Growth characteristics of two bloom‐forming synurophytes (Mallomonas elongata and Synura petersenii) at different nitrate and phosphate concentrations

Two dominant planktonic bloom‐forming algal species in a small shallow eutrophic pond were identified as Mallomonas elongata and Synura petersenii by electron microscopy. Their growth requirements were investigated as uni‐algal cultures in a laboratory study. The maximum population growth and maximum growth rate of M. elongata occurred at concentrations of 24 μM nitrate (NO₃) and 5 μM phosphate (PO₄) at a temperature of 15°C and a pH of 6. Synura petersenii grew maximally and exhibited the highest growth rate at a NO₃ concentration of 24 μM and a PO₄ concentration of 2 μM. Mallomonas elongata and S. petersenii had similar nutrient requirements for optimum growth, suggesting that the biomass of these two species can be controlled by nutrient gradients.     

KINETICS OF SILICON-LIMITED GROWTH IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA HASLE AND HEIMDAL (=CYCLOTELLA NANA HUSTEDT)1,2

The half-saturation constant ( K ₈) for growth and the maximum growth rate (μ_max) were determined for 2 clones of Thalassiosira pseudonana (=Cyclotella nana) under conditions in which external silicon concentrations controlled growth. The estuarine clone (3H) had a higher half-saturation constant and maximum growth rate ( K ₈= 0.98 μM Si; μ_max= 3.6 divisions/day) than the clone from the Sargasso Sea ( K ₈= 0.19 μM Si; μ_max= 2.1 divisions/day). The K ₈ values for each clone are such that the silicate levels found at certain times in both the Sargasso Sea and the coastal regions are rate limiting to growth, hence can be of significance to plant production and to species succession. The yield data are consistent with the concept that growth rate and cellular silicon content vary together in silicon-limited cultures.     

SILICON UPTAKE BY ALGAE WITH NO KNOWN Si REQUIREMENT. I. TRUE CELLULAR UPTAKE AND pH-INDUCED PRECIPITATION BY PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) AND PLATYMONAS SP. (PRASINOPHYCEAE)1

Phaeodactylum tricornutum Bohlin, the one diatom known to lack a silicon requirement for growth, and the prasinophyte Platymonas sp. are two representatives of a taxonomically diverse group of planktonic algae that have been reported to take up Si without a demonstrable requirement for the element. For both species, removal of Si from solution during growth in batch culture has at least two components; true biological uptake throughout the growth of the culture, and spontaneous inorganic precipitation of a solid silicate phase–probably Mg₂Si₃O₈ (sepiolite)–under the elevated pH conditions that prevail late in batch growth. It is not clear to what extent previous observations of Si uptake by algae without siliceous frustules may be influenced by inorganic, non-cellular precipitation. The kinetics of true cellular uptake of Si are similar in Phaeodalylum and Platymonas, and different from those reported for the Si-requiring diatoms. Uptake follows hyperbolic saturation kinetics in both species, with half-saturation concentrations of 97.4 μM in Phaeodactylum and 80.9 μM in Platymonas, as compared to ca. 1–6 μM in diatoms that form siliceous frustules. Uptake by Phaeodactylum and Platymonas is not substrate-saturated until the dissolved Si concentration of the medium exceeds 200 μM. Concentrations this high do not occur in the surface layer of the ocean, and the kinetics suggest that both species deposit much less silica in nature than they can be induced to deposit in culture.     

KINETICS OF SILICON-LIMITED GROWTH IN THE FRESHWATER DIATOM ASTERIONELLA FORMOSA1,2

Growth rates of two clones of the freshwater planktonic diatom Asterionella formosa Hass. were measured under conditions in which external silicon concentrations controlled growth. Clone AfOH2 from Lake Ohrid, Yugoslavia, had a higher maximum growth rate (μ_max= 1.11 doublings/day) and apparent half-saturation constant (K_si] + Si_o= 1.93 μM Si) than clone L262 from Lake Windermere, England. (μ_max= 0.61 doublings/day; K_si+ Si_o= 1.09 μM Si). K_lim, the silicon concentration at μ= 0.9 μ_max, is 13.8 μM Si for clone AfOH2 and 6.5 μM Si for clone L262. These values agree well with published field observations showing A. formosa populations decreasing below 0.5 mg/l SiO₂ (= 8.4 μM Si). Calculations of yield gave a range of 0.5–1.5 μM Si/10⁶ cells for clone AfOH2 and 0.6–1.9 μM Si/10⁶ cells for clone L262.     

