Effects of fundamental nutrient stresses on the lipid accumulation profiles in two diatom species Thalassiosira weissflogii and Chaetoceros muelleri.

Microalgae are considered as attractive feedstocks for biofuel production nowadays because of their high lipid contents and easy cultivation. In the present study, two diatoms, Thalassiosira weissflogii and Chaetoceros muelleri, were cultured under various nutrient-limitation conditions to explore their comprehensive lipid accumulation profiles for further commercialization. In T. weissflogii, the highest neutral lipid accumulation and highest lipid productivity (14.28 mg L-1 day-1) were both recorded under P-limitation. In C. muelleri, the highest lipid content (35.03% of dry cell weight), highest neutral lipid accumulation, and highest lipid productivity (29.07 mg L-1 day-1) were all recorded under N-limitation. Besides, the predominant fatty acids of T. weissflogii and C. muelleri were myristic acid (C14:0), palmitic acid (C16:0), and palmitoleic acid (C16:1), with the amounts of 58.4-74.4 and 74.1-87.7% of the total fatty acids, respectively. Moreover, nutrient limitations led to a lower proportion of polyunsaturated fatty acids (PUFA) than that of saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) in both species. The ratios of (SFA + MUFA) to PUFA were from 1.65 to 3.01 in T. weissflogii, and up to 3.61 to 8.59 in C. muelleri. Our results suggested the feasibility of C. muelleri as biodiesel feedstock due to its more suitable fatty acid composition and higher lipid productivity compared to T. weissflogii.

iTRAQ-based proteomic analysis of the metabolism mechanism associated with silicon response in the marine diatom Thalassiosira pseudonana.

Silicon is a critical element for diatom growth; however our understanding of the molecular mechanisms involved in intracellular silicon responses are limited. In this study, an iTRAQ-LC-MS/MS quantitative proteomic approach was coupled with an established synchrony technique to reveal the global metabolic silicon-response in the model diatom Thalassiosira pseudonana subject to silicon starvation and readdition. Four samples, which corresponded to the time of silicon starvation, girdle band synthesis, valve formation, and right after daughter cell separation (0, 1, 5, 7 h), were collected for the proteomic analysis. The results indicated that a total of 1,831 proteins, representing 16% of the predicted proteins encoded by the T. pseudonana genome, could be identified. Of the identified proteins, 165 were defined as being differentially expressed proteins, and these proteins could be linked to multiple biochemical pathways. In particular, a number of proteins related to silicon transport, cell wall synthesis, and cell-cycle progress could be identified. In addition, other proteins that are potentially involved in amino acid synthesis, protein metabolism, and energy generation may have roles in the cellular response to silicon. Our findings provide a range of valuable information that will be of use for further studies of this important physiological response that is unique to diatoms.

Cellular metabolic responses of the marine diatom Pseudo-nitzschia multiseries associated with cell wall formation.

In this study a comparative proteomics approach involving a mass spectrometric analysis of synchronized cells was employed to investigate the cellular-level metabolic mechanisms associated with siliceous cell wall formation in the pennate diatom Pseudo-nitzschia multiseries. Cultures of P. multiseries were synchronized using the silicate limitation method. Approximately 75% of cells were arrested at the G2+M phase of the cell cycle after 48 h of silicate starvation. The majority of cells progressed to new valve synthesis within 5h of silicon replenishment. We compared the proteome of P. multiseries at 0, 4, 5, and 6h of synchronization progress upon silicon replenishment using two-dimensional gel electrophoresis. Forty-eight differentially expressed protein spots were identified in abundance (greater than two-fold change; P<0.005), some of which are predicted to be involved in intracellular trafficking, cytoskeleton, photosynthesis, lipid metabolism, and protein biosynthesis. Cytoskeleton proteins and clathrin coat components were also hypothesized to play potential roles in cell wall formation. The proteomic profile analysis suggests that P. multiseries most likely employs multiple synergistic biochemical mechanisms for cell wall formation. These results improve our understanding of the molecular mechanisms underlying silicon cell wall formation and enhance our understanding of the important role played by diatoms in silicon biogeochemical cycling.