Ignicoccus hospitalis and Nanoarchaeum equitans: ultrastructure, cell–cell interaction, and 3D reconstruction from serial sections of freeze-substituted cells and by electron cryotomography

Ultrastructure and intercellular interaction of Ignicoccus hospitalis and Nanoarchaeum equitans were investigated using two different electron microscopy approaches, by three-dimensional reconstructions from serial sections, and by electron cryotomography. Serial sections were assembled into 3D reconstructions, for visualizing the unusual complexity of I. hospitalis, its huge periplasmic space, the vesiculating cytoplasmic membrane, and the outer membrane. The cytoplasm contains fibres which are reminiscent to a cytoskeleton. Cell division in I. hospitalis is complex, and different to that in Euryarchaeota or Bacteria. An irregular invagination of the cytoplasmic membrane is followed by separation of the two cytoplasms. Simultaneous constriction of cytoplasmic plus outer membrane is not observed. Cells of N. equitans show a classical mode of cell division, by constriction in the mid-plane. Their cytoplasm exhibits two types of fibres, elongated and ring-shaped. Electron micrographs of contact sites between I. hospitalis and N. equitans exhibit two modes of interaction. One is indirect and mediated by thin fibres; in other cells the two cell surfaces are in direct contact. The two membranes of I. hospitalis cells are frequently seen in direct contact, possibly a prerequisite for transporting metabolites or substrates from the cytoplasm of one cell to the other. Rarely, a transport based on cargo vesicles is observed between I. hospitalis and N. equitans

mRNA localization, reaction centre biogenesis and thylakoid membrane targeting in cyanobacteria

The thylakoid membranes of cyanobacteria form a complex intracellular membrane system with a distinctive proteome. The sites of biogenesis of thylakoid proteins remain uncertain, as do the signals that direct thylakoid membrane-integral proteins to the thylakoids rather than to the plasma membrane. Here, we address these questions by using fluorescence in situ hybridization to probe the subcellular location of messenger RNA molecules encoding core subunits of the photosystems in two cyanobacterial species. These mRNAs cluster at thylakoid surfaces mainly adjacent to the central cytoplasm and the nucleoid, in contrast to mRNAs encoding proteins with other locations. Ribosome association influences the distribution of the photosynthetic mRNAs on the thylakoid surface, but thylakoid affinity is retained in the absence of ribosome association. However, thylakoid association is disrupted in a mutant lacking two mRNA-binding proteins, which probably play roles in targeting photosynthetic proteins to the thylakoid membrane

Electricity generation from digitally printed cyanobacteria

Microbial biophotovoltaic cells exploit the ability of cyanobacteria and microalgae to convert light energy into electrical current using water as the source of electrons. Such bioelectrochemical systems have a clear advantage over more conventional microbial fuel cells which require the input of organic carbon for microbial growth. However, innovative approaches are needed to address scale-up issues associated with the fabrication of the inorganic (electrodes) and biological (microbe) parts of the biophotovoltaic device. Here we demonstrate the feasibility of using a simple commercial inkjet printer to fabricate a thin-film paper-based biophotovoltaic cell consisting of a layer of cyanobacterial cells on top of a carbon nanotube conducting surface. We show that these printed cyanobacteria are capable of generating a sustained electrical current both in the dark (as a ‘solar bio-battery’) and in response to light (as a ‘bio-solar-panel’) with potential applications in low-power devices