Comparative genomic analysis of symbiotic and free-living Fluviibacter phosphoraccumulans strains provides insights into the evolutionary origins of obligate Euplotes-bacterial endosymbioses.

Endosymbiosis is a widespread and important phenomenon requiring diverse model systems. Ciliates are a widespread group of protists that often form symbioses with diverse microorganisms. Endosymbioses between the ciliate Euplotes and heritable bacterial symbionts are common in nature, and four essential symbionts were described: Polynucleobacter necessarius, "Candidatus Protistobacter heckmanni," "Ca. Devosia symbiotica," and "Ca. Devosia euplotis." Among them, only the genus Polynucleobacter comprises very close free-living and symbiotic representatives, which makes it an excellent model for investigating symbiont replacements and recent symbioses. In this article, we characterized a novel endosymbiont inhabiting the cytoplasm of Euplotes octocarinatus and found that it is a close relative of the free-living bacterium Fluviibacter phosphoraccumulans (Betaproteobacteria and Rhodocyclales). We present the complete genome sequence and annotation of the symbiotic Fluviibacter. Comparative analyses indicate that the genome of symbiotic Fluviibacter is small in size and rich in pseudogenes when compared with free-living strains, which seems to fit the prediction for recently established endosymbionts undergoing genome erosion. Further comparative analysis revealed reduced metabolic capacities in symbiotic Fluviibacter, which implies that the symbiont relies on the host Euplotes for carbon sources, organic nitrogen and sulfur, and some cofactors. We also estimated substitution rates between symbiotic and free-living Fluviibacter pairs for 233 genes; the results showed that symbiotic Fluviibacter displays higher dN/dS mean value than free-living relatives, which suggested that genetic drift is the main driving force behind molecular evolution in endosymbionts. IMPORTANCE: In the long history of symbiosis research, most studies focused mainly on organelles or bacteria within multicellular hosts. The single-celled protists receive little attention despite harboring an immense diversity of symbiotic associations with bacteria and archaea. One subgroup of the ciliate Euplotes species is strictly dependent on essential symbionts for survival and has emerged as a valuable model for understanding symbiont replacements and recent symbioses. However, almost all of our knowledge about the evolution and functions of Euplotes symbioses comes from the Euplotes-Polynucleobacter system. In this article, we report a novel essential symbiont, which also has very close free-living relatives. Genome analysis indicated that it is a recently established endosymbiont undergoing genome erosion and relies on the Euplotes host for many essential molecules. Our results provide support for the notion that essential symbionts of the ciliate Euplotes evolve from free-living progenitors in the natural water environment.

[Effects of Nano-copper Oxide on Physiobiochemical Properties of Brassica chinensis L. and Its Heavy Metal Accumulation Under Cadmium Stress].

To investigate the effects of nano-copper oxide (CuO NPs) on plant growth, physio-biochemical characteristics, and heavy metal content under cadmium stress, a hydroponics experiment was conducted on the effects of single and combined treatments of CuO NPs (0, 10, 20, and 50 mg·L-1) and Cd (0, 1, and 5 µmol·L-1) on the fresh weight, photosynthetic pigment content, MDA content, antioxidant enzyme activity (CAT, POD, SOD, and GR), and Cu and Cd contents in Brassica chinensis L. The results showed that under the single addition of CuO NPs, the fresh weight and activities of CAT, POD, and GR were inhibited as a whole. Photosynthetic pigment content and SOD activity increased first and then decreased with the increase in CuO NPs concentration, whereas MDA content in leaves and roots, and Cu content in subcells of B. chinensis L. increased with the increasing of CuO NPs. As compared with that in the control, CuO NPs promoted the growth of B. chinensis L., and the fresh weight increased by 8.70%-44.87% at 1 µmol·L-1 Cd. When the content of Cd was up to 5 µmol·L-1, a low content (10 mg·L-1) of CuO NPs promoted the growth of B. chinensis L., whereas a high concentration (50 mg·L-1) showed an inhibitory effect. The addition of CuO NPs could increase photosynthetic pigment and MDA contents under different Cd stress, and MDA content in leaves and roots of B. chinensis L. increased by 4.34%-36.27% and 13.43%-131.04%, respectively, than that in the control groups. Under the same concentration of 1 µmol·L-1 Cd, the addition of CuO NPs decreased the activities of CAT and GR, whereas the activity of POD increased. When the content of Cd was up to 5 µmol·L-1, CuO NPs increased the POD activity and inhibited the activity of SOD and GR. The activities of CAT and CAT in the leaves of B. chinensis L. initially showed an increasing and then decreasing trend. CuO NPs and Cd showed antagonistic effects, the maximum reduction of Cd content in leaves and roots of Brassica chinensis L. under 1 µmol·L-1 Cd treatment was 45.64% and 33.39%, and that under 5 µmol·L-1 Cd treatment was 18.25% and 25.35%, respectively. The content of Cu and Cd in subcellular organs of the plants decreased, but the proportion of soluble components increased. These results indicated that CuO NPs at low concentrations promoted plant growth under Cd stress and further inhibited the absorption of Cd but increased the oxidative damage to B. chinensis L.

Scientific profile of brain-computer interfaces: Bibliometric analysis in a 10-year period.

BACKGROUND: With the tremendous advances in the field of brain-computer interfaces (BCI), the literature in this field has grown exponentially; examination of highly cited articles is a tool that can help identify outstanding scientific studies and landmark papers. This study examined the characteristics of 100 highly cited BCI papers over the past 10 years. METHODS: The Web of Science was searched for highly cited papers related to BCI research published from 2006 to 2015. The top 100 highly cited articles were identified. The number of citations and countries, and the corresponding institutions, year of publication, study design, and research area were noted and analyzed. RESULTS: The 100 highly cited articles had a mean of 137.1(SE: 15.38) citations. These articles were published in 45 high-impact journals, and mostly in TRANSACTIONS ON BIOMEDICAL ENGINEERING (n=14). Of the 100 articles, 72 were original articles and the rest were review articles. These articles came from 15 countries, with the USA contributing most of the highly cited articles (n=52). Fifty-seven institutions produced these 100 highly cited articles, led by Duke University (n=7). CONCLUSIONS: This study provides a historical perspective on the progress in the field of BCI, allows recognition of the most influential reports, and provides useful information that can indicate areas requiring further investigation.