Cold atmospheric pressure plasma causes protein denaturation and endoplasmic reticulum stress in Saccharomyces cerevisiae

Iron-sulfur cluster proteins present the weak spot in non-thermal plasma-treated Escherichia coli

Non-thermal atmospheric pressure plasmas have an antiseptic activity beneficial in different medical applications. In a genome-wide screening, hydrogen peroxide and superoxide were identified as key species contributing to the antibacterial effects of plasma while [FeS] cluster proteins emerged as potential cellular targets. We investigated the impact of plasma treatment on [FeS] cluster homeostasis in Escherichia coli treated for 1 min with the effluent of a microscale atmospheric pressure plasma jet (μAPPJ). Mutants defective in [FeS] cluster synthesis and maintenance lacking the SufBC2D scaffold protein complex or desulfurase IscS were hypersensitive to plasma treatment. Monitoring the activity of [FeS] cluster proteins of the tricarboxylic acid cycle (aconitase, fumarase, succinate dehydrogenase) and malate dehydrogenase (no [FeS] clusters), we identified cysteine, iron, superoxide dismutase, and catalase as determinants of plasma sensitivity. Survival rates, enzyme activity, and restoration of enzyme activity after plasma treatment were superior in mutants with elevated cysteine levels and in the wildtype under iron replete conditions. Mutants with elevated hydrogen peroxide and superoxide detoxification capacity over-expressing sodA and katE showed full protection from plasma-induced enzyme inactivation and survival rates increased from 34 % (controls) to 87 %. Our study indicates that metabolic and genetic adaptation of bacteria may result in plasma tolerance and resistance, respectively.

Sustained germination-promoting effect of cold atmospheric plasma on spinach seeds

Cold atmospheric plasma (CAP) irradiation exhibits a sterilizing effect without causing thermal denaturation or leaving behind residual toxicants. CAP also has potential applications in various fields, including agriculture, leading to research efforts in recent years. This study investigated the effects of CAP on the seed germination rate of spinach (Spinacia oleracea), which typically has a low seed germination rate. Our results confirmed that irradiation with N2-CAP and Air-CAP significantly enhanced the germination rate of spinach seeds. Notably, we discovered that CAP irradiation promoted germination even in spinach seeds coated with a fungicide (thiuram) and a disinfectant (Captan), which are commonly used. Additionally, we examined whether the interval between CAP irradiation and the subsequent germination-induction treatment influenced the germination efficiency. We found that the germination-promoting effect of CAP on spinach seeds persisted for at least 30 days, demonstrating the high utility and practicality of CAP in the agricultural sector.

The cold atmospheric pressure plasma-generated species superoxide, singlet oxygen and atomic oxygen activate the molecular chaperone Hsp33

Cold atmospheric pressure plasmas are used for surface decontamination or disinfection, e.g. in clinical settings. Protein aggregation has been shown to significantly contribute to the antibacterial mechanisms of plasma. To investigate the potential role of the redox-activated zinc-binding chaperone Hsp33 in preventing protein aggregation and thus mediating plasma resistance, we compared the plasma sensitivity of wild-type E. coli to that of an hslO deletion mutant lacking Hsp33 as well as an over-producing strain. Over-production of Hsp33 increased plasma survival rates above wild-type levels. Hsp33 was previously shown to be activated by plasma in vitro. For the PlasmaDerm source applied in dermatology, reversible activation of Hsp33 was confirmed. Thiol oxidation and Hsp33 unfolding, both crucial for Hsp33 activation, occurred during plasma treatment. After prolonged plasma exposure, however, unspecific protein oxidation was detected, the ability of Hsp33 to bind zinc ions was decreased without direct modifications of the zinc-binding motif, and the protein was inactivated. To identify chemical species of potential relevance for plasma-induced Hsp33 activation, reactive oxygen species were tested for their ability to activate Hsp33 in vitro. Superoxide, singlet oxygen and potentially atomic oxygen activate Hsp33, while no evidence was found for activation by ozone, peroxynitrite or hydroxyl radicals.

