Erwan Le Gélébart

Macroalgae surface is a highly competitive environment as it provides a shelter rich in nutrients for a
wide variety of organisms (1). Seaweed–bacterial associations have been studied from the end of the
19 th century (2) . Molecular investigations have shown that most of these associations are highly
specific (3)(4). Bacteria isolated from their host can be related to a wide range of activity like anti
settlement of invertebrate larvae, growth-enhancing, quorum sensing, morphogenesis, nitrogen
fixation, settlement of zoospores, antibacterial activity (2). Host-Microbiota balance is a key factor to
keep macroalgae in good conditions.
Like for marine sponges it’s not easy to determine who is responsible for the production of specific
compounds, is it the sponge, is it bacteria sheltered by the sponge or is it the association of both?
Today we started to investigate the relation between brown algae gametophytes and their
microbiota and its implication on biomass phytochemistry.
After achieving axenic cultures of brown algae gametophytes, axenic biomass was produced in order
to compare its phytochemical content with biomass grown with its microbiota. Ethanol and water
extracts of axenic and non-axenic biomasses were analysed through Thin Layer Chromatography
(TLC) and High Pressure Liquid Chromatography (HPLC) coupled with Diode Array Detector (DAD) and
Charged Aerosol Detector (CAD).
Results obtained from ethanol and water extracts showed clear differences with apparition and
disapparition of peaks from low polarity to high polarity depending on the presence or the absence
of the associated microbiota.
In the light of these results, controlling and preserving the integrity and the quality of this microbiota
in culture, for instance in avoiding any step of axenisation, could lead us to produce original
compounds or to overexpress molecules. Microbiota appears to have a major role in the
phytochemical composition of gametophytes of brown macroalga.