NEUTRAL LIPID AND CARBOHYDRATE PRODUCTIVITIES AS A RESPONSE TO NITROGEN STATUS IN ISOCHRYSIS SP. (T‐ISO; HAPTOPHYCEAE): STARVATION VERSUS LIMITATION1

Partitioning of the carbon (C) fixed during photosynthesis between neutral lipids (NL) and carbohydrates was investigated in Isochrysis sp. (Haptophyceae) in relation to its nitrogen (N) status. Using batch and nitrate‐limited continuous cultures, we studied the response of these energy reserve pools to both conditions of N starvation and limitation. During N starvation, NL and carbohydrate quotas increased but their specific growth rates (specific rates of variation, μ_CAR and μ_NL) decreased. When cells were successively deprived and then resupplied with NO₃, both carbohydrates and neutral lipids were inversely related to the N quota (N:C). These negative relationships were not identical during N impoverishment and replenishment, indicating a hysteresis phenomenon between N and C reserve mobilizations. Cells acclimated to increasing degrees of N limitation in steady‐state chemostat cultures showed decreasing NL quota and increasing carbohydrate quota. N starvation led to a visible but only transient increase of NL productivity. In continuous cultures, the highest NL productivity was obtained for the highest experimented dilution rate (D = 1.0 d^?1; i.e., for non N‐limited growth conditions), whereas the highest carbohydrate productivity was obtained at D = 0.67 d^?1. We used these results to discuss the nitrogen conditions that optimize NL productivities in the context of biofuel production.     

PRODUCTION AND CELLULAR LOCALIZATION OF NEUTRAL LONG‐CHAIN LIPIDS IN THE HAPTOPHYTE ALGAE ISOCHRYSIS GALBANA AND EMILIANIA HUXLEYI1

Isochrysis galbana Parke, Emiliania huxleyi (Lohm.) Hay and Mohler, and some related prymnesiophyte algae produce as neutral lipids a set of polyunsaturated long‐chain (C_37–39) alkenones, alkenoates, and alkenes (PULCA). These biomarkers are widely used for paleothermometry, but the biosynthesis and cellular location of these unique lipids remain largely unknown. By staining with the fluorescent lipophilic dye Nile Red, we found that I. galbana and E. huxleyi, like many other algae, package their neutral lipid into cytoplasmic vesicles or lipid bodies. We found that these lipid bodies increase in abundance under nutrient limitation and disappear under prolonged darkness and show that this pattern correlates well with the concentration of PULCA as measured by TLC. In addition, we show that lipid vesicles purified by sucrose density gradient centrifugation consist predominantly of PULCA. We also found significant pools of neutral lipid associated with chloroplasts, and PULCA component profiles in lipid vesicles and chloroplasts are similar. Examination of cell ultrastructure shows conspicuous cytoplasmic and chloroplast lipid bodies, and we suggest that PULCA may be synthesized in chloroplasts and then exported to cytoplasmic lipid bodies for storage and eventual metabolism. Our results connect and extend prior observations of lipid bodies and membrane‐unbound PULCA in I. galbana and E. huxleyi, as well as the behavior of PULCA during nutrient and light stress.     

OCCURRENCE OF PHYIWATED CHLOROPHYLL c IN ISOCHRYSIS GALBANA AND ISOCHRYSIS SP. (CLONE T-ISO) (PRYMNESIOPHYCEAE)1

The pigment composition of two clones of Isochrysis galbana Parke (CCMP 1323 and CCAP 927/1), and Isochrysis sp. (clone T-ISO) was analyzed by high-performance liquid chromatography using a polymeric octadecylsilica column. Fluorescent peaks with retention times higher than chlorophyll a were detected for all three clones. The corresponding pigments were isolated and characterized in terms of their visible absorbance and fluorescence spectra. The pigments were similar to phytol-substituted chlorophyll c, previously isolated from Emiliania huxleyi (Lohm.) Hay and Mohler and other species containing chlmophyll c₃. The presence of phytol-substituted chlorophyll c in I. galbana which lacked chlorophyll c₃, increases the diversity of chlorophyll patterns for the Haptophyta, which can be grouped, at present, into six different pigment types. This is the jrst observation of a haptophyte containing the apolar phytylated chlorophyll c-like pigment but lacking chlorophyll c₃.     

