Klaus Heinrich Vanselow

Determination of DPPH Radical Oxidation Caused by Methanolic Extracts of Some Microalgal Species by Linear Regression Analysis of Spectrophotometric Measurements

The demonstrated modified spectrophotometric method makes use of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and its specific absorbance properties. The absorbance decreases when the radical is reduced by antioxidants. In contrast to other investigations, the absorbance was measured at a wavelength of 550 nm. This wavelength enabled the measurements of the stable free DPPH radical without interference from microalgal pigments. This approach was applied to methanolic microalgae extracts for two different DPPH concentrations. The changes in absorbance measured vs. the concentration of the methanolic extract resulted in curves with a linear decrease ending in a saturation region. Linear regression analysis of the linear part of DPPH reduction versus extract concentration enabled the determination of the microalgaes methanolic extracts antioxidative potentials which was independent to the employed DPPH concentrations. The resulting slopes showed significant differences (6 - 34 μmol DPPH g−1 extract concentration) between the single different species of microalgae (Anabaena sp., Isochrysis galbana, Phaeodactylum tricornutum, Porphyridium purpureum, Synechocystis sp. PCC6803) in their ability to reduce the DPPH radical. The independency of the signal on the DPPH concentration is a valuable advantage over the determination of the EC50 value.

In-line recording of PAM fluorescence of phytoplankton cultures as a new tool for studying effects of fluctuating nutrient supply on photosynthesis

Turbidostat cultures of Dunaliella salina (Chlorophyceae) and Thalassiosira weissflogii (Bacillariophyceae) were grown at fluctuating concentrations of nitrate, phosphate and silicate. In-line measurements of PAM fluorescence were used to monitor the effects of fluctuating nutrient supply on the photochemical efficiency of photosystem II reaction centres of light-adapted cells (ΔF/F′m). Besides the maximal photochemical efficiency of photosystem II reaction centres of dark-adapted cells (F v/F m), chlorophyll a, particulate organic carbon, nitrogen and phosphorus, and the cell number were measured frequently during the experiments. Following nutrient-replete growth, the cells were supplied with medium from which either nitrate, phosphate or silicate was omitted. When significant effects of nutrient starvation were indicated by the fluorescence parameters, a pulse of the deficient nutrient was added to the cultures. Our experimental set-up for in-line fluorescence measurements provided sensitive and reprod...

TFA and EPA Productivities of Nannochloropsis salina Influenced by Temperature and Nitrate Stimuli in Turbidostatic Controlled Experiments

The influence of different nitrate concentrations in combination with three cultivation temperatures on the total fatty acids (TFA) and eicosapentaenoic acid (EPA) content of Nannochloropsis salina was investigated. This was done by virtue of turbidostatic controlled cultures. This control mode enables the cultivation of microalgae under defined conditions and, therefore, the influence of single parameters on the fatty acid synthesis of Nannochloropsis salina can be investigated. Generally, growth rates decreased under low nitrate concentrations. This effect was reinforced when cells were exposed to lower temperatures (from 26 °C down to 17 °C). Considering the cellular TFA concentration, nitrate provoked an increase of TFA under nitrate limitation up to 70% of the biological dry mass (BDM). In contrast to this finding, the EPA content decreased under low nitrate concentrations. Nevertheless, both TFA and EPA contents increased under a low culture temperature (17 °C) compared to moderate temperatures of 21 °C and 26 °C. In terms of biotechnological production, the growth rate has to be taken into account. Therefore, for both TFA and EPA production, a temperature of 17 °C and a nitrate concentration of 1800 μmol L−1 afforded the highest productivities. Temperatures of 21 °C and 26 °C in combination with 1800 μmol L−1 nitrate showed slightly lower TFA and EPA productivities.

Rapid effect of light on the K+ channel in the plasmalemma ofNitella

SummaryChlorophyll fluorescence, plasmalemma potential and resistance were measured simultaneously and subjected to a kinetic analysis. It was found that the light-induced changes of all three signals have two time constants in common. The faster one (τ4=ca. 20 sec) was assigned to the action of light-induced proton uptake across the thylakoid membrane on the plasmalemma H+ pump. The slower one (τ5a=40 sec) is related to the light action of an unknown photosynthetic process on the potassium channel. The action on the K+ channel was revealed from the reversal potential of the related effect on membrane potential. The comparison of the data with findings of other authors led to the hypothesis that the unknown photosynthetic mechanism is the depletion of NADP+, which stimulates the uptake of Ca2+ from the cytosol, which is required for the NAD-kinase. The resulting change in cytosolic Ca2+ modulates the number of open K+ channels.

Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments

Background Surface waters of aquatic environments have been shown to both evolve and consume hydrogen and the ocean is estimated to be the principal natural source. In some marine habitats, H2 evolution and uptake are clearly due to biological activity, while contributions of abiotic sources must be considered in others. Until now the only known biological process involved in H2 metabolism in marine environments is nitrogen fixation. Principal Findings We analyzed marine and freshwater environments for the presence and distribution of genes of all known hydrogenases, the enzymes involved in biological hydrogen turnover. The total genomes and the available marine metagenome datasets were searched for hydrogenase sequences. Furthermore, we isolated DNA from samples from the North Atlantic, Mediterranean Sea, North Sea, Baltic Sea, and two fresh water lakes and amplified and sequenced part of the gene encoding the bidirectional NAD(P)-linked hydrogenase. In 21% of all marine heterotrophic bacterial genomes from surface waters, one or several hydrogenase genes were found, with the membrane-bound H2 uptake hydrogenase being the most widespread. A clear bias of hydrogenases to environments with terrestrial influence was found. This is exemplified by the cyanobacterial bidirectional NAD(P)-linked hydrogenase that was found in freshwater and coastal areas but not in the open ocean. Significance This study shows that hydrogenases are surprisingly abundant in marine environments. Due to its ecological distribution the primary function of the bidirectional NAD(P)-linked hydrogenase seems to be fermentative hydrogen evolution. Moreover, our data suggests that marine surface waters could be an interesting source of oxygen-resistant uptake hydrogenases. The respective genes occur in coastal as well as open ocean habitats and we presume that they are used as additional energy scavenging devices in otherwise nutrient limited environments. The membrane-bound H2-evolving hydrogenases might be useful as marker for bacteria living inside of marine snow particles.

