Dimethylsulphopropionate (DMSP) and proline from the surface of the brown alga Fucus vesiculosus inhibit bacterial attachment

It was demonstrated previously that polar and non-polar surface extracts of the brown alga Fucus vesiculosus collected during winter from the Kiel Bight (Germany) inhibited bacterial attachment at natural concentrations. The present study describes the bioassay-guided identification of the active metabolites from the polar fraction. Chromatographic separation on a size-exclusion liquid chromatography column and bioassays identified an active fraction that was further investigated using nuclear magnetic resonance spectroscopy and mass spectrometry. This fraction contained the metabolites dimethylsulphopropionate (DMSP), proline and alanine. DMSP and proline caused the anti-attachment activity. The metabolites were further quantified on the algal surface together with its associated boundary layer. DMSP and proline were detected in the range 0.12–1.08 ng cm^?2 and 0.09–0.59 ng cm^?2, respectively. These metabolites were tested in the concentration range from 0.1 to 1000 ng cm^?2 against the attachment of five bacterial strains isolated from algae and sediment co-occurring with F. vesiculosus. The surface concentrations for 50% inhibition of attachment of these strains were always <0.38 ng cm^?2 for DMSP and in four cases <0.1 ng cm^?2 for proline, while one strain required 1.66 ng cm^?2 of proline for 50% inhibition. Two further bacterial strains that had been directly isolated from F. vesiculosus were also tested, but proved to be the least sensitive. This study shows that DMSP and proline have an ecologically relevant role as surface inhibitors against bacterial attachment on F. vesiculosus.     

CONCENTRATIONS OF DIMETHYLSULFONIOPROPIONATE AND DIMETHYL SULFIDE ARE STRAIN‐SPECIFIC IN SYMBIOTIC DINOFLAGELLATES (SYMBIODINIUM SP., DINOPHYCEAE)1

Dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) are sulfur compounds that may function as antioxidants in algae. Symbiotic dinoflagellates of the genus Symbiodinium show strain‐specific differences in their susceptibility to temperature‐induced oxidative stress and have been shown to contain high concentrations of DMSP. We investigated continuous cultures of four strains from distinct phylotypes (A1, A13, A2, and B1) that can be characterized by differential thermal tolerances. We hypothesized that strains with high thermal tolerance have higher concentrations of DMSP and DMS in comparison to strains with low thermal tolerance. DMSP concentrations were strain‐specific with highest concentrations occurring in A1 (225 ± 3.5 mmol · L^?1 cell volume [CV]) and lowest in A2 (158 ± 3.8 mmol · L^?1 CV). Both strains have high thermal tolerance. Strains with low thermal tolerance (A13 and B1) showed DMSP concentrations in between these extremes (194 ± 19.0 and 160 ± 6.1 mmol · L^?1 CV, respectively). DMS data further confirmed this general pattern with high DMS concentrations in A1 and A13 (4.1 ± 1.22 and 2.1 ± 0.37 mmol · L^?1 CV, respectively) and low DMS concentrations in A2 and B1 (0.3 ± 0.06 and 0.5 ± 0.22 mmol · L^?1 CV, respectively). Hence, the strain‐specific differences in DMSP and DMS concentrations did not match the different abilities of the four phylotypes to withstand thermal stress. Future work should quantify the possible dynamics in DMSP and DMS concentrations during periods of high oxidative stress in Symbiodinium sp. and address the role of these antioxidants in zooxanthellate cnidarians.     

Concentrations of dimethylsulphoniopropionate and activities of dimethylsulphide-producing enzymes in batch cultures of nine dinoflagellate species