SEASONAL PATTERN OF DIEL PERIODICITY IN PHOTOSYNTHESIS BY POLAR PHYTOPLANKTON: SPECIES-SPECIFIC RESPONSES1

The diel patterns of light-saturated and light-limited photosynthesis were measured for three diatom species in McMurdo Sound, Antarctica during the transition from late austral winter to summer. Maximum photosynthetic capacity occurred around mid-day during September, when there was a well defined light/dark cycle, and progressively shifted to about midnight by late october when irradiance was continuous. There was a concomitant shift in minimum photosynthetic capacity from midnight to midday. Rates of light-saturated and -limited photosynthesis covaried, and the magnitude of seasonal and diel changes in photosynthetic characteristics were similar. The linear relationship between light-saturated and -limited photosynthesis suggests that the shapes of the photosynthesis-irradiance curves remained relatively constant over the day and througout the season. The unique diel patterns of photosynthesis of these polar phytoplankton appear to be a response to the persistently low, yet continuous irradiance of the polar summer.     

DIFFERENTIAL RESPONSES OF ANABAENA SP. PCC 7120 (CYANOPHYCEAE) CULTURED IN NITROGEN‐DEFICIENT AND NITROGEN‐ENRICHED MEDIA TO ULTRAVIOLET‐B RADIATION1

Stratospheric ozone depletion increases the amount of ultraviolet‐B radiation (UVBR) (280–320 nm) reaching the surface of the earth, potentially affecting phytoplankton. In this work, Anabaena sp. PCC 7120, a typically nitrogen (N)‐fixing filamentous bloom‐forming cyanobacterium in freshwater, was individually cultured in N‐deficient and N‐enriched media for long‐term acclimation before being subjected to ultraviolet‐B (UVB) exposure experiments. Results suggested that the extent of breakage in the filaments induced by UVBR increases with increasing intensity of UVB stress. In general, except for the 0.1 W · m^?2 treatment, which showed a mild increase, UVB exposure inhibits photosynthesis as evidenced by the decrease in the chl fluorescence parameters maximum photochemical efficiency of PSII (F_v/F_m) and maximum relative electron transport rate. Complementary chromatic acclimation was also observed in Anabaena under different intensities of UVB stress. Increased total carbohydrate and soluble protein may provide some protection for the culture against damaging UVB exposure. In addition, N‐deficient cultures with higher recovery capacity showed overcompensatory growth under low UVB (0.1 W · m^?2) exposure during the recovery period. Significantly increased (～830%) ATPase activity may provide enough energy to repair the damage caused by exposure to UVB.     

INTERACTIONS OF LIGHT/DARK CYCLES AND NITROGEN PULSES ON THE TIMING OF CELL DIVISION IN THE NITROGEN-LIMITED MARINE DIATOM CYLINDROTHECA FUSIFORMIS (BACILLARIOPHYCEAE)1

Cell division in most eukaryotic algae grown on alternating periods of light and dark (LD) is synchronized or phased so that cell division occurs only during a restricted portion of the LD cycle. However, the phase angle of the cell division gate, the time of division relative to the beginning of the light period, is known to be affected by growth conditions such as nutrient status and temperature. In this study, it is shown that the phase angle of cell division in a diatom, Cylindrotheca fusiformis Reimann and Lewin, is affected by the N-limited growth rate; cell division occurred later in the dark period (12:12 h LD cycle) when the growth rate was infradian (D = 0.42 d^?1) than when it was ultradian (D = 1.0 d^?1). Nitrogen-pulses did not affect the phase angle of the division gate, but could shift the time of peak cell division activity within the division gate. The effects, if any, of N-pulses were dependent upon the growth rate and the time of day that the pulses were administered. These responses indicate that the timing of cell division in this diatom is not determined solely by the zeitgeber from the LD cycle, but rather that a LD cycle control mechanism and a N-mediated control mechanism are both involved and are somewhat interdependent. In addition, an increase in protein was observed immediately after administering a N-pulse to C. fusiformis in the ultradian growth mode indicating that the accumulation of protein can be uncoupled from the cell division cycle.     

