Previously uncharacterized rectangular bacteria in the dolphin mouth

Much remains to be explored regarding the diversity of host-associated microbes. Here, we report the discovery of microbial structures in the mouths of bottlenose dolphins that we refer to as rectangular cell-like units (RCUs). DNA staining revealed multiple paired bands that suggested cells in the act of dividing along the longitudinal axis. Deep sequencing of samples enriched in RCUs through micromanipulation indicated that the RCUs are bacterial and distinct from Simonsiella, a genus with somewhat similar morphology and division patterning found in oral cavities of animals. Cryogenic transmission electron microscopy and tomography showed that RCUs are composed of parallel membrane-bound segments, likely individual cells, encapsulated by an S-layer-like periodic surface covering. RCUs displayed pilus-like appendages protruding as bundles of multiple threads that extend parallel to each other, and splay out at the tips and/or intertwine, in stark contrast to all known types of bacterial pili that consist of single, hair-like structures. These observations highlight the diversity of novel microbial forms and lifestyles that await discovery and characterization using tools complementary to genomics such as microscopy.

Networks of Micellar Chains with Nanoplates

Nanocomposite networks of surfactant micellar chains and natural bentonite clay nanoplates are studied by rheometry, small-angle neutron scattering, and cryogenic transmission electron microscopy. It is shown that, in an aqueous medium in the presence of a small part of an anionic surfactant, sodium dodecyl sulfate, the molecules of a biodegradable zwitterionic surfactant, oleyl amidopropyl dimethyl carboxybetaine, form micron-length living micellar chains which entangle and form a network possessing well-defined viscoelastic properties. It is found that addition of negatively charged clay nanoplates leads to an increase in viscosity and relaxation time by an order of magnitude. This is explained by the incorporation of the nanoplates into the network as physical multifunctional crosslinks. The incorporation occurs via the attachment of semispherical end-caps of the micelles to the surface of the particles covered with a surfactant layer, as visualized by cryogenic transmission electron microscopy. As the amount of nanoplates is increased, the rheological properties reach plateau; this is associated with the attachment of all end parts of micelles to nanoplates. The developed nanocomposite soft networks based on safe and eco-friendly components are promising for various practical applications.

Probing the Na metal solid electrolyte interphase via cryo-transmission electron microscopy

Cryogenic transmission electron microscopy (cryo-TEM) is a valuable tool recently proposed to investigate battery electrodes. Despite being employed for Li-based battery materials, cryo-TEM measurements for Na-based electrochemical energy storage systems are not commonly reported. In particular, elucidating the chemical and morphological behavior of the Na-metal electrode in contact with a non-aqueous liquid electrolyte solution could provide useful insights that may lead to a better understanding of metal cells during operation. Here, using cryo-TEM, we investigate the effect of fluoroethylene carbonate (FEC) additive on the solid electrolyte interphase (SEI) structure of a Na-metal electrode. Without FEC, the NaPF6-containing carbonate-based electrolyte reacts with the metal electrode to produce an unstable SEI, rich in Na2CO3 and Na3PO4, which constantly consumes the sodium reservoir of the cell during cycling. When FEC is used, the Na-metal electrode forms a multilayer SEI structure comprising an outer NaF-rich amorphous phase and an inner Na3PO4 phase. This layered structure stabilizes the SEI and prevents further reactions between the electrolyte and the Na metal.