Navicula Pelliculosa Research Articles

Kinetics of nitrate uptake by freshwater algae

The kinetics of nitrate (NO3−) uptake, the maximum uptake velocity (Vm) and the half-saturation constant (Ks), were determined for 18 species of batch-cultured freshwater algae grown without nitrogen limitation. Values of Ks ranged from 0.25 to 6.94 µM l−1Chlorella pyrenoidosa Chick, and Navicula pelliculosa (Breb.) Hilse, respectively. Values of Vm ranged from 0.51 to 5.07 µM l−1 h−1 for Anabaena A7214 and Nitzschia W-32 O'Kelley, respectively. The mean positive values of Ks for Chlorophyta, Cyanophyta and Chrysophyta were 1.89, 3.67 and 4.07 µM l−1, respectively. The mean values of Vm for the same phyla were 1.61, 1.02 and 2.97 µM l−1 h−1 105 cells−1, respectively. The ranges of these kinetic parameters encompass values of kinetic parameters for marine and freshwater species in batch culture, for freshwater algae grown in N-limited chemostats and for natural populations of freshwater phytoplankton. Thus, in spite of variability between species, uptake parameters for both marine and freshwater algae are identical.

Photolytic oxidative demethylation of aqueous dimethylsiloxanols

AbstractDimethylsilanediol and other water‐soluble dimethysiloxanols undergo aqueous photolytic oxidative demethylation with tropospheric ultraviolet radiation in the presence of suitable chromophores, such as nitrogen oxides, to give silicic acid and carbon dioxide. The “biosuitability” of the resulting silicic acid was demonstrated by monitoring the growth of diatoms (Navicula pelliculosa) in the irradiated aqueous media. Thus, a plausible route for the further degradation of such water soluble hydrolysis products of poly(dimethyl‐siloxane) to naturally occurring materials was conclusively demonstrated. Furthermore, di‐ and monomethyl silanol species were shown not to be utilized by the diatom colony, even when present as completely water soluble components.

PHOTOLYTIC OXIDATIVE DEMETHYLATION OF AQUEOUS DIMETHYLSILOXANOLS

Dimethylsilanediol and other water-soluble dimethysiloxanols undergo aqueous photolytic oxidative demethylation with tropospheric ultraviolet radiation in the presence of suitable chromophores, such as nitrogen oxides, to give silicic acid and carbon dioxide. The “biosuitability” of the resulting silicic acid was demonstrated by monitoring the growth of diatoms (Navicula pelliculosa) in the irradiated aqueous media. Thus, a plausible route for the further degradation of such water soluble hydrolysis products of poly(dimethyl-siloxane) to naturally occurring materials was conclusively demonstrated. Furthermore, di- and monomethyl silanol species were shown not to be utilized by the diatom colony, even when present as completely water soluble components.

THE RELEASE OF GLYCOLATE BY A FRESHWATER DIATOM1

ABSTRACT Navicula pelliculosa (Breb) Hilse grown on 2% CO2 in air released glycolate when incubated in light in buffer pH 8.0 containing 10 mM bicarbonate. Excretion ceased about 90 min after transfer to air and no excretion was detected with air‐grown cells. These results indicate that glycolate release in this alga, as in species of other algal phyla, is an artifact of growth on high concentrations of CO2.

DIATOM MINERALIZATION OF SILICIC ACID. V. ENERGETIC AND MACROMOLECULAR REQUIREMENTS FOR Si(OH)4 MINERALIZATION EVENTS DURING THE CELL CYCLE OF NAVICULA PELLICULOSA1

ABSTRACTThe reactions and processes which underlie the silicification mechanism (incorporation of soluble pool Si into insoluble material) in the diatom Navicula pelliculosa (Bréb.) Hilse are quite sensitive to low temperature. Furthermore incorporation is completely blocked in 66Ge‐Si(OH)4 preloaded cells treated with an inhibitor of oxidative phosphorylation (2,4‐dinitrophenol) or a sulfhydryl blocking agent (N ‐ethylmaleimide). De novo protein synthesis is not required for incorporation in cells preloaded 3 h, but cycloheximide added to cells preloaded 1 h inhibits incorporation after 2 h. These results are interpreted to indicate that purely chemical reactions, which are uncoupled from cellular metabolism, cannot completely account for Si(OH)4 polycondensation during silica frustule morphogenesis in the diatom. A temperature sensitive cellular process or reaction, postcytokinesis, is also postulated to be required before silicification can occur.

