Photomovement of the red alga Porphyridium cruentum (Ag.) Naegeli

Phototaxis of the unicellular red alga Porphyridium cruentum was studied by staining the slime tracks of individual cells as well as with the aid of a population method. Because of the increased straightness of the movement the mean linear velocity of a unilaterally illuminated population exceeds considerably that of an only photokinetically stimulated one. In white light the phototactic reaction is saturated already at 100 lx. The zero threshold lies at about 1 lx. Spectral sensitivity curves of phototaxis obtained at high photon fluence rates (>=10^–11 mol cm^–2 s^–1) display two main peaks which shift against each other at intermediate irradiances and, finally, form a single maximum in the blue range (443 nm) at low photon fluence rates (10^–12 and 10^–13 mol cm^–2 s^–1). Photon fluence rate-response curves reveal that supraoptimal irradiances decrease the phototactic reaction, especially in the range of the highest sensitivity of the cells. The action spectrum of phototaxis was calculated on the basis of the photon fluence rate-response curves. It shows a maximum at 443 nm and shoulder at 416 nm and between 467 and 477 nm. Wavelengths longer than 540 nm are phototactically inactive even at very high irradiances (25 W m^–2). Thus, this is the first phototactic action spectrum of a biliprotein-containing organism which does not indicate the participation of biliproteins in the absorption of phototactically active light. DCMU and potassium iodide have no specific effects on phototaxis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

The effect of low temperature on fatty acid composition and tocopherols of the red microalga, <Emphasis Type="Italic">Porphyridium cruentum</Emphasis>

Porphyridium cruentum was grown in 10 L batch culture at 18°C, pH 8.0 and 28‰ salinity. The cells were harvested in the stationary phase and the fatty acid composition analysed by GC and tocopherol content by HPLC. A total of 14 fatty acids were identified including saturated fatty acids (13:0, 14:0, 14:0 iso, 15:0, 16:0, 16:0iso) and monounsaturated fatty acids (MUFAs; 16:1(n-7), 18:1(n-7), 18:1(n-9). Polyunsaturated fatty acids (PUFAs) were the predominant fatty acids detected, reaching 43.7% of total fatty acids in the stationary phase of culture. Among the PUFAs, eicosapentaenoic acid (EPA, 20:5(n-3)) was dominant (25.4%), followed by 12.8% arachidonic acid (AA, 20:4(n-6)). α-Tocopherol and γ-tocopherol contents were 55.2 μg g⁻¹ dry weight and 51.3 μg g⁻¹ dry weight respectively.     

Photomovement of the red alga Porphyridium cruentum (Ag.) Naegeli

Photophobic reactions of the red alga Porphyridium cruentum have been studied by single cell observations and by population experiments with the light trap method. In white light traps photoaccumulation is saturated at about 6000 lx. Experiments with monochromatic light demonstrate the necessity of carefully separating the three basic light reactions, viz. phototaxis, photokinesis and photophobic response by an appropriate experimental set-up: In single-beam experiments trap wavelengths >695 nm cause photodispersal which is not due to photophobic entrance reactions, but is exclusively due to the positive photokinetic effect of the trap light. This photodispersal can be cancelled by a photokinetically active background light. In the short wavelength range not only photokinesis, but also phototaxis interferes with photophobic reactions thus affecting the density of photoaccumulations in the light trap. Phototactic and photokinetic interference can be avoided by a blue background light. The action spectrum measured this way indicates activity of photosystem I and photosystem II pigments in the perception of the step-down photophobic stimulus. Varying the wavelength of the background light at constant trap light absorbed mainly by photosystem I or photosystem II respectively, efficient spill-over of light energy from photosystem II to the light reaction of photosystem I could be demonstrated. From the results it is concluded that phobic reactions are induced by a decrease of the electron flow rate in the linear electron transport chain.     

