Long-read sequencing reveals the shell microbiome of apparently healthy American lobsters Homarus americanus from Atlantic Canada

Shell bacterial community dynamics suggest that American lobster (Homarus americanus) impoundment shell disease is caused by a dysbiosis

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.

Differences in diversity and community composition of the shell microbiome of apparently healthy lobsters Homarus americanus across Atlantic Canada

Host-microbe dynamics are of increasing interest in marine research due to their role in host health and productivity. Changes in the shell microbiome of American lobsters have been associated with epizootic shell disease, a syndrome that is spreading northwards across the eastern U.S. and Canadian Atlantic coast. This study analyzed differences in alpha and beta diversity, as well as differentially abundant taxa, in the shell-associated bacterial community of apparently healthy lobsters from four lobster fishing areas (LFAs) in Atlantic Canada. Over 180 lobsters from New Brunswick, Nova Scotia and Prince Edward Island (PEI) were sampled during seven sampling events over four sampling months. The bacterial community was identified using novel PacBio long-read sequencing, while alpha and beta diversity parameters were analyzed using linear regression models and weighted UniFrac distances. The bacterial richness, diversity and evenness differed by sampling location, sampling month, and molt stage, but not by lobster sex or size, nor sampling depth. Similarly, based on LFA, sampling month, year and lobster molt stage, the shell microbiome differed in microbial community composition with up to 34 out of 162 taxa differing significantly in abundance between sampling groups. This large-scale microbial survey suggests that the shell microbial diversity of apparently healthy lobsters is influenced by spatial and temporal factors such as geographic location, as well as the length of time the carapace is exposed to the surrounding seawater.