BIOGEOGRAPHIC PATTERNS IN ANTARCTIC LACUSTRINE PROKARYOTES

anglais. Amplified climate change, increased human activity and the introduction of alien species likely form the biggest threat to Antarctic terrestrial ecosystems through range size expansions and contractions, regional extirpation and impacts on ecosystem functions. Despite their crucial role in the functioning of Antarctic terrestrial ecosystems , little is known about the present -day diversity and biogeography of microorganisms such as prokaryotes and microeukaryotes in the Antarctic Biogeographic Realm. Furthermore, identification of the key processes underlying microbial biodiversity dynamics is essential to understand and predict the consequences of global change on Antarctic lacustrine ecosystems. We analysed bacterial biodiversity in a total of 152 lacustrine microbial mat samples, distributed over the three main Biogeographic regions in the Antarctic Realm, including continental Antarctica, Maritime Antarctica and the Sub-Antarctic Islands comprising the southern Indian Ocean Province (SIOP) and the southern Pacific Ocean Province (SPOP). We targeted the V1-V3 variable regions of the 16S rRNA gene. Amplicon sequencing was done on an Illumina PE300 MiSeq. Sequences were processed using Usearch and Uparse, Mothur and custom scripts for basic parsing. An OTU cut-off was defined at 97 % sequence similarity, and sequences were mapped against a local GreenGenes database. Downstream analyses were performed using several R packages. We obtained about three million high quality sequences, with an average length of 500 bp. Sequences belonged to 8237 OTUs, and were distributed over 51 phyla and 366 genera. In addition, 649 OTUs remained unclassified at the phylum level and 6263 at the genus level. Mean OTU richness differed strongly between the four biogeographic regions. The lakes from Maritime Antarctica had a higher richness than those from Continental Antarctica. Interestingly, in sub-Antarctica OTU richness was strongly variable, with Marion Island (SIOP) having the lowest and Macquarie Island (SPOP) having on average the highest diversity of all studied regions. Multivariate Analyses showed that microbial community composition varied between biogeographic regions, with Macquarie Island being most different from the other regions. Continental Antarctica, Maritime Antarctica and the lakes from the SIOP share many OTUs, both in the case of Cyanobacteria and other bacteria, but are also characterised by a considerable number of unique OTUs. Within Antarctica, some regions harbour distinct bacterial communities such as the lakes in Schirmacher Oasis, Dronning Maud Land, and those from the eastern and western part of the Antarctic Peninsula.

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