Biomass productivity of Microchloropsis gaditana cultivated in a variety of modes and effect of cobalt and molybdenum on its lipid distribution

Abstract

The autotropic, heterotrophic and mixotrophic cultivation mode of the microalgae Microchloropsis gaditana was studied. Three sets of experiments were carried out: In the first set, six experimental groups were tested; one autotrophic, one heterotrophic and four mixotrophic where cultivation modes carried out and biomass productivities were compared to each other. In the second and in the third set of experiments, the algae were exposed to four or five concentrations of cobalt (Co) or of molybdenum (Mo) respectively; in these sets of experiments the effect of Co and Mo on the biomass productivity and on the lipid content and distribution of M. gaditana was examined. In the 1st set of experiments, the mixotrophic cultivations, the initial carbon concentration, C(0), was equal to 2.87 g/L, 2.92 g/L, 3.96 g/L and 4.96 g/L and in the heterotrophic cultivation C(0) was equal to 2.24 g/L. Nitrogen initial concentration, Ν(0), was held constant at 77.1 mg/L. For the heterotrophic and the three mixotrophic cultivations, the biomass yield, when expressed as g/(per L-g of added carbon) was highest for the heterotrophic growth. In the 2nd and 3rd sets of experiments it was found that both Co and Mo affect biomass productivity and lipid distribution. Co, even at relatively medium concentrations, strongly inhibited the growth. On the other hand, Mo, even at relatively high concentrations, did not affect substantially the growth rate of M. gaditana. The lipid distribution showed that for most treatments with varying concentrations of Co and Mo, MUFA prevailed while, n-3 PUFA up to 26.6% and 19.4% of the total FA were obtained. Lipid and protein contents of the biomass for the treatments with Co were up to 8.18% and 14.97% respectively, while the respective values for the treatments with Mo were higher up to 16.67% and 17.76%.