Dinoflagellates are recognised as one of the major phytoplankton groups that produce dimethylsulphoniopropionate (DMSP), the precursor of the marine trace gas dimethylsulphide (DMS) which has climate-cooling potential. To improve the prospects for including dinoflagellates in global climate models that include DMSP-related processes, we increased the data base for this group by measuring DMSP, DMS-producing enzyme activity (DPEA), carbon, nitrogen and Chl a in nine clonal dinoflagellate cultures (1 heterotrophic and 8 phototrophic strains). Growth rates ranged from 0.11 to 1.92?day^?1 with the highest value being for the heterotroph Crypthecodinium cohnii. Overall, we observed two orders of magnitude variability in DMSP content (11–364?mM) and detected DPEA in five of the nine strains (0.61–59.73?fmol?cell^?1?h^?1). Cell volume varied between 454 and 18,439?μm³ and whilst C and N content were proportional to the cell volume, DMSP content was not. The first DMSP measurements for a dinoflagellate from Antarctic waters and a species with diatom-like plastids are included. Lower DMSP concentrations were found in three small athecate species and a dinoflagellate with haptophyte-like plastids. The highest concentrations and production rates tended to be in globally distributed dinoflagellates and the heterotroph. Photosynthetic species that are distributed in temperate to tropical waters showed low DMSP concentrations and production rates and the polar representative showed moderate concentration and a low production rate. Estuarine species had the lowest concentrations and production rates. These data should help refine the inclusion of dinoflagellates as a functional group in future global climate models.     

Metabolism of DMSP, DMS and DMSO by the cultivable bacterial community associated with the DMSP-producing dinoflagellate Scrippsiella trochoidea

Bacterial species associated with the dimethylsulfoniopropionate (DMSP)-producing phytoplankton Scrippsiella trochoidea were cultured and identified, with the aim of establishing their ability to metabolise DMSP, dimethylsulfide (DMS) and dimethylsulfoxide (DMSO). Results demonstrate that of the cultivable bacteria only α-Proteobacteria were capable of producing DMS from DMSP. The concentration of DMSP was shown to affect the amount of DMS produced. Lower DMSP concentrations (1.5?μmol?dm^?3) were completely assimilated, whereas higher concentrations (10?μmol?dm^?3) resulted in increasing amounts of DMS being produced. By contrast to the restricted set of bacteria that metabolised DMSP,?~?70% of the bacterial isolates were able to ‘consume’ DMS. However, 98-100% of the DMS removed was accounted for as DMSO. Notably, a number of these bacteria would only oxidise DMS in the presence of glucose, including members of the γ-Proteobacteria and Bacteroidetes. The observations from this study, coupled with published field data, identify DMS oxidation to DMSO as a major transformation pathway for DMS, and we speculate that the fate of DMS and DMSP in the field are tightly coupled to the available carbon produced by phytoplankton.     

Effects of increased temperature on dimethylsulfoniopropionate (DMSP) concentration and methionine synthase activity in Symbiodinium microadriaticum

Dinoflagellate algae of the genus Symbiodinium occur as endosymbionts in a variety of hosts including coral. The response of Symbiodinium spp. to environmental changes could dictate survival of their hosts and the ecological success of coral reef ecosystems. Oxidative stress has been linked to a breakdown in this symbiotic relationship, known as bleaching. Increased temperature is one of the primary environmental changes linked to this phenomenon. Preliminary studies have established high concentrations of the sulfur compound dimethylsulfoniopropionate (DMSP) in Symbiodinium spp., with increased temperature. To examine the potential use of DMSP as an antioxidant, a 5?day incubation experiment was conducted at two temperatures with the algae S. microadriaticum (CCMP1633) isolated from the cnidarian host Aiptasia pulchella. An HPLC assay for the activity of the enzyme B₁₂-dependent methionine synthase was modified and used to determine the link between de novo production of methionine, a precursor to DMSP, and temperature induced oxidative stress. DMSP concentrations per cell increased approximately 38?% in the 33?°C treatment cultures over 120?h. However, these cells also increased more than 2-fold in biovolume (127?±?43?%), and SYTO-BC stain indicated increased DNA content (approximately 4-fold), suggesting arrested cell division. Normalization of DMSP to biovolume revealed that the concentrations actually decreased approximately 49?% after 2?days in cultures exposed to elevated temperature (33?°C), but were not significantly different from the control treatment at 120?h (27?°C). Concomitant changes in the 33?°C treatment relative to the control (after 120?h) resulted in an approximately 8-fold increase in reactive oxygen species, a 37?% (±7?%) decrease in photosynthetic efficiency of photosystem II, and a 5-fold increase in xanthophyll cycling. Methionine synthase activity (MSA) correlated to the decrease in DMSP concentration (R ²?=?0.778), with decreasing activity at the high temperature. Given this decrease in MSA, the increase in DMSP per cell may be due to DMSP production utilizing methionine from protein turnover, and not de novo synthesis via MSA. The findings of this study provide insight into the responses of algal symbionts to environmental changes, shed light on the potential use of DMSP and other known photo-protective mechanisms such as xanthophyll cycling under temperature induced oxidative stress, and support the suspected cessation of cell division under these conditions. This information could be crucial to understanding cellular responses to environmental changes and the ability of these organisms to survive under elevated sea surface temperatures projected for the near future.     

