Comprehensive investigations of the Canadian Arctic during late summer and early fall revealed the widespread occurrence of long-lived subsurface chlorophyll maxima (SCM) in seasonally ice-free waters. The vertical position of the SCM corresponded with the depth of the subsurface biomass maximum (SBM), at least in Baffin Bay, suggesting that SCM could be an important source of carbon for the food web. Most of these SCM were located well below the pycnocline in close association with the nitracline, implying that their vertical position was driven mainly by a shortage of inorganic nitrogen in the upper euphotic zone. The diversity of SCM configurations with respect to physical properties of the water column complicates the estimation of euphotic-zone chlorophyll and primary production from surface properties. High photosynthetic yields (F v /F m ) showed the phytoplankton to be photosynthetically competent and well acclimated to conditions of irradiance and nutrient supply near the surface and at the SCM. A well-defined primary nitrite maximum was associated with the SCM in the southwest Canadian Arctic, but not in the northeast where nitrite concentrations were highest much below the euphotic zone. This contrast is consistent with differences in vertical stratification, the light -dark cycle and, possibly, the physiological state and taxonomic composition of the phytoplankton community at the SCM. This study demonstrates that the SCM, once regarded as anecdotal due to under-sampling, are a dominant feature of the Arctic Ocean that should be considered in remote sensing studies and biogeochemical models.

) were observed in brackish waters of the Beaufort Sea. These results confirm that picophytoplankton can dominate not only in warm oligotrophic waters, but also in a perennially cold ocean during late summer. KEY WORDS:Abundance · Photosynthetic eukaryotes · Picophytoplankton · Biomass · Nanophytoplankton · Microphytoplankton · Canadian Arctic Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 54: [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] 2009 1988). However, Richardson & Jackson (2007) challenged this view by showing that the share of picophytoplankton in carbon export can match their relative contribution to total net primary production due to the inclusion of small cells into large aggregates that sink rapidly or are grazed by mesozooplankton. Considering the findings of Richardson & Jackson (2007), the conventional view that picophytoplankton contribute little to carbon export should be revisited. Hence, both large and small phytoplankton play a crucial role in the marine biogeochemical cycle.Large phytoplankton cells, including diatoms, prymnesiophytes and dinoflagellates, produce seasonal blooms under specific hydrographic conditions . For instance, the production of large phytoplankton is governed by variations in the vertical stability of the water column, through its effects on nutrient replenishment and the residence time of algal cells in the euphotic zone (e.g. Tremblay et al. 1997). In addition, the duration of the production period is sensitive to the seasonal melt dynamics of sea ice (Fortier et al. 2002). In northern Baffin Bay (BB), an intense diatom bloom characterized by cells > 5 µm begins as early as the end of April when the North Water polynya opens up . In the Canadian Archipelago, particularly in Barrow Strait, the phytoplankton bloom typically develops in July and August, corresponding to the timing of the ice break-up for this region (Michel et al. 2006). In the Chukchi and Beaufort seas, high chlorophyll concentrations are observed in regions along the ice edge and are associated with an overwhelming predominance of diatoms and prymnesiophytes (Hill et al. 2005). In the Barents Sea, largecelled phytoplankton dominate during blooms at the marginal ice zone and are of particular importance for the production of organic matter and the vertical export of carbon .Several studies have shown that small phytoplankton cells (< 5 µm) can also play an important role in carbon fixation in the Arctic Ocean and adjacent seas (Legendre et al. 1993, Gosselin et al. 1997. Picophytoplankton contribute most of the production and biomass in warm and nutrient-poor waters (Agawin et al. 2000). Recent studies have shown that picophytoplankton are often well represented numerically in cold Arctic seawaters. Indeed, eukaryotic cells < 2 µm often dominate the phytoplankton assemblage, reaching up to 28 000 cells ml -1 during the initial spring bloom in the central Arctic Ocean but usually ranging between 1000 and 10 000 cells ml -1 during t...

Normal human myoblasts were cloned and transplanted in the tibialis anterior of immunodeficient nude and SCID mice and in mdx mice under different immunosuppressive treatments (cyclosporine A, CsA; antilymphocyte serum, ALS) or not immunosuppressed. This permitted us to show the interaction of the immune system in the myoblast transplantation. The graft success was assessed by verifying signs of humoral and cellular immune reactions and the presence of dystrophin produced by the fusion of the donor myoblasts. This study showed that clones of human myoblasts were able to fuse and produce dystrophin in injected muscles of immunodeficient mice and mdx mice receiving an effective immunosuppressive treatment (i.e., ALS+CsA). However, the same pool of human myoblasts injected in mdx mice inadequately immunosuppressed (i.e., CsA alone or ALS alone) triggered an immune reaction and was rejected. Cells expressing CD4 and CD8 antigens were observed in the injected muscles of mice treated with CsA alone. Therefore, evidence of humoral and cellular rejection was observed following human myoblasts transplantation.

Turbidity is a widely used parameter around the world for describing drinking water quality. Sometimes, turbidity at water treatment plant outlets may reach high values during short periods of time, and this is acceptable according to some current drinking water regulations. In this study, the quantity and nature (chemical and microbiological) of suspended matter, which may travel throughout a distribution system (DS) during turbid events — affecting both raw water and water treatment — were evaluated. Treated water included filtration with no coagulant addition. During turbid events, the concentration of suspended particles increased in treated water, and a similar increase (quantity and nature) was observed throughout the DS. Bacterial indicators of contamination (total and fecal coliforms, enteroccocci, spores of Clostridium perfringens) were not found in either treated water nor in the DS during turbid events. Nevertheless, a higher bacterial aerobic spore concentration was associated with turbid events for raw, treated, and distributed water, therefore suggesting the potential passage of pathogens, if present in raw waters. Cultivable bacteria concentrations remained low in treated and distributed water regardless of the turbidity. These results emphasize the need to carefully monitor raw and treated water quality for utilities using "high quality" water resources with limited treatment barriers, especially when such water resources are affected by even slight turbidity variations. Key words: aerobic spore-forming bacteria, distribution system, drinking water, filtration, turbidity, suspended particles, water quality.

Human myoblasts were transplanted in nude mice. The efficacy of these transplantations was analyzed using a monoclonal antibody (NCLDys3) specific for human dystrophin. This antibody did not reveal any dystrophin in nude mice that did not receive a human myoblast transplantation. However, about 30 days after a human myoblast transplantation, dystrophin-positive muscle fibers were observed. They were not abundant, and were present either in small clusters or isolated. This technique follows the fate of myoblast transplantation in animals that already have dystrophin, and distinguishes between new dystrophin-positive fibers due to the transplantation and the revertant fibers in mdx mice. Moreover, this technique does not require any labelling of the myoblasts before transplantation. It can also be used to detect dystrophin produced following the fusion of myoblasts transfected with the human dystrophin gene.