Résultat de la recherche
High-throughput sequencing reveals diverse oomycete communities in oligotrophic peat bog micro-habitat
Oomycete diversity has been generally underestimated, despite their ecological and economic importance. Surveying unexplored natural ecosystems with up-to-date molecular diversity tools can reveal the existence of unsuspected organisms. Here, we have explored the molecular diversity of five microhabitats located in five different oligotrophic peat bogs in the Jura Mountains using a high-throughput sequencing approach (Illumina HiSeq 2500). We found a total of 34 different phylotypes distributed in all major oomycete clades, and comprising sequences affiliated to both well-known phylotypes and members of undescribed, basal clades. Parasitic species, including obligate forms were well-represented, and phylotypes related to highly damaging invasive pathogens (Aphanomyces astaci: X1100 and Saprolegnia parasitica: X1602) were retrieved. Microhabitats differed significantly in their community composition, and many phylotypes were strongly affiliated to free water habitats (pools). Our approach proved effective in screening oomycete diversity in the studied habitat, and could be applied systematically to other environments and other fungal and fungal-like groups.
Incipient loss of flagella in the genus Geolegnia: the emergence of a new clade within Leptolegnia?
The genus Geolegnia represents a poorly documented group of saprolegnialean oomycetes isolated from soils as free-living organisms. Although it is morphologically similar to the facultative parasitic genus Leptolegnia, Geolegnia presents the uncommon property of having lost a flagellate stage in its lifecycle. Based on ITS and large subunit (LSU) rRNA sequence data, we show Geolegnia to be basal to Leptolegnia, and also introduce Geolegnia helicoides sp. nov. Using sequence data of Leptolegnia available in GenBank, supplemented by data derived from culture collections, we show that Geolegnia is nested within Leptolegnia, a genus characterised by its “conventional” biflagellate life cycle. The emergence of Geolegnia is therefore seen as a recent event, and we suggest here an evolutionary context where this loss might have been advantageous. Based on this study, Leptolegnia remains paraphyletic, awaiting the redefinition of genera in this complex.