Dimethylsulphoniopropionate (DMSP) accumulation in green macioalgae from polar to temperate regions: interactive effects of light versus salinity and light versus temperature

Summary The effect of photon fluence rate on the ß-dimethylsulphoniopropionate (DMSP) content of salt-stressed eulittoral green macroalgae from different geographic regions was determined. At 55 mol photons m^–2s^–1 DMSP increased continuously with increasing salinities up to 68 in Ulothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa and Acrosiphonia arcta from Antarctica, while the Subantarctic/cold-temperate Ulva rigida and the temperate Blidingia minima showed a large rise in intracellular DMSP concentration only under gentle hypersaline treatment (51). At the highest salinity tested the DMSP content of the latter species declined. In contrast, the capacity to form DMSP in the dark under hypersaline conditions was very low in all species. In addition, the DMSP content of the Antarctic species was determined after one year cultivation at 0°C under photon fluence rates of 2, 30 and 55 mol m^–2s^–1. All isolates increased their DMSP concentration with increasing irradiance. In contrast to previous experiments done at 10°C, these species exhibited up to 5 fold higher DMSP values at 0°C under most photon fluence rates. The data support the idea of a light-dependent DMSP biosynthesis, and also demonstrate the stimulating effect of low water temperatures on the DMSP content of Antarctic green macroalgae. Apparently, in these plants DMSP may function as a cryoprotectant.Contribution No. 547 of the Institute for Polar and Marine Research, Bremerhaven     

Effect of Salinity on DMSP Production in Gambierdiscus belizeanus (Dinophyceae)

Dimethylsulfoniopropionate (DMSP) is produced by many species of marine phytoplankton and has been reported to provide a variety of beneficial functions including osmoregulation. Dinoflagellates are recognized as major DMSP producers; however, accumulation has been shown to be highly variable in this group. We explored the effect of hyposaline transfer in Gambierdiscus belizeanus between ecologically relevant salinities (36 and 31) on DMSP accumulation, Chl a, cell growth, and cell volume, over 12 d. Our results showed that G. belizeanus maintained an intracellular DMSP content of 16.3 pmol cell^?1 and concentration of 139 mM in both salinities. Although this intracellular concentration was near the median reported for other dinoflagellates, the cellular content achieved by G. belizeanus was the highest reported of any dinoflagellate thus far, owing mainly to its large size. DMSP levels were not significantly affected by salinity treatment but did change over time during the experiment. Salinity, however, did have a significant effect on the ratio of DMSP:Chl a, suggesting that salinity transfer of G. belizeanus induced a physiological response other than DMSP adjustment. A survey of DMSP content in a variety of Gambierdiscus species and strains revealed relatively high DMSP concentrations (1.0–16.4 pmol cell^?1) as well as high intrageneric and intraspecific variation. We conclude that, although DMSP may not be involved in long‐term (3–12 d) osmoregulation in this species, G. belizeanus and other Gambierdiscus species may be important contributors to DMSP production in tropical benthic microalgal communities due to their large size and high cellular content.     

