New insight on a Group A Streptococcus protective antigen contributing to bacterial cell division

Bioinformatic analysis of Group A Streptococcus (GAS) genomes aiming at the identification of new vaccine antigens, revealed the presence of a gene coding for a putative surface-associated protein, named GAS40, inducing protective antibodies in an animal model of sepsis. The aim of our study was to unravel the involvement of GAS40 in cell division processes and to identify the putative interactor. Firstly, bioinformatic analysis showed that gas40 shares homology with ezrA, a gene coding for a negative regulator of Z-ring formation during cell division process. Both scanning and transmission electron microscopy indicated morphological differences between wild-type and the GAS40 knock-out mutant strain, with the latter showing an impaired capacity to divide resulting in the formation of very long chains. Moreover, when the localization of the antigen on the bacterial surface was analyzed, we found that in bacteria grown at exponential phase GAS40 specifically localized at septum, indicating a possible role in cell division. Furthermore, by ELISA and co-sedimentation assays, we found that GAS40 is able to interact with FtsZ, a protein involved in Z-ring formation during cell division process. These data together with the co-localization of GAS40/FtsZ at bacterial septum demonstrated by by confocal microscopy, strongly support the hypothesis for a key role of GAS40 in bacterial cell division.

Low-dimensional carbon allotropes: an electron microscopy investigation

The research reported in this manuscript concerns the structural characterization of graphene membranes and single-walled carbon nanotubes (SWCNTs). The experimental investigation was performed using a wide range of transmission electron microscopy (TEM) techniques, from conventional imaging and diffraction, to advanced interferometric methods, like electron holography and Geometric Phase Analysis (GPA), using a low-voltage optical set-up, to reduce radiation damage in the samples. Electron holography was used to successfully measure the mean electrostatic potential of an isolated SWCNT and that of a mono-atomically thin graphene crystal. The high accuracy achieved in the phase determination, made it possible to measure, for the first time, the valence-charge redistribution induced by the lattice curvature in an individual SWCNT. A novel methodology for the 3D reconstruction of the waviness of a 2D crystal membrane has been developed. Unlike other available TEM reconstruction techniques, like tomography, this new one requires processing of just a single HREM micrograph. The modulations of the inter-planar distances in the HREM image are measured using Geometric Phase Analysis, and used to recover the waviness of the crystal. The method was applied to the case of a folded FGC, and a height variation of 0.8 nm of the surface was successfully determined with nanometric lateral resolution. The adhesion of SWCNTs to the surface of graphene was studied, mixing shortened SWCNTs of different chiralities and FGC membranes. The spontaneous atomic match of the two lattices was directly imaged using HREM, and we found that graphene membranes act as tangential nano-sieves, preferentially grafting achiral tubes to their surface.