Variations in the biochemical profile of the marine microalga Dunaliella tertiolecta (Butcher) cultured with different nutrient concentrations and urea as a nitrogen source

Abstract

[Abstract] Variations in the biochemical profile of the marine microalga Dunaliella tertiolecta (Butcher) cultured with different nutrient concentrations and urea as a nitrogen source. Cultures of the marine microalga Dwwliella tertiolecta were grown in a urea-based medium, using four nutrient concentrations following a geometrical progression of order 2, expressed as x I, x2, x4 and x8, in order to obtain a maximum biomass production and to find out its biochemical variability. The nutrient concentration had little effect on the growth rate in the logari thmic phase, with values between 0.40 and 0.44 doublings.day-I. Maximum cellular densities of7.53x106 and 7.96x106 cells.ml-I were obtained in x2 and x4 cultures (corresponding to 2 and 4 mM of urea). Differences in biochemical composition were found in function of the nutrient concentration. Protein content reached maximum values in the stationary phase in x4 and x8 cultures, with 29.56 and 29.28 pg.ceW I. The maximum value of carbohydrates was obtained in xl cultures, with 14.38 pg.cell- I. Maximum lipids per cell were obtained in the stationary phase in cultures with the higher nutrient concentration asssayed (x8), with 23.12 pg.ceWI. Cultures at the lower nutrient concentration assayed (xl) showed a nitrogen deficiency, with cells with low protein and high carbohydrate content at the stationary phase.

[Resume] Variations du profil biochimique de la microalgue marine Dunaliellatertiolecta (Butcher) cultivee avec differentes concentrations de nourriture et dans un milieu d' uree. Afin d'obtenir les plus gran des quantites de biomasse et de trouver la variabilite biochimique de la microalgue marine D. tertiolecta, nous avons effectue des cultures dans un milieu d'uree, sous quatre concentrations differentes de nourriture, suivant une progress ion geometrique d' ordre (xl, x2, x4, x8). La concentration en nutriment azote n'a guere d'effet sur Ie taux de croissance dans la phase logarithmique (0,40 it 0,44 division.jour- I). Les densites cellulaires maximales (7,53 x 106 et 7,96 x 106 ceII.ml- l) ont ete obtenues dans les cultures x2 et x4, correspondant respectivement it 2 et 4 mM d' uree. Des differences au ni veau de la composition biochimique ont ete observees en fonction de la concentration en nourriture. Les contenus en proteines les plus eleves ont ete observes dans les cultures x4 et x8, soit 29,56 et 29,28 pg. ceWI. La valeur maxima en carbohydrates a ete obtenue dans les cultures x I (14,38 pg.ceW I). Les contenus en lipides par cellule les plus eleves ont ete observes dans les cultures ayant les plus grandes concentrations de nourriture (x8 : 23,12 pg.ceW I). Les cultures effectuees a la plus faible concentration en nutriment ont conduit it la production de cellules aux contenus peu eleves en pfbteines mais eleves en carbohydrates, lies au manque d'azote.