The quantitative role of microzooplankton grazing in dimethylsulfide (DMS) production in the NW Mediterranean

The ubiquitous, biogenic trace gas dimethylsulfide (DMS) represents the largest natural source of atmospheric sulfur. Given DMS involvement in cloud formation and climate, understanding and parameterizing the oceanic DMS source and cycling processes is a necessary challenge. We report DMS cycling rates from microzooplankton dilution grazing experiments conducted monthly during 1 year in coastal northwestern Mediterranean waters. Concentrations of DMS, its algal precursor dimethylsulfoniopropionate (DMSPt) and chlorophyll a (Chla) ranged 0.9–11 nmol L^?1, 10–71 nmol L^?1, and 0.2–1.5 µg L^?1, respectively. By comparing the growth and stock production rates of the DMSP-producing algae to those of total phytoplankton, we estimated that 3?±?4% (range 0.4–12%) of the carbon primary production was invested in DMSP biosynthesis. Microzooplankton grazing rates on DMSP-producing phytoplankton (0.46–1.45 day^?1) were generally higher than those on the bulk assemblage (0.08–0.99 day^?1), except in midsummer months. This could have been due to the smaller size of most DMSP producers. There was no indication of micrograzer selection against DMSP-containing phytoplankton, since they were not grazed at lower rates than the bulk phytoplankton assemblage. A proportion of 6–20% of the grazed DMSP was converted into DMS, and this grazing-derived production accounted for 32–96% of dark gross DMS production by the total community. Bacteria consumed daily?≤?14–100% of the gross DMS production, which resulted in biological DMS turnover times of 1 to?≥?10 days. Throughout the year, grazing-mediated DMS production explained 73% of the variance in the DMS concentration, implying that microzooplankton grazing plays a major role in controlling DMS concentration in surface waters across a broad range of environmental and productivity conditions in the Mediterranean Sea. These findings should help improve the representation of herbivore grazing in prognostic models to predict the distribution and dynamics of the global DMS emission and its feedback response to changing climate.     

Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina

Thermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 °C and irradiances of 15 and 150μmol photons m^?2 s^?1. When measured at a standard temperature (17°C), rates of light-saturated photosynthesis (P_max) were higher in 5 °C-grown algae (c. 3.0 μmol O₂ m^?2 s^?1) than in 17 °C-grown algae (c. 0.9 μmol O₂ m_-2 s_-1). Concentrations of Rubisco were also 3-fold higher (per unit protein) in 5 °C-grown algae than in algae grown at 17 °C. Light-limited photosynthesis responded similarly to high temperature and low light Photon yields (α) were higher in algae grown at high temperature (regardless of light), and at 5 °C in low light, than in algae grown at 5 °C in high light Differences in a were correlated with light absorption; both groups of 17 °C algae and 5 °C low-light algae absorbed c. 75% of incident light, whereas 5 °C high-light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content PSII reaction centre densities and the fucoxanthin-Chl ale protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (0_max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low-light-grown algae was twice that of high-light-grown algae (c. 160.0 versus 80.0 nmol m^?2). We suggest that complex metabolic regulation allows L, saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.     

Use of Microautoradiography Combined with Fluorescence In Situ Hybridization To Determine Dimethylsulfoniopropionate Incorporation by Marine Bacterioplankton Taxa

The fraction of planktonic heterotrophic bacteria capable of incorporating dissolved dimethylsulfoniopropionate (DMSP) and leucine was determined at two coastal sites by microautoradioagraphy (AU). In Gulf of Mexico seawater microcosm experiments, the proportion of prokaryotes that incorporated sulfur from [³⁵S]DMSP ranged between 27 and 51% of 4′,6-diamidino-2-phenylindole (DAPI)-positive cells, similar to or slightly lower than the proportion incorporating [³H]leucine. In the northwest Mediterranean coast, the proportion of cells incorporating sulfur from [³⁵S]DMSP increased from 5 to 42% from January to March, coinciding with the development of a phytoplankton bloom. At the same time, the proportion of cells incorporating [³H]leucine increased from 21 to 40%. The combination of AU and fluorescence in situ hybridization (FISH) revealed that the Roseobacter clade (α-proteobacteria) accounted for 13 to 43% of the microorganisms incorporating [³⁵S]DMSP at both sampling sites. Significant uptake of sulfur from DMSP was also found among members of the γ-proteobacteria and Cytophaga-Flavobacterium groups. Roseobacter and γ-proteobacteria exhibited the highest percentage of DAPI-positive cells incorporating ³⁵S from DMSP (around 50%). Altogether, the application of AU with [³⁵S]DMSP combined with FISH indicated that utilization of S from DMSP is a widespread feature among active marine bacteria, comparable to leucine utilization. These results point toward DMSP as an important substrate for a broad and diverse fraction of marine bacterioplankton.     