The effect of nickel on the growth of the freshwater diatom Navicula pelliculosa

The effect of nickel on the growth of the freshwater diatom Navicula pelliculosa was determined by noting differences in the growth rate and number of cells present in laboratory cultures exposed to 0, 100, 300 and 600 μg/litre nickel for 14 days. Nickel concentrations as low as 100 μg/litre (1·7 × 10 −6M) reduced the population growth rate by 50% and led to decreased 14-day cell numbers. Calculation of the equilibrium composition of the culture medium showed that 99·8% of the total nickel added existed as Ni +2. The occurrence of Ni +2 in the medium was associated with reduced algal growth.

EFFECT OF CYSTEINE AND METHIONINE ON SULFATE UPTAKE AND PRIMARY PRODUCTIVITY BY AXENIC ALGAL CULTURES AND LAKE MICROPLANKTON COMMUNITIES1

ABSTRACTThe presence of up to 500 μg sulfur·l−1 of an equimolar mixture of cysteine and methionine had virtually no effect on the SO42‐ uptake rate of Navicula pelliculosa, (Bréb.) Hilse whereas the rate of Ankistrodesmus falcatus (Corda) Ralfs was decreased by the presence of 500 μg S· l−1 and Anabaena flos‐aquae (Lyngbye) Bréb. by 50 μg S·l−1. Primary productivity in these axenic cultures was affected (decreased) only in A. falcatus. The C:S uptake ratio was lowest in N. pelliculosa and highest in A. falcatus. Considering these species as representative of groups of naturally occurring algae, patterns of SO42‐ uptake and primary productivity in a eutrophic and a moderately oligotrophic lake reflected the results of the algal culturing experiments: SO42‐ uptake rates, relative to primary productivity, were higher in the presence of diatoms and bluegreen algae and lower when green algae were present; the addition of the cysteine I methionine mixture to the lake waters decreased the rate of microplankton SO42‐ uptake in correlation with the makeup of the algal community; primary productivity decreased upon the addition of cysteine I methionine when green algae were relatively abundant. It is concluded that, in most fresh water systems, the effects of organic sulfur pollution on algal SO42‐ uptake and primary productivity are insignificant as compared to other ecological changes that occur due to that pollution.

Measurement of Complexing Materials Excreted from Algae and Their Ability to Ameliorate Copper Toxicity

The complexing capacities of three algal exudates and the conditional stability constants of their copper complexes have been determined by an ion exchange method. Their ability to ameliorate copper toxicity towards the primary production of Chlorella vulgaris is related to the conditional stability constants, which regulate the ionic copper concentration. Anabaena cylindrica, Navicula pelliculosa, and Scenedesmus quadricauda excreted 6.73, 2.86, and 0.66 μmol/L of complexing ligands, respectively, with conditional stability constants of 107.7, 108.1, and 108.6, respectively, for their corresponding copper complexes. When these constants were applied in calculations, a free copper ion concentration of 10−10.3 mol/L was found in each exudate. Key words: algal exudates, free copper ion concentration, complexing capacity, copper ion toxicity, primary productivity

DIATOM MINERALIZATION OF SILICIC ACID IV. KINETICS OF SOLUBLE Si POOL FORMATION IN EXPONENTIALLY GROWING AND SYNCHRONIZED NAVICULA PELLICULOSA1

ABSTRACTSilicic acid taken up from the growth medium by Navicula pelliculosa (Bréb.) Hilse was shown to enter at least two compartments: i) soluble pools; ii) insoluble fraction comprised predominantly of the silica frustule. Soluble Si pools were extracted by a variety of agents from cells uniformly labeled for ten generations in medium containing 68Ge‐Si(OH)4. 100 C water soluble and 0 C perchloric acid (PCA) soluble Si pools of 680 mM Si·l−1 and 490 mM Si·l−1 cell water represented 13 and 9%, respectively, of total, cell Si in exponential growth phase cells. Uniformly labeled cells synchronized by the combined synchronization technique accumulate at the cell cycle stage where silica frustule development is initiated. These cells contain water and PCA soluble pools of 10 nmol Si·106 cells−1 and‐8.8 nmol Si·106 cells−1, respectively. On addition of Si(OH)4, a rapid uptake ensues allowing the Si pool to expand 2.5‐fold, apparently to provide precursors of the silica frustule.

