Impact of organic carbon acquisition on growth and functional biomolecule production in diatoms

Abstract

Diatoms are unicellular photosynthetic protists which constitute one of the most successful microalgae contributing enormously to global primary productivity and nutrient cycles in marine and freshwater habitats. Though they possess the ability to biosynthesize high value compounds like eicosatetraenoic acid (EPA), fucoxanthin (Fx) and chrysolaminarin (Chrl) the major bottle neck in commercialization is their inability to attain high density growth. However, their unique potential of acquiring diverse carbon sources via varied mechanisms enables them to adapt and grow under phototrophic, mixotrophic as well as heterotrophic modes. Growth on organic carbon substrates promotes higher biomass, lipid, and carbohydrate productivity, which further triggers the yield of various biomolecules. Since, the current mass culture practices primarily employ open pond and tubular photobioreactors for phototrophic growth, they become cost intensive and economically non-viable. Therefore, in this review we attempt to explore and compare the mechanisms involved in organic carbon acquisition in diatoms and its implications on mixotrophic and heterotrophic growth and biomolecule production and validate how these strategies could pave a way for future exploration and establishment of sustainable diatom biorefineries for novel biomolecules.

Media engineering in marine diatom Phaeodactylum tricornutum employing cost‐effective substrates for sustainable production of high‐value renewables

“…Higher EPA yield (27 mg L −1 ) along with TAG content (92 mg L −1 ) (Figure 2A, Table 2) indicates that glycerol triggers metabolic changes resembling nitrogen depletion conditions, however, promoting growth thereby increasing the overall productivities. [ 56 ] Moreover, higher EPA content was observed on initial growth days (∼35 mg g −1 on day 6) in all mixotrophic combinations (M1, M2, M3, and M4) and was greater than previous reports showing EPA content (20, 29, 28.30, and 31.66 mg g −1 ) in mixotrophy (Supplementary Information Table S3, Figure 2A, B). [ 8,20,73 ] This indicates the necessity of structural lipids in the log phase but as nitrogen depletes in the medium EPA content did not change (Figure 2A, B) in the respective conditions, though urea‐fed cultures maintain the EPA pool throughout the experiment.…”

“…An increase in EPA content in the initial growth phase was reported earlier in the presence of urea [ 32 ] and mixotrophic condition containing glycerol along with urea in P. tricornutum . [ 17,20,56 ] It was observed that in the M4 condition, EPA content was constant on day 6, 8, and 10 (Figure 2B), and the EPA titer was gradually increased throughout the experiment (Figure 2A).…”

“…Our findings highlight the effect of feeding nitrogen to the glycerol‐supplemented cells (M4), higher nitrogen content results in increasing the biomass and thus enhancing growth‐related metabolites like EPA and fucoxanthin. The presence of glycerol in the medium upregulates the EPA biosynthesis via regulating enzyme‐like stearoyl desaturase, [ 56 ] and the effect of feeding strategies of various nutrients on biomass and lipid productivities [ 74–76 ] is mentioned in previous reports. In conclusion, this study successfully highlights an alternative application of feeding nutrients in a mixotrophic mode to increase HVRs like EPA and fucoxanthin.…”

“…These fatty acids are the main components of storage lipids, which justifies their higher accumulation in the form of TAGs in the mixotrophic conditions. [56,68] Feeding additional nitrogen shifted the fatty acid metabolism toward membrane lipid synthesis, that is, EPA showed a higher percentage of PUFAs in feed conditions (Table 2). The M4 condition accumulates EPA (28% of total FAME) and is the maximum among all the previous studies (Supplementary Information Table S3).…”

Golgi fucosyltransferase 1 reveals its important role in α-1,4-fucose modification of N-glycan in CRISPR/Cas9 diatom Phaeodactylum tricornutum

“…For example, Acetyl-CoA carboxylase (ACC, B7GEB5) harboring core α-1,3-fucose residue was observed in both the wild type and PtFucT1-KO mutant. ACC is a key enzyme responsible for the catalysis of carboxylation of acetyl-CoA into malonyl-CoA in plastids [ 64 ]. However, it is still unknown which protein is responsible for the core fucose modification.…”