Nested spatial and temporal modeling of environmental conditions associated with genetic markers of Vibrio parahaemolyticus in Washington state Pacific oysters

The Pacific Northwest (PNW) is one of the largest commercial harvesting areas for Pacific oysters (Crassostrea gigas) in the United States. Vibrio parahaemolyticus, a bacterium naturally present in estuarine waters, accumulates in shellfish and is a major cause of seafood-borne illness. Growers, consumers, and public-health officials have raised concerns about rising vibriosis cases in the region. V. parahaemolyticus genetic markers (tlh, tdh, trh) were estimated using an MPN-PCR technique in Washington State Pacific oysters regularly sampled between May and October from 2005 to 2019 (N=2,836); environmental conditions were also measured at each sampling event. Multilevel mixed-effects regression models were used to assess relationships between environmental measures and genetic markers as well as genetic marker ratios (trh:tlh, tdh:tlh, and tdh:trh), accounting for variation across space and time. Spatial and temporal dependence were also accounted for in the model structure. Model fit improved when including environmental measures from previous weeks (1-week lag for air temperature, 3-week lag for salinity). Positive associations were found between tlh and surface water temperature, specifically between 15°C and 26°C, and between trh and surface water temperature up to 26°C. tlh and trh were negatively associated with 3-week lagged salinity in the most saline waters (> 27 ppt). There was also a positive relationship between tissue temperature and tdh, but only above 20°C. The tdh:tlh ratio displayed analogous inverted non-linear relationships as tlh. The non-linear associations found between the genetic targets and environmental measures demonstrate the complex habitat suitability of V. parahaemolyticus. Additional associations with both spatial and temporal variables also suggest there are influential unmeasured environmental conditions that could further explain bacterium variability. Overall, these findings confirm previous ecological risk factors for vibriosis in Washington State, while also identifying new associations between lagged temporal effects and pathogenic markers of V. parahaemolyticus.

Anticancer Potential of Lipophilic Constituents of Eleven Shellfish Species Commonly Consumed in Korea

The present study was aimed to investigate the composition and contents and the major lipophilic compounds, including the sterols, fatty acids, and tocols of shellfish species. Moreover, to explore the antitumor activity of these lipophilic constituents, their cytotoxicity potentials were determined against five different human cancer cells, including colon carcinoma (HCT116), epithelial melanoma (A2058), glioblastoma multiforme (T98G), lung carcinoma (A549), and adenocarcinoma (HeLa). The results show a significant variation in the contents and composition of lipophilic constituents among the studied species. The highest omega-3 (n-3) polyunsaturated fatty acids (PUFAs) were recorded from arrow squid and pacific oysters, accounting for 53.2% and 53.0% of their total fatty acids, respectively. However, the highest cholesterol content was also recorded in arrow squid (154.4 mg/100 g; 92.6% of total sterols). In contrast, in the Japanese littleneck, Yesso scallop, and common orient clam, cholesterol was just 17.1%, 18.3%, and 18.9% of total sterols, respectively, making them the richest source of non-cholesterol sterols (NCS). Lipids extracted from shellfish species showed ABTS+•- and DPPH•-scavenging activities. In the cytotoxicity analysis, lipids extracted from the Argentine red shrimp showed the highest cytotoxicity against glioblastoma multiforme T98G cells, with an IC50 value of 12.3 µg/mL. The composition and cytotoxicity data reported herein may help explore the nutritional and anticancer potentials of shellfish species.

Investigation of vitamin B12 concentrations and tissue distributions in larval and adult Pacific oysters and related bivalves

itamin B 12 (B 12 ) is an essential micronutrient for all animals, but is not present in plants and is produced de novo only by bacteria or archaea. Accordingly, humans must derive required B 12 from eating animal products or vitamin supplements, as deficiencies can lead to severe health issues including neuropathy. An often overlooked source in the human diet of B 12 is shellfish, in particular bivalves, which have significantly higher levels of B 12 than other animal sources, including all vertebrate meats. Origins and key metabolic processes involving B 12 in bivalves remain largely unknown, despite the exceptionally high levels. In this study, we examined in several Australian bivalve species, hypotheses concerning B 12 utilisation and uptake through diet or microorganism symbiosis. Vitamin B 12 is not distributed evenly across different tissues types of the Pacific oyster, the commercial scallop and Goolwa cockle (pipi), with higher accumulation in the oyster adductor muscle and gill, and mantle and syphons of the Goolwa cockle. Oyster larvae before first feeding already contained high amount of B 12 ; however, a significant decrease in B 12 concentration post metamorphosis indicates a higher utilisation of B 12 during this life event. We demonstrated that microalgal feed can be supplemented with B 12 , resulting in an enriched feed, but this did not result in an increase in larval B 12 concentrations when oyster larvae were fed with this diet relative to controls, thus supporting the theory that a B 12 producing microbiome within bivalves was the potential source of B 12 rather than feed. However, B 12 concentrations in the digestive tract of adult oysters were low compared to other tissue types, which might challenge this theory, at least in adults. Our findings provide insight into B 12 uptake and function in bivalve species, which will aid the promotion of bivalves as suitable B 12 source for humans as well as provide crucial information to the aquaculture industry in relation to optimisation of vitamin supplementation in bivalve hatchery production.