INFLUENCE OF ENVIRONMENTAL FACTORS AND POPULATION COMPOSITION ON THE TIMING OF CELL DIVISION IN THALASSIOSIRA FLUVIATILIS (BACILLARIOPHYCEAE) GROWN ON LIGHT/DARK CYCLES1

Cell division patterns in Thalassiosira fluviatilis grown in a cyclostat were analyzed as a function of temperature, photoperiod, nutrient limitation and average cell size of the population. Typical cell division patterns in populations doubling more than once per day had multiple peaks in division rate each day, with the lowest rates always being greater than zero. Division bursts occurred in both light and dark periods with relative intensities depending on growth conditions. Multiple peaks in division rate were also found, when population growth rates were reduced to less than one doubling per day by lowering temperature, nutrients, or photoperiod and the degree of division phasing was not enhanced. Temperature and nutrient limitation shifted the timing of the major division burst relative to the light/dark cycle. Average cell volume of the inoculum was found to be a significant determinant of the average population growth rate and the timing and magnitude of the peaks in division rate. The results are interpreted in the context of a cell cycle model in which generation times are “quantized” into values separated by a constant time interval.     

CRYPTIC AND PSEUDO‐CRYPTIC DIVERSITY IN DIATOMS—WITH DESCRIPTIONS OF PSEUDO‐NITZSCHIA HASLEANA SP. NOV. AND P. FRYXELLIANA SP. NOV.1

A high degree of pseudo‐cryptic diversity was reported in the well‐studied diatom genus Pseudo‐nitzschia. Studies off the coast of Washington State revealed the presence of hitherto undescribed diversity of Pseudo‐nitzschia. Forty‐one clonal strains, representing six different taxa of the P. pseudodelicatissima complex, were studied morphologically using LM and EM, and genetically using genes from three different cellular compartments: the nucleus (D1–D3 of the LSU of rDNA and internal transcribed spacers [ITSs] of rDNA), the mitochondria (cytochrome c oxidase 1), and the plastids (LSU of RUBISCO). Strains in culture at the same time were used in mating studies to study reproductive isolation of species, and selected strains were examined for the production of the neurotoxin domoic acid (DA). Two new species, P. hasleana sp. nov. and P. fryxelliana sp. nov., are described based on morphological and molecular data. In all phylogenetic analyses, P. hasleana appeared as sister taxa to a clade comprising P. calliantha and P. mannii, whereas the position of P. fryxelliana was more uncertain. In the phylogenies of ITS, P. fryxelliana appeared to be most closely related to P. cf. turgidula. Morphologically, P. hasleana differed from most other species of the complex because of a lower density of fibulae, whereas P. fryxelliana had fewer sectors in the poroids and a higher poroid density than most of the other species. P. hasleana did not produce detectable levels of DA; P. fryxelliana was unfortunately not tested. In P. cuspidata, production of DA in offspring cultures varied from higher than the parent cultures to undetectable.     

AKINETE PRODUCTION OF ANABAENA LEMMERMANNII AND A. CYLINDRICA (CYANOPHYCEAE) IN NATURAL POPULATIONS OF N‐ AND P‐LIMITED COASTAL MESOCOSMS1

A strong biomass increase of two Anabaena species was observed in natural plankton community enclosed into nine large mesocosms (51 m³) and manipulated with mineral nutrients and an organic carbon source during a 3‐week period in the coastal Baltic Sea. The water column and settled material from the bottom of the mesocosms were sampled at 2‐day intervals. Planktonic populations of Anabaena lemmermannii Richter and A. cylindrica Lemmermann and sedimentation rates of akinetes to the bottom were quantified. Comparing mesocosms with artificially induced nitrogen and phosphorus limitation, we found that during the third week of the experiment, the population size of A. lemmermannii was clearly higher in nitrogen‐limited units (by a factor of 2.4), whereas the production rate of akinetes was higher in the phosphorus‐limited units (by a factor of 2.5). Input of freshly produced A. lemmermannii akinetes to the benthos was on average 15 × 10⁶ and 6 × 10⁶ cells· m^?2·d^?1 in the P^? and N^? limited mesocosms, respectively. Our estimates of specific akinete production rate of A. lemmermannii in P^? and N^? limited mesocosms revealed an even larger divergence (a factor of 5.5), being on average 2.4 and 0.4 akinetes·10^?3 vegetative cells^?1·d^?1, respectively. The phosphorus addition effectively reduced akinete production of A. lemmermannii. Differences in the nutrient manipulation had no apparent effect on the biomass and akinete production of A. cylindrica. The akinete production pattern of A. cylindrica revealed a 1‐week delay compared with the vegetative population peak, whereas such a delay was not obvious in A. lemmermannii.     

