Temperature-associated selection linked to putative chromosomal inversions in king scallop (Pecten maximus).

The genomic landscape of divergence-the distribution of differences among populations or species across the genome-is increasingly characterized to understand the role that microevolutionary forces such as natural selection and recombination play in causing and maintaining genetic divergence. This line of inquiry has also revealed chromosome structure variation to be an important factor shaping the landscape of adaptive genetic variation. Owing to a high prevalence of chromosome structure variation and the strong pressure for local adaptation necessitated by their sessile nature, bivalve molluscs are an ideal taxon for exploring the relationship between chromosome structure variation and local adaptation. Here, we report a population genomic survey of king scallop (Pecten maximus) across its natural range in the northeastern Atlantic Ocean, using a recent chromosome-level genome assembly. We report the presence of at least three large (12-22 Mb), putative chromosomal inversions associated with sea surface temperature and whose frequencies are in contrast to neutral population structure. These results highlight a potentially large role for recombination-suppressing chromosomal inversions in local adaptation and suggest a hypothesis to explain the maintenance of differences in reproductive timing found at relatively small spatial scales across king scallop populations.

Arcobacter lekithochrous sp. nov., isolated from a molluscan hatchery.

Four bacterial strains, LFT 1.7T, LT2C 2.5, LT4C 2.8 and TM 4.6, were isolated from great scallop (Pecten maximus) larvae and tank seawater in a Norwegian hatchery and characterized by a polyphasic approach including determination of phenotypic, chemotaxonomic and genomic traits. All were Gram-stain-negative, motile rods, oxidase- and catalase-positive and required sea salts for growth. Major fatty acids present were summed feature 3 (C16 : 1ω7c/C16 : 1ω6c), summed feature 8 (C18 : 1ω7c or C18 : 1ω6c), C16 : 0, C14 : 0, summed feature 2 (C14 : 0 3-OH/iso-C16 : 1 I), C12 : 0 3-OH and C12 : 0. Strain LFT 1.7T contained menaquinone MK-6 as the sole respiratory quinone. Phylogenetic analysis based on 16S rRNA gene sequences indicated that all strains formed a distinct lineage within the genus Arcobacter with a low similarity to known species (94.77-95.32 %). The DNA G+C content was 28.7 mol%. Results of in silico DNA-DNA hybridization and average nucleotide identity confirmed that the isolates constitute a novel species of Arcobacter, for which the name Arcobacter lekithochrous sp. nov. is proposed. The type strain is LFT 1.7T (=CECT 8942T=DSM 100870T).

Sinobacterium norvegicum sp. nov., isolated from great scallop (Pecten maximus) broodstock and emended description of Sinobacterium caligoides.

Six isolates were recovered from great scallop (Pecten maximus) broodstock in a hatchery in Bergen, Norway. The strains were thoroughly characterized by a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences indicated that these strains are related to the genus Sinobacterium, showing sequence similarities between 96.97 and 97.63 % with the only species of the genus, Sinobacterium caligoides. Phenotypic characterization showed that the strains are typical marine halophiles, Gram negative, aerobic chemoorganotrophs, and allowed their differentiation from the closely related taxa. The G+C content of the novel strains was 52.2 ± 1 mol% and the predominant fatty acids were C16:0, C16:1 ω7c/C16:1 ω6c and C18:1 ω7c. The value for DNA-DNA relatedness between strain 3CM4(T) and the S. caligoides type strain LMG 25705(T) was 46  %. Hybridization values between strain 3CM4(T) and the other scallop isolates ranged from 82 to 93.6 %. Based on all data collected, the six scallop strains represent a novel species of the genus Sinobacterium, for which the name Sinobacterium norvegicum sp. nov., is proposed with strain 3CM4(T) (=CECT 8267(T); =CAIM 1884(T)) as type strain.

Macromolecular sheets direct the morphology and orientation of plate-like biogenic guanine crystals.

Animals precisely control the morphology and assembly of guanine crystals to produce diverse optical phenomena in coloration and vision. However, little is known about how organisms regulate crystallization to produce optically useful morphologies which express highly reflective crystal faces. Guanine crystals form inside iridosome vesicles within chromatophore cells called iridophores. By following iridosome formation in developing scallop eyes, we show that pre-assembled, fibrillar sheets provide an interface for nucleation and direct the orientation of the guanine crystals. The macromolecular sheets cap the (100) faces of immature guanine crystals, inhibiting growth along the π-stacking growth direction. Crystal growth then occurs preferentially along the sheets to generate highly reflective plates. Despite their different physical properties, the morphogenesis of iridosomes bears a striking resemblance to melanosome morphogenesis in vertebrates, where amyloid sheets template melanin deposition. The common control mechanisms for melanin and guanine formation inspire new approaches for manipulating the morphologies and properties of molecular materials.

