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

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 > 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.