Biochemical composition of Rhodomonas baltica as a function of the dilution rate during steady rate of growth
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- Institutt for biologi 
The algae Rhodomonas baltica, Karsten was cultured in Guillard f-medium with the phosphate concentration reduced to 5 µmol/L. The cultures were diluted at seven different dilution rates corresponding approximately to growth rates of 40, 50, 60, 70, 80, 90 and 100% of µmax measured in batch culture. The biochemical composition of the algae was measured for variable specific growth rate in cultures maintained in steady state of growth. The main objective of the thesis was to study the effect of the specific growth rate on biochemical composition of R.baltica. The cellular N:C (QN) was from 134 to 154 µg N/mg C, while the cellular P:C (QP) varied in the range between 16 to 21 µg P/mg C. The data of µ versus QP were adapted to the Droop model, but the data could not be adequately described by the Droop model. The subsistence quota (Q0) were -27.6 ± 217 µg P/mg C. The Droop model, however, described the data of µ versus QN adequately (p<0.05), and the Q0 value was 120 µg N/mg C. The concentration of inorganic nitrogen (Ni) and inorganic phosphorus (Pi) remaining in the cultures were high. The algae R.baltica was probably limited by another factor than N and P.The cellular contents of Chl a, protein, lipid and fatty acids increased with rising specific growth rate beyond 0.25 day-1. The Chl a/C was significantly (p<0.05) correlated to the specific growth rate, and varied from 2.6 to 5.6 µg Chl a/mg C. The protein content per dry weigh was in the range 308 to 354 mg/g dry weight. There was a significantly (p<0.05) positive relationship between the protein content per dry weight and the specific growth rate. In contrast to protein, the lipid content per dry matter was not positively related to the specific growth rate (p>0.05). The lipid content varied in the range from 440 to 633 mg/g dry weight, which much higher than protein. Total fatty acids content varied from 177 to 257 mg/g dry weigh and constituted 42.5 ± 0.78% of content of total lipids, and was not related to the specific growth rate. Regarding n-3 and n-6 PUFAs, the n-3 PUFAs was not affected by the specific growth rate, whereas a significantly (p<0.05) negative relationship between n-6 PUFAs and the specific growth rate was found. The amount of essential n-3 PUFAs accounted for 42.5-53.5% of total fatty acids, while n-6 PUFAs was from 1.7 to 4.3% of total fatty acid. The major fatty acids of the algae were 16:0, 18:1, 18:3n-3, 18.4n-3, 20:5n-3 (EPA) and 22:6n-3 (DHA). The contents of EPA and DHA were 4.3 - 5.2% and 3.6 - 4.8% of total fatty acids, respectively.