Detoxification of the post-harvest antifungal pesticide thiabendazole by cold atmospheric plasma

Cold atmospheric plasma (CAP) irradiation has a sterilizing effect without thermal denaturation or the production of residual substances. Hence, it is considered to be a safe sterilization technology with minimal damage for fresh foods. In addition, its decomposition effect on chemical substances has also been confirmed, and the application of CAP in the food and agricultural domains is increasing. In this study, we examined the potential of CAP to detoxify pesticide residues. Post-harvest chemical treatments using pesticides, such as fungicides, are frequently employed in imported agricultural products and are often disapproved by consumers. Therefore, we assessed the detoxification of thiabendazole (TBZ), a widely used post-harvest pesticide, using low-cost air plasma irradiation. We found that CAP irradiation conditions that detoxified TBZ caused little damage to the edible parts of mandarin oranges. The results of the present study suggest that CAP irradiation is useful for detoxifying and degrading pesticide residues without damaging agricultural products and that CAP irradiation is an effective means of maintaining food safety.

Cold Atmospheric Plasma Triggers Apoptosis via the Unfolded Protein Response in Melanoma Cells

Cold atmospheric plasma (CAP) describes a partially ionized gas carrying large amounts of reactive oxygen (ROS) and nitrogen species (RNS). Numerous studies reported strong antitumor activity of CAP, thus rendering it a promising approach for tumor therapy. Although several cellular mechanisms of its cytotoxicity were identified in recent years, the exact molecular effects and contributing signaling pathways are yet to be discovered. We discovered a strong activation of unfolded protein response (UPR) after CAP treatment with increased C/EBP homologous protein (CHOP) expression, which was mainly caused by protein misfolding and calcium loss in the endoplasmic reticulum. In addition, both ceramide level and ceramide metabolism were reduced after CAP treatment, which was then linked to the UPR activation. Pharmacological inhibition of ceramide metabolism resulted in sensitization of melanoma cells for CAP both in vitro and ex vivo. This study identified a novel mechanism of CAP-induced apoptosis in melanoma cells and thereby contributes to its potential application in tumor therapy.

Nonthermal Plasma Effects on Fungi: Applications, Fungal Responses, and Future Perspectives

The kingdom of Fungi is rich in species that live in various environments and exhibit different lifestyles. Many are beneficial and indispensable for the environment and industries, but some can threaten plants, animals, and humans as pathogens. Various strategies have been applied to eliminate fungal pathogens by relying on chemical and nonchemical antifungal agents and tools. Nonthermal plasma (NTP) is a potential tool to inactivate pathogenic and food-contaminating fungi and genetically improve fungal strains used in industry as enzyme and metabolite producers. The NTP mode of action is due to many highly reactive species and their interactions with biological molecules. The interaction of the NTP with living cells is believed to be synergistic yet not well understood. This review aims to summarize the current NTP designs, applications, and challenges that involve fungi, as well as provide brief descriptions of underlying mechanisms employed by fungi in interactions with the NTP components.

Study of the synergistic effect of singlet oxygen with other plasma-generated ROS in fungi inactivation during water disinfection

Cold atmospheric plasma (CAP) possesses the ability of high-efficiency disinfection. It is reported that mixtures of reactive oxygen species (ROS) including ^·OH, ¹O₂, O₂^- and H₂O₂ generated from CAP have better antimicrobial ability than mimicked solution of mixture of single ROS type, but the reason is not clear. In this study, CAP was applied to treat yeasts in water in order to investigate the fungal inactivation efficiency and mechanism. The results showed that plasma treatment for 5 min could result in >2-log reduction of yeast cells, and application of varied ROS scavengers could significantly increase the yeast survival rate, indicating that ^·OH and ¹O₂ played the pivotal role in yeast inactivation. Moreover, the synergistic effect of ¹O₂ with other plasma-generated ROS was revealed. ¹O₂ could diffuse into cells and induce the depolarization of mitochondrial membrane potential (MMP), and different levels of MMP depolarization determined different cell death modes. Mild damage of mitochondria during short-term plasma treatment could lead to apoptosis. For long-term plasma treatment, the cell membrane could be severely damaged by the plasma-generated ^·OH, so a large amount of ¹O₂ could induce more depolarization of MMP, leading to increase of intracellular O₂^- and Fe²⁺ which subsequently caused cell inactivation. ¹O₂ could also induce protein aggregation and increase of RIP1/RIP3 necrosome, leading to necroptosis. With participation of ¹O₂, endogenous ^·OH could also be generated via Fenton and Haber-Weiss reactions during plasma treatment, which potentiated necroptosis. Adding l-His could mitigate membrane damage, inhibit the drop of MMP and the formation of necrosome, and thus prevent the happening of necroptosis. These findings may deepen the understanding of plasma sterilization mechanisms and provide guidance for microbial killing in the environment.

