Inferring functional traits in a deep-sea wood-boring bivalve using dynamic energy budget theory.

For species in the deep sea, there is a knowledge gap related to their functional traits at all stages of their life cycles. Dynamic energy budget (DEB) theory has been proven to be an efficient framework for estimating functional traits throughout a life cycle using simulation modelling. An abj-DEB model, which compared with the standard DEB model includes an extra juvenile stage between the embryo and the usual juvenile stages, has been successfully implemented for the deep-sea Atlantic woodeater Xylonora atlantica. Most of the core and primary parameter values of the model were in the range of those found for shallow marine bivalve species; however, in comparison to shallow marine bivalves, X. atlantica required less energy conductance and energy to reach the puberty stage for the same range of body sizes, and its maximum reserve capacity was higher. Consequently, its size at first reproduction was small, and better survival under starvation conditions was expected. A series of functional traits were simulated according to different scenarios of food density and temperature. The results showed a weak cumulative number of oocytes, a low growth rate and a small maximum body size but an extended pelagic larval duration under deep-sea environmental conditions. Moreover, DEB modelling helped explain that some male X. atlantica individuals remain dwarfs while still reproducing by changing their energy allocation during their ontogenetic development in favour of reproduction. The estimation of functional traits using DEB modelling will be useful in further deep-sea studies on the connectivity and resilience of populations.

Relative abundances of methane- and sulphur-oxidising symbionts in the gills of a cold seep mussel and link to their potential energy sources.

Bathymodiolus mussels are key species in many deep-sea chemosynthetic ecosystems. They often harbour two types of endosymbiotic bacteria in their gills, sulphur- and methane oxidisers. These bacteria take up sulphide and methane from the environment and provide energy to their hosts, supporting some of the most prolific ecosystems in the sea. In this study, we tested whether symbiont relative abundances in Bathymodiolus gills reflect variations in the highly spatially dynamic chemical environment of cold seep mussels. Samples of Bathymodiolus aff. boomerang were obtained from two cold seeps of the deep Gulf of Guinea, REGAB (5°47.86S, 9°42.69E, 3170 m depth) and DIAPIR (6°41.58S, 10°20.94E, 2700 m depth). Relative abundances of both symbiont types were measured by means of 3D fluorescence in situ hybridisation and image analysis and compared considering the local sulphide and methane concentrations and fluxes assessed via benthic chamber incubations. Specimens inhabiting areas with highest methane content displayed higher relative abundances of methane oxidisers. The bacterial abundances correlated also with carbon stable isotope signatures in the mussel tissue, suggesting a higher contribution of methane-derived carbon to the biomass of mussels harbouring higher densities of methane-oxidising symbionts. A dynamic adaptation of abundances of methanotrophs and thiotrophs in the gill could be a key factor optimising the energy yield for the symbiotic system and could explain the success of dual symbiotic mussels at many cold seeps and hydrothermal vents of the Atlantic and Gulf of Mexico.

Colonization of organic substrates deployed in deep-sea reducing habitats by symbiotic species and associated fauna.

In this study, our goal was to test whether typical vent/seep organisms harbouring symbionts or not, would be able to settle on organic substrates deployed in the vicinity of chemosynthetic ecosystems. Since 2006, a series of novel standardized colonization devices (CHEMECOLI: CHEMosynthetic Ecosystem COlonization by Larval Invertebrates) filled with three types of substrates (wood, alfalfa and carbonate) have been deployed in different types of reducing habitats including cold seeps in the eastern Mediterranean, a mud volcano in the Norwegian Sea, and hydrothermal vents on the Mid-Atlantic Ridge for durations of 2 weeks to 1 year. For all deployments, highest species diversities were recovered from CHEMECOLIs filled with organic substrates. Larvae from species associated with thiotrophic symbionts such as thyasirid, vesicomyid and mytilid bivalves, were recovered in the eastern Mediterranean and at the Mid-Atlantic Ridge. At the Haakon Mosby Mud Volcano, larvae of symbiotic siboglinids settled on both organic and carbonate substrates. Overall, novel colonization devices (CHEMECOLI) filled with organic substrates attracted both fauna relying on chemosynthesis-derived carbon as well as fauna relying on heterotrophy the latter being opportunistic and tolerant to sulphide.

Synthesis and biological evaluation of analogues of the tetrapeptide N-Acetyl-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of primitive haematopoietic cell proliferation.