Effect of nutrients and light intensity on growth of Mallomonascaudata (Synurophyceae)

We used batch cultures of three strains of the unicellular synurophyte Mallomonascaudata to investigate the effects of nitrate, phosphate, silicate and light intensity on population growth and growth rate. The three strains were isolated from three different reservoirs in Kyungpook Province, Korea. For all three strains, we observed high population growth under all nutrient concentrations studied, except at nitrate concentration below 0.8 μM. The maximum growth rate (μ_max) occurred at 8.2 μM or 16.5 μM nitrate, depending on the strain, and at 11.5 μM phosphate. Silicate concentration had no effect on growth rate. With respect to light intensity, the maximum population growth and maximum growth rates (μ_max) occured between 42 and 104 μmol m^?2 s^?1 depending on strain and culture temperature. Population growth of these three strains under batch culture occurred over a wide range of nutrient and light intensities, but there seemed to be strain‐specific differences that may represent adaptations to local environments.     

TEMPERATURE EFFECTS ON SILICON LIMITED GROWTH OF THE LAKE MICHIGAN DIATOM STEPHANODISCUS MINUTUS (BACILLARIOPHYCEAE)1

The effect of temperature on the silicon limited growth and nutrient kinetics of Stephanodiscus minutus Grun. was examined using batch and semicontinuous culture methods. Short-term batch culture methods gave maximum growth rates which were essentially constant over the temperature range of 10° to 20°C (μ₃= 0.71–0.80 d^?1). The half-saturation constant for growth (K_s) was significantly lowest at 10°C (K_s= 0.31 μM Si; 0.22–0.41), and higher at both 15°C (K_s= 1.03 μM Si; 0.68–1.47) and 20°C (K_s= 0.88 μM Si; 0.60–1.22). Two methods were used to evaluate the semicontinuous experiments. The Droop relationship showed that the minimum cell quota was about 1.50 × 10^?7 nmol Si cell^?1, but there was much overlap in the results at all three temperatures. The Monod growth relationship for the semicontinuous experiments gave estimates of K_s which were lowest at 15°C (K_s= 0.12 μM Si), and higher at 10°C (K_s= 0.68 μM Si) and 20°C (K_s= 1.24 μM Si), although 95% confidence intervals overlapped. The maximum growth rate estimates for the semicontinuous experiments were similar at 10° and 15°, and higher at 20°C, but the number of points used in making the calculations makes the results less reliable than those from batch cultures. Generally, there were no consistent significant differences in the silicon limited growth of S. minutus over the temperature range studied. Our values of K_s for S. minutus are the lowest recorded for a freshwater diatom, and are consistent with the distribution of this species in nature. Generally, this species becomes abundant in areas with high phosphorus loading and very low silicon levels (low Si:P loading rates). Stephanodiscus species are also fossil indicators of eutrophication in north temperate lakes.     

EVALUATION OF COMPETITIVE ABILITY OF STAURASTRUM LUETKEMUELLERII (CHLOROPHYCEAE) AND MICROCYSTIS AERUGINOSA (CYANOPHYCEAE) UNDER P LIMITATION1