Effects of agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum

The effect of mechanical agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum was investigated in aerated continuous cultures with and without the added shear protectant Pluronic F68. Damage to cells was quantified through a decrease in the steady state concentration of the biomass in the photobioreactor. For a given aeration rate, the steady state biomass concentration rose with increasing rate of mechanical agitation until an upper limit on agitation speed was reached. This maximum tolerable agitation speed depended on the microalgal species. Further increase in agitation speed caused a decline in the steady state concentration of the biomass. An impeller tip speed of >1.56 m s^–1 damaged P. tricornutum in aerated culture. In contrast, the damage threshold tip speed for P. cruentum was between 2.45 and 2.89 m s^–1. Mechanical agitation was not the direct cause of cell damage. Damage occurred because of the rupture of small gas bubbles at the surface of the culture, but mechanical agitation was instrumental in generating the bubbles that ultimately damaged the cells. Pluronic F68 protected the cells against damage and increased the steady state concentration of the biomass relative to operation without the additive. The protective effect of Pluronic was concentration-dependent over the concentration range of 0.01–0.10% w/v.     

Photomovement of the red alga Porphyridium cruentum (Ag.) naegeli I. Photokinesis

Photokinesis of the red alga Porphyridium cruentum was studied with the aid of a population method. Because of the slow spreading velocity (0.35 m/min) the duration of the experiments was 7 days in general. According to the white light illuminance-response curve the zero threshold of photokinesis lies below 10 lx and the optimum around 10,000 lx. With further increasing illuminance the photokinetic effect decreases, reaching zero at about 100,000 lx. The action spectrum indicates that the photokinetically active radiation is absorbed by photosynthetic pigments, namely the biliproteins B-phycoerythrin, R-phycocyanin and allo-phycocyanin, as well as by chlorophyl a, although the photokinetic effect of blue light is relatively low. From the action spectrum and the results of inhibitor experiments with DCMU, DBMIB and DSPD it is concluded that the photokinetic effect is due to an additional ATP supply from non-cyclic and/or pseudo-cyclic photophosphorylation to the motor apparatus.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1, 1-dimethylurea - DBMIB Dibromothymoquinone (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) - DSPD Disalicylidenepropanediamine-(1,3)     

Investigations on the arrangement and fine structure ofPorphyridium cruentum phycobilisomes

Summary Phycobilisomes ofPorphyridium cruentum were investigated in ultrathin sectionsin situ and after isolation and positive or negative staining. The phycobilisomes have the approximate shape of one half of a compressed rotation ellipsoid with the following dimensions: length 2 a=40±4 nm, width 2 b=19±2 nm, height c=28±3 nm. The phycobilisomes form rows and pillars on the thylakoid membranes. A plug-like structure (foot) which apparently fixes the phycobilisomes to the thylakoid membrane is described.     

Structure and organization of phycobilisomes on membranes of the red alga Porphyridium cruentum

In the present work, electron microscopy and single particle averaging was performed to investigate the supramolecular architecture of hemiellipsoidal phycobilisomes from the unicellular red alga Porphyridium cruentum. The dimensions were measured as 60 × 41 × 34 nm (length × width × height) for randomly ordered phycobilisomes, seen under high-light conditions. The hemiellipsoidal phycobilisomes were found to have a relatively flexible conformation. In closely packed semi-crystalline arrays, observed under low-light conditions, the width is reduced to 31 or 35 nm, about twice the width of the phycobilisome of the cyanobacterium Synechocystis sp. PCC 6803. Since the latter size matches the width of dimeric PSII, we suggest that one PBS lines up with one PSII dimer in cyanobacteria. In red algae, a similar 1:1 ratio under low-light conditions may indicate that the red algal phycobilisome is enlarged by a membrane-bound peripheral antenna which is absent in cyanobacteria. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Ana A. Arteni and Lu-Ning Liu equally contributed to the work.     

Eicosapentaenoic and arachidonic acids purification from the red microalga Porphyridium cruentum

The polyunsaturated fatty acids (PUFA) eicosapentaenoic and arachidonic acids (EPA and AA), which have several pharmaceutical properties, have been purified from the red microalga Porphyridium cruentum. The process consists of only four main steps: (i) simultaneous extraction and saponification of the microalgal biomass; (ii) urea inclusion method (iii) PUFA esterification (iv) argentated silica gel column chromatography of the urea concentrate. Total AA and EPA recoveries reached 39.5% and 50.8% respectively for a purity 97% for both fatty acids. Therefore, recovery of highly pure PUFA could be improved in organisms that are rich in two or more fatty acids of interest. The results of several procedures for AA and EPA recovery from several authors by using this microalga were compared.     