Gene expression analyses of essential catch factors in the smooth and striated adductor muscles of larval, juvenile and adult great scallop (Pecten maximus).

The scallop adductor muscle consists of striated fibres responsible for the fast closure of the shells, and smooth fibres able to maintain tension in a prolonged state of contraction called catch. Formation of the force-bearing catch linkages has been demonstrated to be initiated by dephosphorylation of the key catch-regulating factor twitchin by a calcineurin-like phosphatase, while the involvement of other thick filament proteins is uncertain. Here we report on the development of catchability of the adductor smooth muscle in the great scallop (Pecten maximus) by analysing the spatio-temporal gene expression patterns of the myosin regulatory light chain (MLCr), twitchin, myorod and calcineurin using whole mount in situ hybridization and real-time quantitative PCR. The MLCr signal was identified in the retractor and adductor muscles of the pediveliger larvae, and the juvenile and adult scallop displayed abundant mRNA levels of MLCr in the smooth and striated adductor muscles. Twitchin was mainly expressed in the smooth adductor muscle during metamorphosis, whereas the adult striated adductor muscle contained seven-folds higher twitchin mRNA levels compared to the smooth portion. Calcineurin expression predominated in the gonads and in the smooth adductor, and five-folds higher mRNA levels were measured in the smooth than in the striated fibres at the adult stage. In contrast to the other genes examined, the expression of myorod was confined to the smooth adductor muscle suggesting that myorod plays a permissive role in the molluscan catch muscles, which are first required at the vulnerable settlement stage as a component of the predator defence system.

Complete characterization of new isolates of Neptunomonas phycophila leads to emend its description and opens possibilities of biotechnological applications.

Five strains were isolated from gonad of Great scallop (Pecten maximus) broodstock in a Norwegian hatchery. The study of 16S rRNA gene sequences showed that these isolates belong to Neptunomonas phycophila, a bacterium originally isolated from a symbiont of the anemone Aiptasia tagetes from Puerto Rico. The gyrB and rpoB genes sequences confirmed the affiliation of the scallop isolates to this species. Phenotypic characterization was performed and some differences between the Norwegian isolates and the type strain of N. phycophila were detected, such as ranges of temperature, pH, and tolerance to salinity or the use of several substrates as sole carbon source which lead to an emended description of the species. The strain 3CM2.5 showed phosphatidylethanolamine and phosphatidylglycerol as the major polar lipids. The whole genomes of the scallop strain 3CM2.5 and type strain of the species CECT 8716T were obtained and the annotation of these genomes revealed the presence of genes involved in degradation of aromatic compounds in both strains. Results obtained not only widen the geographical and host ranges of N. phycophila, but also point out possible biotechnological applications for this bacterial species.

Neptuniibacter pectenicola sp. nov. and Neptuniibacter marinus sp. nov., two novel species isolated from a Great scallop (Pecten maximus) hatchery in Norway and emended description of the genus Neptuniibacter.

Nine isolates obtained from a great scallop hatchery in Norway were characterized using a polyphasic approach. Strains were Gram-negative, aerobic and motile rods with oxidative metabolism. Phylogenetic analysis based on the sequences of 16S rRNA and rpoB genes showed that these strains formed two different groups associated with members of the genus Neptuniibacter. DNA-DNA hybridization (DDH) and Average Nucleotide Identity (ANI) demonstrated that the isolates constituted two novel species of this genus, which can be phenotypically differentiated from their closest relatives. The names Neptuniibacter marinus sp. nov. and Neptuniibacter pectenicola sp. nov are proposed, with ATR 1.1T (=CECT 8938T=DSM 100783T) and LFT 1.8T (=CECT 8936T=DSM 100781T) as respective type strains.

Immunohistochemistry of great scallop Pecten maximus larvae experimentally challenged with pathogenic bacteria.

