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The two-peptide (class IIb) bacteriocins are generally thermostable small-molecule (< 10 kDa) two-component antimicrobial peptides produced by Gram-positive bacteria. This class of peptides mainly rely on peptide-peptide interactions mediated by typical motifs to form active dimeric transmembrane proteins. Numerous studies have shown that two-peptide bacteriocins have reliable safety and desirable bacteriostatic effect, holding great potential in the control of drug-resistant bacteria. Therefore, the structural features and action mechanisms of two-peptide bacteriocins have received considerable research attention. From the perspectives of the structure formation of two-peptide bacteriocins, peptide-peptide interaction, and peptide-membrane interaction, this article summarizes the mechanism of action of this class of antimicrobial peptides. Meanwhile, the structural regularity of two-peptide bacteriocins and the structural features affecting their activities are elaborated by synthesizing current research. This review will provide new ideas for future research on two-peptide bacteriocins.

Loosening failure of bolted joints often occurs in a vibration environment. This may induce the separation of clamped components and even result in catastrophic consequences in certain situations. Various anti-loosening bolted connections have been developed and widely applied to prevent loosening. Tightening and fatigue resistance performances are also two important characteristics of anti-loosening bolted connections. However, a comprehensive comparison study of the tightening, anti-loosening, and fatigue resistance performances of typical anti-loosening bolted connections is lacking, meaning that there is a lack of material to assist in the selection of anti-loosening bolted connections in engineering. In this study, accurate three-dimensional finite element models of typical anti-loosening bolted connections with the forms of washers or nuts are established. The processes of tightening, vibration-induced loosening, and fatigue are simulated via finite element analysis (FEA). Based on the results of FEA, the tightening, anti-loosening, and fatigue resistance performances of regular bolted joints and several anti-loosening bolted connections are comprehensively compared. The results reveal that bolted joints installed with both a variable-diameter nut and an eccentric double nut are difficult to tighten. We confirm that the researched structures all have superior anti-loosening capacities compared to regular bolted joints. Additionally, the results show that the regular bolted joint achieved the worst fatigue resistance performance, i.e., the application of anti-loosening bolted connections improves fatigue resistance. Finally, the effects of preload distributions on the two nuts in bolted joints with double nuts are discussed in terms of tightening, anti-loosening, and fatigue resistance performances. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) has become the most promising converter technology for high-voltage direct current (HVdc) transmission systems. MMC submodule (SM) topologies with dc fault ride-through capabilities are emerging which are suitable for overhead line applications. The hybrid SM design of each converter arm can get the compromise of higher capability of handling dc fault and lower capital investments and losses. In this paper, the initial hybrid SM numbers design method for supporting the dc-link voltage and riding-through dc faults and the optimized hybrid SM redundancy configuration strategy for effectively increasing the reliability of MMC are proposed and calculated. In contrast with the previously proposed redundancy configuration for MMC with the single SM topology, this approach solves the curvature of three-dimensional surface to calculate the recommended redundant hybrid SM numbers which takes both the semiconductor device utilization rate and the reliability of MMC into consideration. [ABSTRACT FROM PUBLISHER]

Lactobacillus plantarum is an important industrial lactic acid bacteria, which can be used as a starter culture for fermented milk and meat products. Many Lactobacillus plantarum strains can produce bacteriocins with broad-spectrum antibacterial properties, heat stability, and easy to be hydrolyzed by protease in the process of food fermentation and metabolism, and their potential as biopreservative starter culture in the preservation of fermented food has been recognized. However, the high salt environment in the food matrix can affect bacteriocin production. Hence, the objective of this research is to reveal how salt stress affects the production of bacteriocin and the expression of related genes in this strain by transcriptome sequencing and to further analyze possible regulatory mechanisms, to provide references for the use of bacteriocin as a natural biological preservative in salt-containing foods. The number of viable counts and the antibacterial activity of bacteriocin over the whole growth stages were determined under the stress of 0%, 2%, 3%, 4%, and 6% NaCl. When the strain was cultured at low nanoparticle NaCl concentration (2% or 3%), the growth of the experimental group had no significant difference compared with the control group; however, bacteriocin antibacterial activity increased significantly in the stable phase. When the target strain was cultured under 2% NaCl stress for 24 h, the antimicrobial activity reached the maximum. Subsequently, based on the transcriptome sequencing results obtained by Illumina HiSEq 2500 sequencing system, the differentially expressed genes under 0% and 2% NaCl stress were compared, and the enrichment pathways of these genes were analyzed. A total of 260 genes displayed significant differential expression induced by NaCl: Among them, 159 genes were significantly up-regulated, and 101 genes were down-regulated. Bioinformatic analysis revealed that differentially expressed genes related to bacteriocin synthesis were mainly enriched in bacterial secretion pathway, amino acid synthesis pathway, proteolytic enzyme regulation pathway, purine metabolism pathway, two-component reg- ulation pathway, etc. It is preliminarily speculated that nanoparticle NaCl stress can regulate the synthesis and release of bacteriocin by affecting the expression of secY and ftsY in the cell membrane secretion pathway. We also speculate that nanoparticle NaCl stress can provide raw materials for bacteriocin by affecting the expression levels of genes hisH, cysE, cysM, metB, metA, lysA, and argH in the amino acid synthesis pathway. In addition, our research signified that the expression levels of sat and rpoB in the purine metabolism pathway were up-regulated under nanoparticle NaCl stress, which is beneficial to provide energy for bacteriocin production. The results will be helpful to understand how salt stress regulates bacteriocin synthesis of Lactobacillus plantarum . Furthermore, this study also provides guidance for using bacteriocin-producing strains as biocontrol bacteria in the salt-containing food matrix.