Morphological and biochemical changes in Phaeodactylum tricornutum triggered by culture media: Implications for industrial exploitation

Abstract

Phaeodactylum tricornutum is a polymorphic marine diatom, displaying three main morphotypes: fusiform, triradiate and oval. It is of great interest for industrial biotechnology as a natural rich source of valuable eicosapentaenoic acid (EPA) and fucoxanthin. Changing culture conditions such as temperature and salinity has been shown to elicit morphological changes in P. tricornutum. However, limited information is available about the conditions that can be used for controlling cell morphology and growth of a particular cell morphotype with high biomass productivity. While the phenomenon of pleiomorphy is intrinsically interesting, there has not been a systematic study linking this behavior to the ability of P. tricornutum to perform as a platform for industrial biotechnology. In this study, the effects of culture medium and culture age on morphological and biochemical changes in P. tricornutum were investigated. Mann and Myers' medium was identified as eliciting significant morphotype conversion from fusiform to oval in P. tricornutum. Liquid cultures containing more than 90% oval cells were obtained and well-maintained in this medium under constant shaking condition, allowing high dry biomass concentration (0.73 g L -1 ) to be achieved. Biochemical composition analyses revealed that higher protein (% dry weight) was obtained from oval cell cultures compared to fusiform cell cultures maintained in f/2 medium over 21 days cultivation. Meanwhile, pigment was markedly accumulated in oval cell cultures whereas lipid and carbohydrate were highly accumulated in fusiform cell cultures. This work offered a novel way to regulate cell morphology of P. tricornutum and provided significant implications for upstream cultivation strategies to optimise manufacture of different classes of product in P. tricornutum.

Comparative Structural and Functional Analyses of the Fusiform, Oval, and Triradiate Morphotypes of Phaeodactylum tricornutum Pt3 Strain

“…Oval cells are able to release rapidly a higher amount of proteins, fusiform cells present a constant secretory activity at a mid-level while triradiate cells release progressively proteins over time from low-level to mid-level. Such results are complementary to recent findings published by Song et al (2020) that quantified higher protein content in oval cell cultures than in fusiform cell cultures for both Pt1 and Pt4 strains of P. tricornutum. In addition, as previously reported in Ovide et al (2018), RNA-Seq transcriptomic analysis performed on the three morphotypes of P. tricornutum Pt3 strain highlighted, in the oval morphotype, overexpression of genes encoding proteins involved in vesicular transports like the SAR1, a GTPase found in COP II vesicles; BET1 a Golgi vesicular transport from the ER to the Golgi complex; the SNARE SEC22 and the syntaxin 6, which displays important role in protein trafficking between the trans-Golgi network and the endosomal system.…”

“…In 2020, Song et al (2020) observed more and larger lipid bodies in Pt1 and Pt4 fusiform cells over time compared to oval cells. This implies higher neutral lipid accumulation in the fusiform cells from these P. tricornutum strains (Song et al, 2020).…”

“…Interestingly, an additional cruciform morphotype of P. tricornutum resulting from triradiate cells transformation with low temperature culture conditions presented a unique fatty acids characteristics suitable for biodiesel production (He et al, 2014). In 2020, Song et al (2020) observed more and larger lipid bodies in Pt1 and Pt4 fusiform cells over time compared to oval cells. This implies higher neutral lipid accumulation in the fusiform cells from these P. tricornutum strains (Song et al, 2020).…”

Optimal Nitrate Supplementation in Phaeodactylum tricornutum Culture Medium Increases Biomass and Fucoxanthin Production

“…In fact, previous studies aiming to optimise the medium composition in order to increase EPS production highlight the role of sodium nitrate. It has been reported that increasing nitrogen concentration results in elevated EPS production (reviewed in [ 64 , 65 ]), although this is not consensual, and some authors have observed opposing effects [ 66 ]. Further studies need to be carried out in order to fully understand the intricate relationship between microalgae communities (including associated bacteria), nitrogen usage and response to challenging environmental conditions.…”

Iron-dependent mutualism between Chlorella sorokiniana and Ralstonia pickettii forms the basis for a sustainable bioremediation system

“…The algal cells from a 7-day old culture in BBM-Fe were washed and centrifuged at 2000× g for 3 min at RT. The cell pellets were resuspended in PBS buffer containing Dowex Marathon C (25g g -1 ) and gently mixed in a rotatory mixer (50 RPM) at 4°C for 1 h. Subsequently, the algal cells were centrifuged at 4000×g for 4 min, and the supernatant was subjected to overnight precipitation of exopolysaccharides in 70% ethanol (3:1 to supernatant) at 4°C [44]. Thereafter, the supernatant was centrifuged at 10,000×g for 10 min, and the pellet was collected for analyses by high-performance anion-exchange chromatography (HPAEC).…”