Effect of Pulsed Electric Field on Membrane Lipids and Oxidative Injury of Salmonella typhimurium

Growth Reduction of Vibrionaceae and Microflora Diversity in Ice-Stored Pacific White Shrimp (Penaeus vannamei) Treated with a Low-Frequency Electric Field

A novel storage technique that combines the low-frequency electric field (LFEF) and ice temperature was used to extend the shelf life of Pacific white shrimp (Penaeus vannamei). The study investigated the effect of LFEF treatment on the quality and microbial composition of Penaeus vannamei during storage at ice temperature. The results showed that the LFEF treatment significantly extended the shelf life of shrimp during storage at ice temperature. The total volatile base nitrogen (TVB-N) and pH of samples increased over time, while the total viable count (TVC) showed a trend of first decreasing and then increasing. Obviously, shrimp samples treated with LFEF had a lower pH, TVB-N and TVC values than the untreated samples (p < 0.05) at the middle and late stages of storage. LFEF treatment increased the diversity and altered the composition of the microbial communities in Penaeus vannamei. Additionally, the treatment led to a decrease in the relative abundance of dominant spoilage bacteria, including Aliivibrio, Photobacterium and Moritella, in Penaeus vannamei stored at ice temperature for 11 days. Furthermore, correlation analysis indicated that TVB-N and pH had a significant and positive correlation with Pseudoalteromonas, suggesting that Pseudoalteromonas had a greater impact on shrimp quality. This study supports the practical application of accelerated low-frequency electric field-assisted shrimp preservation as an effective means of maintaining shrimp meat quality.

The effect of emulsifier type and oil inclusion on stress-related gene expression of Salmonella typhimurium in oil-in-water emulsion

Salmonella has been associated with numerous outbreaks from contaminated food products, including emulsions. Emulsions are influenced by emulsifier type and oil presence, which can have varying degrees of stress or protection on bacteria. Although our previous research has shown that emulsifier solutions, rather than emulsions, provide a protective effect on Salmonella typhimurium after thermal treatment, the underlying mechanism remains unclear. This study selected S. typhimurium as the model microorganism and utilized the same emulsifiers (Tween 20, Tween 80, Triton X-100) to create emulsifier solutions and emulsions with the same oil fraction (60% (v/v)) to examine their effect on the expression of nine selected genes (rpoE, rpoH, otsB, proV, fadA, fabA, dnaK, ibpA, ompC) associated with stress response. Specifically, the study observed variations in gene expression under normal and thermal stress at 55°C. After 20-h incubation, Triton X-100 emulsion caused an upregulation of stress-related genes, rpoE, otsB, and fabA, suggesting stressful environment. After thermal treatment, S. typhimurium in Triton X-100 solution showed a longer 5-log reduction time with increased proV and decreased fabA and ompC expression, suggesting enhanced thermal protection compared to its emulsion. Conversely, Tween 80 solution increased fabA and ompC expression, indicating greater membrane fluidity and passive diffusion, potentially reducing thermal resistance. However, according to the upregulation of ibpA, this effect was likely mitigated by the overproduction of heat shock proteins. Notably, Triton X-100 environments exhibited the most significant gene expression changes after heat treatment, whereas Tween 80 without oil was the most inhospitable for bacterial survival. These findings inform bacterial responses under various conditions, aiding food safety strategies.

Effects of certain physical stresses on the composition of the membrane of bacteria implicated in food and environmental contamination

Bacterial membranes are implicated in the adaptation process of bacteria to numerous environmental conditions. In this context, our aim was to explain the consequences of a few physical stressor factors, like UV radiations and magnetic fields underlying the structural adaptation of cellular membranes to physical factors. The goal was also to review the state of the art about the link between membrane composition and bacterial resistance. According to comparative studies between ionizing γ-radiation, non-ionizing UVc radiations and Static Magnetic Field SMF, the response of some Gram negative bacteria appears to be generalized and was manifested by a membrane unsaturation, because of a production peak of unsaturated fatty acids. However, disturbances found inside the membrane, after UVB and Pulsed Electric Field (PEF) exposure were marked by a lower unsaturated fatty acids rate. This result is not concordant to disturbance seen after UVC treatment, even if the treatment is by UV radiation.