Pyocyanin biosynthesis protects Pseudomonas aeruginosa from nonthermal plasma inactivation

Pseudomonas aeruginosa is an important opportunistic human pathogen, which raises a worldwide concern for its increasing resistance. Nonthermal plasma, which is also called cold atmospheric plasma (CAP), is an alternative therapeutic approach for clinical infectious diseases. However, the bacterial factors that affect CAP treatment remain unclear. The sterilization effect of a portable CAP device on different P. aeruginosa strains was investigated in this study. Results revealed that CAP can directly or indirectly kill P. aeruginosa in a time‐dependent manner. Scanning electron microscopy and transmission electron microscope showed negligible surface changes between CAP‐treated and untreated P. aeruginosa cells. However, cell leakage occurred during the CAP process with increased bacterial lactate dehydrogenase release. More importantly, pigmentation of the P. aeruginosa culture was remarkably reduced after CAP treatment. Further mechanical exploration was performed by utilizing mutants with loss of functional genes involved in pyocyanin biosynthesis, including P. aeruginosa PAO1 strain‐derived phzA1::Tn, phzA2::Tn, ΔphzA1/ΔphzA2, phzM::Tn and phzS::Tn, as well as corresponding gene deletion mutants based on clinical PA1 isolate. The results indicated that pyocyanin and its intermediate 5‐methyl phenazine‐1‐carboxylic acid (5‐Me‐PCA) play important roles in P. aeruginosa resistance to CAP treatment. The unique enzymes, such as PhzM in the pyocyanin biosynthetic pathway, could be novel targets for the therapeutic strategy design to control the growing P. aeruginosa infections.

Hsp104 contributes to freeze-thaw tolerance by maintaining proteasomal activity in a spore clone isolated from Shirakami kodama yeast

The supply of oven-fresh bakery products to consumers has been improved by frozen dough technology; however, freeze-thaw stress decreases the activity of yeast cells. To breed better baker's yeasts for frozen dough, it is important to understand the factors affecting freeze-thaw stress tolerance in baker's yeast. We analyzed the stress response in IB1411, a spore clone from Saccharomyces cerevisiae Shirakami kodama yeast, with an exceptionally high tolerance to freeze-thaw stress. Genes encoding trehalose-6-phosphate synthase (TPS1), catalase (CTT1), and disaggregase (HSP104) were highly expressed in IB1411 cells even under conditions of non-stress. The expression of Hsp104 protein was also higher in IB1411 cells even under non-stress conditions. Deletion of HSP104 (hsp104Δ) in IB1411 cells reduced the activity of the ubiquitin-proteasome system (UPS). By monitoring the accumulation of aggregated proteins using the ΔssCPY*-GFP fusion protein under freeze-thaw stress or treatment with proteasomal inhibitor, we found that IB1411 cells resolved aggregated proteins faster than the hsp104Δ strain. Thus, Hsp104 seems to contribute to freeze-thaw tolerance by maintaining UPS activity via the disaggregation of aggregated proteins. Lastly, we found that the IB1411 cells maintained high leavening ability in frozen dough as compared with the parental strain, Shirakami kodama yeast, and thus will be useful for making bread.

Cold Atmospheric-Pressure Plasma Caused Protein Damage in Methicillin-Resistant Staphylococcus aureus Cells in Biofilms

Biofilms formed by multidrug-resistant bacteria are a major cause of hospital-acquired infections. Cold atmospheric-pressure plasma (CAP) is attractive for sterilization, especially to disrupt biofilms formed by multidrug-resistant bacteria. However, the underlying molecular mechanism is not clear. In this study, CAP effectively reduced the living cells in the biofilms formed by methicillin-resistant Staphylococcus aureus, and 6 min treatment with CAP reduced the S. aureus cells in biofilms by 3.5 log₁₀. The treatment with CAP caused the polymerization of SaFtsZ and SaClpP proteins in the S. aureus cells of the biofilms. In vitro analysis demonstrated that recombinant SaFtsZ lost its self-assembly capability, and recombinant SaClpP lost its peptidase activity after 2 min of treatment with CAP. Mass spectrometry showed oxidative modifications of a cluster of peaks differing by 16 Da, 31 Da, 32 Da, 47 Da, 48 Da, 62 Da, and 78 Da, induced by reactive species of CAP. It is speculated that the oxidative damage to proteins in S. aureus cells was induced by CAP, which contributed to the reduction of biofilms. This study elucidates the biological effect of CAP on the proteins in bacterial cells of biofilms and provides a basis for the application of CAP in the disinfection of biofilms.