The desmid Staurastrum luetkemuellerii Donat et Ruttner and the cyanobacterium Microcystis aeruginosa Kütz. showed pronounced differences in chemical composition and ability to maintain P fluxes. The cellular P:C ratio (Q_p) and the surplus P:C ratio (Q_sp) were higher in M. aeruginosa, indicating a lower yield of biomass C per unit of P. The subsistence quota (Q_p) was 1.85 μg P·mg C^?1in S. luetkemuellerii and 6.09 μg P·mg C^?1in M. aeruginosa, whereas the respective Q_p of P saturnted organisms (Q_s) were 43 and 63 μg P·mg C^?1. These stores could support four divisions in S. luetkemuellerii and three divisions in M. aeruginosa, which suggests that the former exhibited highest storage capacity (Q_s/Q₀). M. aeruginosa showed a tenfold higher activity of alkaline phosphatase than S. luetkemuellerii when P starved. The optimum N:P ratio (by weight) was 5 in S. luetkemuellerii and 7 in M. aeruginosa. The initial uptake of P_i pulses in the organisms was not inhibited by rapid (<1 h) internal feedback mechanisms and the short term uptake rote could be expressed solely as a function of ambient P_i. The maximum cellular C-based uptake rate (V_m) in P starved M. aeruginosa was up to 50 times higher than that of S. luetkemuellerii. It decreased with increasing growth rate (P status) in the former species and remained fairly constant in the latter. The corresponding cellular P-based value (U_m= V_m/Q_p) decreased with growth rate in both species and was about 10 times higher in P started M. aeruginosa than in S. luetkemuellerii. The average half saturation constant for uptake (K_m) was equal for both species (22 μg P·L^?1) and varied with the P status. S. luetkemuellerii exhibited shifts in the uptake rate of P_i that were characterized by increased affinity (U^m/K^m) at low P_i, concentrations (<4 μg P·L^?1) compared to that at higher concentrations. The species thus was well adapted to uptake at low ambient P_i, but M. aeruginosa was superior in P_i uptake under steady state and transient conditions when the growth rate was lower than 0.75 d^?1. Moreover, M. aeruginosa was favored by pulsed addition of P_i. M. aeruginosa relpased P_i at a higher rate than S. luetkemuellerii. Leakage of P_i from the cells caused C-shaped μ vs. P_i curves. Therefore, no unique K_s for growth could be estimated. The maximum growth rate (μ_m) (23° C) was 0.94 d^?1for S. luetkemuellerii and 0.81 d^?1for M. aeruginosa. The steady state concentration of P_i (P*) was lower in M. aeruginosa than in S. luetkemuellerii at medium growth rates. The concentration of P_i at which the uptake and release of P_i was equal (P_c was, however, lower in S. luetkemuellerii.     

A STATISTICAL CHARACTERIZATION OF GROWTH AMONG CLONES OF SYNURA PETERSENII (SYNUROPHYCEAE)1

Each of four clones from the Synura petersenii complex was grown at different pHs (5.5, 6.5, 7.5, 8.5) in batch culture experiments. Growth response curves and exponential growth rates were compared among clones and pH treatments in order to examine growth trend variation among the clonal groups. The clones were isolated from geographically distant North American localities. The clonal groups represented distinct mating types, an isolate and its subisolate, and S. petersenii- and S. glabra-like scale morphologies. No consistent relationship existed between growth response curve, and culture medium pH. Additionally, the trends across time differed according to clone and pH combination. Pairwise comparisons of linear trends from transformed growth response curves indicated two distinct clonal associations. Although the clonal associations corresponded with the final cell density of the cultures, growth response curves did not correspond with mating type, the parent-isolate and subisolate, or scale morphology. Clones with glabra-like scales had greater growth rates than the clone with petersenii-like scales. The conflicting results generated from growth response curve and growth rate analyses support the concept that S. petersenii and S. glabra form a highly variable, homogeneous grouping.     

Production of the taste/odor-causing compound,trans-2,cis-6-nonadienal,within the Synurophyceae

Although several species of the Synurophyceae have been associated with taste and odor problems in potable water supplies, electron microscopic-based field studies linked problematic blooms only toSynura petersenii Korshikov. Eventually, the organic compoundtrans-2,cis-6-nonadienal was implicated to cause the associated cucumberlike odors. The objective of this study was to survey unialgal cultures of various Synurophycean species for the occurrence oftrans-2,cis-6-nonadienal. The compound was detected throughout a 24-day growth assay with aS. petersenii isolate, but was not detected in an identical assay withSynura sphagnicola (Korshikov) Korshikov. In separate 24-day cultures,trans-2,cis-6-nonadienal was detected in two isolates from theS. petersenii species complex, but was not detected in isolates of twoMallomonas or fourSynura taxa not from theS. petersenii complex. These results support the hypothesis that production oftrans-2,cis-6-nonadienal is unique to taxa within theS. petersenii complex. When contrast-enhancing optics and specific specimen preparation techniques are employed, light microscopy can be used to distinguish taxa in theS. petersenii complex from all other Synurophycean taxa. These methods are suggested as an efficient way to monitortrans-2,cis-6-nonadienal-producing taxa in potable water supplies.Author for correspondence     

彼得森黄群藻孢囊的形成及形态

利用光镜及扫描电镜对彼得森黄群藻的形态结构、孢囊形成进行详细观察和描述.结果显示,彼得森黄群藻分布广泛,营养体形态变化也大,可以分为不同的变种和变型,其孢囊形态也有多种形态.根据鳞片结构,鉴定出其中的2个变型,并对其所产生的孢囊形态进行了对应.     

