Haptophyte Isochrysis Galbana Research Articles

Characterization of the LI818 polypeptide from the green unicellular alga Chlamydomonas reinhardtii.

The LI818 gene from Chlamydomonas encodes a polypeptide that is related to the chlorophyll a/b-binding proteins (CAB) of higher plants and green algae. However, despite this relatedness, LI818 gene expression is not coordinated with that of cab genes and is regulated differently by light, suggesting a different role for LI818 polypeptide. We show here that, in contrast to CAB polypeptides, LI818 polypeptide is not tightly embedded into the thylakoid membranes and is localized in stroma-exposed regions. Moreover, during chloroplast development, LI818 polypeptide accumulates before CAB polypeptides. We also show that the LI818 polypeptide forms with certain chlorophyll a/c-binding proteins (CAC) from the haptophyte Isochrysis galbana and the diatom Cyclotella cryptica a natural group that is distinct from those constituted by CAB, CAC and the chlorophyll a/a-binding proteins (CAA). Such an association suggests a very ancient origin for this group of polypeptides, which predates the division of the early photosynthetic eukaryotes into green (chlorophyte), red (rhodophyte) and brown (chromophyte) algae. Possible roles for the LI818 polypeptide are discussed.

The fate of lipids during development and cold-storage of eggs in the laboratory-reared calanoid copepod, Acartia tonsa Dana, and in response to different algal diets

The calanoid copepod Acartia tonsa was sampled throughout one generation to examine the fate of lipids during development in culture. Effects of dietary input were examined by feeding A. tonsa for at least one generation with specific monoalgal cultures. Four different algae were tested: the cryptophyte Rhodomonas baltica, the haptophyte Isochrysis galbana clone T-iso, the diatom Thalassiosira weissflogii and the dinoflagellate Heterocapsa triquetra. Further, the effect of cold storage of eggs on the lipid composition of the newly hatched nauplii was examined. During development, the fatty acid composition changes from a tendency towards high levels of long-chain polyunsaturated fatty acids in the early developmental stages towards a tendency to accumulate more saturated and monounsaturated fatty acids in the later developmental stages. However, the content and composition of polyunsaturated fatty acids can be influenced by the dietary input. The highest ratio of 22:6 n−3/20:5 n−3 was achieved using H. triquetra or I. galbana. Higher levels of 20:5 n−3 were achieved by feeding with R. baltica or T. weissflogii. I. galbana and T. weissflogii were particularly suitable for increasing levels of arachidonic acid (20:4 n−6; AA) in A. tonsa.

Effects of temperature and growth phase on lipid and biochemical composition of Isochrysis galbana TK1

The lipid and biochemical composition of the haptophyte Isochrysis galbana TK1 was examined. Cultures were grown at 15 °C and 30 °C, and harvested in the exponential and early stationary growth phases. Carbohydrate and protein content varied at the two culture temperatures and growth phases. The highest protein content was found at the exponential growth phase at 15 °C, and the highest carbohydrate content was found at the stationary phase at the same culture temperature. Lipid accumulated in the stationary growth phase and its content was higher at 30 °C than at 15 °C regardless of the growth phase. The neutral lipids were the major class of lipid found in all the cultures. The stationary phase culture had a higher proportion of neutral lipids than the exponential phase culture and the proportion decreased slightly when culture temperature was increased from 15 °C to 30 °C. Phospholipid levels remained constant at the two temperatures, but slightly decreased in the stationary phase. Glycolipids in the exponentially growing cells were higher than those from stationary growth phase and increased with temperature. Polyunsaturated fatty acids (PUFAs) predominated in glycolipids and phospholipids. Cells grown at 15 °C contained higher proportion of 18:3 (n–3) and 22:6 (n–3) with a corresponding decrease in 18:2 (n–6), monounsaturated and saturated fatty acids.

Dynamics of prey selection by an omnivorous flagellate

The heterotrophic flagellate Paraphysomonas imperforata, a raptorial grazer, sustained maximum specific growth rates of ca 1.5 d-' at 20°C when fed 3 phytoplankton species of different sizes and shapes (the relatively small diatom Phaeodactylum tricornutum and haptophyte Isochrysis galbana, and the larger chlorophyte Dunaliella tertiolecta), either singularly or in combinations of 2 species. When prey combinations included D, tertiolecta, the chlorophyte was grazed only after a large fraction of the other species was first grazed. Diatom and haptophyte were grazed concurrently when offered in combination. Changing the relative proportions of starting biomass of the different species in combination had no effect on the order of grazing. However, in all cases the switch to the chlorophyte occurred rapidly and the maximum ingestion rate attained after the switch was proportional to the contribution of the chlorophyte to total starting biomass. From a hydrodynamic standpoint, specific clearance rate C' increased as the ratio of predator radius to prey radius R: r decreased and C' increased as R decreased for a given value of R: r. We suggest that the preference for the 2 smaller species is governed by the ability of the flagellate to adjust its own size downward to accomodate the smaller prey in order to maintain R : r at ca 2 : 1. When sized to graze these smaller species, the flagellate simply is too small to graze the chlorophyte. Thus, although there is clear evidence that the flagellate is a non-passive grazer and will not graze certain species at all, mechanoreception clearly plays a major role in the dynamics of grazing desired species. Raptorial grazers such as P. imperforata, by having the ability to graze prey almost as big as themselves, may be effective competitors with larger protozoa for nanoplankton-size food particles and also contribute to making the food chain (web) withln the microbial loop long and complicated with high losses of energy and materials.

