The carbon sensor SbtB perceives diurnal oscillation of c-di-AMP to control glycogen synthesis and nighttime survival.

Scanning probe microscopes are widely used to study surfaces with atomic resolution in many areas of nanoscience. Ultracold atomic gases trapped in electromagnetic potentials can be used to study electromagnetic interactions between the atoms and nearby surfaces in chip-based systems. Here we demonstrate a new type of scanning probe microscope that combines these two areas of research by using an ultracold gas as the tip in a scanning probe microscope. This cold-atom scanning probe microscope offers a large scanning volume, an ultrasoft tip of well-defined shape and high purity, and sensitivity to electromagnetic forces (including dispersion forces near nanostructured surfaces). We use the cold-atom scanning probe microscope to non-destructively measure the position and height of carbon nanotube structures and individual free-standing nanotubes. Cooling the atoms in the gas to form a Bose-Einstein condensate increases the resolution of the device.

A sharp-tipped gold nanocone and the vertically aligned metallic tip of a near-field optical microscope together form a three-dimensional optical antenna with a highly controllable gap. Confocal measurements with different laser modes show the efficient axial excitation of the cones with a longitudinally polarized field. In the antenna configuration, extremely strong field enhancement up to a factor of 100 is obtained by tuning the gap between the two sharp tips down to few nanometers.

The PII superfamily consists of widespread signal transduction proteins found in all domains of life. In addition to canonical PII proteins involved in C/N sensing, structurally similar PII-like proteins evolved to fulfill diverse, yet poorly understood cellular functions. In cyanobacteria, the bicarbonate transporter SbtA is co-transcribed with the conserved PII-like protein, SbtB, to augment intracellular inorganic carbon levels for efficient CO 2 fixation. We identified SbtB as a sensor of various adenine nucleotides including the second messenger nucleotides cyclic AMP (cAMP) and c-di-AMP. Moreover, many SbtB proteins possess a C-terminal extension with a disulfide bridge of potential redox-regulatory function, which we call R-loop. Here, we reveal an unusual ATP/ADP apyrase (diphosphohydrolase) activity of SbtB that is controlled by the R-loop. We followed the sequence of hydrolysis reactions from ATP over ADP to AMP in crystallographic snapshots and unravel the structural mechanism by which changes of the R-loop redox state modulate apyrase activity. We further gathered evidence that this redox state is controlled by thioredoxin, suggesting that it is generally linked to cellular metabolism, which is supported by physiological alterations in site-specific mutants of the SbtB protein. Finally, we present a refined model of how SbtB regulates SbtA activity, in which both the apyrase activity and its redox regulation play a central role. This highlights SbtB as a central switch point in cyanobacterial cell physiology, integrating not only signals from the energy state (adenyl-nucleotide binding) and the carbon supply via cAMP binding but also from the day/night status reported by the C-terminal redox switch.

Summary The amount of inorganic carbon (Ci) fluctuates in aquatic environments. Cyanobacteria evolved a Ci‐concentrating mechanism (CCM) that is regulated at different levels. The regulator SbtB binds to the second messengers cAMP or c‐di‐AMP and is involved in acclimation to low Ci (LC) in Synechocystis sp. PCC 6803. Here, we investigated the role of SbtB and of associated second messengers at different Ci conditions. The transcriptome of wild‐type (WT) Synechocystis and the ΔsbtB mutant were compared with Δcya1, a mutant defective in cAMP production, and ΔdacA, a mutant defective in generating c‐di‐AMP. A defined subset of LC‐regulated genes in the WT was already changed in ΔsbtB under high Ci (HC) conditions. This response of ΔsbtB correlated with a diminished induction of many CCM‐associated genes after LC shift in this mutant. The Δcya1 mutant showed less deviation from WT, whereas ΔdacA induced CCM‐associated genes under HC. Metabolome analysis also revealed differences between the strains, whereby ΔsbtB showed slower accumulation of 2‐phosphoglycolate and ΔdacA differences among amino acids compared to WT. Collectively, these results indicate that SbtB regulates a subset of LC acclimation genes while c‐di‐AMP and especially cAMP appear to have a lesser impact on gene expression under different Ci availabilities.