Influence of silicon on cobalt, zinc, and magnesium in baker's yeast, Saccharomyces cerevisiae

Silicon (Si, as silicate) is involved in numerous important structure and function roles in a wide range of organisms, including man. Silicate availability influences metal concentrations within various cell and tissue types, but, as yet, clear mechanisms for such an influence have been discovered only within the diatoms and sponges. In this study, the influence of silicate on the intracellular accumulation of metals was investigated in baker's yeast (Saccharomyces cerevisiae). It was found that at concentrations up to 10 mM, silicate did not influence the growth rate of S. cerevisiae within a standard complete medium. However, an 11% growth inhibition was observed when silicate was present at 100 mM. Intracellular metal concentrations were investigated in yeast cultures grown without added silicate (−Si) or with the addition of 10 mM silicate (+Si). Decreased amounts of Co (52%), Mn (35%), and Fe (20%) were found within +Si-grown yeast cultures as compared to −Si-grown ones, whereas increased amounts of Mo (56%) and Mg (38%) were found. The amounts of Zn and K were apparently unaffected by the presence of silicon. +Si enhanced the yeast growth rate for low-Zn²⁺ medium, but it decreased the growth rate under conditions of a low Mg²⁺ medium and did not alter the growth rates in high Zn²⁺ and Co²⁺ media. +Si doubled the uptake rate of Co²⁺ but did not influence that of Zn²⁺. We propose that a possible explanation for these results is that polysilicate formation at the cell wall changes the cell wall binding capacity for metal ions. The toxicity of silicate was compared to germanium (Ge, as GeO₂), a member of the same group of elements as Si (group 14). Hence, Si and Ge are chemically similar, but silicate starts to polymerize to oligomers above 5 mM, whereas Ge salts remain as monomers at such concentrations. Ge proved to be far more toxic to yeast than Si and no influence of Si on Ge toxicity was found. We propose that these results relate to differences in cellular uptake.     

PHOSPHORUS AND THE GROWTH OF JUVENILE MACROCYSTIS PYRIFERA (PHAEOPHYTA) SPOROPHYTES1

The effect of phosphate (P_i) supply on growth rate and tissue phosphorus content of juvenile Macrocystis pyrifera (L.) C. Ag. sporophytes was examined. Sporophytes were batch cultured in aquaria with flowing recirculated seawater enriched by 30 μM nitrate. Each aquarium was supplemented with a different seawater P_i concentration, 0, 0.3, 1, 2, 3, and 6 μM. Sporophyte mean specific growth rates declined with time in all cultures presumably due to the normal developmental decrease in the proportion of meristematic tissue of each plant. Growth rate declines were more pronounced in cultures that were nutrient limited. Sporophyte growth was P-limited after two-week exposure to P_i less than 1 μM, corresponding to a tissue P concentration of less than 0.20% dry weight. Plants cultured at 6 μM P_i contained tissue P levels of 0.53% dry weight after three weeks. Luxury consumption and storage of P occurred.     

GROWTH RATES AND ULTRASTRUCTURE OF SILICEOUS SETAE OF CHAETOCEROS GRACILIS (BACILLARIOPHYCEAE) 12

The growth of setae in post-division Chaeloceros gracilis Schütt was triphasic. Following cell separation there was an initial lag phase of about 30 min after which setae grew linearly at rates ranging from 0.20 to 0.38 μm-min^?1. The growth rate was independent of whether diatoms cultured in medium containing 200 μM Si were transferred for experimentation to media containing 10 or 200 μM Si. When developing setae had attained a length of approximately 2 μm, their growth rate slowed as they entered a clearly defined plateau phase. The amount of silicon per unit length of setae was found to be 0.02 pg Si μm^?1, and the deposition rate was estimated as 0.005 Pg Si min^?1. Transmission electron microscopy revealed an axial structure resembling a microlubule extending the length of each seta and membrane bound polyphosphate bodies postulated to be the energy source for growth and associated biomineralization processes.     