Optimization of photosynthesis,growth, and biochemical composition of the microalga <Emphasis Type="Italic">Rhodomonas salina</Emphasis>—an established diet for live feed copepods in aquaculture

The cryptophyte Rhodomonas salina is widely used as feed for copepod cultures. However, culturing conditions to obtain high-quality algae have not yet been efficiently optimized. Therefore, we aimed to develop a cultivation protocol for R. salina to optimize its nutritional value and provide technical recommendations for later large-scale production in algal photobioreactors. We studied photosynthesis, growth, pigments, fatty acid (FA) and free amino acid (FAA) composition of R. salina cultured at different irradiances (10–300 μmol photons m^?2 s^?1) and nutrient availability (deficiency and excess). The optimal range of irradiance for photosynthesis and growth was 60–100 μmol photons m^?2 s^?1. The content of chlorophylls a and c decreased with increasing irradiance while phycoerythrin peaked at irradiances of 40–100 μmol photons m^?2 s^?1. The total FA content was maximal at optimal irradiances for growth, especially under nutrient deficiency. However, highly unsaturated fatty acids, desired components for copepods, were higher under nutrient excess. The total FAA content was highest at limiting irradiances (10–40 μmol photons m^?2 s^?1) but a better composition with a higher fraction of essential amino acids was obtained at saturated irradiances (60–140 μmol photons m^?2 s^?1). These results demonstrate that quality and quantity of FA and FAA of R. salina can be optimized by manipulating the irradiance and nutrient conditions. We suggest that R. salina should be cultivated in a range of irradiance 60–100 μmol photons m^?2 s^?1 and nutrient excess to obtain algae with high production and a balanced biochemical composition as feed for copepods.     

Identification and Stereospecificity of the First Three Enzymes of 3-Dimethylsulfoniopropionate Biosynthesis in a Chlorophyte Alga

Many marine algae produce 3-dimethylsulfoniopropionate (DMSP), a potent osmoprotective compound whose degradation product dimethylsulfide plays a central role in the biogeochemical S cycle. Algae are known to synthesize DMSP via the four-step pathway, l-Met → 4-methylthio-2-oxobutyrate → 4-methylthio-2-hydroxybutyrate → 4-dimethylsulfonio-2-hydroxy-butyrate (DMSHB) → DMSP. Substrate-specific enzymes catalyzing the first three steps in this pathway were detected and partially characterized in cell-free extracts of the chlorophyte alga Enteromorpha intestinalis. The first is a 2-oxoglutarate-dependent aminotransferase, the second an NADPH-linked reductase, and the third an S-adenosylmethionine-dependent methyltransferase. Sensitive radiometric assays were developed for these enzymes, and used to show that their activities are high enough to account for the estimated in vivo flux from Met to DMSP. The activities of these enzymes in other DMSP-rich chlorophyte algae were at least as high as those in E. intestinalis, but were ≥20-fold lower in algae without DMSP. The reductase and methyltransferase were specific for the d-enantiomer of 4-methylthio-2-hydroxybutyrate in vitro, and both the methyltransferase step and the step(s) converting DMSHB to DMSP were shown to prefer d-enantiomers in vivo. The intermediate DMSHB was shown to act as an osmoprotectant, which indicates that the first three steps of the DMSP synthesis pathway may be sufficient to confer osmotolerance.     

