Browsing by Author "Chen, Feng"

Bacteria in the Roseobacter lineage have been studied extensively due to their significant biogeochemical roles in the marine ecosystem. However, our knowledge on bacteriophage which infects the Roseobacter clade is still very limited. Here, we report a new bacteriophage, phage DSS3 Phi 8, which infects marine roseobacter Ruegeria pomeroyi DSS-3. DSS3 Phi 8 is a lytic siphovirus. Genomic analysis showed that DSS3 Phi 8 is most closely related to a group of siphoviruses, CbK-like phages, which infect freshwater bacterium Caulobacter crescentus. DSS3 Phi 8 contains a smaller capsid and has a reduced genome size (146 kb) compared to the CbK-like phages (205-279 kb). DSS3 Phi 8 contains the DNA polymerase gene which is closely related to T7-like podoviruses. DSS3 Phi 8 also contains the integrase and repressor genes, indicating its potential to involve in lysogenic cycle. In addition, four GTA (gene transfer agent) genes were identified in the DSS3 Phi 8 genome. Genomic analysis suggests that DSS3 Phi 8 is a highly mosaic phage that inherits the genetic features from siphoviruses, podoviruses, prophages and GTAs. This is the first report of CbK-like phages infecting marine bacteria. We believe phage isolation is still a powerful tool that can lead to discovery of new phages and help interpret the overwhelming unknown sequences in the viral metagenomics.

Aims. We study the magnetic field and current structure associated with a coronal loop. Through this we investigate to what extent the assumptions of a force-free magnetic field break down and where they might be justified. Methods. We analyze a three-dimensional (3D) magnetohydrodynamic (MHD) model of the solar corona in an emerging active region with the focus on the structure of the forming coronal loops. The lower boundary of this simulation is taken from a model of an emerging active region. As a consequence of the emerging magnetic flux and the horizontal motions at the surface a coronal loop forms self-consistently. We investigate the current density along magnetic field lines inside (and outside) this loop and study the magnetic and plasma properties in and around this loop. The loop is defined as the bundle of field lines that coincides with enhanced emission in extreme UV. Results. We find that the total current along the emerging loop changes its sign from being antiparallel to parallel to the magnetic field. This is caused by the inclination of the loop together with the footpoint motion. Around the loop, the currents form a complex non-force-free helical structure. This is directly related to a bipolar current structure at the loop footpoints at the base of the corona and a local reduction of the background magnetic field (i.e., outside the loop) caused by the plasma flow into and along the loop. Furthermore, the locally reduced magnetic pressure in the loop allows the loop to sustain a higher density, which is crucial for the emission in extreme UV. The action of the flow on the magnetic field hosting the loop turns out to also be responsible for the observed squashing of the loop. Conclusions. The complex magnetic field and current system surrounding it can only be modeled in 3D MHD models where the magnetic field has to balance the plasma pressure. A one-dimensional coronal loop model or a force-free extrapolation cannot capture the current system and the complex interaction of the plasma and the magnetic field in the coronal loop, despite the fact that the loop is under low-β conditions.

Platelets are a critical element in coagulation and inflammation, and activated platelets are linked to cancer risk through diverse mechanisms. However, a causal relationship between platelets and risk of lung cancer remains unclear.