Effect of growth temperature and salt concentration on the fatty acid composition of Flavobacterium halmephilum CCM2831

Abstract In this study the fatty acid composition of Flavobacterium halmephilum CCM2831 grown at different temperatures and salt concentrations is reported. At elevated growth temperatures the amount of cellular saturated long-chain acids (C_18:0 and C_20:0) and the branched-chain acid br-C_17:0 increased, and the concentrations of both cyclic acids and the branched chain acid br-C_15:0 decreased. Increasing the salt concentration in the medium resulted in a gradual increase in cellular cyclopropanoic acids and a concomitant decrease in the monounsaturated fatty acid content.     

Changes in fatty acid composition of Mytilus galloprovincialis (Lmk) fed on microalgal and wheat germ diets

Dietary fatty acid incorporation and changes in various lipid and phospholipid classes in the mussel Mytilus galloprovincialis subjected to three different dietary regimens were analysed and compared. Group A was unfed; group B received a diet consisting of 100% Thalassiosira weissflogii, exhibiting the typical fatty acid composition of diatoms, and group C received a diet consisting of 100% wheat germ conferring a 18:2:n-6 abundance. Biochemical analyses of diets and mussels were carried out at the beginning and at the end of the 30-day experimental period. Starvation and T. weissflogii based diet poorly affected mussel growth and fatty acid composition which remained unchanged. On the contrary, the wheat germ-based diet increased the condition index and deeply affected the fatty acid profile of all lipid and phospholipid classes. The high dietary 18:2n-6 level drastically reduced tissue content of 20:4n-6, 20:5n-3 and 22:6n-3. The biosynthesis of Non Methylene Interrupted (NMI) dienoic fatty acid appeared to be insensitive to the high input of 16:1n-7 and 18:1n-9 respectively from diet B and C, and to the PUFA shortage of diet C. Nevertheless the two NMI trienoic derivatives, 20:3Δ5,11,14 and 22:3Δ7,13 16, were found higher in C with respect to other groups, presumably due to the high 18:2n-6 content of this diet.     

The amino acid sequences of the cytochromes c553 from Porphyridium cruentum and Aphanizomenon flos-aquae

The amino acid sequences of cytochrome c₅₅₃ from the eukaryotic red alga Porphyridium cruentum and from the prokaryotic cyanobacterium Aphanizomenon flos-aquae have been determined from the tryptic and cyanogen bromide peptides. The results indicate that a charged region of these proteins has evolved with special rapidity to accomodate a rapid evolution of a binding site in the P₇₀₀ electron acceptor complex.     

Effect of supplementation with exogenous fatty acid on the biological properties of a fatty acid requiring auxotroph ofSalmonella typhimurium

The effects of changes in fatty acid composition of the cell membrane on different biological functions ofSalmonella typhimurium have been studied with the help of a temperature sensitive fatty acid auxotroph which cannot synthesise unsaturated fatty acids at high temperature. On being shifted to nonpermissive temperature the cells continue growing for another one and half to two generations. The rates of protein and DNA syntheses run parallel to the growth rate but the rate of RNA synthesis is reduced. Further, there is a gradual reduction in the rate of transport of exogenous uridine and thymidine into the soluble pool. The transport process can be restored by supplementing the growth medium with cis-unsaturated fatty acids but not trans-unsaturated ones although the growth of the cells is resumed by supplementation with eithercis or trans-unsaturated fatty acids. However, supplementation withtrans, trans-unsaturated fatty acids leads to only partial recovery of the transport process. The rate of oxygen uptake is also affected in cells grown in the presence of thetrans-unsaturated fatty acids, elaidic acid and palmitelaidic acid. Analysis of cells grown under different fatty acid supplementation indicate that fatty acid composition of the cell membrane, especially the ratio of unsaturated to saturated fatty acids varies with temperature shift and supplementation of the growth media with fatty acids.     