In Vivo Characterization of Dimethylsulfoniopropionate Lyase in the Fungus Fusarium lateritium

A fungus, Fusarium lateritium, with dimethylsulfoniopropionate (DMSP) lyase activity was isolated from both seawater and a salt marsh due to its ability to grow on DMSP (with the evolution of dimethyl sulfide) as the sole source of carbon. This is the first reported case of DMSP lyase activity in a fungus. Several other common fungal genera tested did not have DMSP lyase activity. DMSP was taken up more rapidly by F. lateritium than it was utilized, leading to its intracellular accumulation. Inhibitor studies with nystatin and cyanide indicated that DMSP uptake was an energy-dependent process. The lyase was inducible by its substrate, DMSP (K_m, 1.2 mM), and by the substrate analogs choline and glycine betaine. During induction, DMSP lyase activity increased with time and then dropped rapidly. This loss of activity could be prevented by spiking the culture with fresh DMSP or choline. The V_max for DMSP lyase was 34.7 mU · mg of protein⁻¹. The inhibitory effects of nystatin, and p-chloromercuriphenylsulfonate on DMSP lyase activity suggested that the enzyme is cytosolic. Because plants like Spartina (a marsh grass) and marine algae contain high concentrations of DMSP, we speculate that DMSP-utilizing fungi may be involved in their decay.     

The distribution of dimethylsulfoniopropionate in tropical Pacific coral reef invertebrates

Dimethylsulfoniopropionate (DMSP) is an important component of the global sulfur cycle and may be involved, via its cleavage product dimethylsulfide, in climate regulation. Although it is common in many algae, reports of DMSP in animals, particularly tropical invertebrates, are limited. This study examined the distribution of DMSP in a diverse group of coral reef invertebrates. DMSP was present in all 22 species of cnidarians and ranged from 9 to 723 μmol g⁻¹ of dry mass (DM) with a mean (± 1SD) of 110 ± 180 μmol g⁻¹ DM. It was not detected in a flatworm and an ascidian or in two of five sponges. Concentrations in sponges ranged from undetectable to 16 μmol g⁻¹ DM with a mean of 4 ± 7 μmol g⁻¹ DM. Within the cnidarians, DMSP concentrations did not differ among orders. Among cnidarian species, DMSP concentrations were correlated with symbiotic zooxanthellae densities. Within cnidarian species, DMSP concentrations of individuals were positively correlated with zooxanthellae densities in three of the four species examined. We speculate that DMSP is dietarily derived in sponges and derived from zooxanthellae in the cnidarians. The functions of DMSP in coral reef invertebrates are not known.     

A novel inhibitory interaction between dimethylsulfoniopropionate (DMSP) and the denitrification pathway

Dimethylsulfoniopropionate (DMSP) is an abundant organic sulfur compound in marine algae and denitrification influences nitrogen availability to primary producers, the key regulators of coastal eutrophication. In this study, we tested the effect of DMSP on the nitrous oxide (N₂O) reduction step of denitrification in sediments and biofilms from the Douro and Ave estuaries (NW Portugal) and in pure cultures of a denitrifying bacterium, Ruegeria pomeroyi. N₂O accumulation rates were monitored in sediment slurries and bacterial cell suspensions amended with DMSP concentrations ranging from 0 to 5 mM. In these treatments N₂O accumulation rates increased linearly with DMSP concentration (R ² from 0.89 to 0.99, p < 0.001), suggesting an inhibitory effect of DMSP on the nitrous oxide reductase activity. The addition of DMSP to sediments and bacterial culture resulted in accumulation of dimethylsulfide (DMS) as well as N₂O. However, no direct inhibition on N₂O reductase activity by DMS was observed. Natural concentrations of DMSP in the different estuarine sites were found to be linearly correlated to natural N₂O effluxes (R ² = 0.64, p < 0.001), suggesting that DMSP may negatively affect N₂O reductase in situ. This newly identified interaction between DMSP and N₂O emissions may have a significant ecological role as the inhibition of the nitrous oxide reduction enhances nitrogen loss via N₂O. Since N₂O is a powerful greenhouse gas, the results from our study may be important for evaluating climate change scenarios.     