COPPER TOXICITY TO SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1,2

Copper toxicity to Skeletonema costatum (Grev.) Cleve has been studied in batch cultures of chemically defined culture media. The alga is relatively insensitive to cupric ion activity, demonstrating no effect on growth up to (Cu²⁺) = 10^?8.5 M. Cultures inoculated from stationary phase stocks exhibit a prolongation of the lag phase with increasing copper concentrations near and above the point of precipitation of the copper. The toxicity of copper is a function of the silicic acid concentration in the medium. This effect is observed in a range of Si(OH)₄ concentrations (10^?5 M to 10^?4 M) above known values for the saturation of silicon uptake kinetics, thus suggesting an influence of copper on silicate metabolism.     

DIFFERENT RESPONSE MECHANISMS OF TWO PLANKTONIC DESMID SPECIES (CHLOROPHYCEAE) TO A SINGLE SATURATING ADDITION OF PHOSPHATE

Two planktonic algal species, Staurastrum chaetoceras (Schr.) G. M. Smith and Cosmarium abbreviatum Rac. var. planctonicum W. et G. S. West, from trophically different alkaline lakes, were compared in their response to a single saturating addition of phosphate (P) in a P-limited growth situation. Storage abilities were determined using the luxury coefficient R = Q_max/Q₀. Maximum cellular P quotas differed, depending on whether cells were harvested during exponential growth at μ_max (Q_max, R being 26.7 and 9.1 for C. abbreviatum and S. chaetoceras, respectively) or harvested after a saturating pulse at P-limited growth conditions (Q′_max, R being 53.5 and 20.2 for C. abbreviatum and S. chaetoceras, respectively). At stringent P-limited conditions, maximum initial uptake rates were higher in S. chaetoceras than in C. abbreviatum (0.094 and 0.073 pmol P·cell^?1·h^?1, respectively), but long-term (net) uptake rates (over ～20 min) were higher in C. abbreviatum than in S. chaetoceras (0.048 and 0.019 pmol P·cell^?1·h^?1, respectively). Before growth resumed after the onset of a large P addition (150 μmol·L^?1), a lag phase was observed for both species. This period lasted 2–3 days for S. chaetoceras and 3–4 days for C. abbreviatum, corresponding with the time to reach Q^′_max. Subsequent growth rates (over ～10 days) were 0.010 h^?1 and 0.006 h^?1 for S. chaetoceras and C. abbreviatum, respectively, being only 20%–30% of maximum growth rates. In conclusion, S. chaetoceras, with a relatively high initial P-uptake rate, short lag phase, and high initial growth rate, is well adapted to a P pulse of short duration. Conversely, C. abbreviatum, with a high long-term uptake rate and high storage capacity, appears competitively superior when exposed to an infrequent but lasting pulse. These characteristics provide information about possible strategies of algal species to profit from temporarily high P concentrations.     

NUTRIENT REQUIREMENTS OF THE DINOFLAGELLATE PERIDINIUM GATUNENSE1

Optimum nutrient conditions for growth and photosynthesis of Peridinium gatunense (Nygaard) (Peridinium cinctum fa. westii) were investigated using axenic clones in batch cultures. Selenium (Se) had previously been found to be an indispensable growth factor for P. gatunense. Optimal, suboptimal, and supraoptimal concentrations of HCO₃^?, N, Ca, Cl, Mg, P, K, S, Si, EDTA-Na, Fe, Mo, Zn, Mn, Co, Se, B, Br, I, and various trace element mixtures were determined by measuring biomass development, growth rates, ¹⁴C uptake, and/or oxygen production at various concentration gradients of these elements. The general characteristics of the best formulation, medium-L 16, relative to other media, are its high content of NaHCO₃ (1 meq · L^?1) and Mo (0.2 μM) but low concentrations of NO_3-N (150 μM), PO_4-P (10 μM), and Fe (0.4 μM), in addition to its content of Se. The total content of trace metals, except for Se, may be reduced to one-fourth of that in medium-L 16 without altering the major growth-promoting properties of the medium. Medium-L 16 deviated considerably from Lake Kinneret (Israel) water, being much lower in macroelements except for N and P. The pH (8.1–8.4) was in the same range, but the values of conductivity (140 μS · cm^?1), alkalinity (1 meq · L^?1) and NaCl (200 μM) were > 8, 2, and 30 times higher, respectively, in the lake water. Selenium deficiency may limit the growth of P. gatunense in this lake.     

