Antimicrobial Peptides for Use in Oyster Aquaculture: Effect on Pathogens, Commensals, and Eukaryotic Expression Systems

Two antimicrobial peptides (AMPs) of marine origin, tachyplesin from the Japanese horseshoe crab, Tachypleus tridentatus, and pleurocidin-amide from the winter flounder, Pseudopleuronectes americanus, were tested for their potential effectiveness in disease treatment in oyster aquaculture. Tachyplesin had a greater antimicrobial effect than pleurocidin-amideagainst a range of gram-positive and gram-negative bacteria, with minimum inhibitor concentrations in the range of 0.625 to 5ug mL–1. Tachyplesin (50 mg mL–1) was also more effective than pleurocidin-amide (250 mg mL–1) against the oyster protozoan parasite Perkinsus marinus, reducing its viability to 9% versus 22% in vitro. Both peptides were unaffected by variations in pH and salinity that would be encountered in marine culture conditions. Candidate algal and yeast for expression and feed-based delivery of recombinant AMPs were largely unaffected by tachyplesin and pleurocidin at concentrations that inhibited bacterial growth but were sensitive to concentrations that reduced the viability of P. marinus. Several proteases, including those of oyster and parasitic origin, decreased AMP activity, but tachyplesin was affected to a much lesser degree than pleurocidin-amide. Coincubation of homogenates from oyster digestive tissues with tachyplesin and pleurocidin-amide was found to reduce the abundance of colony forming units in the tissue. Tachyplesin was more effective against gram-negative bacteria present in oyster tissues, whereas pleurocidin-amide was more effective against gram-positive bacteria. Tachyplesin was considered a better candidate than pleurocidin-amide for feed-based delivery applications in oyster aquaculture

\u3cem\u3eVibrio parahaemolyticus\u3c/em\u3e in Rhode Island Coastal Ponds and the Estuarine Environment of Narragansett Bay

Quantification of the abundance of Vibrio parahaemolyticus in water and oysters from Rhode Island showed the presence of environmental strains and low levels of potentially pathogenic strains when water temperatures were ≥18°C, with peak levels in late July to early August. A higher abundance of the trh gene than of the tdh gene was observed

The expanded inhibitor of apoptosis gene family in oysters possesses novel domain architectures and may play diverse roles in apoptosis following immune challenge

Background: Apoptosis plays important roles in a variety of functions, including immunity and response to environmental stress. The Inhibitor of Apoptosis (IAP) gene family of apoptosis regulators is expanded in molluscs, including eastern, Crassostrea virginica, and Pacific, Crassostrea gigas, oysters. The functional importance of IAP expansion in apoptosis and immunity in oysters remains unknown. Results: Phylogenetic analysis of IAP genes in 10 molluscs identified lineage specific gene expansion in bivalve species. Greater IAP gene family expansion was observed in C. virginica than C. gigas (69 vs. 40), resulting mainly from tandem duplications. Functional domain analysis of oyster IAP proteins revealed 3 novel Baculoviral IAP Repeat (BIR) domain types and 14 domain architecture types across gene clusters, 4 of which are not present in model organisms. Phylogenetic analysis of bivalve IAPs suggests a complex history of domain loss and gain. Most IAP genes in oysters (76% of C. virginica and 82% of C. gigas), representing all domain architecture types, were expressed in response to immune challenge (Ostreid Herpesvirus OsHV-1, bacterial probionts Phaeobacter inhibens and Bacillus pumilus, several Vibrio spp., pathogenic Aliiroseovarius crassostreae, and protozoan parasite Perkinsus marinus). Patterns of IAP and apoptosis-related differential gene expression differed between the two oyster species, where C. virginica, in general, differentially expressed a unique set of IAP genes in each challenge, while C. gigas differentially expressed an overlapping set of IAP genes across challenges. Apoptosis gene expression patterns clustered mainly by resistance/susceptibility of the oyster host to immune challenge. Weighted Gene Correlation Network Analysis (WGCNA) revealed unique combinations of transcripts for 1 to 12 IAP domain architecture types, including novel types, were significantly co-expressed in response to immune challenge with transcripts in apoptosis-related pathways. Conclusions: Unprecedented diversity characterized by novel BIR domains and protein domain architectures was observed in oyster IAPs. Complex patterns of gene expression of novel and conserved IAPs in response to a variety of ecologically-relevant immune challenges, combined with evidence of direct co-expression of IAP genes with apoptosis-related transcripts, suggests IAP expansion facilitates complex and nuanced regulation of apoptosis and other immune responses in oysters

Bloom-forming macroalgae (\u3cem\u3eUlva\u3c/em\u3e spp.) inhibit the growth of co-occurring macroalgae and decrease eastern oyster larval survival

Macroalgal blooms have increased in frequency worldwide due to anthropogenic activities. Algal blooms can disrupt recreational activities, interfere with fisheries, and deplete oxygen during decomposition. Narragansett Bay has experienced macroalgal blooms dominated by blade-forming macroalgae of the genus Ulva for over a century. Evidence from other systems has suggested that Ulva can negatively impact other organisms. The first objective of this study was to determine whether bloom-forming U. compressa and U. rigida inhibit the growth of co-occurring macroalgae—Gracilaria vermiculophylla, Cystoclonium purpureum, and Chondrus crispus—during co-culture via laboratory based assays. We found that U. compressa and U. rigida significantly inhibited the growth of all 3 macroalgae. We were able to verify the negative effect of U. compressa, but not U. rigida, on the growth of G. vermiculophylla in flow-through seawater tanks. Our second objective was to determine if Ulva exudate decreased the survival of eastern oyster larvae in laboratory challenge experiments. We documented a significant negative effect of Ulva exudate on oyster survival, which depended on both the Ulva species and the nutrient condition. The strongest effect on oyster larval survival was seen in larvae exposed to nutrient-replete U. compressa exudate, which hadUlva has the potential to inhibit co-occurring macroalgae and cause oyster larval mortality

Draft Genome Sequence of the Marine Pathogen \u3cem\u3eVibrio coralliilyticus\u3c/em\u3e RE22

Vibrio coralliilyticus RE22 is a causative agent of vibriosis in larval bivalves. We report here the draft genome sequence of V. coralliilyticus RE22 and describe additional virulence factors that may provide insight into its mechanism of pathogenicity