Platinum Nanoparticles Obtained at Mild Conditions on S-Layer Protein/Polymer Particle Supports

Biomineralized manganese oxide mediated nitrogen-contained wastewater treatment

In recent years, manganese (Mn) has emerged as an accelerator for nitrogen metabolism. However, the bioactivity of manganese is limited by the restricted contact between microbes and manganese minerals in the solid phase and by the toxicity of manganese to microbes. To enhance the bioactivity of solid-phase manganese, biomineralized manganese oxide (MnOx) modified by Lactobacillus was introduced. Nitrogen removal performance have confirmed the effective role of biomineralized MnOx in accelerating the removal of total inorganic nitrogen (TIN). Metagenomic analysis has confirmed the enhancement of the nitrogen metabolic pathway and microbial extracellular electron transfer (MEET) in biomineralized MnOx treatment group (BIOA group). Additionally, the enrichment of manganese oxidation and denitrification genus indicates a coupling between nitrogen metabolism and manganese metabolism. One point of views is that biomineralized MnOx-mediated nitrogen transformation processes could serve as a substitute for traditional nitrogen removal processes.

Catalytic Performance in Nitroarene Reduction of Nanocatalyst Based on Noble Metal Nanoparticles Supported on Polymer/s-Layer Protein Hybrids

We present a novel bionanocatalyst fabricated by the adsorption-reduction of metal ions on a polyurethane/S-layer protein biotemplate. The bioinspired support was obtained by the adsorption of S-layer proteins (isolated from Lentilactobacillus kefiri) on polyurethane particles. Silver and platinum nanoparticles were well-loaded on the surface of the support after the combination with metallic salts and reduction with H2 at room temperature. Transmission electron microscopy analysis revealed the strawberry-like morphology of the bionanocatalysts with a particle size, dn, of 2.39 nm for platinum and 9.60 nm for silver. Both systems catalyzed the hydrogenation of p-nitrophenol to p-aminophenol with high efficiency in water at mild conditions in the presence of NaBH4. Three different amounts of bionanocatalyst were tested, and in all cases, conversions between 97 and 99% were observed. The catalysts displayed excellent recyclability over ten cycles, and no extensive damage in their nanostructure was noted after them. The bionanocatalysts were stable during their production, storage, and use, thanks to the fact that the biosupport provides an effective driving force in the formation and stabilization of the metallic nanoparticles. The successful bioinspired production strategy and the good catalytic ability of the systems are encouraging in the search for nontoxic, simple, clean, and eco-friendly procedures for the synthesis and exploitation of nanostructures.

S-layer proteins as immune players: tales from pathogenic and non-pathogenic bacteria

In bacteria, as in other microorganisms, surface compounds interact with different pattern recognition receptors expressed by host cells, which usually triggers a variety of cellular responses that result in immunomodulation. The S-layer is a two-dimensional macromolecular crystalline structure formed by (glyco)-protein subunits that covers the surface of many species of Bacteria and almost all Archaea. In Bacteria, the presence of S-layer has been described in both pathogenic and non-pathogenic strains. As surface components, special attention deserves the role that S-layer proteins (SLPs) play in the interaction of bacterial cells with humoral and cellular components of the immune system. In this sense, some differences can be predicted between pathogenic and non-pathogenic bacteria. In the first group, the S-layer constitutes an important virulence factor, which in turn makes it a potential therapeutic target. For the other group, the growing interest to understand the mechanisms of action of commensal microbiota and probiotic strains has prompted the studies of the role of the S-layer in the interaction between the host immune cells and bacteria bearing this surface structure. In this review, we aim to summarize the main latest reports and the perspectives of bacterial SLPs as immune players, focusing on those from pathogenic and commensal/probiotic most studied species.

Nanoarchitectonics for enhanced antibacterial activity with Lactobacillus buchneri S-layer proteins-coated silver nanoparticles

Various multi-drug-resistant microorganisms have appeared while a single antibacterial agent is increasingly no longer adequate for dealing with these resistant microorganisms. Herein, commercially purchased 50 nm-average-diameter silver nanoparticles (AgNPs) and Lactobacillus buchneri-isolated surface-layer proteins (SLPs) as a capping agent were used to fabricate a hybrid antibacterial agent (SLP-AgNPs) with enhanced antibacterial activity, and the possible synergistic antibacterial mechanism was explored. Characterization results revealed that SLP-AgNPs were uniformly surrounded by protein corona provided from SLP, and the formulations were mainly mediated by the electrostatic interactions and hydrogen bonding, which was evidenced by the results of Fourier transform infrared spectroscopy. According to the antibacterial tests, the minimum inhibitory concentration of SLP-AgNPs against Salmonella enterica (0.010 mg/mL) and Staphylococcus aureus (0.005 mg/mL) was 5-10 times lower than that of bare AgNPs, and while SLP-AgNPs showed a higher antibiofilm activity. Furthermore, bacterial cells exposed to SLP-AgNPs exhibited higher cell membrane permeability and stronger inhibition of respiratory-chain dehydrogenase activity, resulting in more severe cell death compared with bare AgNPs. The synergistic effect of SLP on AgNPs was probably carried out by enhanced function of adhesion to bacteria and antibacterial ability of SLP and SLP's supramolecular lattice structure on the sustained release of silver ion.

Synthesis and Catalytic Application of Silver Nanoparticles Supported on Lactobacillus kefiri S-Layer Proteins

Research on nanoparticles obtained on biological supports is a topic of growing interest in nanoscience, especially regarding catalytic applications. Silver nanoparticles (AgNPs) have been studied due to their low toxicity, but they tend to aggregation, oxidation, and low stability. In this work, we synthesized and characterized AgNPs supported on S-layer proteins (SLPs) as bidimensional regularly arranged biotemplates. By different reduction strategies, six AgNPs of variable sizes were obtained on two different SLPs. Transmission electron microscopy (TEM) images showed that SLPs are mostly decorated by evenly distributed AgNPs; however, a drastic reduction by NaBH4 led to large AgNPs whereas a smooth reduction with H2 or H2/NaBH4 at low concentration leads to smaller AgNPs, regardless of the SLP used as support. All the nanosystems showed conversion values between 75-80% of p-nitrophenol to p-aminophenol, however, the increment in the AgNPs size led to a great decrease in Kapp showing the influence of reduction strategy in the performance of the catalysts. Density functional theory (DFT) calculations indicated that the adsorption of p-nitrophenolate species through the nitro group is the most favored mechanism, leading to p-aminophenol as the only feasible product of the reaction, which was corroborated experimentally.