Acquired Resistance to Severe Ethanol Stress in Saccharomyces cerevisiae Protein Quality Control

Acute severe ethanol stress (10% [vol/vol]) damages proteins and causes the intracellular accumulation of insoluble proteins in Saccharomyces cerevisiae On the other hand, a pretreatment with mild stress increases tolerance to subsequent severe stress, which is called acquired stress resistance. It currently remains unclear whether the accumulation of insoluble proteins under severe ethanol stress may be mitigated by increasing protein quality control (PQC) activity in cells pretreated with mild stress. In the present study, we examined the induction of resistance to severe ethanol stress in PQC and confirmed that a pretreatment with 6% (vol/vol) ethanol or mild thermal stress at 37°C significantly reduced insoluble protein levels and the aggregation of Lsg1, which is prone to denaturation and aggregation by stress, in yeast cells under 10% (vol/vol) ethanol stress. The induction of this stress resistance required the new synthesis of proteins; the expression of proteins comprising the bichaperone system (Hsp104, Ssa3, and Fes1), Sis1, and Hsp42 was upregulated during the pretreatment and maintained under subsequent severe ethanol stress. Since the pretreated cells of deficient mutants in the bichaperone system (fes1Δ hsp104Δ and ssa2Δ ssa3Δ ssa4Δ) failed to sufficiently reduce insoluble protein levels and Lsg1 aggregation, the enhanced activity of the bichaperone system appears to be important for the induction of adequate stress resistance. In contrast, the importance of proteasomes and aggregases (Btn2 and Hsp42) in the induction of stress resistance has not been confirmed. These results provide further insights into the PQC activity of yeast cells under severe ethanol stress, including the brewing process.IMPORTANCE Although the budding yeast S. cerevisiae, which is used in the production of alcoholic beverages and bioethanol, is highly tolerant of ethanol, high concentrations of ethanol are also stressful to the yeast and cause various adverse effects, including protein denaturation. A pretreatment with mild stress improves the ethanol tolerance of yeast cells; however, it currently remains unclear whether it increases PQC activity and reduces the levels of denatured proteins. In the present study, we found that a pretreatment with mild ethanol upregulated the expression of proteins involved in PQC and mitigated the accumulation of insoluble proteins, even under severe ethanol stress. These results provide novel insights into ethanol tolerance and the adaptive capacity of yeast. They may also contribute to research on the physiology of yeast cells during the brewing process, in which the concentration of ethanol gradually increases.

Effects of Non-Thermal Plasma on Yeast Saccharomyces cerevisiae

Cold plasmas generated by various electrical discharges can affect cell physiology or induce cell damage that may often result in the loss of viability. Many cold plasma-based technologies have emerged in recent years that are aimed at manipulating the cells within various environments or tissues. These include inactivation of microorganisms for the purpose of sterilization, food processing, induction of seeds germination, but also the treatment of cells in the therapy. Mechanisms that underlie the plasma-cell interactions are, however, still poorly understood. Dissection of cellular pathways or structures affected by plasma using simple eukaryotic models is therefore desirable. Yeast Saccharomyces cerevisiae is a traditional model organism with unprecedented impact on our knowledge of processes in eukaryotic cells. As such, it had been also employed in studies of plasma-cell interactions. This review focuses on the effects of cold plasma on yeast cells.

