Scientific Activities

Members of the Koren group were sent to measure marine aerosol properties during the Tara Pacific Expedition, a 2.5 year research project that began on May 2016 in Lorient, France and returned on October 2018. They installed a custom-made filter collector for biological, chemical and morphological analyses of the marine aerosols. One of their aims is to determine the composition and size of individual particles with diameters as small as 0.8 microns (μm). Since returning with their samples, the Koren team has been performing single-particle analysis using a scanning electron microscope (SEM) with an energy dispersive X-ray analyzer to quantify the size, shape, quantity, and elemental composition of all aerosols. They are using the Quantax 800 automatic software from Bruker which was recently acquired by the SEM unit of the Weizmann Institute.

They found that the air parcels descend through a range of pressure differentials from 250 to 500 pascals of pressure (hPa), and the time window for the descent varied between 24 to 96 hours. Their results, combined with individual case studies of known impactful cyclones in the Mediterranean region, indicate that intrusions that show a pressure difference of at least 350 hPa in 48 hours lead to significant storm activity.

Based on their chosen criterion, the team is generating a new dataset for the years 1979-2018. They will use the same criterion for a new reanalysis of the ERA5 dataset that was used for the study of the Mistral wind in the Gulf of Lion, a phenomenon directly related to such cold and dry intrusions. The new datasets will serve as a basis for subsequent studies aiming to understand high-impact weather and the coupling of the atmospheric circulation to the water cycle in this region. 

In a collaboration with Dr. Julia Mahamid at the European Molecular Biology Laboratory, Dr. Gal and Dr. Zohar Eyal, a postdoc working in his lab, have conducted very promising experiments on campus and in Heidelberg, using cryo-electron tomography—an imaging technique used to produce high-resolution three-dimensional views of samples.

Dr. Eyal has established the experimental pipeline in which the calcifying cells are vitrified on a transmission electron microscope grid, and then thinned to 200 nanometers (nm) by a focused ion beam instrument. The final step in this process is acquiring the electron microscope images at different tilt angles. All aspects of this process are now properly functioning in the newly purchased cryo-electron microscopes on campus. Dr. Gal and his team are collecting data from their samples.

[Image on the left: (A, B) Sections in P. carterae whole cells show both the homogenous lumen of the vacuole that is punctuated with calcium and phosphorus rich (Ca-P) bodies, and the contrasting dense internal organization of the ion-rich compartments (orange arrowheads) that contain particles, spheres, membranes, and more. (Credit: Journal of Structural Biology, 2020)]

They found that these bacterial communities correlate highly to the concentration of E. huxleyi and available nutrients in the environment. Low concentration of the alga in the beginning of growth resulted mainly in bacterial communities that are adapted to environments with low nutrient concentration.

However, when the alga reaches high concentrations, the scientists observed a shift in the bacterial community. This shift was characterized by a dominance of bacterial communities that are well adapted to environments with high concentration of nutrients. The results indicate that E. huxleyi contributes to the nutrient availability in the environment, and as a consequence to the changes in the bacterial communities.