Eukaryotic microbial life at abyssal depths remains "uncharted territory" in eukaryotic microbiology. No phylogenetic surveys have focused on the largest benthic environment on this planet, the abyssal plains. Moreover, knowledge of the spatial patterns of deep-sea community structure is scanty, and what little is known originates primarily from morphology-based studies of foraminiferans. Here we report on the great phylogenetic diversity of microbial eukaryotic communities of all 3 abyssal plains of the southeastern Atlantic Ocean-the Angola, Cape, and Guinea Abyssal Plains-from depths of 5,000 m. A high percentage of retrieved clones had no close representatives in genetic databases. Many clones were affiliated with parasitic species. Furthermore, differences between the communities of the Cape Abyssal Plain and the other 2 abyssal plains point to environmental gradients apparently shaping community structure at the landscape level. On a regional scale, local species diversity showed much less variation. Our study provides insight into the community composition of microbial eukaryotes on larger scales from the wide abyssal sea floor realm and marks a direction for more detailed future studies aimed at improving our understanding of deep-sea microbes at the community and ecosystem levels, as well as the ecological principles at play.benthic | clone library | deep sea | protists | protozoa

OBJECTIVECarotid intima-media thickness (CIMT) is a marker of subclinical organ damage and predicts cardiovascular disease (CVD) events in the general population. It has also been associated with vascular risk in people with diabetes. However, the association of CIMT change in repeated examinations with subsequent CVD events is uncertain, and its use as a surrogate end point in clinical trials is controversial. We aimed at determining the relation of CIMT change to CVD events in people with diabetes.RESEARCH DESIGN AND METHODSIn a comprehensive meta-analysis of individual participant data, we collated data from 3,902 adults (age 33–92 years) with type 2 diabetes from 21 population-based cohorts. We calculated the hazard ratio (HR) per standard deviation (SD) difference in mean common carotid artery intima-media thickness (CCA-IMT) or in CCA-IMT progression, both calculated from two examinations on average 3.6 years apart, for each cohort, and combined the estimates with random-effects meta-analysis.RESULTSAverage mean CCA-IMT ranged from 0.72 to 0.97 mm across cohorts in people with diabetes. The HR of CVD events was 1.22 (95% CI 1.12–1.33) per SD difference in mean CCA-IMT, after adjustment for age, sex, and cardiometabolic risk factors. Average mean CCA-IMT progression in people with diabetes ranged between −0.09 and 0.04 mm/year. The HR per SD difference in mean CCA-IMT progression was 0.99 (0.91–1.08).CONCLUSIONSDespite reproducing the association between CIMT level and vascular risk in subjects with diabetes, we did not find an association between CIMT change and vascular risk. These results do not support the use of CIMT progression as a surrogate end point in clinical trials in people with diabetes.

Heterotrophic flagellates are key components of all ecosystems. Understanding the patterns of biodiversity of these organisms is thus particularly important. Here we analyzed the intraspecific diversity of 10 morphospecies of heterotrophic flagellates comprising representatives of the Apusozoa (2 morphospecies) and Kinetoplastea (8 morphospecies), all belonging to the most common flagellates with worldwide distribution. Most morphospecies showed a mixing of lineages isolated from diverse habitats, indicating that some lineages of these morphospecies had been able to colonize different habitats several times. Furthermore, our results revealed remarkable levels of genetic divergence within most of the morphospecies studied, underlining the difficulty of correctly determining species by means of morphology alone. Many cryptic or pseudocryptic species seem to occur. Our results revealed clear divergence between marine and freshwater lineages of the morphospecies Ancyromonas sigmoides, showing that freshwater lineages have not been able to colonize marine environments and marine lineages have not been able to colonize freshwater environments for a long time.

Whereas much is known about the biodiversity of prokaryotes and macroorganisms in the deep sea, knowledge on the biodiversity of protists remains very limited. Molecular studies have changed our view of marine environments and have revealed an astonishing number of previously unknown eukaryotic organisms. Morphological findings have shown that at least some widely distributed nanoflagellates can also be found in the deep sea. Whether these flagellates have contact with populations from other habitats is still uncertain. We performed a molecular comparison of strains isolated from deep-sea sediments (> 5000 m depth) and surface waters on the basis of their small subunit ribosomal DNA (SSU rDNA). Sequences of Rhynchomonas nasuta, Amastigomonas debruynei, Ancyromonas sigmoides, Cafeteria roenbergensis and Caecitellus parvulus were analysed, and 2 contrasting results obtained. Firstly, we found nearly identical genotypes within 1 morphospecies (C. roenbergensis), and secondly, quite different genotypes within certain morphospecies (R. nasuta, A. sigmoides and C. parvulus). In addition, high genetic distances between the different strains of A. sigmoides and C. parvulus indicate that these morphospecies should be divided into different at least genetically distinguishable species. In contrast, some heterotrophic nanoflagellates must indeed be regarded as being cosmopolitan. According to the low genetic distances between isolates of R. nasuta, A. debruynei and C. roenbergensis as well as between our isolates of A. sigmoides from deep-sea and surface waters, exchanges between these habitats and also on a global scale might be possible. In summary, our results show that 3 morphospecies obviously contain several cryptic species, while some of the investigated genotypes occur in both deep-sea as well as in surface waters.

Knowledge of the spatial scales of diversity is necessary to evaluate the mechanisms driving biodiversity and biogeography in the vast but poorly understood deep sea. The community structure of kinetoplastids, an important group of microbial eukaryotes belonging to the Euglenozoa, from all abyssal plains of the South Atlantic and two areas of the eastern Mediterranean was studied using partial small subunit ribosomal DNA gene clone libraries. A total of 1364 clones from 10 different regions were retrieved. The analysis revealed statistically not distinguishable communities from both the South-East Atlantic (Angola and Guinea Basin) and the South-West Atlantic (Angola and Brazil Basin) at spatial scales of 1000-3000 km, whereas all other communities were significantly differentiated from one another. It seems likely that multiple processes operate at the same time to shape communities of deep-sea kinetoplastids. Nevertheless, constant and homogenous environmental conditions over large spatial scales at abyssal depths, together with high dispersal capabilities of microbial eukaryotes, maintain best the results of statistically indistinguishable communities at larger spatial scales.