Subcellular mechanism of microbial inactivation during water disinfection by cold atmospheric-pressure plasma

Although the identification of effective reactive oxygen species (ROS) generated by plasma has been extensively studied, yet the subcellular mechanism of microbial inactivation has never been clearly elucidated in plasma disinfection processes. In this study, subcellular mechanism of yeast cell inactivation during plasma-liquid interaction was revealed in terms of comprehensive factors including cell morphology, membrane permeability, lipid peroxidation, membrane potential, intracellular redox homeostasis (intracellular ROS and H₂O₂, and antioxidant system (SOD, CAT and GSH)), intracellular ionic equilibrium (intracellular H⁺ and K⁺) and energy metabolism (mitochondrial membrane potential, intracellular Ca²⁺ and ATP level). The ROS analysis show that ·OH, ¹O₂, ·O₂^-and H₂O₂ were generated in this plasma-liquid interaction system and ·O₂^-served as the precursor of ¹O₂. Additionally, the solution pH was reduced. Plasma can effectively inactivate yeast cells mainly via apoptosis by damaging cell membrane, intracellular redox and ion homeostasis and energy metabolism as well as causing DNA fragmentation. ROS scavengers (l-His, d-Man and SOD) and pH buffer (phosphate buffer solution, PBS) were employed to investigate the role of five antimicrobial factors (·OH, ¹O₂, ·O₂^-, H₂O₂ and low pH) in plasma sterilization. Results show that they have different influences on the aforementioned cell physiological activities. The ·OH and ¹O₂ contributed most to the yeast inactivation. The ·OH mainly attacked cell membrane and increased cell membrane permeability. The disturb of cell energy metabolism was mainly attributed to ¹O₂. The damage of cell membrane as well as extracellular low pH could break the intracellular ionic equilibrium and further reduce cell membrane potential. The remarkable increase of intracellular H₂O₂ was mainly due to the influx of extracellular H₂O₂ via destroyed cell membrane, which played a little role in yeast inactivation during 10-min plasma treatment. These findings provide comprehensive insights into the antimicrobial mechanism of plasma, which can promote the development of plasma as an alternative water disinfection strategy.

Effect of Non-Thermal Atmospheric Plasma on Food-Borne Bacterial Pathogens on Ready-to Eat Foods: Morphological and Physico-Chemical Changes Occurring on the Cellular Envelopes

Currently, there is a need for new technological interventions to guarantee the microbiological safety of ready-to-eat (RTE) foods. Non-thermal atmospheric plasma (NTAP) has emerged as a promising strategy for inactivating microorganisms on thermo-sensitive foods, and the elucidation of its mechanisms of action will aid the rational optimization and industrial implementation of this technology for potential applications in the food industry. In this study, the effectiveness of NTAP for inactivating strains of Salmonella Enteritidis, Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes contaminating the surface of different sliced RTE foods (“chorizo”, salami, bacon, smoked salmon, tofu and apple) was investigated. In addition, to further assess the bacterial inactivation mechanisms of NTAP, the morphological and physico-chemical damages in bacterial cells were analyzed. NTAP was effective for the surface decontamination of all products tested and, especially, of cut apple, where the microbial populations were reduced between 1.3 and 1.8 log units for the two Salmonella strains and E. coli O157: H7, respectively, after 15 min of exposure. In the rest of foods, no significant differences in the lethality obtained for the E. coli O157:H7 strain were observed, with inactivation rates of between 0.6 and 0.9 log cycles after a 15-min treatment. On the other hand, the strains from the rest of pathogenic microorganisms studied were extremely resistant on tofu, where barely 0.2–0.5 log units of inactivation were achieved after 15 min of plasma exposure. S. Enteritidis cells treated for 10 min exhibited noticeable morphological and structural changes, as observed by transmission electron microscopy, which were accompanied by a loss in membrane integrity, with an increased leakage of intracellular components and uptake of propidium iodide and marked changes in regions of their FTIR spectra indicating major alterations of the cell wall components. Overall, this indicates that loss of viability was likely caused for this microorganism by a significant damage in the cellular envelopes. However, the plasma-treated cells of L. monocytogenes did not show such obvious changes in morphology, and exhibited less marked effects on the integrity of their cytoplasmic membrane, what suggests that the death of this pathogenic microorganism upon NTAP exposure is more likely to occur as a consequence of damages in other cellular targets.

