Guide-free Cas9 from pathogenic Campylobacter jejuni bacteria causes severe damage to DNA

CRISPR-Cas9 systems are enriched in human pathogenic bacteria and have been linked to cytotoxicity by an unknown mechanism. Here, we show that upon infection of human cells, Campylobacter jejuni secretes its Cas9 (CjeCas9) nuclease into their cytoplasm. Next, a native nuclear localization signal enables CjeCas9 nuclear entry, where it catalyzes metal-dependent nonspecific DNA cleavage leading to cell death. Compared to CjeCas9, native Cas9 of Streptococcus pyogenes (SpyCas9) is more suitable for guide-dependent editing. However, in human cells, native SpyCas9 may still cause some DNA damage, most likely because of its ssDNA cleavage activity. This side effect can be completely prevented by saturation of SpyCas9 with an appropriate guide RNA, which is only partially effective for CjeCas9. We conclude that CjeCas9 plays an active role in attacking human cells rather than in viral defense. Moreover, these unique catalytic features may therefore make CjeCas9 less suitable for genome editing applications

The GEOTRACES Intermediate Data Product 2014

The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-? data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes

Dissolved and dissolvable iron concentrations and ligand characteristics in samples taken during POLARSTERN expedition ARK-XXII/2 to the Arctic Ocean

The speciation of iron was investigated in three shelf seas and three deep basins of the Arctic Ocean in 2007. The dissolved fraction ( 3 nM on the shelves and [TDFe] 13.5) in the Nansen and Amundsen basins than in the Makarov Basin (log alpha <13) where the sources of Fe and ligands were limited. The ligands became nearly saturated with depth in the Amundsen and Nansen Basins, favoring Fe removal in the deep ocean, whereas in the deep Makarov Basin, they became unsaturated with depth. Still here scavenging occurred. Although scavenging of Fe was attenuated by the presence of unsaturated organic ligands, their low reactivity in combination with a lack of sources of Fe in the Makarov Basin might be the reason of a net export of Fe to the sediment

Radionuclides measured on 27 water bottle profiles during POLARSTERN cruise ANT-XXIV/3

As part of the GEOTRACES Polarstern expedition ANT XXIV/3 (ZERO and DRAKE) we have measured the vertical distribution of 234Th on sections through the Antarctic Circumpolar Current along the zero meridian and in Drake Passage and on an EW section through the Weddell Sea. Steady state export fluxes of 234Th from the upper 100m, derived from the depletion of 234Th with respect to its parent 238U, ranged from 621±105 dpm/m**2/d to 1773±90 dpm/m**2/d. This 234Th flux was converted into an export flux of organic carbon ranging from 3.1-13.2 mmolC/m**2/d (2.1-9.0 mmolC/m**2/d) using POC/234Th ratio of bulk (respectively >50 µm) suspended particles at the export depth (100 m). Non-steady state fluxes assuming zero flux under ice cover were up to 23% higher. In addition, particulate and dissolved 234Th were measured underway in high resolution in the surface water with a semi-automated procedure. Particulate 234Th in surface waters is inversely correlated with light transmission and pCO2 and positively with fluorescence and optical backscatter and is interpreted as a proxy for algal biomass. High resolution underway mapping of particulate and dissolved 234Th in surface water shows clearly where trace elements are absorbed by plankton and where they are exported to depth. Quantitative determination of the export flux requires the full 234Th profile since surface depletion and export flux become decoupled through changes in wind mixed layer depth and in contribution to export from subsurface layers. In a zone of very low algal abundance (54-58 °S at the zero meridian), confirmed by satellite Chl-a data, the lowest carbon export of the ACC was observed, allowing Fe and Mn to maintain their highest surface concentrations (Klunder et al., this issue, Middag et al., this issue). An ice-edge bloom that had developed in Dec/Jan in the zone 60-65 °S as studied during the previous leg (Strass et al., in prep) had caused a high export flux at 64.5 °S when we visited the area two months later (Feb/March). The ice-edge bloom had then shifted south to 65-69 °S evident from uptake of CO2 and dissolved Fe, Mn and 234Th, without causing export yet. In this way, the parallel analysis of 234Th can help to explain the scavenging behaviour of other trace elements