Analysis of pH-stat continuous cultivation and the stability of the mixed fermentation in continuous yogurt production

A pH-stat fermentor is a continuous cultivator in which the feed rate is controlled to maintain a constant pH, i.e., end-product acid concentration. This fermentor has application to the continuous cultivation of lactic acid-producing organisms in milk-based media. The equations describing the operation of this fermentor are developed. It is shown that, where the limiting substrate is the carbon and energy source, the operation of the fermentor is essentially equivalent to that of a turbidostat. In contrast to this, where the carbon and energy source is in excess and growth is limited by another substrate, pH-state fermentation is stable both in regions of substrate excess, where D = μ_max, comparable with turbidostat operation, and substrate limitation where D < μ_max, comparable with chemostat operation. These conditions are met in milk-based media. An analysis is presented, allowing the prediction of the degree of substrate limitation, cell density, and dilution rate in a pH-stat fermentor from batch-growth kinetics. This was confirmed using experimental data for the growth of Streptococcus thermophilus TS2 and Lactobacillus LB1 in skim milk. Stable simultaneous growth of two organisms in continuous culture occurs if their growth rates are determined by separate conditions, so that, at steady state, their growth rqtes are separately madeequal to the dilution rate. It is then predicted, and confirmed by experiment, that a mixed culture of S. thermophilus TS2 and L. bulgaricus LB1 in a pH-stat continuous fermentor in yogurt mix at pH 5.5 would be stable with the growth of L. bulgaricus being substrate unlimited and the fermentor operting with D = μ_max for L. bulgaricus LB1, and the growth of S. thermophilus TS2 being substrate limited so that its growth rate is equal to the existing dilution rate. Finally, it is predicted and confirmed by experiment that if the conditions are altered so that the growth of S. thermophilus TS2 is substrate unlimited the stable association is broken down, the fermentor operates with D approaching μ_max for S. thermophilus TS2, and L. bulgaricus LB1 is washed out to the level maintained by wall growth.     

Impact of Atmospheric Sulfur Deposition on Sulfur Metabolism in Plants: H2S as Sulfur Source for Sulfur Deprived Brassica oleracea L.

Brassica oleracea L. was rather insensitive to atmospheric H₂S: growth was only negatively affected at ≥0.4 μl I^?1. Shoots formed a sink for H₂S and the uptake rate showed saturation kinetics with respect to the atmospheric concentration. The H₂S uptake rate was high in comparison with other species, which may reflect the high sulfur need of Brassica. The net uptake of sulfate by roots of hydroponically grown plants was substantially reduced after one week of exposure to 0.25 μl l^?1 H₂S, indicating that plants switched in part from sulfate to H₂S as sulfur source for plant growth. Plants were sulfur deficient after two weeks of sulfur deprivation, illustrated by reduced growth, which was more pronounced for shoots than for roots, and in enhanced shoot dry matter content. The latter could for the greater part be attributed to enhanced levels of soluble sugars and starch. Sulfur deficiency was further characterized by a low pigment content, extremely low levels of sulfate and water-soluble non-protein thiols, and by enhanced levels of nitrate and free amino acids, particularly in the shoots. Furthermore, sulfur deficient plants contained a lower total lipid content in shoots, whereas its content in roots was unaffected. The level of sulfolipids was decreased in both roots and shoots. When sulfur deprived plants were exposed to 0.25 μl I^?1 H₂S for one week, all sulfur deficiency symptoms were abolished and growth was restored. Furthermore, plants were able to grow with 0.4 μl I^?1 H₂S as the sole sulfur source. Water-soluble non-protein thiol content was enhanced in both shoots and roots of H₂S exposed plants, irrespective of the sulfate supply to the roots, whereas plants grown with H₂S as sole sulfur source contained very low sulfate levels. The interaction between atmospheric and pedospheric sulfur nutrition in plants is discussed.