Pulsed electric field promotes the growth metabolism of aerobic denitrifying bacteria Pseudomonas putida W207-14 by improving cell membrane permeability

The purpose of this study was to explore the stimulation mechanism of low pulsed electric field (PEF) strength treatment to promote the growth metabolism of aerobic denitrifying bacteria Pseudomonas putida W207-14. The results indicated that compared with the control group, the strain W207-14 treated with PEF entered the logarithmic growth phase 5 h earlier, the growth time to reached the maximum cell optical density at 600 nm (OD600) of 1.935 ± 0.04 was only 24 h, which shortened by half. With the reduction of growth time, the metabolic rate of the strain increased significantly, in which the removal efficiency of COD, NO₃^--N and TN was 97.67 ± 1.12%, 90.34 ± 0.73% and 90.13 ± 0.10% in 24 h, respectively. The maximum nitrate removal rate increased from 3.49 mg/L/h to 7.53 mg/L/h. A large number of cells with simultaneous cell membrane damage and high physiological activity were observed by flow cytometry (FCM) in combination with fluorescence staining analysis, which confirmed the reversible electroporation on the cell membrane of strain W207-14 treated with PEF. Transcriptomic analysis indicated that PEF activated the highly significant differential expression of membrane porin (opdB, opdC, and oprB) and cytochrome oxidoreductase related genes (ccoP, ccoN, cioA and cioB) on the cell membrane, which promoted the transport of nutrients through the cell membrane and electron transfer during aerobic respiration and provided an explanation for the possible mechanism of PEF promoting the growth metabolism of strain W207-14 at the micro level. These results lay a foundation for the practical application of PEF enhanced aerobic denitrification technology.

Coordinated regulation of symbiotic adaptation by NodD proteins and NolA in the type I peanut bradyrhizobial strain Bradyrhizobium zhanjiangense CCBAU51778

Type I peanut bradyrhizobial strains can establish efficient symbiosis in contrast to symbiotic incompatibility induced by type II strains with mung bean. The notable distinction in the two kinds of key symbiosis-related regulators nolA and nodD close to the nodABCSUIJ operon region between these two types of peanut bradyrhizobia was found. Therefore, we determined whether NolA and NodD proteins regulate the symbiotic adaptations of type I strains to different hosts. We found that NodD1-NolA synergistically regulated the symbiosis between the type I strain Bradyrhizobium zhanjiangense CCBAU51778 and mung bean, and NodD1-NodD2 jointly regulated nodulation ability. In contrast, NodD1-NolA coordinately regulated nodulation ability in the CCBAU51778-peanut symbiosis. Meanwhile, NodD1 and NolA collectively contributes to competitive nodule colonization of CCBAU51778 on both hosts. The Fucosylated Nod factors and intact type 3 secretion system (T3SS), rather than extra nodD2 and full-length nolA, were critical for effective symbiosis with mung bean. Unexpectedly, T3SS-related genes were activated by NodD2 but not NodD1. Compared to NodD1 and NodD2, NolA predominantly inhibits exopolysaccharide production by promoting exoR expression. Importantly, this is the first report that NolA regulates rhizobial T3SS-related genes. The coordinated regulation and integration of different gene networks to fine-tune the expression of symbiosis-related genes and other accessory genes by NodD1-NolA might be required for CCBAU51778 to efficiently nodulate peanut. This study shed new light on our understanding of the regulatory roles of NolA and NodD proteins in symbiotic adaptation, highlighting the sophisticated gene networks dominated by NodD1-NolA.

Relative expression and validation of Aeromonas salmonicida subsp. salmonicida reference genes during ex vivo and in vivo fish infection

The genus Aeromonas is found worldwide in freshwater and marine environments and has been implicated in the etiology of human and animal diseases. In fish, among Aeromonas species, A. salmonicida causes massive mortality and great economic losses in marine and continental aquaculture species. Currently, several aspects of the clinical signs and pathogenesis of this Gram-negative bacterium have been described; however, determination of an appropriate reference gene is essential to normalize cellular mRNA data remain unknown. Here we evaluate the stability of seven candidate reference genes to be used for data normalization during ex vivo and in vivo experiments conducted in Atlantic cod, Atlantic salmon, and lumpfish. To assess this, raw Ct values obtained were evaluated by using geNorm, NormFinder, BestKeeper, Delta Ct comparison, and the comprehensive ranking, through the bioinformatic open-access portal RefFinder. We determined that fabD and era were most suitable reference genes in Atlantic cod primary macrophages, hfq and era in Atlantic salmon primary macrophages, rpoB and fabD in lumpfish head kidney samples, and hfq and era in lumpfish spleen. Our study demonstrates that use of multiple reference genes and its validation before measurements helps to minimize variability arising in qPCR studies that evaluate A. salmonicida gene expression in fish tissues. Overall, this study provided with an expanded list of reliable reference genes for A. salmonicida gene expression using qPCR during fish infection studies.