Effect of germanic acid on developing cell walls of diatoms

The effects of 0.1 and 1.0 germanic acid/silicic acid concentrations on wall development inNitzschia alba, Navicula pelliculosa, Cylindrotheca fusiformis, and Cyclotella nana are described. Valve development and differentiation are interrupted, and sometimes completely blocked. Girdle band formation is also affected.N. alba produces multiple walls (at 0.1 [Ge]/[Si]) and dense cytoplasmic granules (at 1.0 [Ge]/[Si]).

The effect of two organophosphate insecticides on the growth of freshwater algae

Seven freshwater algae were grown in the presence of Abate® 4-E (O,O,O′,O′-tetramethyl-O,O′-thiodi-p-phenylene phosphorothioate) and Dursban® M-3633 (O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate) at 1,10, and 100 μg/ℓ active ingredient. The response of different algal groups to the insecticides was highly variable.The growth rate of the nitrogen-fixing blue-green alga Anabaena flos-aquae was increased from 22% at 10 μg/ℓ Abate to 58% at 100 μg/ℓ Abate when grown on nitrogen-free medium. Dursban caused similar growth stimulation. The green alga Chlamydomonas reinhardii showed growth stimulation in response to 100 μg/ℓ Dursban.Significant decreases in growth rate were observed for the green alga Chlorella pyrenoidosa after treatment with 10 μg/ℓ Abate (8%) and 100 μg/ℓ Dursban (12%). The diatom Navicula pelliculosa gave decreases in growth rate of the same order with 10 μg/ℓ Abate or Dursban.No significant effect on the growth rates of the diatom Navicula minima or the blue-green algae Coccochloris peniocystis, Oscillatoria sp., and Anabaena flos-aquae grown in the presence of nitrate was detected after treatment with either insecticide.

DIATOM MINERALIZATION OF SILICIC ACID. II. REGULATION OF Si (OH)4 TRANSPORT RATES DURING THE CELL CYCLE OF NAVICULA PELLICULOSA1

ABSTRACTSynchronized populations of Navicula pelliculosa (Bréb.) Hilse show a 10‐fold increase in Si(OH)4 transport rate during traverse through the cell division cycle. The transport activity pattern is similar to a “peak enzyme.” Kinetic analysis showed there was a significant change in Ks values, indicating increased “affinity” for Si(OH)4 as cells neared maximal uptake rates. However, the dramatic changes in transport rate at various cell cycle stages were also reflected by alterations in the Vmax, values of the transport process, suggesting a change in the number of functional transport “sites” in the plasma membrane. Cells in the wall forming stage, arrested from further development by Si(OH)4 deprivation, maintained high transport rates for as long as 7 h. The rates decreased rapidly if protein synthesis were blocked or if Si(OH)4 was added, the latter allowing the cells to traverse the rest of the cycle. The half‐life of the transport activity ranged from 1.0 to 2.2 h when protein synthesis was inhibited at various cell cycle stages and during the natural decline of activity late in the cycle. The transport system appears to be metabolically unstable as is typical for a “peak protein.” The rise in transport rate through the cell cycle did not depend on the presence of Si(OH)4 in the medium; therefore, the transport system does not appear to be induced by its substrate. The rise in transport is also observed in L:D synchronized cells developing in the presence of Si(OH)4; neither does the transport system appear to be derepressed. The transport rate was strongly cell cycle‐stage dependent; the data appeared to fit the “dependent pathway” model proposed by Hart‐well to explain oscillations in enzyme synthesis during the cell cycle.

