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Free keywords:
macroalga; bacterial community; surface chemistry; antifouling; settlement control; seaweed
Abstract:
The macroalga Fucus vesiculosus carries a specific community of surface bacteria.
To identify chemical compounds that possibly mediate abundance and
community composition of algae-associated bacteria, we tested the effect of
surface-available algal compounds on bacterial settlement and community
composition under field conditions. Compounds on algal thalli were separated
from the surface by extraction with organic solvents and investigated on
growth inhibition and settlement of bacterial isolates. Based on in vitro data,
partially purified extract fractions were then exposed to bacterial colonizers
in vivo followed by bacterial enumeration and community analysis. The polar
fraction of the algal surface extract revealed a significant profouling effect for
Vibrionales, whereas the nonpolar fraction – containing the xanthophyll pigment
fucoxanthin and other unidentified nonpolar surface compounds –
revealed a significant 80% reduction of surface colonizing bacteria. The analysis
of bacterial surface communities by 454 pyrosequencing demonstrated that the
antifouling activity of nonpolar algal surface compounds was targeting the
abundance of natural bacterial colonizers rather than the relative composition
of bacterial members within the community. Moreover, the bacterial community
composition on F. vesiculosus was markedly different from artificial control
substrates and chemically manipulated experimental treatments, suggesting
that other, nonextractable surface features and/or physical properties render
algal-specific epiphytic bacterial communities.