Detection of Escherichia albertii in retail oysters

Escherichia albertii is an emerging foodborne pathogen. Owing to its distribution in river water, it is important to determine the presence of E. albertii in aquaculture-related foods. In this study, we investigated the distribution of E. albertii in retail oyster samples. A total of 427 raw oyster samples (385 Pacific oysters, and 42 Japanese rock oysters) were enriched in modified Escherichia coli broth (mEC) or mEC supplemented with novobiocin (NmEC) at 42 °C. The cultures were used for E. albertii -specific nested PCR assay, as well as for E. albertii isolation using deoxycholate hydrogen sulfide lactose agar (DHL), DHL supplemented with rhamnose and xylose (RX-DHL), and MacConkey agar supplemented with rhamnose and xylose (RX-MAC). The population of E. albertii in nested PCR-positive samples was determined using the most probable number (MPN) method. E. albertii isolates were subjected to biochemical and genetic characterization. E. albertii was detected in 5 of 315 (1.6%) Pacific oyster samples (one piece each), 2 of 70 (2.9 %) Pacific oyster samples (25 g each), and 2 of 42 (4.8 %) Japanese rock oyster samples procured from four geographically distant regions. A total of 64 E. albertii strains were isolated from eight of the nine nested PCR assay-positive oyster samples, and the MPN value was under the detection limit (< 3 MPN/10 g). A specific season or month for detecting E. albertii was not observed in this study, suggesting that the pathogen is present in seawater. All the E. albertii isolates, except one, were positive for the virulence factor eae, indicating that these isolates have the potential to infect humans.

Temporally balanced selection during development of larval Pacific oysters ( Crassostrea gigas ) inherently preserves genetic diversity within offspring

Balancing selection is one of the mechanisms which has been proposed to explain the maintenance of genetic diversity in species across generations. For species with large populations and complex life histories, however, heterogeneous selection pressures may create a scenario in which the net effects of selection are balanced across developmental stages. With replicated cultures and a pooled sequencing approach, we show that genotype-dependent mortality in larvae of the Pacific oyster ( Crassostrea gigas ) is largely temporally dynamic and inconsistently in favour of a single genotype or allelic variant at each locus. Overall, the patterns of genetic change we observe to be taking place are more complex than what would be expected under classical examples of additive or dominant genetic interactions. They are also not easily explained by our current understanding of the effects of genetic load. Collectively, temporally heterogeneous selection pressures across different larval developmental stages may act to maintain genetic diversity, while also inherently sheltering genetic load within oyster populations.

Prey preferences, consumption rates and predation effects of Asian shore crabs (Hemigrapsus takanoi) in comparison to native shore crabs (Carcinus maenas) in northwestern Europe

The Asian brush-clawed shore crab Hemigrapsus takanoi was introduced to the northern Wadden Sea (southeastern North Sea) in 2009 and now represents one of the most abundant brachyuran crab species. Abundance studies revealed an increase of mean crab densities on mixed reefs of native blue mussels (Mytilus edulis) and Pacific oysters (Magallana gigas) from 18 individuals m−2 in 2011 to 216 individuals m−2 in 2020. Despite its current high densities only little is known about the feeding habits of H. takanoi, its effects on prey populations and on the associated community in the newly invaded habitat. We summarize results of individual field and laboratory experiments that were conducted to assess feeding habits and consumption effects caused by Asian brush-clawed shore crabs and, additionally, compare the feeding ecology of H. takanoi with the one of the native shore crab Carcinus maenas. Field experiments manipulating crab densities revealed that both crab species affected the recruitment success of blue mussels, Pacific oysters and Australian barnacles (Austrominius modestus) with highest number of recruits at crab exclusion. However, endobenthic polychaetes within the reefs were differently affected. Only the native C. maenas caused a significant reduction in polychaete densities, whereas the introduced H. takanoi had no effect. Additional comparative laboratory studies revealed that single C. maenas consume more juvenile blue mussels than Asian brush-clawed shore crabs of the same size class. When offering amphipods as a mobile prey species, we found the same pattern with higher consumption rates by C. maenas than by H. takanoi. For Asian but not for native shore crabs, we detected a sex-dependent feeding behavior with male H. takanoi preferring blue mussels, while females consumed more amphipods. Considering mean crab densities and feeding behavior, our results suggest that despite lower consumption rates of single crabs, Asian brush-clawed shore crabs can cause stronger impacts on prey organisms than the native C. maenas, because H. takanoi exceeds their densities manifold. A strong impact of the invader on prey populations is supported by low amphipod occurrence at sites where H. takanoi density is high in the study area. Thus, the introduced Asian brush-clawed shore crab is an additional consumer with significant effects on the associated community of mixed reefs of mussels and oysters in the Wadden Sea.

Bioaccessibility and Intestinal Transport of Deltamethrin in Pacific Oyster (Magallana Gigas) Using Simulated Digestion/NCM460 Cell Models

Deltamethrin (DEL) can be introduced into the food chain through bioaccumulation in Pacific oysters, and then potentially threaten human health. The objective of this study was to investigate the bioaccessibility of DEL in oysters with different cooking methods after simulated digestion. DEL content in different tissues of oysters going from high to low were gills, mantle, viscera, and adductor muscle. Bioaccessibility of DEL in oysters decreased after steaming (65%) or roasting (51%) treatments compared with raw oysters (82%), which indicated that roasting can be used as a recommended cooking method for oysters. In the simulated digestion process, the concentration of DEL in the digestive juice and the bioaccessibility of DEL were affected by the pH in the gastric phase. And the transport efficiency of DEL through the monolayer molecular membrane of NCM460 cells ranged from 35 to 45%. These results can help assess the potential harm to consumers of DEL in shellfish. Furthermore, it provides a reference for the impact of lipophilic toxins in seafood.