The objective of this study was to characterize the oxygen dependent regulation of pyruvate oxidase (SpxB) gene expression and protein production in Streptococcus sanguinis (S. sanguinis). SpxB is responsible for the generation of growth-inhibiting amounts of hydrogen peroxide (H 2 O 2 ) able to antagonize cariogenic Streptococcus mutans (S. mutans). Furthermore, the ecological consequence of H 2 O 2 production was investigated in its self-inhibiting ability towards the producing strain. Expression of spxB was determined with quantitative Real-Time RT-PCR and a fluorescent expression reporter strain. Protein abundance was investigated with FLAG epitope engineered in frame on the C-terminal end of SpxB. Self inhibition was tested with an antagonism plate assay. The expression and protein abundance decreased in cells grown under anaerobic conditions. S. sanguinis was resistant against its own produced H 2 O 2 , while cariogenic S. mutans was inhibited in its growth. The results suggest that S. sanguinis produces H 2 O 2 as antimicrobial substance to inhibit susceptible niche competing species like S. mutans during initial biofilm formation, when oxygen availability allows for spxB expression and Spx production.

The thermodynamics of the association between 4,4 ,4 -tris(dimethylamino)triphenylmethyl chloride (crystal violet or CV) and sodium bis(2-ethylhexyl)sulfosuccinate (aerosol OT or AOT) in water/AOT/n-decane microemulsion and the kinetics of the basic hydrolysis of CV in a water-in-oil microemulsion were investigated by UV-vis spectroscopic measurements. An association model of CV and AOT was used to analyze the experimental data to obtain the association constants at various temperatures. By taking the association into account, the "actual" rate constants and the activation energies of the basic hydrolysis of CV in the media of water/AOT/oil were obtained. The difference in thermodynamics and kinetics between the two media of water/AOT/n-decane and water/AOT/isooctane is discussed. C

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This article reports ZnO‐assisted growth of three‐dimensional (3D) dendritic hexapods of tin(II) oxyhydroxide (Sn6O4(OH)4) from acidic aqueous solution of stannous sulfate (SnSO4). Each Sn6O4(OH)4 hexapod has four long horizontally and two short vertically oriented dendritic branches. The formation of Sn6O4(OH)4 can be ascribed to the presence of ZnO whose surfaces are rich in hydroxyl groups. When covered by SnSO4 acidic aqueous solution, a large amount of hydroxyl groups is released from ZnO surfaces and further promotes the hydrolysis of SnSO4 towards Sn6O4(OH)4. Time‐dependent shape evolution from the nanoparticles‐assembled hierarchical octahedra to the 3D dendritic hexapods has been explored. The growth of Sn6O4(OH)4 3D dendritic hexapods has been explained based on a nanoparticle‐mediated, diffusion‐limited dendritic growth mechanism. Sn6O4(OH)4 can be selectively converted to semiconducting SnO or SnO2 for potential sensing and catalytic applications.