Pseudoalteromonas ostreae sp. nov., a new bacterial species harboured by the flat oyster Ostrea edulis

Three bacterial strains, named hOe-66T, hOe-124 and hOe-125, were isolated from the haemolymph of different specimens of the flat oyster Ostrea edulis collected in Concarneau bay (Finistère, France). These strains were characterized by a polyphasic approach, including (i) whole genome analyses with 16S rRNA gene sequence alignment and pangenome analysis, determination of the G+C content, average nucleotide identity (ANI), and in silico DNA–DNA hybridization (isDDH), and (ii) fatty acid methyl ester and other phenotypic analyses. Strains hOe-66T, hOe-124 and hOe-125 were closely related to both type strains Pseudoalteromonas rhizosphaerae RA15T and Pseudoalteromonas neustonica PAMC 28425T with less than 93.3% ANI and 52.3% isDDH values. Regarding their phenotypic traits, the three strains were Gram-negative, 1–2 µm rod-shaped, aerobic, motile and non-spore-forming bacteria. Cells grew optimally at 25 °C in 2.5% NaCl and at 7–8 pH. The most abundant fatty acids were summed feature 3 (C16:1 ω7c/C16:1 ω6c), C16:0 and C17:1 ω8c. The strains carried a genome average size of 4.64 Mb and a G+C content of 40.28 mol%. The genetic and phenotypic results suggested that strains hOe-66T, hOe-124 and hOe-125 belong to a new species of the genus Pseudoalteromonas . In this context, we propose the name Pseudoalteromonas ostreae sp. nov. The type strain is hOe-66T (=CECT 30303T=CIP 111911T).

Development of eDNA tools for the detection of marine invasive non-native species to support European flat oyster (Ostrea edulis) restoration projects.

The European flat oyster (Ostrea edulis) is an important keystone species in Scottish coastal waters. However due to anthropogenic pressures, significant reductions to oyster beds have been observed across Europe. In Scotland, several projects are currently aiming to restore European flat oyster habitats through the translocation of juvenile oysters from various sources including hatcheries and aquaculture. However, translocation of shellfish is not risk free and can increase the risk of accidental translocation of invasive non-native species (INNS). If INNS become established outside of their native range they can cause irreversible harm to native organisms and habitats. This study aims to develop molecular tools to detect environmental DNA of INNS which can be potentially associated with the translocation of live shellfish stocks. We have developed a species-specific real-time PCR assay for detection of Pacific oyster (Crassostrea gigas) and tested its sensitivity in a large-scale replicated mesocosm based experiment with varying densities of C.gigas. A secondary objective of the experiment was to assess the detection of another invasive species, the carpet sea squirt Didemnum vexillum which was cohabited with C. gigas. We aim to quantify the detection probability of increasing densities of C. gigas from repeat water samples and qPCR replicates. This project also aims to investigate the feasibility of using portable, real-time sequencing technologies such as the Oxford Nanopore MinION to develop robust tools to support native oyster restoration programmes.

The late Holocene demise of a sublittoral oyster bed in the North Sea

A fossil oyster bed (Ostrea edulis) was recently encountered offshore Helgoland (German Bight). Oysters are important filter feeders in marine environments and their habitat structure supports a large associated biodiversity. The European flat oyster Ostrea edulis has historically occurred in vast populations in the North Sea, but declined massively in the early 20th century. The ecological restoration of Ostrea habitats is a current focal point in the North Sea. To better understand the mechanisms that caused the local collapse of the oyster population, this study investigated the size structure, weight, and age of the shells, along with the spatial dimensions, seafloor properties, and environmental context of the oyster bed. The results show that the demise of the population occurred around 700 CE, ruling out excessive harvest as a driver of decline. Synchronicity of increased geomorphological activity of rivers and concurrent major land use changes in early medieval Europe suggest that increased sedimentation was a viable stressor that reduced the performance of the oysters. The shells provided no indication of a demographically poor state of the oyster bed prior to its demise, but manifested evidence of the wide-spread occurrence of the boring sponge Cliona sp. Our study challenges the assumption of a stable preindustrial state of the European flat oyster in the North Sea, and we conclude that the long-term variability of environmental conditions needs to be addressed to benchmark success criteria for the restoration of O. edulis.