Interaction between marine bacterium Stappia sp. K01 and diatom Phaeodactylum tricornutum through extracellular fatty acids

Fucoxanthin, a marine carotenoid with biological activities including anti-obesity activity, is generally produced from macroalgae, but several microalgae have been suggested as new sources. A standardized fucoxanthin extract was recently developed from the diatom Phaeodactylum tricornutum. Here, we illustrate that a marine bacterium, Stappia sp. K01, isolated from xenic cultures of P. tricornutum, improves growth (72%) and pigment biosynthesis (172% fucoxanthin and 144% chlorophylls, respectively) of P. tricornutum by co-culture. In addition, six major extracellular fatty acids (FAs) including C14:0, C16:0, C18:0, C16:1, C18:1, and C20:5 secreted by P. tricornutum play an important role in this effect of Stappia sp. K01. These FAs were secreted from P. tricornutum in a range of 0.1~4.9 μg L−1 and each maximum concentration in the culture medium was decreased to 25~83% by Stappia sp. K01 inoculation. In the treatment of a mixed FA solution with their maximum concentrations to P. tricornutum culture, these FAs showed 30% growth inhibition of P. tricornutum and this effect was removed by Stappia sp. K01 inoculation. Each FA was utilized as a nutrient for Stappia sp. K01 in M9 minimum medium. Several growth regulation-related genes in P. tricornutum were downregulated by FA treatment and upregulated by co-culturing with Stappia sp. K01. These results indicate that Stappia sp. K01 can be used as an inducer to promote biomass production and fucoxanthin biosynthesis in P. tricornutum.