The effects of temperature and salinity on growth of green algae Chlorella ellipsoidea and Nannochloris oculata were determined to compare the optimum culture conditions. A fourtemperature (15, 20, 25, and 30°C) ¥ three-salinity (10, 20, and 30) factorial design with triplicates was applied. Specific growth rate (SGR), maximum density, and duration to reach maximum density of C. ellipsoidea were significantly affected by both temperature and salinity. The highest SGR was observed in C. ellipsoidea at 25°C and salinity 10, but the maximum density was very low. The highest maximum density was achieved in C. ellipsoidea at 15°C and 10. The slope constant of the linear relationship between semilogarithmic growth of C. ellipsoidea and day of culture was highest at 15°C and 10. The SGR and duration to reach maximum density of N. oculata were significantly affected by both temperature and salinity. However, maximum density of N. oculata was significantly affected by temperature, but not salinity. The highest maximum density was achieved in N. oculata at 25°C and 30, but SGR was significantly lower than that of N. oculata at 25°C and 10. The slope constant of the linear relationship between semilogarithmic growth of N. oculata and day of culture was highest at 25°C and 30. Based on these results, the condition of 15°C and salinity 10 seemed to be optimal for maximum density of C. ellipsoidea, and the condition of 25°C and 10 and 30 for SGR and maximum density for N. oculata, respectively.
Some Chlorella species grow heterotrophically with organic substrate in dark condition. However, heterotrophic Chlorella species are limited and their optimum culture conditions are not fully known. In this study, three heterotrophic Chlorella species, two strains (C4-3 and C4-4) of C. vulgaris and one Chlorella sp. (C4-8) were examined on optimum culture conditions such as carbon source, temperature, and concentrations of nitrogen and phosphorus in Jaworski's medium (JM). And the growth and fatty acid composition of Chlorella were analyzed. For three heterotrophic Chlorella species, glucose (1-2%) as a carbon source only increased the growth and the range of optimum culture temperature was 26-28°C. Doubled concentrations of the nitrogen or phosphorus in JM medium also improved the growth of Chlorella. Chlorella cultured heterotrophically showed significantly higher growth rate and bigger cell size than those autotrophically did. C. vulgaris (C4-3) cultured heterotrophically showed the highest biomass in dry weight (0.8 g L -1 ) among three species. With respect to fatty acid composition, the contents of C16:0 and n-3 highly unsaturated fatty acid (HUFA) were significantly higher in autotrophic Chlorella than in heterotrophic one and those of total lipid were not different between different concentrations of nitrogen and phosphorus in JM medium. Among three Chlorella species in this study, C. vulgaris (C4-3) appeared to be the most ideal heterotrophic Chlorella species for industrial application since it had a high biomass and lipid content.
Molecular genetic tools are widely used to learn more about the identical characterization of obscure microalgal strains. At the Korea Marine Microalgae Culture Center (KMMCC), the authors deduced the genetic relationship of 41 strains of the genus Tetraselmis by analysing a small subunit ribosomal DNA (18S rDNA) sequences. Forty-one strains were seperated into five groups, which showed over a 98-99% similarity to Tetraselmis striata or Tetraselmis sp. Tsbre. Also, 13 strains among them had an identical genotype to Tetraselmis striata while 5 strains had with Tetraselmis sp. Tsbre, respectively. The mean size of each strain generally showed the tendency of different variation according to the groups.
To find seasonally optimal microalgae for mass culture of the rotifer Brachionus plicatilis, the growth rates of 12 microalgal species (two marine Chlorella spp., five marine Nannochloris spp., two marine Nannochloropsis spp., one estuarine Nannochloropsis sp., and two estuarine Chlorella spp.) were compared at 25°C at 15 psu and 30 psu. Among these, six species showing high growth rates were chosen and examined again at high (30°C and 32°C) and low (10°C) temperatures. Their amino and fatty acids and the dietary value of the rotifers that fed on each microalgal species were examined. Nannochloris sp. (KMMCC-119) and Chlorella vulgaris (KMMCC-120) showed the highest growth rates at temperatures over 30 o C and at 10°C, respectively. The growth rate of Nannochloris was higher than those of Chlorella and Nannochloropsis at high temperatures, but lower than those of the latter at low temperatures. The growth rate of rotifers fed on Nannochloropsis was highest and that of those fed on Chlorella was lowest. Levels of eicosapentaenoic acid and docosahexaenoic acid were highest in Nannochloropsis and lowest in Nannochloris. However, total amino acid content was highest in Nannochloris and lowest in Chlorella. In conclusion, Nannochloropsis sp. (KMMCC-33) was the best microalgal species for the mass culture of the rotifer. However, during high-or low-temperature seasons in which Nannochloropsis does not grow well, Nannochloris spp. (KMMCC-119, 395) and C. vulgaris (KMMCC-120) would adequately replace Nannochloropsis sp. (KMMCC-33).
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