A photobioreactor system for computer controlled cultivation of microalgae

A bioreactor system was developed for the cultivation of the microalgae Synechocystis sp. PCC6803 under controlled physiological conditions. The determination of the actual physiological state of the microalgae was provided by inline recording of chlorophyll fluorescence parameters. A feed-back loop was employed to keep the microalgae in a defined physiological state. For the construction of this feed-back loop, the temporal behaviour of the system was investigated using changes in light conditions (as caused by modulated UVB radiation) as input signal and chlorophyll fluorescence as output signal. The reproducibility of the responses was high. Kinetic analysis based on curve fitting revealed two time constants in the UVB-induced responses. The knowledge of these time constants was utilised for the development of an efficient feed-back loop which allows the cultivation of the microalgae in a defined physiological state. This new process strategy (called physiostat) was successfully tested. The performance in a culture of growing microalgae is shown.

Indication of transthylakoid proton-fluxes in Aegopodium podagraria L. by light-induced changes of plasmalemma potential, chlorophyll fluorescence and light-scattering.

The time course of the responses of chlorophyll fluorescence in leaves of Aegopodium podagraria to changes in irradiance does not necessarily show the time constant of thylakoid energization at energy fluence rates below 10–25 W·m-2. In addition, other measures of thylakoid energization, such as lightscattering at 532 nm and the responses to saturating flashes, show that the related component disappears from these signals at low fluence rates, but not necessarily all together at the same fluence rate. However, this time constant still appears in the light-induced responses of the plasmalemma potential. This implies that the effect on the electrogenic proton pump in the plasmalemma is the most sensitive indicator of proton fluxes into the inner thylakoid space. These results are a further indication that energy-quenching is coupled ther indication that energy-quenching is coupled to transthylakoid proton fluxes via an intermediate, which is not active in Aegopodium podagraria at low irradiances.

The 1-Hz fluorometer: A new approach to fast and sensitive long-term studies of active chlorophyll and environmental influences

A new instrument for environmental monitoring, called at 1-Hz fluorometer, provides two modes of application. First, it enables a quantitative determination of algal concentrations down to 20 ng/l. Second, it can be used as a biosensor for changes in environmental conditions. The distinction between the signals from living chlorophyll-containing algae and other fluorescent material is achieved by using two modulated light-sources resulting in a mean fluence rate of 200 μE. The measuring light induces changes in chlorophyll fluorescence (yield) with a frequency of 1 kHz, and the actinic light modulates the redox state of the quenchers of PS II with a frequency of 1 Hz. This leads to a modulation of the yield which is detected by two phase-sensitive rectifiers (double correlation). Measurements from different sites in a river, and in the Baltic and North Seas, show that correction by the built-in simultaneously-measured attenuation is necessary in order to obtain values which are identical with those determined by a photometric analysis (Uvikon 860). This applies if the transmission becomes less than about 95%. Suspensions ofDunaliella salina exposed to ammonia and phosphate were used for illustrating the usage for environmental monitoring. It is shown that this system can measure changes in the chlorophyll fluorescence of living algae caused by changes in concentration of ammonia down to 1 μg/l and of phosphate down to 10 μg/l.

Solar Driven Geomagnetic Anomalies and Sperm Whale (Physeter macrocephalus) Strandings Around the North Sea: An Analysis of Long Term Datasets

To stimulate the discussion about possible reasons for whale strandings, we suggest solar driven geomagnetic variations as one further explanation for this phenomenon. Following this hypothesis that whales may strand due to geomagnetic disturbances we compared annual means of stranding event numbers of sperm whales (Physeter macrocephalus) along the North Sea coasts with yearly averaged numbers of geomagnetic anomaly intensities (aa- indices). Based on a Generalised Additive Model technique, our new approach suggests that over the last 400 years 20% of the stranding events can be correlated with aa-index variabilities. Furthermore, the increased stranding numbers of the last decades could be explained by the exceptional intensive disturbances of the earths magnetic field in the same period.

Comparison of two different modes of UV-B irradiation on synthesis of some cellular substances in the cyanobacterium Synechocystis sp. PCC6803

Two different modes of UV-B irradiation of the cyanobacterium Synechocystis sp. PCC 6803 are compared: turbidostatic control and additional physiostatic control. Under turbidostatic control, the cells were exposed to different constant UV-B irradiances, whereas under physiostatic control, an electronic control loop modulated UV-B irradiance in such a way that photosynthetic efficiency ϕPSII was kept constant at a fixed set point. The UV-B-induced stimulation of the synthesis of pigments, α-tocopherol, and the antioxidative potential of methanolic soluble components of Synechocystis showed significant differences depending on the mode of irradiation, even though the overall doses were equal. For example, compared to the initial values, the concentrations of myxoxanthophyll and zeaxanthin increased to 226–244% and 453% upon constant UV-B irradiation in turbidostatic processes, whereas maxima of 600% and 740% were reached in turbidostatic process with additional physiostatic control. The α-tocopherol concentration increased under constant UV-B irradiances, up to a maximum of 150%. Under physiological control, however, maximum increases of 390% over the initial values were measured. Furthermore, a reaction scheme is given explaining the higher yield under physiostatic control.