Inactivation of Salmonella typhimurium SL1344 by Chlorogenic Acid and the Impairment of Cellular Integrity

Chlorogenic acid (CGA) is an antibacterial agent that can be isolated from Eucommia ulmoides Oliver, a Chinese medicinal and edible plant food. The inhibitory effect of CGA on bacterial growth and stiffness of the outer membrane (OM) had been reported, while more evidence were required to elucidate its impairment of cell wall. In this study, the morphological and physiochemical changes of Salmonella cells under CGA treatment were investigated. Firstly, the minimum inhibitory concentration (MIC) of CGA against Salmonella was assayed. Later, the permeability of OM and activity of the proteins released were measured and observed to reveal the alteration of OM characteristic and cellular morphology. Finally, reactive oxygen species and cell membrane fluidity were analyzed, respectively, to elucidate how CGA damaged cell surface. The results showed that MIC of CGA against Salmonella was 6.25 mg/L. Under sub-lethal doses of CGA, the OM permeability and the release of soluble proteins were enhanced evidently, and Salmonella cells showed more deformed and shrunken, confirming the impairment of cellular integrity under CGA. Finally, the possible cause of cell surface damage was investigated. the fluidity of the membrane was increased upon CGA treatment, which may the possible cause of OM by CGA.

Molecular dynamics simulations of the effects of lipid oxidation on the permeability of cell membranes

The formation of transient pores in their membranes is a well-known mechanism of permeabilization of cells exposed to high-intensity electric pulses. However, the formation of such pores is not able to explain all aspects of the so-called electroporation phenomenon. In particular, the reasons for sustained permeability of cell membranes, persisting long after the pulses' application, remain elusive. The complete resealing of cell membranes takes indeed orders of magnitude longer than the time for electropore closure as reported from molecular dynamics (MD) investigations. Lipid peroxidation has been suggested as a possible mechanism to explain the sustainable permeability of cell membranes. However, theoretical investigations of membrane lesions containing excess amounts of hydroperoxides have shown that the conductivities of such lesions were not high enough to account for the experimental measurements. Here, expanding on these studies, we investigate quantitatively the permeability of cell membrane lesions that underwent secondary oxidation. MD simulations and free energy calculations of lipid bilayers show that such lesions provide a better model of post-pulse permeable and conductive electropermeabilized cells. These results are further discussed in the context of sonoporation and ferroptosis, respectively a procedure and a phenomenon, among others, in which, alike electroporation, substantial lipid oxidation might be triggered.

Modifications of Plasma Membrane Organization in Cancer Cells for Targeted Therapy

Modifications of the composition or organization of the cancer cell membrane seem to be a promising targeted therapy. This approach can significantly enhance drug uptake or intensify the response of cancer cells to chemotherapeutics. There are several methods enabling lipid bilayer modifications, e.g., pharmacological, physical, and mechanical. It is crucial to keep in mind the significance of drug resistance phenomenon, ion channel and specific receptor impact, and lipid bilayer organization in planning the cell membrane-targeted treatment. In this review, strategies based on cell membrane modulation or reorganization are presented as an alternative tool for future therapeutic protocols.

Rapid Airborne Influenza Virus Quantification Using an Antibody-Based Electrochemical Paper Sensor and Electrostatic Particle Concentrator

Airborne influenza viruses are responsible for serious respiratory diseases, and most detection methods for airborne viruses are based on extraction of nucleic acids. Herein, vertical-flow-assay-based electrochemical paper immunosensors were fabricated to rapidly quantify the influenza H1N1 viruses in air after sampling with a portable electrostatic particle concentrator (EPC). The effects of antibodies, anti-influenza nucleoprotein antibodies (NP-Abs) and anti-influenza hemagglutinin antibodies (HA-Abs), on the paper sensors as well as nonpulsed high electrostatic fields with and without corona charging on the virus measurement were investigated. The antigenicity losses of the surface (HA) proteins were caused by H₂O₂ via lipid oxidation-derived radicals and ¹O₂ via direct protein peroxidation upon exposure of a high electrostatic field. However, minimal losses in antigenicity of NP of the influenza viruses were observed, and the concentration of the H1N1 viruses was more than 160 times higher in the EPC than the BioSampler upon using NP-Ab based paper sensors after 60 min collection. This NP-Ab-based paper sensors with the EPC provided measurements comparable to quantitative polymerase chain reaction (qPCR) but much quicker, specific to the influenza H1N1 viruses in the presence of other airborne microorganisms and beads, and more cost-effective than enzyme-linked immunosorbent assay and qPCR.

