AXENIC CULTURES OF ACETABULARIA (CHLOROPHYTA): A DECONTAMINATION PROTOCOL WITH POTENTIAL APPLICATION TO OTHER ALGAE1

We developed an easy, reliable decontamination protocol for caps of Acetabularia acetabulum (L.) Silva; with minimal labor hundreds of caps can be decontaminated. In addition, cysts isolated from these caps do not exhibit dormancy and can be used immediately to establish large populations of axenic cell cultures. This method consists of three successive incubations: 1) proteinase K/sodium dodecyl sulfate/1,3-bis[tris(hydroxymethyl)-methylamino]propane for 1 h, 2) mild silver protein for 5 min, and 3) an antibiotic solution (neomycin, chloramphenicol, nystatin, ampicillin, streptomycin)for 3 days. This protocol eliminates bacterial, algal, fungal, and yeast contaminants. It is useful for decontaminating caps from lab cultures and caps collected from the wild and may also be effective in decontaminating the reproductive structures of other algae. Cyst dormancy was reduced from 15 weeks to less than 1 week, which represents a 40% reduction of the life cycle of A. acetabulum. We routinely obtained 90-100% gamete release from cysts 3-14 days after they were made axenic. The component of our culturing methods that allows gamete release without a “dormant” period is unknown.     

OPTICAL PROPERTIES OF DENSE ALGAL CULTURES OUTDOORS AND THEIR APPLICATION TO REMOTE ESTIMATION OF BIOMASS AND PIGMENT CONCENTRATION IN SPIRULINA PLATENSIS (CYANOBACTERIA)1

Reflectance and vertical attenuation coefficient spectra from 400 to 1100 nm were investigated in detail on dense algal cultures of Spirulina in order to create algorithms for remote estimation of pigment and biomass concentration. Reflectance and the vertical attenuation coefficients were compared with biomass and pigment concentration in outdoor algal cultures. For assessing biomass concentration, the sum of reflectance above the base line from 670 to 950 nm was used. This allows the estimation of biomass with an error of less than 0.06 g·L^?1 For chlorophyll a and phycocyanin estimation, vertical attenuation coefficients at the wavelengths 440 nm (or 676 nm) and 624 nm, respectively, were employed. The developed algorithms were tested by using independent data sets in the range of chlorophyll a from 0.2 to 20mg·L^?1 and biomass from 0.15 to 1.1 g·L^?1. An error of pigment estimation of less than 0.80 mg·L^?1 was achieved. The potential use of the algorithms in algal biotechnology is further discussed.     

STRATEGIES AND RATES OF PHOTOACCLIMATION IN TWO MAJOR SOUTHERN OCEAN PHYTOPLANKTON TAXA: PHAEOCYSTIS ANTARCTICA (HAPTOPHYTA) AND FRAGILARIOPSIS CYLINDRUS (BACILLARIOPHYCEAE)1

We investigated rates and mechanisms of photoacclimation in cultures of Phaeocystis antarctica G. Karst. and Fragilariopsis cylindrus (Grunow) Willi Krieg, phytoplankton taxa that each dominate distinct areas of the Ross Sea, Antarctica. Both P. antarctica and F. cylindrus acclimated to increases in irradiance by reducing the effective size of the pigment antenna (σPSII) via xanthophyll‐cycle activity and reductions in chl. While enhanced photoprotection facilitated increases in specific growth rate and eventually led to higher light‐saturated photosynthetic rates (P^cell_m) in P. antarctica, increases in those variables were much smaller in F. cylindrus. In response to a lower irradiance, relaxation of xanthophyll‐cycle activity led to an increase in σPSII in both taxa, which occurred much more slowly in F. cylindrus. A surprising increase in specific growth rate over the first 36 h of acclimation in P. antarctica may have facilitated the significant reductions in P^cell_m observed in that taxon. In general, P. antarctica acclimated more quickly to changes in irradiance than F. cylindrus, exhibited a wider range in photosynthetic rates, but was more susceptible to photoinhibition. This acclimation strategy is consistent with growth in deeply mixed water columns with variations in irradiance that allow time for repair. In contrast, the slower acclimation rates, extensive photoprotection, and low photoinhibition exhibited by F. cylindrus suggest that it does not require the same period for repair as P. antarctica and is best suited for growth in habitats with relatively uniform irradiance, such as shallow mixed layers or sea ice.     