TAXONOMIC STUDY OF BIGELOWIELLA LONGIFILA SP. NOV. (CHLORARACHNIOPHYTA) AND A TIME‐LAPSE VIDEO OBSERVATION OF THE UNIQUE MIGRATION OF AMOEBOID CELLS1

A new species of a chlorarachniophyte alga, Bigelowiella longifila sp. nov., is described. It is classified as a member of Bigelowiella as flagellate cells constitute the main stage of the life cycle. However, this alga is different from the only described species of the genus, B. natans Moestrup, in having a unique amoeboid stage in the life cycle. We observed an interesting behavior of amoeboid daughter cells after cell division: One of the two daughter cells inherits the long filopodium of the parental cell, and it subsequently transports its cell contents through the filopodium to develop at its opposite end. The other daughter cell forms a new filopodium. This unequal behavior of daughter cells may have evolved before the chlorarachniophytes and some colorless cercozoans diverged.     

PULSED‐FIELD GEL ELECTROPHORESIS ANALYSIS OF GENOME SIZE AND STRUCTURE IN PAVLOVA GYRANS AND DIACRONEMA SP. (HAPTOPHYTA)1

Information regarding genome size and structure is a prerequisite for selecting model organisms and for facilitating the most efficient study of their chromosomal DNA. The goal of this study was to identify future candidates for complete‐genome‐sequencing projects among economically or evolutionarily important species of haptophyte algae. Using pulsed‐field gel electrophoresis (PFGE), we identified relatively small genomes and chromosome sizes in two haptophyte species from the class Pavlovophyceae, Pavlova gyrans Butcher and Diacronema sp. The basal position of Pavlovophyceae in the Haptophyta; the key position of this group in the chromalveolates; and their economic and potential biomedical importance, ease of culturing, and small genome size make these taxa ideal models for complete‐genome sequencing.     

FLUORESCENCE EMISSION SPECTRA OF MARINE AND BRACKISH‐WATER ECOTYPES OF FUCUS VESICULOSUS AND FUCUS RADICANS (PHAEOPHYCEAE) REVEAL DIFFERENCES IN LIGHT‐HARVESTING APPARATUS1

The Bothnian Sea in the northerly part of the Baltic Sea is a geologically recent brackish‐water environment, and rapid speciation is occurring in the algal community of the Bothnian Sea. We measured low‐temperature fluorescence emission spectra from the Bothnian Sea and the Norwegian Sea ecotypes of Fucus vesiculosus L., a marine macroalga widespread in the Bothnian Sea. Powdered, frozen thallus was used to obtain undistorted emission spectra. The spectra were compared with spectra measured from the newly identified species Fucus radicans Bergström et L. Kautsky, which is a close relative of F. vesiculosus and endemic to the Bothnian Sea. The spectrum of variable fluorescence was used to identify fluorescence peaks originating in PSI and PSII in this chl c–containing alga. The spectra revealed much higher PSII emission, compared to PSI emission, in the Bothnian Sea ecotype of F. vesiculosus than in F. radicans or in the Norwegian Sea ecotype of F. vesiculosus. The results suggest that more light‐harvesting chl a/c proteins serve PSII in the Bothnian Sea ecotype of F. vesiculosus than in the two other algal strains. Treatment of the Bothnian Sea ecotype of F. vesiculosus in high salinity (10, 20, and 35 practical salinity units) for 1 week did not lead to spectral changes, indicating that the measured features of the Bothnian Sea F. vesiculosus are stable and not simply a direct result of exposure to low salinity.