The kinetics of photoinhibition and its recovery in the red alga Porphyridium cruentum

When Porphyridium cruentum cells were illuminated with high fluence rate between 1900 and 4800 mol photons m^-2s^-1, a decrease in the photosynthetic activity of the cells was observed. Within the time frame of 20 min, and under the fluence rates studied, the sum of photons to be absorbed by cells (mg of chlorophyll (Chl), sufficient to initiate photoinhibition was calculated to be 9235.8 mol. The minimal specific light absorption rate to initiate photoinhibition in P. cruentum ranges between 2.29 and 4.26 mol photons s^-1 mg^-1 chl.a. There was a linear relationship between the specific rate of photoinhibition and the specific light absorption rate. A photon number of 2.56×10⁴ mol mg^-1 chl.a photoinhibited photosynthesis instantaneously. At 15°C, no photoinhibitory effect was observed at 2300 mol photons m^-2 s^-1 even after 45 min of illumination. At the other extreme of 35°C, 84% inhibition of photosynthetic activity was observed within 10 min of exposure to 2300 mol photons m^-2 s^-1. Between 20 and 30°C, the photoinhibitory effect was comparable. Photoinhibited P. cruentum cells recovered readily when transferred to low light (90 mol photons m^-2 s^-1) and darkness, and the specific rate of recovery was independent of the light intensity to which the cells were exposed, during the photoinhibitory treatment.Abbreviations Chlorophyll QL, specific light absorption rate Publication No. 28 of the Microalgal Biotechnology Laboratory     

Lipid classes and fatty acid composition of rotifers (Brachionus plicatilis) fed two algal diets

Rotifers (Brachionus plicatilis), maintained on baker's yeast, were fed for 24h upon two algal diets, Isochrysis galbana (diet A) and Isochrysis galbana + Nannochloropsis gaditana (diet B). (These algal diets were selected for their potential use as essential fatty acid (EFA) boosters, taking into account the requirements of fish larvae). The effect of these algal diets on total lipid content, lipid classes and fatty acid composition was studied. The total lipid content increased after feeding upon both diets but no significant differences were found between the two types. Neutral lipid and polar lipid contents increased and a positive correlation was observed between the neutral lipids content of rotifers and that of the food supplied. However, the content of polar lipids in rotifers did not depend upon that of the diet. The increase in neutral lipid content was found to be higher in rotifers fed upon diet B, compared to diet A which increased the phospholipid content. Non-enriched rotifers contained only small amounts of polyenoic fatty acids, i.e. 18:3n-6, 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3, the contents of which increased significantly by feeding both diets. The EFA composition (20:4n-6, 20:5n-3 and 22:6n-3) of neutral lipids and phopholipids in rotifers reflected the EFA composition of each diet. Diet B-fed rotifers had the highest content in 20:4n-6 and 20:5n-3, whereas rotifers fed diet A and the highest 22:6n-3 content. The mixed diet I. galbana + N. gaditana enhanced substantially the composition of lipid classes i.e. neutral lipids and of n-3 PUFA of rotifers in comparison with Isochrysis or yeast diets.     

Effect of growth temperature on the fatty acid composition of Mycobacterium phlei

In Mycobacterium phlei, fatty acid unsaturation increased with decreasing temperature. The 10-hexadecenoic acid content increased as the temperature was reduced from 35°C to 26–20°C. At lower temperatures tuberculostearic acid decreased while oleic and linoleic acids increased, the latter being found in M. phlei for the first time. Concomitantly palmitic acid content decreased, and the 6- and 9-hexadecenoic acids increased slightly on reducing the temperature from 35 to 10°C. Thus, down to 26–20°C palmitic acid was mainly replaced by 10-hexadecenoic acid. From this range down to 10°C, palmitic and tuberculostearic acids were replaced by oleic and linoleic acids. Consequently, fatty acid branching decreased and mean chain length increased, as the temperature was reduced. These observations support the view that regulation of membrane fatty acid composition is part of microbial temperature adaptation, and that themechanism behind the responses might be more complex than generally believed.Abbreviations ACP acyl carrier protein - FAS I (Type I) fatty acid synthetase I - FAS II (Type II) fatty acid synthetase II - MGLP methylglucose containing lipopolysaccharide - MMP methylmannose containning polysaccharide     

Microalgae for use in tropical aquaculture II: Effect of salinity on growth,gross chemical composition and fatty acid composition of three species of marine microalgae