SILICA, NITROGEN AND PHOSPHORUS REQUIREMENTS OF SOME SOUTHERN AFRICAN DIATOMS

SUMMARY The yield coefficients and minimum cell concentrations of silica, nitrogen and phosphorus have been determined for four diatoms, Navicula pell iculosa (Brebisson ex Kutzing) Hilse, Nitzschia elliptica Hustedt, N. palea (Kutzing) W. Smith and N. perpusilla Rabenhorst. It was found that the three Nitzschia species require more Si > N > P whereas the Navicula species needs more N > Si >P. Where possible the results are evaluated in terms of the morphological and ecological characteristics of these diatoms.

DIATOM MINERALIZATION OK SILICIC ACID. I Si(OH)4 TRANSPORT CHARACTERISTICS IN NAVICULA PELLICULOSA

SUMMARYSilicic acid transport was studied in the photosynthetic diatom Navicula pelliculosa (Bréb.) Hilse using [68Ge] germanic acid (68Ge(OH)4) as a tracer of silicic acid (Si(OH)4). The initial uptake rate of Si(OH)4 was dependent on cell number, pH, temperature, light and was promoted by certain monovalent cations in the medium. Na+ was more effective than K+, whereas Li+ and NH+4 were ineffective at promoting uptake.Uncouplers and inhibitors of oxidative phosphorylation and of photophosphorylation reduced uptake by 40–99% of control values. Uptake was also especially sensitive to the sulfhydryl blocking agents at 10−5 M and to the ionophorous compound valinomycin (10−7 M) which inhibited uptake by 82%.The Si(OH)4 transport system displayed Michaelis‐Menten‐type saturation kinetics with kinetic parameters of KS= 4.4 p. mol Si(OH)4· 1−1, Vmax= 334 pmol Si(OH)4· 106 cells−1· min−1. Calculations of the acid soluble silicic acid pool size based on 60 s uptake at 20 μM Si(OH)4 suggested that intracellular levels of Si could reach 20 mM and as much as 5 mM could exist as free silicic acid, representing maintenance of a 250‐fold concentration gradient compared with the medium.Efflux from preloaded cells was dependent on temperature and the Si(OH)4 concentration of the external medium. In the presence of 100 μMM “cold” Si(OH)4, approximately 30% of the Si(OH)4 in preloaded cells was exchanged in 20 min.The initial uptake rate of Si(OH)4 in logarithmic phase cells was constant, but the uptake rate increased in a linear fashion for 6 h in stationary phase cells.These results suggest that the first step in silica mineralization by diatoms is the active transmembrane transport of Si(OH)4 by an energy dependent, saturable, membrane‐carrier mechanism which requires the monovalent cations Na+ and K+ and is sensitive to sulfhydryl blocking agents. Silicic acid transport activity also appears to be regulated during different growth stages of the diatom.

Structural observations and notes on the freshwater diatomNavicula pelliculosa(Brébisson ex Kützing) Hilse

Based on transmission electron microscopy the identity and structure of Navicula pelliculosa (Brebisson ex Kutzing) Hilse, a small diatom common in eutrophic waters, is discussed. The examination of a culture of “Navicula pelliculosa” from the Indiana University Culture Collection (strain No. 668), which has been used fairly extensively in laboratory studies, shows that it has been misidentified. In the light of the present study it is suggested that this strain represents Navicula muralis Grunow.

Change in the Ratio of Cytochrome Oxidase Activity to Nitrite Reductase Activity of Pseudomonas aeruginosa Nitrite Reductase with the Kind of C-Type Cytochrome Used as an Electron Donor

The ratio between the nitrite reductase and cytochrome oxidase activities of Pseudomonas aeruginosa nitrite reductase [EC 1.9.3.2.] varies with kind of C-type cytochrome used as the electron donor. Withe cytochrome c-548, 554 (Micrococcus sp.), the nitrite reductase activity is greater than the cytochrome oxidase activity, while the former is smaller than the latter with cytochrome c-554 (Navicula pelliculosa). The aerobic oxidation catalyzed by this enzyme of denitrifying bacterial ferrocytochrome c is greatly accelerated on addition of nitrite, while that of the algal ferrocytochrome c is not affected or is even depressed by the salt. An accelerative effect of nitrite is generally observed with many kinds of C-type cytochromes which react with the enzyme very or fairly rapidly. The difference in the ratio of the two activities of the enzyme seems to arise according to whether or not nitrite affects the interaction of C-type cytochrome with the enzyme.

