Gjert Knutsen

Fatty acid and elemental composition of the marine diatom Chaetoceros gracilis Schütt. Effects of silicate deprivation, temperature and light intensity

Fatty acid composition and content of C, N and P were measured in cultures of the marine diatom Chaetoceros gracilis Schutt at different degrees of silicate limitation in continuous and batch cultures, and in batch cultures with different temperatures and light intensities. Temperature optimum for growth was between 30 and 32 °C. Levels of total (n−3) and long-chained (C ⩾ 20) highly unsaturated (number of double bonds ⩾ 4) (n−3) fatty acids decreased with decreasing silicate availability. Silicate limitation did not affect C: N: P ratios. C: Si ratios increased with increasing degree of limitation. C: N ratios were higher in batch cultures than in continuous cultures, and N: P ratios were similar in batch and continuous cultures. Levels of (n−3) fatty acids which increased with increasing light intensity had no effect on elemental composition of cells in the range from 83 to 1428 μE · s−1 · m−2. Temperature clearly influenced fatty acid composition. Levels of unsaturated fatty acids and ratios of (n−3)(n−6) fatty acids were highest at the lowest temperatures. Levels of C and N per biovolume unit followed a pattern of temperature dependence similar to growth rate.

Influence of light and temperature on photoinhibition of photosynthesis inSpirulina platensis

Photoinhibition of photosynthesis and its recovery in the cyanobacteriumSpirulina platensis was studied to find how photosynthetic rates were influenced by light and temperature. By exposing cell samples from a turbidostat culture to combinations of light and temperature, a connection between light, temperature and photoinhibition was found. The experiments showed that a 10 degree increase from 20 °C to 30 °C considerably reduced the photoinhibition. At 25 °C a photon flux density of 1720 µmol m−2 s−1 reduced the photosynthetic rate by 50 % in 1 h, but a similarly high photon flux density had nearly no negative effect at 35 °C. Reactivation in low light from 50% photoinhibition was fast and complete in 60 min at 30 °C, while at 20 °C only about 1/6 of the full capacity was regained in the same time. Addition of the protein synthesis inhibitor streptomycin to cultures undergoing photoinhibition and regeneration indicated the presence also in this organism of a repair mechanism based on protein synthesis.

SYNCHRONOUS GROWTH OF CHLAMYDOMONAS REINHARDTII (CHLOROPHYCEAE): A REVIEW OF OPTIMAL CONDITIONS1

Chlamydomonas reinhardtii Dangeard was synchronized at optimal growth conditions under a 12:4 LD regime at 35 C and 20,000 lx with serial dilution to a standard starting cell density of (1.4 ± 0.2) × 106 cells/ml. Synchronous growth and division were characterized by measuring cell number, cell volume and size distribution, dry weight, protein, carbon, nitrogen, chlorophyll, carotenoids, nucleic acids, nuclear and cytoplasmic division during the vegetative life cycle. The main properties of the present system are: Exponential growth with high productivity, high degrees of synchrony and reproducibility during repeated life cycles. The degree of synchrony of this light‐dark synchronization system was evaluated and compared with those described in the literature using probit analysis of the time course of DNA synthesis, nuclear and cytoplasmic division and sporulation (increase in cell number). The results showed that the degree of synchrony is highest for cells grown under optimal conditions.

Induction of nitrite reductase in synchronized cultures of Chlorella pyrenoidosa

Abstract Synchronously growing and dividing cultures of the green alga Chlorella pyrenoidosa were utilized to study the ability of cells to reduce nitrite after induction of nitrite reductase (NAD(P)H2: nitrite oxidoreductase, EC 1.6.6.4). The inducibility was found to vary throughout the life cycle, in a manner similar to the stepwise synthesis of DNA. It was further found that the rate of induction of enzyme-synthetic capability, realizable during a subsequent incubation in the presence of actinomycin D, showed the same close relationship with DNA synthesis as did the inducibility. The data suggest that Chlorella DNA is only available for synthesis of nitrite reductase messenger RNA when it is self-reproducing.

Marine benthic diatoms contain compounds able to induce leukemia cell death and modulate blood platelet activity.

