Streptococcus pneumoniae Infection Promotes Histone H3 Dephosphorylation by Modulating Host PP1 Phosphatase

Pathogenic bacteria can alter host gene expression through post-translational modifications of histones. We show that a natural colonizer, Streptococcus pneumoniae, induces specific histone modifications, including robust dephosphorylation of histone H3 on serine 10 (H3S10), during infection of respiratory epithelial cells. The bacterial pore-forming toxin pneumolysin (PLY), along with the pyruvate oxidase SpxB responsible for H₂O₂ production, play important roles in the induction of this modification. The combined effects of PLY and H₂O₂ trigger host signaling that culminates in H3S10 dephosphorylation, which is mediated by the host cell phosphatase PP1. Strikingly, S. pneumoniae infection induces dephosphorylation and subsequent activation of PP1 catalytic activity. Colonization of PP1 catalytically deficient cells results in impaired intracellular S. pneumoniae survival and infection. Interestingly, PP1 activation and H3S10 dephosphorylation are not restricted to S. pneumoniae and appear to be general epigenomic mechanisms favoring intracellular survival of pathogenic bacteria.

H3K4me1 Supports Memory-like NK Cells Induced by Systemic Inflammation

Natural killer (NK) cells are unique players in innate immunity and, as such, an attractive target for immunotherapy. NK cells display immune memory properties in certain models, but the long-term status of NK cells following systemic inflammation is unknown. Here we show that following LPS-induced endotoxemia in mice, NK cells acquire cell-intrinsic memory-like properties, showing increased production of IFNγ upon specific secondary stimulation. The NK cell memory response is detectable for at least 9 weeks and contributes to protection from E. coli infection upon adoptive transfer. Importantly, we reveal a mechanism essential for NK cell memory, whereby an H3K4me1-marked latent enhancer is uncovered at the ifng locus. Chemical inhibition of histone methyltransferase activity erases the enhancer and abolishes NK cell memory. Thus, NK cell memory develops after endotoxemia in a histone methylation-dependent manner, ensuring a heightened response to secondary stimulation.

Chemistry of single-walled carbon nanotubes

In this Account we highlight the experimental evidence in favor of our view that carbon nanotubes should be considered as a new macromolecular form of carbon with unique properties and with great potential for practical applications. We show that carbon nanotubes may take on properties that are normally associated with molecular species, such as solubility in organic solvents, solution-based chemical transformations, chromatography, and spectroscopy. It is already clear that the nascent field of nanotube chemistry will rival that of the fullerenes.

The sporulation transcription factor Spo0A is required for biofilm development in Bacillus subtilis

Biofilms are structured communities of cells encased in a polymeric matrix and adherent to a surface, interface or each other. We report here that the soil bacterium Bacillus subtilis forms biofilms. By confocal scanning laser microscopy, we observed that B. subtilis adhered to abiotic surfaces and formed a three-dimensional structure > or =30 microm in depth. These biofilms appeared to be at least partly encased in an extracellular polysaccharide matrix, as they could be stained with Calcofluor, a polysaccharide-binding dye. To understand the molecular mechanism of biofilm formation, we screened previously characterized mutants for a defect in biofilm formation. We found that mutations in spo0A, which encodes the major early sporulation transcription factor, caused a defect in biofilm formation. spo0A mutant cells adhered to a surface in a monolayer of cells rather than a three-dimensional biofilm. The requirement of Spo0A for biofilm development appears to result from its role in negatively regulating AbrB. Mutations in abrB suppressed the biofilm defect of a spo0A mutant, indicating that AbrB negatively regulates at least one gene that is required for the transition from a monolayer of attached cells to a mature biofilm. Implications of biofilm development for the ecology of B. subtilis are discussed.

Chromatographic purification and properties of soluble single-walled carbon nanotubes

We report an improved chromatographic purification of soluble single-walled carbon nanotubes (s-SWNTs) using gel permeation chromatography. Three fractions are separated by gel permeation chromatography, and the first fraction contains 74% of the s-SWNTs as detected by atomic force microscopy and UV and near-infrared spectroscopy.

Solution properties of single-walled carbon nanotubes

Naked metallic and semiconducting single-walled carbon nanotubes (SWNTs) were dissolved in organic solutions by derivatization with thionychloride and octadecylamine. Both ionic (charge transfer) and covalent solution-phase chemistry with concomitant modulation of the SWNT band structure were demonstrated. Solution-phase near-infrared spectroscopy was used to study the effects of chemical modifications on the band gaps of the SWNTs. Reaction of soluble SWNTs with dichlorocarbene led to functionalization of the nanotube walls.