Protein measurements of microalgal and cyanobacterial biomass.

The protein content of dry biomass of the microalgae Porphyridium cruentum, Scenedesmus almeriensis, and Muriellopsis sp. and of the cyanobacteria Synechocystis aquatilis and Arthrospira platensis was measured by the Lowry method following disruption of the cells by milling with inert ceramic particles. The measurements were compared with the Kjeldahl method and by elemental analysis. The nitrogen-to-protein conversion factors for biomass obtained from exponentially growing cells with a steady state doubling time of approximately 23 h were 5.95 for nitrogen measured by Kjeldahl and 4.44 for total nitrogen measured by elemental analysis. The protein content in dry biomass ranged from 30% to 55%. The above conversion factors are useful for estimating the protein content of microalgal biomass produced in rapid steady state growth as encountered in many commercial production processes.

New culture approaches for yessotoxin production from the dinoflagellate Protoceratium reticulatum.

Fed-batch and perfusion cultures were carried out in a traditional glass 2-L bioreactor with the toxic dinoflagellate Protoceratium reticulatum. The maximum cell concentration obtained was 2.3 x 105 cell.mL-1, which is almost 1 order of magnitude higher than the maximum previously referenced for this species. L1 medium was shown to be clearly deficient in nitrate and phosphate for this strain, and addition of highly concentrated aliquots of these nutrients allowed higher cell concentrations to be obtained. This species consumed high amounts of nitrate and phosphate, 2.1 x 10-3 and 2.3 x 10-4 micromol.h-1.cell-1, respectively. However, this consumption produced a very low number of cells compared to other classes of microalgae, indicating that this species is, like other dinoflagellates, a poor competitor in terms of utilization of inorganic nutrients. Higher production of toxins and pigments was strongly associated with cell number in the culture, with maximum values of 700 ng.mL-1 and 1321 microg.mL-1, respectively. Most yessotoxins remained within the cells and not in the cell-free culture medium, and their production was not related to either the age of the culture or the cell growth phase.