Effect of salinity on growth,biochemical composition,and lipid productivity of Nannochloropsis oculata CS 179

Effect of salinity (15, 25, 35, 45, and 55‰) on growth, biochemical composition, and lipid productivity of Nannochloropsis oculata CS 179 was investigated under controlled cultivation in a 19‐day study. The results demonstrate that the dry biomass of N. oculata was the highest at a salinity of 25‰ among the treatments in the first 10‐day cultivation (P<0.05). During days 14–19 (stage III), the dry biomass productivity was the highest at a salinity of 35‰ (P<0.05). The algae had the highest chlorophyll a content (26.47 mg g^?1) at 25‰ in stage I, and it decreased continuously at stage III. Protein content (as% of dry biomass) of algae reached the highest value of 42.25 ± 2.10% at 15‰, and the lipid content was the highest of 32.11 ± 1.30% of dry biomass at 25‰. However, the lipid productivity of these algae was the highest at 35‰ (64.71 mg L^?1 d^?1; P<0.001). C16 series content was the highest among the total fatty acid methyl esters (FAME), and eicosapentaenoic acid C20:5n‐3 (EPA) content was high at the low salinity. Fatty acid profiles of N. oculata varied significantly under different salinities.     

Formation of N-Carboxymethyl Amino Acid from the Reaction of α-Amino Acid with Glyoxal

Enrichment cultures in a medium containing 0.1% methanol and 0.1% bicarbonate at pH 7.0 under anaerobic conditions in the light became mainly green in color. Forty-four enrichment cultures, which showed abundant growth, were obtained from 46 different sources and found to contain cells of methanol-utilizing bacteria and green algae as predominant members. From these enrichment cultures, two strains of bacteria and two strains of algae were isolated. The microorganisms isolated were designated as bacterium No. 7, bacterium No. 8, Chlorella sp. A-1 and Chlorella sp. B-1, respectively. Stable mixed cultures were easily formed by mixing the isolated cultures of bacteria and algae. Both methanol and bicarbonate were necessary for the growth of the mixed cultures under anaerobic-light conditions. Growth behavior of the mixed cultures was examined on a medium containing 0.1% methanol and 0.1 % bicarbonate at 30°C in the light (about 6000 lx). The maximum specific growth rate for the cultures, µ_max, was 0.092 hr^?1 (doubling time, 7.5 hr). The maximum cell yield was 0.87 g dry-cell weight per g of methanol used. The protein content of the biomass was 65%.     

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I_K values were between 18 and 53 μmol m^?2 s^?1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I_K values between 70 and 74 μmol m^?2 s^?1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m^?2 s^?1. Values of α were high: between 0.4 and 1.1 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the brown and red algae and between 2.1 and 4.9 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the green algal species. At 0°C P_max values of the brown and red algae ranged from 6.8 to 19.1 μmol O₂ g^?1 FW h^?1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q₁₀ values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.     

Growing microalgae as aquaculture feeds on twin-layers: a novel solid-state photobioreactor

Four strains of marine microalgae commonly used as live feeds in hatcheries (Isochrysis sp. T.ISO, Tetraselmis suecica, Phaeodactylum tricornutum, Nannochloropsis sp.) were grown in a novel solid-state photobioreactor, the twin-layer system. Microalgae were immobilized by self adhesion to vertically oriented twin-layer modules which consisted of two different types of ultrathin layers, a macroporous source layer (glass fiber nonwoven) through which the culture medium was transported by gravity flow, and a microporous substrate layer (plain printing paper) which carried the algae on both surfaces of the source layer. This simple open cultivation system effectively separated the immobilized microalgae from the bulk of the growth medium and permitted prolonged cultivation of microalgae with average biomass yields of 10–15 g dry weight m^?2 growth area after 14–25 days of cultivation. Algal biomass was harvested as fresh weight (with 72–84 % water content) without the need to pre-concentrate algae. No aeration or external CO₂ supply was necessary, and due to the microporous substrate layer, no eukaryotic contaminations were observed during the experiment. All experiments were conducted in Germany under greenhouse conditions with natural sunlight. Small-scale growth experiments performed under the same conditions revealed that growth over most of the experimental period (24 days) was linear in all tested algae with growth rates (dry weight per square meter growth area) determined to be 0.6 g ?m^?2?day^?1 (Isochrysis), 0.8 g? m^?2?day^?1 (Nannochloropsis), 1.5 g ?m^?2?day^?1 (Tetraselmis), and 1.8 g? m^?2?day^?1 (Phaeodactylum). Due to its cost-effective construction and with further optimisation of design and productivity at technical scales, the twin-layer system may provide an attractive alternative to methods traditionally used to cultivate live microalgae.