Proteomics-Based Mechanistic Investigation of Escherichia coli Inactivation by Pulsed Electric Field

The pulsed electric field (PEF) technology has been widely applied to inactivate pathogenic bacteria in food products. Though irreversible pore formation and membrane disruption is considered to be the main contributing factor to PEF's sterilizing effects, the exact molecular mechanisms remain poorly understood. In this study, by using mass spectrometry (MS)-based label-free quantitative proteomic analysis, we compared the protein profiles of PEF-treated and untreated Escherichia coli. We identified a total of 175 differentially expressed proteins, including 52 candidates that were only detected in at least two of the three samples in one experiment group but not in the other group. Functional analysis revealed that the differential proteins were primarily involved in the regulation of cell membrane composition and integrity, stress response, as well as various metabolic processes. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis was conducted on the genes of selected differential proteins at varying PEF intensities, which were known to result in different cell killing levels. The qRT-PCR data confirmed that the proteomic results could be reliably used for further data interpretation, and that the changes in the expression levels of the differential candidates were, to a large extent, caused directly by the PEF treatment. The findings of the current study offered valuable insight into PEF-induced cell inactivation.

Membrane Electroporation and Electropermeabilization: Mechanisms and Models

Exposure of biological cells to high-voltage, short-duration electric pulses causes a transient increase in their plasma membrane permeability, allowing transmembrane transport of otherwise impermeant molecules. In recent years, large steps were made in the understanding of underlying events. Formation of aqueous pores in the lipid bilayer is now a widely recognized mechanism, but evidence is growing that changes to individual membrane lipids and proteins also contribute, substantiating the need for terminological distinction between electroporation and electropermeabilization. We first revisit experimental evidence for electrically induced membrane permeability, its correlation with transmembrane voltage, and continuum models of electropermeabilization that disregard the molecular-level structure and events. We then present insights from molecular-level modeling, particularly atomistic simulations that enhance understanding of pore formation, and evidence of chemical modifications of membrane lipids and functional modulation of membrane proteins affecting membrane permeability. Finally, we discuss the remaining challenges to our full understanding of electroporation and electropermeabilization.

Cinnamaldehyde inhibit Escherichia coli associated with membrane disruption and oxidative damage

In this study, the antimicrobial mechanism of cinnamaldehyde (CIN) against Gram-negative Escherichia coli ATCC 25922 (E. coli) based on membrane and gene regulation was investigated. Treatment with low concentration (0, 1/8, 1/4, 3/8 MIC) of CIN can effectively suppress the growth of E. coli by prolonging its lag phase and Raman spectroscopy showed obvious distinction of the E. coli after being treated with these concentration of CIN. The determination of relative conductivity indicated that CIN at relatively high concentration (0, 1, 2, 4 MIC) can increase the cell membrane permeability, causing the leakage of cellular content. Besides, the content of malondialdehyde (MDA) and the activity of total superoxide dismutase (SOD) of E. coli increased with increasing treatment concentration of CIN, implying that CIN can cause oxidative damage on E. coli cell membrane and induce the increase of total SOD activity to resist this oxidative harm. Moreover, quantitative real-time RT-PCR (qRT-PCR) analysis revealed the relationship between expression of antioxidant genes (SODa, SODb, SODc) and treatment CIN concentration, suggesting that SOD, especially SODc, played a significant role in resistance of E. coli to CIN. The underlying inactivation processing of CIN on E. coli was explored to support CIN as a potential and natural antimicrobial agent in food industry.

Optimization of antioxidative peptides from mackerel (Pneumatophorus japonicus) viscera

Mackerel (Pneumatophorus japonicus) viscera contain large amount of protein. We used five proteases to hydrolyze the viscera, and the hydrolysate treated by neutrase exhibited the highest nitrogen recovery (NR). Then we optimized the preparation conditions for mackerel viscera hydrolysate (MVH) by response surface methodology and investigated the antioxidant activity of MVH. The optimal conditions were as follows: enzyme concentration of 1,762.87 U/g, pH of 6.76, temperature of 43.75 °C, extraction time of 6.0 h and water/material ratio of 20.37 (v/w), and the maximum NR was 37.84%. Furthermore, the molecular weight distribution of MVH was almost below 3,000 Da determined by TSK G2000 SWXL gel filtration chromatography, and the MVH exhibited good antioxidant activities in various in vitro assays, including DPPH radical, hydroxyl radical and superoxide anion scavenging activities, reducing power and similar effectivelness as butylated hydroxytoluene and Vitamin E to inhibit lipid peroxidation. The results suggested that MVH could be used as a potential source of antioxidant peptide in food industries.