Effects of Saharan dust on the microbial community during a large in situ mesocosm experiment in the NW Mediterranean Sea
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Laghdass M, Blain S, Besseling M, Catala P, Guieu C, Obernosterer I
Aquatic Microbial Ecology
Saharan dust deposition, mesocosms, CE-SSCP, CARD-FISH, clone libraries, Alteromonas macleodii, NW Mediterranean Sea, Corsica, 52 m3
The response of the microbial community to Saharan dust deposition was investigatedin 6 large mesocosms (52 m3) deployed at an oligotrophic coastal site in the NW Mediterranean Seain June 2008 (DUNE project). The mesocosms represented well the environmental conditionsobserved at the study site during the 8 d experimental period, and the triplicate mesocosms exhibitedhigh reproducibility for each treatment. Dust deposition resulted in an increase in chlorophyll a concentration(0.22 ± 0.03 ?g l–1), as compared to that in the control treatments (0.12 ± 0.01 ?g l–1), but notreatment effect was observed for bacterial heterotrophic abundance at 5 m depth. Results from thefingerprinting technique CE-SSCP indicate a temporal evolution of the structure of the total (16SrRNA gene) and active (16S rRNA transcripts) bacterial community, and Saharan dust deposition hada noticeable structuring effect on the active bacterial community. Combining results from 16S rRNAgene clone libraries and CE-SSCP indicates that the relative contribution of Alteromonas macleodiito the active bacterial community was enhanced 2-fold following dust addition. The 2 operational taxonomicunits (OTUs) Thiothrix and Alteromonas, belonging to Gammaproteobacteria, and the BacteroidetesOTU NS5-1 were specific to the clone libraries from the dust-amended mesocosms or moreabundant in these than in the control ones. CARD-FISH analyses, however, indicate that these OTUshad overall low abundances (1 to 5% of total DAPI-counts). Despite the pronounced temporal trendobserved during the experimental period, dust deposition had a small, but noticeable structuringeffect on the heterotrophic bacterial community that was detectable only at the OTU level at 99%similarity of the 16S rRNA gene.
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