The tetrapeptide N-Acetyl-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of haematopoietic stem cell proliferation, reduces in vivo and in vitro the damage to the stem cell compartment resulting from treatment with chemotherapeutic agents or ionizing radiations. In order to provide new molecules likely to improve the myeloprotection displayed by this tetrapeptide, we have prepared a set of analogues of AcSDKP. These compounds are derived from the parent peptide by substitution or modification of the N- or of the C-terminus, or substitution of side chains. We report here that almost all investigated analogues retain the antiproliferative activity reducing in vitro the proportion of murine Colony-Forming Units Granulocyte, Macrophage (CFU-GM) in S-phase and inhibiting the entry into cycle of High Proliferative Potential Colony-Forming Cells (HPP-CFC). This shows that the polar groups of Ser, Asp or Lys are critical for the expression of biological activity, but that the modification of the N- or C-terminus mostly yielded compounds still retaining antiproliferative activity and devoid of toxicity. The efficacy of AcSDKP analogues in preventing in vitro the primitive haematopoietic cells from entering into cycle makes these molecules new candidates for further in vivo investigations.

Factors influencing spawning and pairing in the scale worm Harmothoe imbricata (Annelida: Polychaeta).

Endocrine and environmental factors control reproduction of the polynoid scale worm Harmothoe imbricata. We confirmed that the rate of vitellogenesis was greater in winter specimens transferred from ambient regimes of photoperiod and temperature to a light:dark (LD) photoperiod of 16:8 at 10 degrees C and showed that the number of females spawning was significantly greater than for those transferred to LD8:16 at 10 degrees C. The endocrine mediation of this response was investigated using prostomium implantations. Significantly more LD8:16 females implanted with prostomia from LD16:8 conditioned females spawned than LD8:16 females implanted with LD8:16 prostomia. Females without prostomia failed to spawn. LD16:8 exposure may increase levels of a possible "spawning hormone" in the prostomium. Spawning proceeded in these LD16:8 females and allowed spawning to occur in LD8:16 females implanted with LD16:8 prostomia. In LD8:16 prostomia, titers of the spawning hormone reached the threshold in significantly fewer individuals, so that significantly fewer females implanted with LD8:16 prostomia spawned. Using Y-maze choice chambers, pair formation was shown to be under pheromonal control, with males being attracted to mature females but not to females carrying fertilized oocytes or to LD8:16 conditioned females. Production of this attraction pheromone can, therefore, be manipulated through photoperiodic control, suggesting a link between oogenesis, spawning, and pheromone production.

In vitro effect of acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) analogs resistant to angiotensin I-converting enzyme on hematopoietic stem cell and progenitor cell proliferation.

The tetrapeptide Acetyl-N-Ser-Asp-Lys-Pro (AcSDKP), an inhibitor of hematopoietic stem cell proliferation, is known to reduce in vivo the damage resulting from treatment with chemotherapeutic agents or ionizing radiation on the stem cell compartment. Recently, AcSDKP has been shown to be a physiological substrate of the N-active site of angiotensin I-converting enzyme (ACE). Four analogs of the tetrapeptide expressing a high stability towards ACE degradation in vitro have been synthesized in order to provide new molecules likely to improve the myeloprotection displayed by AcSDKP. These analogs are three pseudopeptides with a modified peptidic bond, Ac-Serpsi(CH2-NH)Asp-Lys-Pro, Ac-Ser-Asppsi(CH2-NH)Lys-Pro, Ac-Ser-Asp-Lyspsi(CH2-N)Pro, and one C-terminus modified peptide (AcSDKP-NH2). We report here that these analogs reduce in vitro the proportion of murine colony-forming units-granulocyte/macrophage in S-phase and inhibit the entry into cycle of high proliferative potential colony-forming cells. The efficacy of AcSDKP analogs in preventing in vitro primitive hematopoietic stem cells from entering into cycle suggests that these molecules could be new candidates for the powerful inhibition of hematopoietic stem and progenitor cell proliferation in vivo.

NAcSDKP analogues resistant to angiotensin-converting enzyme.

Two series of analogues of the tetrapeptide NAcSDKP, an inhibitor of hematopoietic stem cell proliferation, were prepared, and their enzymatic stability toward rabbit lung angiotensin-converting enzyme (ACE) was evaluated as well as their capacity to inhibit NAcSDKP hydrolysis by this enzyme. In the first series, each of the peptide bonds has been successively replaced by an aminomethylene bond. In the second one, the C-terminus of the peptide has been modified by decarboxylation or amidation. The results reported here indicate that all of these molecules but one have good stability toward the enzyme but none of the compounds is able to inhibit NAcSDKP hydrolysis by ACE.