Amyloid Fibrils Produced by Streptococcus sanguinis Contribute to Biofilm Formation and Immune Evasion

Bacterial surface proteins assembled into amyloids contribute to biofilm formation and host immune evasion. Streptococcus sanguinis, a pioneer colonizer of teeth commonly involved in cardiovascular infections, expresses about thirty-three proteins anchored to the cell wall by sortase A. Here, we characterized the production of amyloid in S. sanguinis strains differing in biofilm and immune evasion phenotypes and investigated the role of sortase A in amyloidogenesis. Amyloid was identified in biofilms formed by nine strains, using Congo red (CR) staining and cross-polarized light microscopy. Additionally, EGCG, an amyloid inhibitor, impaired biofilm maturation in a strain-specific fashion. The amounts of amyloid-like components quantified in culture fluids of nine strains using thioflavin T and fluorimetry negatively correlated with bacterial binding to complement-activating proteins (SAP, C1q), C3b deposition and rates of opsonophagocytosis in PMNs, implying amyloid production in immune evasion. The deletion of the sortase A gene (srtA) in strain SK36 compromised amyloid production and sucrose-independent biofilm maturation. The srtA mutant further showed increased susceptibility to C3b deposition and altered interactions with PMNs as well as reduced persistence in human blood. These findings highlight the contribution of amyloids to biofilm formation and host immune evasion in S. sanguinis strains, further indicating the participation of sortase A substrates in amyloidogenesis.

Magnetic iron species highly dispersed over silica: use as catalysts for removal of pollutants in water

Fe₂O₃-SiO₂ composites were prepared by impregnation (sample FeIMP) or doping (sample FeDOP) in the structure of porous silica. The dye removal capacity of the materials was investigated through adsorption and oxidation studies of methylene blue and rhodamine B. N₂ adsorption/desorption measurements on FeIMP and FeDOP resulted in specific areas of 27 and 235 m² g^-1, respectively. Mössbauer spectroscopy and XRD data detected hematite and maghemite as the iron phases in the samples FeIMP and FeDOP, respectively. Adsorption isotherms and kinetic studies of the dyes were better fitted in DKR model for FeDOP, where the process follows a pseudo-second order with the interparticle diffusion step being the rate-limiting step. On the other hand, FeIMP has better fit in the Langmuir model. Photocatalytic activity was observed in FeDOP under UV irradiation by the presence of reaction-hydroxylated intermediates for MB (m/z = 301) and RhB (m/z = 459). However, the photocatalytic activity was strongly influenced by the adsorption affinity between dye/catalyst. Photogenerated holes are the species responsible for the dye degradation when the adsorption is too strong, while hydroxyl radical action will be favored when the adsorption is not vigorous as detected by ESI-MS. Graphical Abstract Action of photogenerated holes and free electrons into the photocatalytically mechanism of methylene blue degradation over a semiconductor.