Lakes have a central role in the carbon cycle of the boreal landscape. These systems typically stratify in summer and their hypolimnetic microbial communities influence burial of biogenic organic matter in sediments. The composition of bacterial communities in these suboxic habitats was studied by pyrosequencing of 16S rRNA amplicons from five lakes with variable dissolved organic carbon (DOC) concentrations. Bacterioplankton communities in the hypolimnetic waters were clearly different from the surface layer with candidate division OD1, Chlorobi and Bacteroidetes as dominant community members. Several operational taxonomic units (OTUs) affiliated with candidate division OD1 were abundant and consistently present in the suboxic hypolimnion in these boreal lakes. The overall representation of this group was positively correlated with DOC and methane concentrations. Network analysis of time-series data revealed contrasting temporal patterns but suggested similar ecological roles among the abundant OTUs affiliated with candidate division OD1. Together, stable isotope data and taxonomic classification point to methane oxidation and autotrophic denitrification as important processes in the suboxic zone of boreal lakes. Our data revealed that while hypolimnetic bacterial communities are less dynamic, they appear to be more diverse than communities from the oxic surface layer. An appreciable proportion of the hypolimnetic bacteria belong to poorly described phyla.
16S rRNA; 454 pyrosequencing; anoxic; diversity; hypolimnion; OD1
The bacterial signaling molecule, cyclic diguanosine monophosphate (c-di-GMP), plays a key role in controlling biofilm formation, organelle formation for motility, cell-cycle differentiation, and pathogenic virulence, among many other functions.(Cotter & Stibitz 2007, Hengge 2009, Romling & Amikam 2006, Schirmer & Jenal 2009, Tamayo et al. 2007) It acts by relaying extracellular signals to internal receptors, including PilZ proteins(Ko et al. 2010) as well as two different classes of riboswitches.(Kulshina et al. 2009, Lee et al. 2010, Smith et al. 2009, Smith et al. 2011, Sudarsan et al. 2008) It has widespread consequences for human health, and current research is actively exploring its molecular mechanisms. The convenient one-flask, gram-scale synthesis of c-di-GMP described here will facilitate these efforts.
Stable isotope analyses are increasingly employed to characterise population niche widths. The convex hull area (TA) in a δ13C–δ15N biplot has been used as a measure of isotopic niche width, but concerns exist over its dependence on sample size and associated difficulties in among-population comparisons. Recently a more robust method was proposed for estimating and comparing isotopic niche widths using standard ellipse areas (SEA), but this approach has yet to be tested with empirical stable isotope data. The two methods measure different kind of isotopic niche areas, but both are now widely used to characterise isotopic niche widths of populations. We used simulated data and an extensive empirical dataset from two fish populations to test the influence of sample size on the observed isotopic niche widths (TA and SEA). We resampled the original datasets to generate 5000 new samples for different numbers of observations from 5 to 80 to examine the statistical distributions of niche area estimates for increasing sample size. Our results illustrate how increasing sample size increased the observed TA; even sample sizes much higher than n = 30 did not improve the precision for the TA method. SEA was less sensitive to sample size, but the natural variation in our empirical fish δ13C and δ15N data still resulted in considerable uncertainty around the mean estimates of niche width, reducing the precision particularly with sample sizes n<30. These results confirm that the TA method is less appropriate for estimating population isotopic niche areas using small samples, especially when considerable population level isotope variation is expected. The results also indicate a need for caution when using SEA as a measure of trophic niche widths for consumers, particularly with low sample sizes and when the distribution and range for population isotope values are not known.
New legislation in Greece towards presumed consent for organ donation, effective as of June 2013, has come at a critical moment. This pilot study aims to explore awareness, specific concerns and intentions about the new organ donation framework among patients attending Greek general practices in a rural and urban setting. Only 2.6% of respondents had a donor card, a mere 9.6% was aware of new legislation, whereas only 3.8% considered that the public had been adequately informed. Higher income respondents were more likely to be aware that they would be considered organ donors upon death, unless declared differently. Urban practice respondents were less likely to have previously discussed with a significant other their intentions in regards to presumed consent. One quarter of all respondents (22.4%) intended to carry out their right to prohibit organ removal upon death. Survey results reveal that organ donation reform has yet to be disseminated by the Greek society, underscoring the urgency for targeted information campaigns.
organ donation; presumed consent; opt-out; general practice; Greece