Parallel analysis of miRNAs and mRNAs suggests distinct regulatory networks in Crassostrea gigas infected by Ostreid herpesvirus 1.

BACKGROUND: Since 2008, the aquaculture production of Crassostrea gigas was heavily affected by mass mortalities associated to Ostreid herpesvirus 1 (OsHV-1) microvariants worldwide. Transcriptomic studies revealed the major antiviral pathways of the oyster immune response while other findings suggested that also small non-coding RNAs (sncRNA) such as microRNAs might act as key regulators of the oyster response against OsHV-1. To explore the explicit connection between small non-coding and protein-coding transcripts, we performed paired whole transcriptome analysis of sncRNA and messenger RNA (mRNA) in six oysters selected for different intensities of OsHV-1 infection. RESULTS: The mRNA profiles of the naturally infected oysters were mostly governed by the transcriptional activity of OsHV-1, with several differentially expressed genes mapping to the interferon, toll, apoptosis, and pro-PO pathways. In contrast, miRNA profiles suggested more complex regulatory mechanisms, with 15 differentially expressed miRNAs (DE-miRNA) pointing to a possible modulation of the host response during OsHV-1 infection. We predicted 68 interactions between DE-miRNAs and oyster 3'-UTRs, but only few of them involved antiviral genes. The sncRNA reads assigned to OsHV-1 rather resembled mRNA degradation products, suggesting the absence of genuine viral miRNAs. CONCLUSIONS: We provided data describing the miRNAome during OsHV-1 infection in C. gigas. This information can be used to understand the role of miRNAs in healthy and diseased oysters, to identify new targets for functional studies and, eventually to disentangle cause and effect relationships during viral infections in marine mollusks.

Identification of a newly described OsHV-1 µvar from the North Adriatic Sea (Italy).

The surveillance activities for abnormal bivalve mortality events in Italy include the diagnosis of ostreid herpesvirus type 1 (OsHV-1) in symptomatic oysters. OsHV-1-positive oysters (Crassostrea gigas) were used as a source for in vivo virus propagation and a virus-rich sample was selected to perform shotgun sequencing based on Illumina technology. Starting from this unpurified supernatant sample from gills and mantle, we generated 3.5 million reads (2×300 bp) and de novo assembled the whole genome of an Italian OsHV-1 microvariant (OsHV-1-PT). The OsHV-1-PT genome encodes 125 putative ORFs, 7 of which had not previously been predicted in other sequenced Malacoherpesviridae. Overall, OsHV-1-PT displays typical microvariant OsHV-1 genome features, while few polymorphisms (0.08 %) determine its uniqueness. As little is known about the genetic determinants of OsHV-1 virulence, comparing complete OsHV-1 genomes supports a better understanding of the virus pathogenicity and provides new insights into virus-host interactions.

Mortality occurrence and pathogen detection in Crassostrea gigas and Mytilus galloprovincialis close-growing in shallow waters (Goro lagoon, Italy).

The complex interactions occurring between farmed bivalves and their potential pathogens in the circumstances of global climate changes are current matter of study, owing to the recurrent production breakdowns reported in Europe and other regions of the world. In the frame of Project FP7-KBBE-2010-4 BIVALIFE, we investigated the occurrence of mortality and potential pathogens during the Spring-Summer transition in Crassostrea gigas and Mytilus galloprovincialis cohabiting in the shallow waters of one northern Italian lagoon (Sacca di Goro, Adriatic Sea) and regarded as susceptible and resistant species, respectively. In 2011, limited bivalve mortality was detected in the open-field trial performed with 6-12 month old spat whereas subsequent trials with 2-3 month old spat produced almost complete (2012) and considerable (2013) oyster mortality. Macroscopical examination and histology excluded the presence of notifiable pathogens but, in the sampling preceding the massive oyster spat mortality of 2012, a µdeleted variant of OsHV-1 DNA was found in wide-ranging amounts in all analyzed oysters in conjunction with substantial levels of Vibrio splendidus and Vibrio aestuarianus. The large oyster spat mortality with borderline OsHV-1 positivity recorded in 2013 supports the multi-factorial etiology of the syndrome. This is the first report of a OsHV-1 (under a form interpreted as the variant µVar) in the Goro lagoon. Transcriptional host footprints are under investigation to better understand the bivalve response to environmental factors, included viral and bacterial pathogens, in relation to the observed mortalities.

Manila clam and Mediterranean mussel aquaculture is sustainable and a net carbon sink.

Aquaculture is a globally expanding industry that contributes to feeding an increasing global population. Shellfish cultivation is one of the largest sectors of aquaculture and one of the few food productions that have the potential capacity of acting as carbon sink. In fact, >90 % of bivalve shells are calcium carbonate (CaCO3), synthetized during biocalcification process, which incorporates a molecule of CO2. Manila clam (Venerupis philippinarum, Adams & Reeves, 1850) and Mediterranean mussel (Mytilus galloprovincialis, Lamarck, 1819) are two of the major groups of cultivated shellfish. Our aim was to assess the potential role of those two bivalve species in the overall marine carbon balance using an ecosystem approach, and to evaluate if they can be definitely regarded as carbon sink. The contribution to CO2 emissions (as CO2 eq./kg of fresh products) due to mollusk farming has been also calculated as carbon-source term by means of Life Cycle Assessment (LCA). LCA is nowadays the most shared and accepted tool for evaluating the environmental impacts of aquaculture productions. As a case study, the Sacca di Goro coastal lagoon (Northern Adriatic Sea, Italy) has been considered, because it is the premier site in Europe for clam farming, and one of the most important for mussels. Our study has shown that for each kilogram of harvested and packaged clams and mussels, shell formation throughout the mollusk growth allows to permanently capture 254 and 146 g of CO2, in the face of 22 and 55 g CO2 eq. emitted for farming, respectively. As a result, clams and mussel aquaculture could be considered as a carbon sink, with a net carbon capture capacity of 233 and 91 g CO2/kg of fresh product, respectively. In a wider context, bivalve aquaculture could be included in the carbon trading system and played a role towards the carbon-neutral economy.

The Chinese mitten crab Eriocheir sinensis H. Milne Edwards, 1853 (Crustacea: Decapoda: Varunidae) reappears in the northern Adriatic Sea: Another intrusion attempt or the trace of an overlooked population?

Eriocheir sinensis is included among the 100 most invasive aquatic invertebrates due to its colonization history and the impacts to biodiversity and economy in the newly invaded environments. Despite of that, its attempts of colonization of the Mediterranean basin seem to have failed so far. In this paper, we summarize the status and the distribution of the species in the Mediterranean and report a further finding from the northern Adriatic Sea, confirmed through an integrative taxonomy approach. We finally discuss the vectors of introduction that may be at the basis of the present record, highlighting the unexplored possibility that an undetected population is already thriving in the area. Whatever of the hypotheses done here is true, the Adriatic Sea could be a new perfect house for this invader, suggesting that more attention should be paid by stakeholders in preventing rather than in remediating possible impacts.