NITROGEN UPTAKE AND ASSIMILATION KINETICS IN ALEXANDRIUM MINUTUM (DYNOPHYCEAE): EFFECT OF N‐LIMITED GROWTH RATE ON NITRATE AND AMMONIUM INTERACTIONS1

Uptake and assimilation kinetics of nitrate and ammonium were investigated along with inhibition of nitrate uptake by ammonium in the harmful dinoflagellate Alexandrium minutum Halim at different nitrogen (N)–limited growth rates. Alexandrium minutum had a strong affinity for nitrate and ammonium (K_s=0.26±0.03 and 0.31±0.04 μmol·L^?1, respectively) whatever the degree of N deficiency of the cells. Ammonium was always the preferred form of nitrogen taken up (=0.42–0.50). In the presence of both forms, nitrate uptake was inhibited by ammonium, and inhibition was particularly marked in N‐sufficient cells (I_max～0.9 and K_i=0.31–0.56 μmol·L^?1). In the case of N assimilation, ammonium was also the preferred form in N‐deficient cells (=0.54–0.72), whereas in N‐sufficient cells, both N sources were equally preferred (=0.90–1.00). The comparison of uptake and assimilation rates highlighted the ability of A. minutum to significantly store in 1 h nitrate and ammonium in amounts sufficient to supply twice the daily N requirements of the slowest‐growing N‐deficient cells. Nitrogen uptake kinetic parameters of A. minutum and their ecological implications are discussed.     

GROWTH CHARACTERISTICS OF MARINE PHYTOPLANKTON DETERMINED BY CELL CYCLE PROTEINS: THE CELL CYCLE OF ETHMODISCUS REX (BACILLARIOPHYCEAE) IN THE SOUTHWESTERN NORTH ATLANTIC OCEAN AND CARIBBEAN SEA1

Ethmodiscus spp. is an important contributor to oceanic tropical-ooze sediments and thus might be an important transport vehicle of carbon from the ocean surface to sediments. The knowledge of its cell cycle and growth rate, which is still lacking, is necessary to evaluate the importance of Ethmodiscus in nutrient cycling and to solve the discrepancy between its high sedimentary abundance and rarity in the plankton. We used immunofluorescence of a cell cycle protein, prolqerating cell nuclear antigen (PCNA), and DNA-specific staining to study the progression of the cell cycle and roughly estimate the growth rate for E. rex (Rattray) Wiseman and Hendey in the southwestern North Atlantic Ocean and Caribbean Sea in June 1994 and January 1995. During the cell division cycle, the chloroplasts appeared to synthesize DNA before the nucleus (S phase). Following the S phase, the nucleus moved from one end of the cell toward the center underneath the midline of the girdle band (G2 phase) where it divided (M phase). During a very brief period, the parent cell split and moved apart from the girdle midline, and two new valves were produced (late M phase). The two daughter nuclei apparently remained attached at the joint of the two newly produced valves, where they appeared to be responsible for coordinating the symmetrical formation of the new valves. The morphologically complete daughter cells remained joined for a short period of time before separating into solitary cells whose nucleus was located at one end of the cell. Derived from the phase fraction curves, the duration of the cell cycle phases decreased in the order from G1, S, G2, to M. A conservative estimate of the growth rate in the study area obtained by using PCNA immunostaining was 0.39–0.46 d^?1 in June and 0.15 d^?1 in January. The validity and implication of the growth rate estimates are discussed.