Rapid Freezing and Cryo-SEM-EDS Imaging of Foraminifera (Unicellular Eukaryotes) Using a Conductive Viscous Cryogenic Glue.

Spatial distribution of water-soluble molecules and ions in living organisms is still challenging to assess. Energy-dispersive X-ray spectroscopy (EDS) via cryogenic scanning electron microscopy (cryo-SEM) is one of the promising methods to study them without loss of dissolved contents. High-resolution cryo-SEM-EDS has challenges in sample preparation, including cross-section exposure and sample drift/charging due to insulative surrounding water. The former becomes problematic for large and inseparable organisms, such as benthic foraminifera, a unicellular eukaryote playing significant roles in marine ecosystems, which often exceed the size limit for the most reliable high-pressure freezing. Here we show graphite oxide dispersed in sucrose solution as a good glue to freeze, expose cross-section by cryo-ultramicrotome, and analyze elemental distribution owing to the glue's high viscosity, adhesion force, and electron conductivity. To demonstrate the effectiveness and applicability of the glue for cryo-SEM-EDS, deep-sea foraminifer Uvigerina akitaensis was sampled during a cruise and plunge frozen directly on the research vessel, where the liquid nitrogen supply is limited. The microstructures were preserved as faithfully in cryo-SEM images as those with the conventional resin-substituted transmission electron micrograph. We found elements colocalized within the cytoplasm originating from water-soluble compounds that can be lost with conventional dehydrative fixation.

Ostracoda and foraminifera from Paleocene (Olinda well), Paraíba Basin, Brazilian Northeast

ABSTRACT Paleocene ostracods and planktonic foraminifera from the Maria Farinha Formation, Paraíba Basin, are herein presented. Eleven ostracod species were identified in the genera Cytherella Jones, Cytherelloidea Alexander, Eocytheropteron Alexander, Semicytherura Wagner, Paracosta Siddiqui, Buntonia Howe, Soudanella Apostolescu, Leguminocythereis Howe and, probably, Pataviella Liebau. The planktonic foraminifera are represented by the genera Guembelitria Cushman, Parvularugoglobigerina Hofker, Woodringina Loeblich and Tappan, Heterohelix Ehrenberg, Zeauvigerina Finlay, Muricohedbergella Huber and Leckie, and Praemurica Olsson, Hemleben, Berggren and Liu. The ostracods and foraminifera analyzed indicate an inner shelf paleoenvironment for the studied section. Blooms of Guembelitria spp., which indicate either shallow environments or upwelling zones, were also recorded reinforcing previous paleoenvironmental interpretations based on other fossil groups for this basin.