Studies on the biochemistry and fine structure of silica shell formation in diatoms

Cell division in Navicula pelliculosa (Bréb.) Hilse, strain 668 was synchronized with an alternating regime of 5 h light and 7 h dark. Cell volume and dry weight increased only during the light period. DNA synthesis, which began during the third h of light, was followed sequentially by mitosis, cytokinesis, silicic acid uptake, cell wall formation, and cell separation. Silicification and a small amount of net synthesis of DNA, RNA and protein occurred during the dark at the expense of carbohydrate reserves accumulated during the light period. Cells kept in continuous light, after synchronization with the light-dark regime, remained synchronized through a second division cycle; the sequence of morphological events was the same as that in the light-dark division cycle, but the biosynthesis of macromolecular components changed from a stepwise to a linear pattern. The silicon-starvation synchrony was improved by depriving light-dark synchronized cells of silicic acid at the beginning of their division cycle, then resupplying silicic acid to cells blocked at wall formation.

MOLYBDENUM DEPENDENCE, NITRATE UPTAKE AND PHOTOSYNTHESIS OF FRESHWATER PLANKTON ALGAE1,2

SUMMARYThe effects of molybdenum on photosynthesis and nitrate uptake by two species of freshwater algae, Navicula pelliculosa (Bréd.) Hilse and Chlamydomonas reinhardtii Dang. Were examined. Photosynthetic rates in cells of N. Pelliculosa deprived of Mo for 48 h were significantly lower than in nondeprived cells; the rates were 2.6 and 4.5 μg C/106 cells/h, respectively. There was no significant reduction in photosynthetic rates of C. reinhardtii under the 2 treatments, the rates were both ca. 6.0 μg C/106 cells/h. These observed rates in the 2 species were not altered by added Mo concentrations as high as 1.0 ppm. The chlorophyll a values in 48 h Mo‐deprived cells were 1.15 μg/106 cells compared to 1.57 μg/106 cells provided with this metal. Molybdenum deficiency did not affect the chlorophyll a concentration in Chlamydomonas; the chlorophyll levels were 2.44μg/106 cells.Nitrate uptake by Mo‐deprived cells of N. Pelliculosa was significantly lower than in cells cultured in Mo; the rates were 0.087 and 0.238 μM NOa−/106 cells/h, respectively. Uptake rates by C. reinhardtii were similar with or deprived of Mo. The Km values for No3− uptake were 14.9 and 148.0 μM for N. Pelliculosa and C. reinhardtii, respectively.

TOXICITY OF THE PESTICIDE ZECTRAN ON PHOTOSYNTHESIS, RESPIRATION, AND GROWTH IN FOUR ALGAE1,2

SUMMARYThe insecticide Zectran decreased both respiration and photosynthesis in Oscillatoria terebriformis and Synechococcus lividus at concentrations between 0.5 and 12.5 ppm, whereas Navicula pelliculosa and Scenedesmus quadricauda were, relatively unaffected by these, same concentrations in the short‐term, manometric experiments. In long‐term growth experiments all 4 species exhibited a toxicity threshold between 1 and 10 ppm Zectran.

Silicic-acid uptake in diatoms studied with [68Ge]germanic acid as tracer

Uptake of silicic acid in the diatoms Navicula pelliculosa and Nitzschia alba was studied, using the natural isotope, (28)Si, or a radioisotope, (31)Si. The rate of uptake of silicic acid was also determined by using [(68)Ge]germanic acid as a tracer of silicic acid. At a given silicicacid concentration in the growth medium, the fractions of [(68)Ge]germanic acid taken up followed closely the fraction of silicic acid taken up in the same time period. When the initial concentration of silicic acid was varied at a constant (trace) concentration of [(68)Ge]-germanic acid, the uptake of (68)Ge followed the fraction of silicic acid removed, and not the absolute amount removed from the medium, at all silicic-acid concentrations. The usefulness of this approach in studying silicic-acid uptake is discussed.