Surface-associated fucoxanthin mediates settlement of bacterial epiphytes on the rockweedFucus vesiculosus

Abstract

The chemical defence against microfouling in the brown seaweed Fucus vesiculosus was investigated and an inhibitor of bacterial settlement was isolated by bioassay-guided fractionation of non-polar surface extracts. UV-vis and mass spectrometry were used to identify the compound as the carotenoid fucoxanthin. The metabolite was tested at the natural concentration (in a surface volume based assay) against the settlement of four bacterial strains isolated from F. vesiculosus and 11 strains isolated from co-occurring algae and marine sediment. Surface concentrations between 1.4 and 6 μg cm(-2) resulted in 50% inhibition of four of these isolates, which were studied in more detail using a surface area-based assay, while a fifth isolate proved to be less sensitive. The presence of fucoxanthin on the surface of F. vesiculosus was demonstrated with two different surface extraction methods. Fucoxanthin was detected at concentrations between 0.7 and 9 μg cm(-2) on the algal surface. Fucoxanthin was still present at the algal surface after removal of associated diatoms through mechanical cleaning and germanium dioxide treatment and was thus mainly produced by F. vesiculosus rather than by diatoms. Thus, the photosynthetic pigment fucoxanthin appears to be ecologically relevant as a surface-associated antimicrobial agent, acting against the settlement of bacteria on the surface of the macroalga F. vesiculosus.

Defence Chemistry Modulation by Light and Temperature Shifts and the Resulting Effects on Associated Epibacteria of Fucus vesiculosus

“…This method is non-destructive to the epidermal cells of Fucus vesiculosus (see [10], online supplementary material). The extracts were vacuum-dried in a rota-evaporator and fractionated into non-polar (hexane) and polar (MeOH) extracts as described in [10] and stored at −20°C until further use. Fucoxanthin was quantified using a Macherey- Nagel (Düren, Germany) Nucleodur analytical normal phase Si column (4.6 mm×25 cm) on a Varian (Palo Alto, Cal.)…”

“…Detrimental effects include – but are not limited to – pathogenicity and attraction of macrofoulers. In order to limit these negative effects algal hosts often develop chemical defence strategies to control the colonisation by unwanted microbial foulers [9], [10].…”

“…Artificial substrates containing surface extracts of this alga maintain microbial communities that are relatively similar to those associated with F. vesiculosus [11]. Furthermore, the alga harbours at its surface fucoxanthin, dimethylsulfopropionate (DMSP) and proline, which all reduce bacterial settlement [10], [12]. This activity is strain-specific and while many strains are repelled by those compounds, others can be attracted [12].…”

“…To answer this question, surface concentrations of fucoxanthin, DMSP and proline were quantified after different temperature and light treatments. To evaluate the potential effect of changing concentrations upon microbial settlers two different approaches were chosen: (1) Detected concentrations were compared to the known necessary doses for half maximal settlement inhibition of potential bacterial colonisers of Fucus [10], [12]; and (2) detected concentrations were correlated to the relative abundance of major bacterial groups, that were identified in both experiments by in-depth sequencing of the 16S-rRNA gene. The concentration of mannitol, the main primary energy storage compound of Fucus , was used to quantify the degree of light limitation stress.…”

Dual effect of macroalgal extracts on growth of bacteria in Western Baltic Sea

“…Although several studies have shown stimulation of bacterial growth by algae, unfortunately, they have been based generally on exudates rather than extracts, and usually of phytoplanktonic sources (see Bell et al 1974, Larsson & Hagström 1979, Brock & Clyne 1984, Murray et al 1986, Coveney & Wetzel 1989. Algal exudates, unknown or partially specified, have been shown to significantly affect the community structure of bacteria in biofilms and in the pelagic zone near the macroalgae (see Dobretsov et al 2006, Lam & Harder 2007, Lachnit et al 2010, Persson et al 2011, Saha et al 2011, Sneed & Pohnert 2011a. It is well known that macroalgae release large amounts of organic carbon into the surrounding environment, providing nutrients for microorganisms (Koop et al 1982, Wada et al 2007.…”