Phytoplankton division rates in light-limited environments: two adaptations

Red tide-forming dinoflagellates maximize cell numbers during periods of low light intensities in two ways. For short-term exposures to suboptimal light intensities such as might occur during recirculation in frontal convergences, cell division rates can be maintained at the expense of stored carbon for up to two generation times. During longer periods, corresponding to subsurface transport below a pycnocline, cell division rates eventually decrease as a portion of the fixed carbon is diverted to replenishing stored carbon. As a result, maximum rates of cell division can be resumed rapidly upon advection into surface waters where light intensities are optimal for growth.

Mesoscale Iron Enrichment Experiments 1993-2005: Synthesis and Future Directions

Since the mid-1980s, our understanding of nutrient limitation of oceanic primary production has radically changed. Mesoscale iron addition experiments (FeAXs) have unequivocally shown that iron supply limits production in one-third of the world ocean, where surface macronutrient concentrations are perennially high. The findings of these 12 FeAXs also reveal that iron supply exerts controls on the dynamics of plankton blooms, which in turn affect the biogeochemical cycles of carbon, nitrogen, silicon, and sulfur and ultimately influence the Earth climate system. However, extrapolation of the key results of FeAXs to regional and seasonal scales in some cases is limited because of differing modes of iron supply in FeAXs and in the modern and paleo-oceans. New research directions include quantification of the coupling of oceanic iron and carbon biogeochemistry.

Isolation of mesenchymal stem cells from G-CSF-mobilized human peripheral blood using fibrin microbeads

Adult mesenchymal stem cells (MSC) that are able to differentiate into various mesenchymal cell types are typically isolated from bone marrow, but their significant presence in human peripheral blood (PB) is controversial. Fibrin microbeads (FMB) that bind matrix-dependent cells were used to isolate MSC from the mononuclear fraction of mobilized PB of adult healthy human donors treated with a granulocyte colony-stimulating factor. Isolation by plastic adherence resulted in a negligible number of MSC in all samples tested, whereas FMB-based isolation yielded spindle-shaped cell samples that could further expand on plastic or on FMB in eight out of the 11 samples. The yield of these cells at days 17-18 after the harvest was approximately 0.5% of the initial cell number. The isolated cells were grown on plastic and characterized by FACS analysis and immunohistochemistry for specific markers. Following culturing and first passage, the FMB-isolated cells stained positive for mesenchymal stromal cell markers CD90 and CD105, expressed vimentin and fibronectin and were negative for hematopoietic markers CD45 and CD34. These cells could differentiate into osteoblasts, adipocytes and chondrocytes. This study indicates that FMB may have special advantage in isolating MSC from sources such as mobilized PB, where the number of such cells is scarce.

Fibrin microbeads (FMB) as a 3D platform for kidney gene and cell therapy

Cell and gene therapy may alter the outcome of renal diseases, such as hereditary nephropathies, acute and chronic glomerulonephritis and allograft nephropathy. However, owing to blockade of many viral and cellular vehicles by the complex glomerular architecture, the exact nature of gene and cell delivery into specific renal compartments remains currently unknown. To study the interaction of viral vectors with a variety of renal cells and mesenchymal stem cells (MSCs), we employed a novel biological three-dimensional (3D) matrix comprised of fibrin microbeads (FMB) in comparison to monolayer cell culture. Our studies showed that renal cells of both established and primary lines can grow efficiently on FMB and differentiate into epithelial structures, as shown by electron microscopy. Gene delivery into renal cells in 3D was observed for several viral vectors and growth in 3D on FMB conferred resistance to renal cancer cells in the context of oncolytic adenoviruses. Finally, MSCs from various rodent species attached to FMB, grew robustly, survived for several weeks and could efficiently be transduced on FMB. Thus, on the basis of growth, differentiation and transduction of renal cells in 3D, FMB emerge as a novel 3D cellular microenvironment that differs substantially from monolayer cell cultures.

Biogenic carbon cycling in the upper ocean: effects of microbial respiration

Food-web processes are important controls of oceanic biogenic carbon flux and ocean-atmosphere carbon dioxide exchange. Two key controlling parameters are the growth efficiencies of the principal trophic components and the rate of carbon remineralization. We report that bacterial growth efficiency is an inverse function of temperature. This relationship permits bacterial respiration in the euphotic zone to be computed from temperature and bacterial production. Using the temperature-growth efficiency relationship, we show that bacterial respiration generally accounts for most community respiration. This implies that a larger fraction of assimilated carbon is respired at low than at high latitudes, so a greater proportion of production can be exported in polar than in tropical regions. Because bacterial production is also a function of temperature, it should be possible to compute euphotic zone heterotrophic respiration at large scales using remotely sensed information.

Vertical Flux of Biogenic Carbon in the Ocean: Is There Food Web Control?

Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions.

Diel Periodicity of Photosynthesis in Polar Phytoplankton: Influence on Primary Production

In the Southern Ocean, primary production estimated from seasonal chemical and geochemical changes is two to four times greater than the value calculated from carbon-14 uptake. Since carbon uptake had typically been measured only during midday incubations, the influence of diel periodicity of photosynthesis on daily productions was not considered. Phytoplankton from McMurdo Sound, Antarctica, exhibited distinct, but seasonally variable diel patterns of light-saturated and light-limited photosynthesis. Maximum photosynthetic capacity occurred about noon in early September, and its occurrence progressively shifted to about midnight by late October. This shift was accompanied by a concomitant phase shift in the occurrence of minimum photosynthetic capacity from midnight to midday. Daily production estimated from time-of-day corrected photosynthetic characteristics and from 24-hour incubations was 2.5 to 4 times greater than that predicted from 6-hour midday incubations. If similar diel periodicity in photosynthesis occurs in other polar oceans, primary production would be significantly higher than previously estimated from carbon-14 uptake measurements.

Effects of Flow Cytometric Analysis and Cell Sorting on Photosynthetic Carbon Uptake by Phytoplankton in Cultures and from Natural Populations

Photosynthetic rates of phytoplankton were significantly lower after analysis by flow cytometry (FCM) than before. Exposure to the laser beam during the sorting process caused significant physiological damage. The cellular content of a radiolabel accumulated prior to FCM was not affected by FCM. Although it may not be possible to use FCM to preconcentrate cells for further physiological studies, samples may be incubated with stable or radioactive isotopes and then analyzed by FCM.

Bacterivory: A Novel Feeding Mode for Asteroid Larvae

Planktotrophic larvae that occur beneath the annual sea ice in the Antarctic assimilate organic solutes and preferentially ingest bacteria, whereas they actively exclude phytoplankton. In regions where phytoplankton biomass is temporally limited by light or nutrient concentrations, the growth and development of planktotrophic larvae may not be directly coupled to phytoplankton production.

Radioisotopic Method for Measuring Cell Division Rates of Individual Species of Diatoms from Natural Populations

Silicon is an essential element for diatom frustule synthesis and is usually taken up only by dividing cells. With 68 Ge, a radioactive analog of Si, the cell cycle marker event of frustule formation was identified for individual species of diatom. The frequency of cells within a population undergoing this division event was estimated, and the cell division rate was calculated. In laboratory cultures, these rates of cell division and those calculated from changes in cell numbers were similar. By dual labeling with 68 Ge(OH) 4 and NaH 14 CO 3 , rates of cell division and photosynthesis were coincidently measured for diatoms both in laboratory cultures and when isolated from natural populations in estuarine, offshore, and polar environments. These techniques permit the coupling between photosynthesis and cell division to be examined in situ for individual species of diatom.