Three challenge experiments were carried out on larvae of the great scallop Pecten maximus. Larvae were bath-challenged with Vibrio pectenicida and 5 strains resembling Vibrio splendidus and one Pseudoalteromonas sp. Unchallenged larvae were used as negative controls. The challenge protocol was based on the use of a multidish system, where the scallop larvae (10, 13 and 15 d post-hatching in the 3 experiments, respectively) were distributed to 2 ml wells with stagnant seawater and exposed to the bacterial cultures by bath challenge. Presence of the challenge bacteria in the wells was verified by polymerase chain reaction (PCR). A significantly increased mortality was found between 24 and 48 h in most groups challenged with V. pectenicida or V. splendidus-like strains. The exception was found in larval groups challenged with a Pseudoalteromonas sp. LT 13, in which the mortality rate fell in 2 of the 3 challenge experiments. Larvae from the challenge experiments were studied by immunohistochemistry protocol. Examinations of larval groups challenged with V. pectenicida revealed no bacterial cells, despite a high degree of positive immunostaining. In contrast, intact bacterial cells were found in larvae challenged with V. splendidus. In the case of larvae challenged with the Pseudoalteromonas sp., positive immuno-staining was limited to visible bacteria inside the digestive area and cells of the mucosa. The experiments confirm that V. splendidus and V. pectenicida are pathogenic to scallop larvae, and that the Pseudoalteromonas strain is probably not a primary pathogen, although it cannot be ruled out as a secondary pathogen.

Characterisation of the bacterial community associated with early stages of Great Scallop (Pecten maximus), using denaturing gradient gel electrophoresis (DGGE).

Denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA was used to characterise and compare bacterial communities associated with scallop larvae (Pecten maximus), in different production units in a shellfish hatchery. Water and larvae samples were collected from three different aquaculture systems; stagnant, flow-through and a flow- through system with seawater treated with ozone. Samples were also collected from different algal cultures, inlet tanks and water pipes leading to the different aquaculture systems. Clear differences were seen between the bacterial community associated with the larvae and in the water from the different aquaculture systems. However, there were high similarities in the community composition between different water samples and between larvae samples collected at different time periods, indicating a high stability in the bacterial communities. Fifty three percent of the sequences from these samples were similar to 16S rRNA gene sequences of members of the gamma-subclass of the Proteobacteria. The different algal cultures had different bacterial communities, however 73 percent of the sequences were similar to 16S rRNA gene sequences of members of the alpha-subclass of the Proteobacteria. Differences in the DGGE profiles were also seen between the samples taken from the inlet tanks and water pipes, indicating a change in the bacterial community composition as the water passed through the pipes. To our knowledge this is the first study investigating bacterial communities associated with Great Scallop larvae in different aquaculture systems including noncultured components.

Effects of reduced diameter of bag cultures on content of essential fatty acids and cell density in a continuous algal production system.

Cell density and fatty acid (FA) content of Pavlova lutheri and Chaetoceros muelleri were analysed in a continuous algal production system (250-L bags) with reduced diameter. The cell density and FA content and composition in the algal production system were determined in replicate bags over a period of 5 weeks. The results showed that the cell density and essential FAs increased during the experiment for both species. After 5 weeks the mean cell numbers had increased to 6.0 ± 0.3 × 10(6) cells mL(-1) in the P. lutheri bags and 6.0 ± 0.4 × 10(6) cells mL(-1) in the C. muelleri bags. The content of total FAs increased significantly (p < 0.05) in all of the bags during the experiment. At the end of the experiment the mean total FA content were 2.7 ± 0.3 pg cell(-1) in the P. lutheri bags and 1.8 ± 0.1 pg cell(-1) in the C. muelleri bags. Maximum total FA content registered was 3.0 pg cell(-1) in one of the P. lutheri bags. The content of the essential FAs (ARA, EPA, DHA) increased over time in both of the species. At the end of the experiment the content of EPA (0.6 ± 0.1 pg cell(-1)) and DHA (0.3 ± 0.0 pg cell(-1)) were highest in the P. lutheri bags, while ARA (0.1 ± 0.0 pg cell(-1)) was highest in C. muelleri. EPA and DHA constituted 22% and 11%, respectively, of total FA content in P. lutheri, while ARA constituted 6% of total FA content in C. muelleri. The results from this experiment indicate that flagellates such as P. lutheri perform better in narrow bags with improved light conditions, while diatoms like C. muelleri perform better in wider bags under light limitation. Implications for bivalve hatcheries are discussed. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10811-011-9655-6) contains supplementary material, which is available to authorized users.