISD lesions; but others, such as Cellvibrionaceae, Polaribacter, Maribacter and Sulfitobacter were not. Altogether, the findings of this study indicate that ISD is driven by dysbiosis. Moreover, the inconsistency of taxa with previous studies may indicate that ISD consists of a combination of specific functional groups of bacteria, rather specific taxa.