Marine diatoms rely on essential micronutrients, vitamins and many other mostly unknown growth factors delivered by bacteria. In-vitro experiments reliably show that axenic diatoms (bacteria-free) grow slower than xenic ones (containing associated bacteria), despite the provision of complete nutrient profiles in standard culture media. Microalgae synthesise and convert fatty acids (FA) into cell and thylakoid membrane lipids and energy-rich triacylglycerols. As bacteria potentially have dual effects on diatoms, such as provision of essential growth factors but competition for N and P-rich macronutrients, we tested the hypothesis that microbiome bacteria affect diatom FA profiles and result in qualitative and quantitative differences. The diatom Thalassiosira rotula was grown both, axenically and xenically, to stationary growth phase and sampled over the course of eight days. FA methylesters (FAME) profiles in algal extracts were analysed by GC-FID. Our results showed a difference in the relative FA composition as well as different concentrations of long-chain and very long-chain FA between treatments. Especially C16 FA were up to twice the concentration in axenic diatoms compared to xenic diatoms. This might indicate a disruption in mitochondrial beta-oxidation and thus less energy production.  In conclusion, this demonstrates a distinct microbial effect on the diatom FA profile.

Primary Presenter: Alessandra Kronschnabel, University of Bremen (alekro@uni-bremen.de)

Authors:

Alessandra Kronschnabel, Marine Chemistry, Department of Biology and Chemistry, University of Bremen; Section Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research  (alekro@uni-bremen.de)

Tom-Niklas Hollwedel, Marine Chemistry, Department of Biology and Chemistry, University of Bremen  (tomnikla@uni-bremen.de)

Jan Tebben, Section Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research  (jan.tebben@awi.de)

Tilmann Harder, Marine Chemistry, Department of Biology and Chemistry, University of Bremen; Section Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research  (t.harder@uni-bremen.de)