NITROGEN LIMITATION IN ISOCHRYSIS GALBANA (HAPTOPHYCEAE). I. PHOTOSYNTHETIC ENERGY CONVERSION AND GROWTH EFFICIENCIES1

ABSTRACTThe effect of steady‐state nitrogen limitation on photo‐synthetic characteristics and growth efficiency was examined in the marine haptophyte Isochrysis galbana Green. Nitrate limited chemostats were maintained at nine dilution rates, ranging from 0.18‐0.96 d−1, under continuous irradiance levels of 175 μmole quanta·m−2·s−1, an irradiance level which saturated photosynthesis at all growth rates. Nitrogen limitation led to an overall reduction in pigmentation and a decrease in the cellular concentration of reaction centers; however, the optical absorption cross section, normalized to Chl a, increased. Moreover, Chl c/a ratios were higher in nitrogen‐limited cells: the change in Chl c/a ratios were correlated with an increase in the functional size of Photosystem II. Both light saturated photosynthetic rates normalized per cell and specific respiratory losses were positively linearly correlated with growth rate. Light saturated photosynthetic rates normalized to Chl a remained relatively insensitive to the rate of nitrogen supply. The minimum quantum requirement for gross photosynthetic oxygen evolution increased from 12.4 to 17.0 quanta/O2. At the growth irradiance, the quantum requirement increased 88%, from 19.9 to 37.5 quauta/O2 Photosynthesis/respiration ratios remained relatively constant at dilution rates greater than 35% of the maximum relative growth rate. Consequently, net growth efficiency, defined as the ratio of the specific growth rate, μ, to specific gross photosynthesis, P, also remained relatively constant over this range of growth rates averaging 85 ± 3%.

The catabolism of L-phenylalanine, L-tyrosine, and some related aromatic compounds by two marine species of phytoplankton

Abstract Phytoplankton catabolism of L-phenylalanine and L-tyrosine was investigated with axenic cultures of the marine haptophyte Isochrysis galbana and the marine diatom Navicula incerta. Metabolic conversion and 14C-tracer studies indicated that phenylalanine is catabolized through pbenylpyruvate, phenylacetate, mandelate, benzoylformate and benzoate to p-hydroxybenzoate and its m-bromo derivative as major end-products, with marginal formation of CO2 from aromatic-ring degradation. Tyrosine is similarly metabolized through the corresponding p-hydroxylated derivatives to p-hydroxybenzoate. The side chains of these amino acids are degraded stepwise and each C1-fragment was identified as CO2. Cinnamate or p-coumarate were not detected as intermediates, nor could the ammonia-lyases for phenylalanine and tyrosine be demonstrated. However, externally supplied cinnamic acids were metabolized via hydracrylate intermediates to the corresponding benzoic acids. It was concluded that the phytoplankters catabolize ...

GROWTH OF A MARINE DIATOM AND A HAPTOPHYCEAN ALGA ON PHENYLALANINE OR TYROSINE SERVING AS SOLE NITROGEN SOURCE1

ABSTRACTThe marine diatom Navicula incerta Hustedt and the haptophyte Isochrysis galbana Parke, both accustomed to grow on nitrate, were tested for their adaptive capacity for growth in axenic culture on 0.025–2.0 mM l‐, d‐, and dl‐isomers of phenylalanine and tyrosine as sole nitrogen sources. The diatom showed immediate and excellent growth (superior to nitrate) on l‐phenylalanine and l‐tyrosine but required prolonged periods of adaptation before growing on the d‐isomers, which growth was considerably slower. Isochrysis showed good growth on l‐phenylalanine after short adaptation, fair growth on low but poor growth on high concentrations of l‐tyrosine and no growth on the d‐isomers of both amino acids. The racemate (dl‐mixture) of each amino acid produced growth responses, from both algae, inferior to those of the corresponding l‐isomer, indicating competitive inhibition from the d‐isomer in the presence of equal amounts of its counterpart. Increasing tyrosine concentration was beneficial to growth of Navicula but markedly inhibitory or toxic to that of Isochrysis. Phenylalanine concentration appeared to benefit growth of both algae. Ecological considerations suggest that N. incerta may be habituated to utilize both aromatic amino acids in its native milieu.