Nutrient Deficiency and an Algicidal Bacterium Improved the Lipid Profiles of a Novel Promising Oleaginous Dinoflagellate, Prorocentrum donghaiense, for Biodiesel Production

Abstract

The lipid production potentials of 8 microalgal species were investigated. Among these 8 species, the best strain was a dominant bloom-causing dinoflagellate, Prorocentrum donghaiense; this species had a lipid content of 49.32% ± 1.99% and exhibited a lipid productivity of 95.47 ± 0.99 mg liter^-1 day^-1, which was 2-fold higher than the corresponding values obtained for the oleaginous microalgae Nannochloropsis gaditana and Phaeodactylum tricornutum. P. donghaiense, which is enriched in C_16:0 and C_22:6, is appropriate for commercial docosahexaenoic acid (DHA) production. Nitrogen or phosphorus stress markedly induced lipid accumulation to levels surpassing 75% of the dry weight, increased the C_18:0 and C_17:1 contents, and decreased the C_18:5 and C_22:6 contents, and these effects resulted in decreases in the unsaturated fatty acid levels and changes in the lipid properties of P. donghaiense such that the species met the biodiesel specification standards. Compared with the results obtained under N-deficient conditions, the enhancement in the activity of alkaline phosphatase of P. donghaiense observed under P-deficient conditions partly alleviated the adverse effects on the photosynthetic system exerted by P deficiency to induce the production of more carbohydrates for lipogenesis. The supernatant of the algicidal bacterium Paracoccus sp. strain Y42 culture lysed P. donghaiense without decreasing its lipid content, which resulted in facilitation of the downstream oil extraction process and energy savings through the lysis of algal cells. The Y42 supernatant treatment improved the lipid profiles of algal cells by increasing their C_16:0, C_18:0, and C_18:1 contents and decreasing their C_18:5 and C_22:6 contents, which is favorable for biodiesel production. IMPORTANCE This study demonstrates the high potential of Prorocentrum donghaiense, a dominant bloom-causing dinoflagellate, for lipid production. Compared with previously studied oleaginous microalgae, P. donghaiense exhibit greater potential for practical application due to its higher biomass and lipid contents. Nutrient deficiency and the algicidal bacterium Paracoccus sp. strain Y42 improved the suitability of the lipid profile of P. donghaiense for biodiesel production. Furthermore, Paracoccus sp. Y42 effectively lysed algal cells, which facilitates the downstream oil extraction process for biodiesel production and results in energy savings through the lysing of algal cells. This study provides a more promising candidate for the production of docosahexaenoic acid (DHA) for human nutritional products and of microalgal biofuel as well as a more cost-effective method for breaking algal cells. The high lipid productivity of P. donghaiense and algal cell lysis by algicidal bacteria contribute to reductions in the production cost of microalgal oil.

Keywords: DHA; Prorocentrum donghaiense; algicidal bacteria; biodiesel production; lipid accumulation; nutrient starvation.

FIG 1

Growth and lipid accumulation of Nannochloropsis gaditana (A), Phaeodactylum tricornutum (B), Prorocentrum donghaiense (C), Prorocentrum minimum (D), Prorocentrum micans (E), Scrippsiella trochoidea (F), Alexandrium minutum (G), and Amphidinium carterae (H). (I) Growth and lipid accumulation of algal cells. (II) Photographs of algal cells. (III) Lipid droplets were stained with Nile red and observed with a fluorescence microscope. Bars, 10 μm.

FIG 2

Comparison of the fatty acid composition of 8 microalgal strains. (A) Fatty acid compositional profiles. (B) The percentages of SFAs, MUFAs, and PUFAs in the total fatty acids. SFAs: C_14:0, C_16:0, C_18:0, C_20:0, and C_22:0; MUFAs: C_16:1, C_17:1, C_18:1, and C_22:1; PUFAs: C_16:2, C_16:3, C_18:2, C_18:3, C_18:4, C_18:5, C_20:2, C_20:4, C_20:5, and C_22:6.

FIG 3

Growth, lipid accumulation, and fatty acid compositions of P. donghaiense under N- and P-deficient conditions. (A) Growth and lipid accumulation of P. donghaiense under different conditions. (B) Photographs of algal cells under different conditions. Lipid droplets were stained with Nile red and observed with a fluorescence microscope. The values are the means ±SDs (n = 3). *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001; *****, P < 0.00001 versus the control.

FIG 4

Photosynthetic response of P. donghaiense to N- and P-deficient conditions. Chlorophyll a contents (A), carotenoid contents (B), Fv/Fm (C), rETR at day 0 (D), rETR at day 4 (E), and rETR at day 12 (F). The values are the means ±SDs (n = 3). *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001 versus the control.

FIG 5

Alkaline phosphatase activities (A) and protein contents (B) of P. donghaiense under N- and P-deficient conditions. AP, alkaline phosphatase. The values are the means ±SDs (n = 3). *, P < 0.05; **, P < 0.01; ****, P < 0.0001 versus the control.

FIG 6

Fatty acid compositions of P. donghaiense under different culture conditions. (A) Fatty acid compositional profiles. (B) Percentages of SFAs, MUFAs, and PUFAs among the total fatty acids. SFAs: C_14:0, C_15:0, C_16:0, C_18:0, C_20:0, and C_22:0; MUFAs: C_16:1, C_17:1, C_18:1, and C_22:1; PUFAs: C_18:2, C_18:4, C_18:5, C_20:2, C_20:5, and C_22:6. The values are the means ±SDs (n = 3). *, P < 0.05; **, P < 0.01; ***, P < 0.001 versus the control.

FIG 7

Effects of the algal-lytic bacterium Paracoccus sp. Y42 on the lipid content and fatty acid composition of P. donghaiense. (A) Algal-lytic activities of different concentrations of the Y42 supernatant. (B) Lipid contents of algal cells treated with different concentrations of the Y42 supernatant for 72 h. (C) Fatty acid compositions of algal cells treated with different concentrations of the Y42 supernatant for 72 h. Values are the means ± SDs (n = 3). *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001 versus the control.

FIG 8

Efficiency of the Y42 supernatant to lyse P. donghaiense. (A) P. donghaiense culture. (B) P. donghaiense lysed by 1% Y42 supernatant. (C) P. donghaiense lysed by 3% Y42 supernatant. (D) P. donghaiense lysed by 5% Y42 supernatant.