Antarctic Microbial Biodiversity : the Importance of Geographical Versus Ecological Factors

Antarctic Microbial BIOdiversity : the importance of geographical versus ecological fac tors

D. Obbels1,, P. De Carvalho Maalouf2, A. De Wever2, K. Peeters3, A. Willems3, E. Verleyen1, W. Wyverman1, and A. Wilmotte2 1Protistology and Aquatic Ecology, Ghent University, Gent, Belgium. 2Centre for Protein Engineering, University of Liège, Liège, Belgium; and 3Lab of Microbiology, Ghent University, Gent, Belgium.

Antarctica is a prime region to test whether microbes have a biogeography and to study their metacommunity dynamics, because (i) it is isolated from the other continents, (ii) its extreme environmental conditions allow microorganisms to dominate its ecosystems, and (iii) lacustrine and terrestrial habitats occur isolated in a matrix of ice and ocean. We compiled a large set of samples from benthic microbial mats from Antarctic lakes in different ice-free regions and used a polyphasic approach to study their microbial biodiversity by combining morphological characterization of diatoms with molecular techniques such as Denaturing Gradient Gel Electrophoresis (green algae and cyanobacteria), 454 pyrosequencing and cultivation (prokaryotes).

A variation partitioning analysis of a selection of 41 samples revealed that geographical variables explained a significant part of the variation in the eukaryotic microorganisms, whereas they failed to significantly explain patterns in the prokaryotes. The incidence of endemism also differed between the different taxonomic groups. For cyanobacteria, DGGE bands of 59 samples were grouped into 39 OTUs. The majority (64.9%) had a cosmopolitan distribution whereas the rest seemed to be restricted to polar and alpine environments. 16.2% were restricted to Antarctica. Diatoms showed a relatively high incidence of endemism (49%) based on the morphospecies concept. For bacteria, 42% of phylotypes based on the 16S rRNA gene are at present only known from Antarctica. A high number of prokaryotic sequences obtained by pyrosequencing and almost 20% of the Chlorophyte sequences (DGGE) had less than 97.5% similarity with a sequence in public databases, which might indicate the presence of new species and potential endemics.

The contrasting patterns in the metacommunity dynamics and the incidence of endemism between the different microbial groups might be related to cell size and life cycle characteristics, such as the formation of spores and the presence of a sexual phase. We conclude that findings from one particular microbial group cannot be generalized to microbes as a whole.