Consortia cultivation

Invasive macrophytes constitute an environmental problem in aquatic ecosystems. They can also have health issues since periphytons colonizing aquatic roots are hot spot of mercury methylation. Being at the base of the trophic chain, the methylmercury neurotoxin produced bioamplify through the trophic chain.In this work, a consortia cultivation approach was applied in order to investigate methylmercury producers in the periphyton developing on the aquatic roots of Ludwigia grandiflora, an invasive macrophyte covering the shores of Sanguinet lake (SW France). Five growing conditions were applied in order to favor growth of different sulfate reducer taxa, which are the principal mercury methylators in this periphyton. We could grow 33 consortia containing putative Hg methylators. Based on the sequence of HgcA (essential enzyme for Hg methylation), the consortia could be grouped in 5 main clusters, affiliated with the Desulfovibrionaceae, the Desulfobulbaceae and the Syntrophbacteraceae. One main cluster (related to Desulfovibrionaceae) showed high diverse sequences, without any close representative. We were also able to grow species that are not isolated to date, probably because they profit from metabolites produced by other members of the consortium. The analysis of the microbial composition of the consortia allowed us to propose a model concerning the microbial interactions that can take place within this complex environment.In conclusion, by applying consortia cultivation approaches, we could grow mercury methylators that are minor in the community, difficult to cultivate, not isolated to date, that drive mercury methylation in the periphyton of L. grandiflora.