In situ observations and modelling revealed environmental factors favouring occurrence of Vibrio in microbiome of the pelagic Sargassum responsible for strandings

2020

Article référencé dans le Web of Science WOS:000581049800022

Michotey V., Blanfuné A., Chevalier Cristèle, Garel M., Diaz F., Berline L., Le Grand L., Armougom Fabrice, Guasco S., Ruitton S., Changeux Thomas, Belloni B., Blanchot Jean, Ménard Frédéric, Thibaut T.

Science of the Total Environment, 2020, 748, 141216 [10 p.] ISSN 0048-9697

Historically, pelagic Sargassum were only found in the Sargasso Sea. Since 2011, blooms were regularly observed in warmer water, further south. Their developments in Central Atlantic are associated with mass strandings on the coasts, causing important damages and potentially dispersion of new bacteria. Microbiomes associated with pelagic Sargassum were analysed at large scale in Central Atlantic and near Caribbean Islands with a focus on pathogenic bacteria. Vibrio appeared widely distributed among pelagic Sargassum microbiome of our samples with higher occurrence than previously found in Mexico Gulf. Six out the 16 Vibrio-OTUs (Operational Taxonomic Unit), representing 812 +/- 13.1% of the sequences, felt in cluster containing pathogens. Among the four different microbial profiles of pelagic Sargassum microbiome, Vibrio attained about 2% in two profiles whereas it peaked, in the two others, at 6.5 and 26.8% respectively, largely above the concentrations found in seawater surrounding raft (0.5%). In addition to sampling and measurements, we performed backward lagrangian modelling of trajectories of rafts, and rebuilt the sampled rafts environmental history allowing us to estimate Sargassum growth rates along raft displacements. We found that Vibrio was favoured by high Sargassum growth rate and in situ ammonium and nitrite, modelled phosphate and nitrate concentrations, whereas zooplankters, benthic copepods, and calm wind (proxy of raft buoyancy near the sea surface) were less favourable for them. Relations between Vibrio and other main bacterial groups identified a competition with Alteromonas. According to forward Lagrangian tracking, part of rafts containing Vibrio could strand on the Caribbean coasts, however the strong decreases of modelled Sargassum growth rates along this displacement suggest unfavourable environment for Vibrio. For the conditions and areas observed, the sanitary risk seemed in consequence minor, but in other areas or conditions where high Sargassum growth rate occurred near coasts, it could be more important.

Sciences fondamentales / Techniques d'analyse et de recherche [020] ; Limnologie biologique / Océanographie biologique [034] ; Biotechnologies [084]

ATLANTIQUE

Fonds IRD [F B010079905]

fdi:010079905