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Although mathematical models suggest that competition between primary producers in response to dynamical changes in the availability of a limiting nutrient is non-linear, experimental data supporting this basic hypothesis are sparse. Using continuous culture systems with nitrate as a single limiting nutrient, we present results of competition experiments between 2 species of marine phytoplankton, a diatom Thalassiosira pseudonana and a coccolithophore Coccolithus braarudii. These 2 organisms of similar size represent biogeochemically and ecologically distinct functional groups. Consistent with classical resource competition theory, under steady-state nitrate limitation (i.e. continuous flow chemostats), the diatom was outcompeted by the coccolithophore. However, when pulses of nitrate were provided to the chemostats (i.e. non-equilibrium, dynamical conditions) the diatom outcompeted the coccolithophore. The rate of exclusion was a linear function of the frequency of nitrate pulses. These results experimentally demonstrate that dynamical nutrient supply allows co-existence of 2 primary producers competing for a single limiting nutrient and may help us to understand phytoplankton succession in the ocean.

Marine microalgae are a promising source of organisms that can be cultured and targeted to isolate the broad spectrum of functional metabolites. In this study, two species of cyanobacteria, Chlorella ovalis Butcher and Nannchloropsis oculata Droop, one species of bacillariophyta, Phaeoductylum tricornutum Bohlin, and one species of Dinophyceae, Amphidinium carterae (Hulburt) were cultured and biomasses used to evaluate the proximate comical compositions. Among the determined proximate chemical compositions of the cultured marine microalgae, the highest content of crude proteins and lipids were exhibited in P. tricornutum and A. carterae, respectively. Solvent-solvent partition chromatography was subjected to fractionate each of the cultured species and separated n-hexane, chloroform, ethyl acetate, and aqueous fractions. Nitric oxide production inhibitory level (%) and cytotoxicity effect on lipo-polysaccharide-induced RAW 264.7 macrophages were performed to determine the anti-inflammatory activity. N. oculata hexane and chloroform fractions showed significantly the strongest anti-inflammatory activity at 6.25 µg mL -1 concentration. The cancer cell growth inhibition (%) was determined on three different cell lines including HL-60 (a human promyelocytic leukemia cell line), A549 (a human lung carcinoma cell line), and B16F10 (a mouse melanoma cell line), respectively. Among the extracts, C. ovalis ethyl acetate and A. carterae chloroform fractions suppressed the growth of HL-60 cells significantly at 25 and 50 µg mL -1 concentrations. Thus, the cultured marine microalgae solvent extracts may have potentiality to isolate pharmacologically active metabolites further using advance chromatographic steps. Hence, the cultured marine microalgae can be described as a good candidate for the future therapeutic uses.

Five fractions separated from Nannochloropsis oculata using solvent-solvent partition chromatography of 80% methanolic extract of N. oculata (NOM) followed by the open silica column chromatography of its hexane fraction (NOMH) for the anti-inflammatory on RAW 264.7 cells and anti-cancer activities on HL-60, A-549, HEP-3B, HCT-116, and SW-480 cancer cells. All the five fractions showed potential anti-inflammatory activities against lipo polysaccharide-stimulated RAW 264.7 macrophages cells with IC 50 values less than 6.25 µg mL-1. Moreover, 90% n-hexane column elution of NOMH (NOMH90) down-regulated lipopolysaccharide-stimulated protein levels of inducible nitric oxide synthase and cyclooxygenase-2. Furthermore, NOMH90 showed marked cytotoxic effect on the HL-60 cells with IC 50 value of 23.58 ± 0.09 µg mL-1. In addition, Hoechst 33342 cell permeable dye used to visualize the apoptosis nucleus and cell cycle analysis measured Sub-G1 DNA contents to confirm reduction of the cell viability in NOMH90 treated cells due to induction of apoptosis in HL60. These results are quite related to the phytosterol contents of the NOMH fractions and the results suggest N. oculata extracts might be useful as potential sources of natural anti-inflammatory and anti-cancer compounds. In conclusion, the sterol content in N. oculata might provide a promising role in future medicines in anti-inflammatory and anti-cancer.

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