Enhanced Biomass Production of Phaeodactylum tricornutum by Co-cultivation with Mutualistic Bacteria

Co-cultivation of microalgae and bacteria has emerged as a strategy in applied biotechnology, particularly in the context of the biosynthesis of high-value metabolites. The microalga Phaeodactylum tricornutum has attracted a lot of interest due to its production of high-value bioproducts, such as fucoxanthin and omega-3 polyunsaturated fatty acids, but its commercial application is hampered by its low biomass production. To examine potential uses of growth-promoting bacteria on P. tricornutum, two symbiotic strains of bacteria, Salipiger marinus and Mesonia mobilis, were isolated from xenic algal cultures and cocultured with P. tricornutum independently. Both bacteria were shown to be able to stimulate microalgal growth when cocultivated with P. tricornutum using axenic microalgal seed culture inoculation. It was also confirmed that both bacteria species could retain their beneficial effects with xenic microalgae inoculation. The results indicated that both species were efficient in boosting P. tricornutum cultivation, with S. marinus demonstrating more statistically significant growth-promoting effects. These effects were confirmed to be present in xenic algal cultures under semi-continuous cultivation conditions, indicating that consortia with these bacteria could be a potential method of enhancing algal growth without requiring axenicity. The growth-promoting effects of S. marinus and M. mobilis were shown for both algal growth rates and biomass, demonstrating their potential for enhancing the productivity of algae-bacteria consortia of P. tricornutum.