Structuring effects of climate-related environmental factors on Antarctic microbial mat communities

Abstract

Both ground-based and satellite data show that parts of Antarctica have entered a period of rapid climate change, which already affects the functioning and productivity of limnetic ecosystems. To predict the consequences of future climate anomalies for lacustrine microbial communities, we not only need better baseline information on their biodiversity but also on the climaterelated environmental factors structuring these communities. Here we applied denaturing gradient gel electrophoresis (DGGE) of the small subunit ribosomal DNA (SSU rDNA) to assess the genetic composition and distribution of Cyanobacteria and eukaryotes in 37 benthic microbial mat samples from east Antarctic lakes. The lakes were selected to span a wide range of environmental gradients governed by differences in lake morphology and chemical limnology across 5 ice-free oases. Sequence analysis of selected DGGE bands revealed a high degree of potential endemism among the Cyanobacteria (mainly represented by Oscillatoriales and Nostocales), and the presence of a variety of protists (alveolates, stramenopiles and green algae), fungi, tardigrades and nematodes, which corroborates previous microscopy-based observations. Variation partitioning analyses revealed that the microbial mat community structure is largely regulated by both geographical and local environmental factors of which salinity (and related variables), lake water depth and nutrient concentrations are of major importance. These 3 groups of environmental variables have previously been shown to change drastically in Antarctica in response to climate change. Together, these results have obvious consequences for predicting the trajectory of biodiversity under changing climate conditions and call for the continued assessment of the biodiversity of these unique ecosystems.KEY WORDS: Antarctica · Climate change · Lake · Microbial mats · DGGE Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 59: [11][12][13][14][15][16][17][18][19][20][21][22][23][24] 2010 showing a rapid net cooling trend, such as the McMurdo Dry Valleys, where temperatures dropped by 0.7°C per decade between 1986 and 2000 (Doran et al. 2002). In east Antarctica, many regions are similarly experiencing marked changes in their weather, including increased wind speeds (Gillett & Thompson 2003) and changing patterns of snow and ice accumulation .The recent temperature and climate anomalies have also had impacts on both terrestrial and marine ecosystems in the Antarctic (Walther et al. 2002). Experiments measuring the ecological changes occurring at inland nunataks, dry valleys and coastal ice-free areas, have likened these ecosystems to 'canaries in a coalmine' and 'natural experiments' with which to identify biological responses to changing climate variables that are applicable on a wider (global) scale (see Convey 2001, Robinson et al. 2003, Lyons et al. 2006 for reviews). Already lacustrine ecosystems in some icefree regions have been shown to respond quickly to air t...

Late Holocene changes in cyanobacterial community structure in maritime Antarctic lakes

“…S2). Other sequences assigned to this genus were detected in Antarctic lakes and sediment cores Powell et al 2005;Coolen et al 2008;Verleyen et al 2010), but the sequences from Beak Island were different from those observed previously (Fig. S2).…”

“…In general, heterocystous cyanobacteria of the order Nostocales were more diverse in shallower Lake Beak-2 (four OTUs instead of two in Beak-1). These differences in community structure of cyanobacteria between the two lakes were likely related to differences in lake water depth, which has a profound influence on the light climate, which in turn is one of the major factors influencing the structure, diversity and formation of microbial mat communities in Antarctic lakes Verleyen et al 2005Verleyen et al , 2010. Many benthic cyanobacteria are adapted to high light levels, compared to, for instance, diatoms and mosses.…”

“…1). DGGE allows relatively rapid and inexpensive inventory of the most abundant taxa in microbial communities and was successfully used to study present-day cyanobacterial communities in Antarctic lakes (Taton et al 2003;Verleyen et al 2010). It separates PCR products of equal length, but different sequence (and thus melting temperature), on an acrylamide gel containing a gradient of chemical denaturants (Muyzer 1999).…”

Ecology and biogeochemistry of cyanobacteria in soils, permafrost, aquatic and cryptic polar habitats

“…However Nodularia, described regularly for Antarctic microbial mats, in particular in the McMurdo Ice Shelf, McMurdo Dry Valleys and Larsemann and Vestfold Hills (Taton et al 2003a;Jungblut et al 2005;Taton et al 2006), was not found at any of the Arctic sites. These findings, as well as others (Papke et al 2003;Verleyen et al 2010;Bahl et al 2011), suggest that cyanobacteria follow biogeographic patterns more typical of macroscopic organisms, and that both dispersal and/ or settlement limitation likely play important roles in explaining the distribution of cyanobacterial genotypes. In fact, the high morphological diversification of Phormidum autumnale, thriving in the Antarctic from Paleozoic times, suggests the coevolution of lineages and formation of complex associations, resulting in a specific endemic Antarctic cyanobacterial flora (Strunecky´ et al 2012).…”

Bacterial degradation of dissolved organic matter released by Planktothrix agardhii (Cyanobacteria)

“…Also, Langenheder et al (2004) showed an increase on bacterial richness by DGGE profile in batch cultures during the stationary growth phase of the bacteria. Different bands representing the same OTU in DGGE gel (Figure 2) may be due to ambiguities in the sequences (Verleyen et al, 2010), since differences less than 0.6% may result in different bands (Bondoso et al, 2014) and we defined OTUs at 97% identity threshold.…”