In spite of the high abundance and species diversity of diatoms, only a few bioactive compounds from them have been described. The present study reveals a high number of mammalian cell death inducing substances in biofilm-associated diatoms sampled from the intertidal zone. Extracts from the genera Melosira, Amphora, Phaeodactylum and Nitzschia were all found to induce leukemia cell death, with either classical apoptotic or autophagic features. Several extracts also contained inhibitors of thrombin-induced blood platelet activation. Some of this activity was caused by a high content of adenosine in the diatoms, ranging from 0.07 to 0.31 μg/mg dry weight. However, most of the bioactivity was adenosine deaminase-resistant. An adenosine deaminase-resistant active fraction from one of the extracts was partially purified and shown to induce apoptosis with a distinct phenotype. The results show that benthic diatoms typically found in the intertidal zone may represent a richer source of interesting bioactive compounds than hitherto recognized.

The capacity for arylsulfatase synthesis in synchronous and synchronized cultures of Chlamydomonas reinhardti

The green algae Chlamydomonas reinhardti synthesizes arylsulfatase (arylsulfate sulfohydrolase EC 3.1.6.1) by derepression when the concentration of SO4-2-minus in the growth medium is less than about 5-10-minus 5 M. The following observations indicate that the arylsulfatase enzyme is stable while its mRNA was unstable: (1) The increase in enzyme activity stopped and remained constant after addition of cycloheximide to derepressed cells. (2) After readdition of SO4-2-minus the increase in enzyme activity continued at a lower rate whereafter it remained constant. (3) No decay of radioactivity was observed after readdition of SO4 2-minus in labelled enzyme protein isolated from pulse-labelled --S cells. The maximum rate of arylsulfatase synthesis. Measurements of this capacity in cells taken at different developmental stages from a selection synchronous and from a light-dark synchronized culture showed that: (1) Arylsulfatase was derepressible at all stages of the life cycle. (2) The same periodic capacity patterns were found, both with the synchronized and the synchronous cells. Furthermore, the rate of accummulation of RNA and protein changed in the same periodic manner during the life cycle as did the enzyme capacity.

Variations in the carotenoid content of Chlamydomonas reinhardii throughout the cell cycle

Synchronous cultures of Chlamydomonas reinhardii have been examined for the total amounts of carotenoid and chlorophyll present throughout a 12 hrs light–4 hrs dark life cycle. Variations in the carotenoid distribution at different points within the cell cycle have been found. During the greater part of the light period all major carotenoids increased at a proportionally similar rate. However, the increases in lutein and violaxanthin preceded those in β-carotene and neoxanthin by some 2 hrs and that in loroxanthin, an algal xanthophyll, by about 3 hrs. A marked drop in total carotenoid accumulation, corresponding to similar temporary falling away in the accumulation of β-carotene, lutein and violaxanthin occurred at 9 hrs. The correspondence of this with the established drop in RNA accumulation and the break-up of the nucleolus was pointed out. Considerable redistribution among the carotenoids occurred during the dark period, notably the amount of β-carotene increased relative to the total xanthophylls. The full significance of these results can not be estimated in the absence of comparative data on related organisms.

Fluorometric determination of DNA in Chlamydomonas

Abstract The diaminobenzoic acid dihydrochloride fluorescence method has been examined to determine optimal conditions for the assay of DNA in perchloric acid extracts and in pretreated Chlamydomonas cells on glass-fiber filters. Maximal fluorescence yield was obtained by allowing: (a) the perchloric acid extract to react with 4–6% diaminobenzoic acid dihydrochloride for 20–40 min at 60–80°C at about pH 3.0; (b) the pretreated cells on glass-fiber filters to react with a 20% solution of diaminobenzoic acid dihydrochloride for 40 min at 60°C.

Repressed and derepressed synthesis of phosphatases during synchronous growth of Chorella pyrenoidosa

Abstract Synchronized cultures of the green alga Chlorella pyrenoidosa were used to study the repressed and derepressed synthesis of acid and alkaline phosphatases. These enzymes were synthesized stepwise during the cells life cycle, the synthesis being derepressed after removal of orthophosphate from the growth medium. Derepression of enzyme synthesis at different times during the life cycle showed that the rates of derepressed enzyme synthesis varied with cell age. A decrease in rate parallel with the mitotic activity was observed.

Synchronous cultures of Chlamydomonas reinhardti: Synthesis of repressed and derepressed phosphatase during the life cycle

Abstract The synthesis of repressed and derepressed phosphatase has been followed during synchronous vegetative growth of the green algae Chlamydomonas reinhardti . The synthesis of repressed phosphatase followed a stepwise pattern. The enzyme was derepressible at all stages of the life cycle, and the capacity to synthesize phosphatase followed a periodic pattern during the life cycle. In addition to the derepression of phosphatase, the removal of orthophosphate from the growth medium led to cell division earlier in the life cycle than found in the cells in complete medium.