Morphological And Phylogenetic Study Of Oomycetes In Three Tropical Reservoirs

Oomycetes are also called fungal-like organisms based on their mode of life and morphological similarities with the fungi, although they are not phylogenetically related to the Kingdom Fungi. Their diversity has been underexplored in lentic habitats of tropical regions, though in Brazil special focus has been placed on lotic ecosystems. The aim of this study was to evaluate the occurrence and distribution of the Oomycetes, as identified by observation of morphologies and phylogenetic placement, in the water column and sediments of three tropical reservoirs, and to correlate their occurrence with the trophic state of the aquatic system. For this, samples from the water column and the surface sediments were collected and baited with different substrates. The Oomycetes obtained were isolated, purified in agar media and included in phylogenetic reconstructions (ITS, LSU rDNA and COX1 mDNA) to corroborate their morphological identification. During the study, 176 samples were collected, and 83 specimens were isolated in baits and recognized by microscopic examination, corresponding to 27 taxa. Among these, 25 could be purified and identified to genus or species based on morphological and molecular data, with Pythium and Achlya species most commonly sampled. In general, most taxa occurred in mesotrophic conditions, however, Achlya caroliniana and Pythium middletonii were isolated from oligotrophic sites. The phylogenetic reconstructions of Peronosporales showed that several strains do not match with any described or sequenced taxa. Our data indicate that reservoirs represent interesting ecosystems to address diversity studies since new records and unknown species were detected in our survey. This study unprecedentedly evaluates the occurrence and distribution of Oomycetes in tropical reservoirs from South America and discusses for the first time the diversity of these organisms in sediments of Brazilian reservoirs.