Persistent infections caused by Staphylococcus aureus biofilms pose a major threat to global public health. 10-Hydroxy-2-decenoic acid (10-HDA), a main fatty acid in royal jelly, has been shown to possess various biological activities. The purpose of this study was to explore the effects of 10-HDA on the biofilms and virulence of S. aureus and its potential molecular mechanism. Quantitative crystal violet staining indicated that 10-HDA significantly reduced the biofilm biomass at sub-minimum inhibitory concentration (MIC) levels (1/32MIC to 1/2MIC). Scanning electron microscope (SEM) observations demonstrated that 10-HDA inhibited the secretion of extracellular polymeric substances, decreased bacterial adhesion and aggregation, and disrupted biofilm architecture. Moreover, 10-HDA could significantly decrease the biofilm viability and effectively eradicated the mature biofilms. It was also found that the hemolytic activity of S. aureus was significantly inhibited by 10-HDA. qRT-PCR analyses revealed that the expressions of global regulators sarA, agrA, and α-hemolysin gene hla were downregulated by 10-HDA. These results indicate that 10-HDA could be used as a potential natural antimicrobial agent to control the biofilm formation and virulence of S. aureus.

Multiple enzyme systems are being increasingly used for their high-efficiency and co-immobilization is a key technology to lower the cost and improve the stability of enzymes. In this study, poly glycidyl methacrylate (PGMA) spheres were synthesized using suspension polymerization, and were used as a support to co-immobilize glucose oxidase (GOx) and catalase (CAT). Surface modification was carried out via a combination of plasma and amination to promote the properties of the catalyzer. The co-immobilized enzymes showed a more extensive range of optimum pH and temperature from 5.5 to 7.5 and 25 to 40°C, respectively, compared to free enzymes. Furthermore, the maximum activity and protein adsorption quantity of the co-immobilized enzymes reached 25.98 U/g and 6.07 mg/g, respectively. The enzymatic activity of the co-immobilized enzymes was maintained at ~70% after storage for 5 days and at 82% after three consecutive cycles, indicating that the immobilized material could be applied industrially.

Glucosamine (GlcN) is a major and valuable component in the cell wall of fungi. In this study, the cell wall was treated via a two-stage alkali and acid process, and chitin and chitosan were fully deacetylated, partially depolymerized, and converted to GlcN oligosaccharides. Then, the oligosaccharides were analyzed by high performance liquid chromatography. The influences of Actinomucor elegans on GlcN production in a flask culture were investigated to achieve an optimum yield of GlcN. The experimental result showed that cultivation in condition of pH 6.0, 100 mL working volume (500 mL flask), 10 % (v/v) inoculum concentration, at 28 °C and 200 rpm for 6 days yielded highest dry cell weight (DCW) which was 23.43 g L⁻¹, with a GlcN concentration of 5.12 g L⁻¹. Methanol as stimulating factor was found to exert the best effect in concentration of 1.5 % (v/v). With addition of methanol into medium, the DCW increased from 23.69 to 32.42 g L⁻¹, leading to maximum GlcN concentration of 6.85 g L⁻¹ obtained. Here, the methanol addition may be useful for industrial production of GlcN, and may also be meaningful for the production of other fine chemicals by filamentous fungi.

L-Lysine, an essential amino acid for humans and mammals, is widely used in the food, feed, medicine, and cosmetics industries. In this study, a lysine over-producing Escherichia coli mutant was isolated using a fluorescence-based screen and an E. coli strain lacking five of the six L-lysine tRNA-UUU genes. Firstly, an l-lysine codon-rich protein was fused with a green fluorescent protein (all AAG codons were replaced with AAA), yielding a rare codon-rich screening marker positively correlated with l-lysine content. After association and room temperature plasma (ARTP) mutagenesis and induced fluorescent protein expression culture, mutant strains with strong fluorescence were sorted using flow cytometry. The fermentation performance of the high-yielding l-lysine strains were evaluated, which resulted in 16 of the 29 mutant strains showing increased L-lysine yields compared with those of the wild-type strains and a screening efficiency of up to 55.2%. Following a 48 h fermentation, the production of l-lysine (14.8 g/L) and biomass by E. coli QD01ΔtRNA L2 were 12.1 and 4.5% higher than those of the wild-type strain. The screening strategy for high-yielding strains based on the artificial rare cryptosystem established in this study will provide an efficient, accurate, and simple method for screening other amino-acid-producing microorganisms.