S-layer proteins as possible immobilization matrix for photocatalysts – OH radical scavenging capacity and protein stability

Functional CdS nanocomposites recovered from biomineralization treatment of sulfate wastewater and its applications in the perspective of photocatalysis and electrochemistry

The sulfur ions generated during the microbial treatment of sulfate wastewater could cause secondary pollution problem, however, the application of the biomineralization technique could convert sulfur ions into sulfide nanocomposites with diverse properties. This study constructed a multi-stage process for sulfate wastewater treatment and CdS nanocomposites (CdS-NCs) recovery by using biomineralization, which simultaneously achieved the removal of pollutants and recovery of functional nanocomposites. In this process, about 97% of the sulfate could be removed, and the CdS-NCs with a diameter of 16.0-20.2 nm were collected at different pHs. The results of FTIR and Raman proved that the biomacromolecules derived from microorganisms participated in the formation of CdS-NCs. The Mott-Schottky curve suggested that the CdS-NCs belonged to n-type semiconductors with the energy gap of 2.29-2.38 eV and could be applied as the photocatalyst, and up to 78.2% of 200 mg/L tetracycline was photodegraded catalytically by CdS-NCs obtained at pH 6.5. In the application of CdS-NCs as anodes of lithium-ion batteries, all the batteries assembled by CdS-NCs exhibited a very strong cycle performance of more than 500 cycles. This research not only effectively recovered nanocomposites with great application potential from sulfate wastewater but also provided a perspective for the utilization of recovered resources.

Analysis in protein profile, antioxidant activity and structure-activity relationship based on ultrasound-assisted liquid-state fermentation of soybean meal with Bacillus subtilis

This study investigated effects of ultrasound on the contents of peptide and soluble protein, antioxidant activity, functionalities and structural characteristics of fermented soybean meal (FSBM) with Bacillus subtilis systematically. The results showed that there were significant effects of ultrasound treatments (frequency, treatment time and power density) on the contents of peptide and soluble protein (p < 0.05). Under the optimum ultrasound conditions (power density of 0.08 W/mL, frequency of 33 kHz and treatment time of 1 h) by single factor experiment, the contents of peptide and soluble protein increased by 31.27% and 18.79% compared to those of the control, respectively. Additionally, the in vitro antioxidant activity (•OH scavenging rate, Fe2+ chelating capacity and DPPH radical scavenging rate) and functional properties (emulsifying activity and emulsifying stability) of FSBM were found to be noticeably improved by ultrasound (p < 0.05). The fourier transform infrared (FTIR) spectroscopy revealed that ultrasound caused protein molecules to unfold with a decrease content of α-helix and β-turn and an increase in the proportion of β-sheet and random coil. Besides, atomic force microscope (AFM) results indicated that ultrasonication generally increased the surface roughness of protein and the protein sonicated with higher frequency (≥33 kHz) exhibited a greater height compared to lower frequency ultrasonication. Structure-activity relationship analysis illustrated that there was a good linear relationship between •OH scavenging rate and β-sheet/β-turn with Pearson's correlation coefficient r of -0.86/0.90. Collectively, the selection of ultrasonic parameters is essential for the preparation of functional protein and bioactive peptide by enhancing fermentation of agroindustrial by-products.

S-Layer-Based Nanocomposites for Industrial Applications

This chapter covers the fundamental aspects of bacterial S-layers: what are S-layers, what is known about them, and what are their main features that makes them so interesting for the production of nanostructures. After a detailed introduction of the paracrystalline protein lattices formed by S-layer systems in nature the chapter explores the engineering of S-layer-based materials. How can S-layers be used to produce "industry-ready" nanoscale bio-composite materials, and which kinds of nanomaterials are possible (e.g., nanoparticle synthesis, nanoparticle immobilization, and multifunctional coatings)? What are the advantages and disadvantages of S-layer-based composite materials? Finally, the chapter highlights the potential of these innovative bacterial biomolecules for future technologies in the fields of metal filtration, catalysis, and bio-functionalization.