The influence of salinity on the growth, gross chemical composition and fatty acid composition of three species of marine microalgae,Isochrysis sp.,Nannochloropsis oculata andNitzschia (frustulum), was investigated. There was no significant change in growth rate ofIsochrysis sp. andN. (frustulum) over the experimental range of salinity (10–35 ppt), whileN. oculata had a significantly slower growth rate only at 35 ppt. The ash content of all three species increased with increasing salinity. Two species,Isochrysis sp. andN. oculata, showed significant linear increases in total lipid content with increasing salinity over the range 10 to 35 ppt.N. (frustulum) showed significant linear decrease in total lipids, with the highest percentage at low salinity within the range 10–15 ppt. Variation in salinity had only a slight effect on the total protein, the soluble carbohydrate and chlorophylla content of all species. All species responded to change in salinity by modifying their cellular fatty acid compositions. Significant positive correlations were observed between increase in salinity and increase in the percentage ofcis-9-hexadecenoic acid [16:1 (n-7)] over the entire experimental range inN. (frustulum) and between 25–35 ppt inN. oculata. There were curved relationships between salinity and percentage of hexadecanoic acid [16:0] inN. oculata andN. (frustulum), with maxima within the range 25–30 ppt for both species. A curved relationship was found between salinity and percentage of eicosapentaenoic acid [20–5(n-3)], forN. (frustulum), with lowest percentages of the fatty acid within the range 25–30 ppt. There was no consistent pattern in the percentages of other major fatty acids as functions of salinity. The Northern Territory isolateN. (frustulum) was unusual in having a substantial increase in total fatty acids with decreasing salinity (85 mg g^–1 dry wt at 10 ppt compared with 33 mg g^–1 at 35 ppt). The optimum salinities for the production of maximum amount of lipids and the essential fatty acids 20:5(n-3) and/or 22:6(n-3) were as follows:25 ppt forIsochrysis sp. [22:6(n-3)]; 20–30 ppt forN. oculata [20:5(n-3)]; 10–15 ppt forN. (frustulum) [20:5(n-3) and 22:6(n-3)].Author for correspondence     

Polar lipids and fatty acid composition ofThermus strains from New Zealand

The polar lipids and fatty acid composition ofThermus aquaticus YT-1 and YS 041,T. filiformis Wai33 A1 and eighteen isolates from New Zealand, several of which are attributed toT. filiformis, were compared to complement the taxonomy of these organisms. The polar lipid patterns were essentially similar in all strains and consisted of one major phospholipid and one major glycolipid. The fatty acid analysis produced three basic groups corresponding toT. filiformis Wai33 A1,T. aquaticus and the third to the other New Zealand strains. The presence of hydroxy fatty acids is reported inThermus spp. for the first time.     

Effect of C/N ratio and aeration on the fatty acid composition of heterotrophicChlorella sorokiniana

The effect of the carbon to nitrogen (C/N) ratio of the medium and the aeration rate on the lipid content and fatty acid composition ofChlorella sorokiniana was investigated using heterotrophic, batch culture. Both parameters had a significant effect. A C/N ratio of approximately 20, was found to indicate a change from carbon to nitrogen limitation forC. sorokiniana. Cell lipid content was at a minimum at this value and increased at both higher and lower C/N values. Low C/N ratios favoured a high proportion of trienoic fatty acids at the expense of monoenoic acids. Aeration enhanced cell growth, fatty acid yield and the synthesis of unsaturated dienoic and trienoic fatty acids, but reduced cell lipid content. The results demonstrate that the fatty acid composition and lipid content of heterotrophically-grown microalgae can be favourably manipulated by varying culture conditions.     

Suitability of lipid materials for culture ofMalassezia as evaluated from its cellular fatty acid composition

Malassezia is a facultative or obligatory lipophilic yeast. We devised new lipid-supplemented media suitable for the culture ofMalassezia. Malassezia furfur andM. pachydermatis grew well on both solid and liquid media supplemented with creaming powder preparations which are commercially available at moderate prices. Striking differences were found between the cellular fatty acid compositions ofM. furfur grown on media supplemented with creaming powder and that grown on media with conventional olive oil.Malassezia furfur grown on media with olive oil had nearly the same fatty acid composition as olive oil, with C18:1 amounting to 80%, while that grown on media supplemented with creaming powder had C16, C18:1 and C18:2 as the principal components. The use of these supplementary lipids appeared not to inhibit the normal synthesis of fatty acid inM. furfur. For the culture ofM. pachydermatis, media supplemented with creaming powder were also found more suitable than lipid-free media. The media devised are considered excellent, because they appear to provide a more natural growth environment forMalassezia.