Possibility to extend the shelf life of NFC tomato juice using cold atmospheric pressure plasma

Cold Atmospheric pressure Plasma (CAP) is a non-thermal method used in food processing. CAP generated with the use of nitrogen in a Glide-arc device for 300 to 600 s exhibited high potential for microbial decontamination and did not induce substantial changes in the physicochemical properties of NFC tomato juice. Samples exposed to cold atmospheric plasma had mostly an intact structure, as revealed by digital microscopy. The investigations indicate that CAP can be applied for biological and chemical waste-free decontamination of food and extension of its shelf life.

Cold atmospheric plasma induces stress granule formation via an eIF2α-dependent pathway

Cold atmospheric plasma is an ionized gas that shows promise in regenerative medical treatments, yet the mechanisms underlying its effects are still poorly understood. Plasma treatment promotes cell growth or cell death depending on the cell type and exposure parameters. To date, no early cell response to plasma, such as stress granule (SG) formation has been addressed. Cytoplasmic SGs are formed as an immediate cell response to acute stress stimuli by recruitment of over 140 proteins intertwined with cytoplasmic RNAs that leads to transient suspension of protein translation. Encouraged by the plasma effects in regenerative medicine and oncology, the atmospheric pressure plasma jet with argon gas flow is being utilized to treat SH-SY5Y cells with an inducible expression of the stress granule marker G3BP1, to gain an insight into early cell response to plasma and SG formation dynamics. Plasma effectively induces SG formation in the exposed cells in a flow/time-dependent manner, with the SG assembly clearly prompted by plasma-induced oxidative stress. Plasma causes SG formation via eIF2α-signaling, which is repressed with the SG formation inhibitor ISRIB. This insight into the early cell response to plasma treatment may lead to improved therapies in regenerative medicine and cancer treatment.

A systematic study of the antimicrobial mechanisms of cold atmospheric-pressure plasma for water disinfection

Waterborne diseases caused by pathogenic microorganisms pose a severe threat to human health. Cold atmospheric-pressure plasma (CAP) has recently gained much interest as a promising fast, effective, economical and eco-friendly method for water disinfection. However, the antimicrobial mechanism of CAP in aqueous environments is still not clearly understood. Herein, we investigate the role of several short-lived reactive oxygen species (ROS) and cellular responses in the CAP inactivation of yeast cells in water. The results show that singlet oxygen (¹O₂), hydroxyl radical (OH) and superoxide anion (O₂^-) are generated in this plasma-water system, and O₂^- served as the precursor of OH. The 5-min plasma treatment resulted in the effective inactivation (more than 2-log reduction) of yeast cells in water. The ROS scavengers significantly increased the survival ratio in the following order: water < D-Man (scavenging OH) < SOD (scavenging O₂^-) < L-His (scavenging ¹O₂), indicating that ¹O₂ contributes the most to the yeast inactivation. In addition, the acidic pH had a synergetic antimicrobial effect with ROS against the yeast cells. During the CAP inactivation process, yeast cells underwent apoptosis in the first 3 min due to the accumulation of intracellular ROS, mitochondrial dysfunction and intracellular acidification, later followed by necrosis under longer exposure times, attributed to the destruction of the cell membrane. Additionally, L-His could switch the cell fate from necrosis to apoptosis through mitigating plasma-induced oxidative stress, indicating that the level of oxidative stress is a critical factor for cell death fate determination. These findings provide comprehensive insights into the antimicrobial mechanism of CAP, which can promote the development of CAP as an alternative water disinfection strategy.

Molecular Mechanisms of the Efficacy of Cold Atmospheric Pressure Plasma (CAP) in Cancer Treatment

Recently, the potential use of cold atmospheric pressure plasma (CAP) in cancer treatment has gained increasing interest. Especially the enhanced selective killing of tumor cells compared to normal cells has prompted researchers to elucidate the molecular mechanisms for the efficacy of CAP in cancer treatment. This review summarizes the current understanding of how CAP triggers intracellular pathways that induce growth inhibition or cell death. We discuss what factors may contribute to the potential selectivity of CAP towards cancer cells compared to their non-malignant counterparts. Furthermore, the potential of CAP to trigger an immune response is briefly discussed. Finally, this overview demonstrates how these concepts bear first fruits in clinical applications applying CAP treatment in head and neck squamous cell cancer as well as actinic keratosis. Although significant progress towards understanding the underlying mechanisms regarding the efficacy of CAP in cancer treatment has been made, much still needs to be done with respect to different treatment conditions and comparison of malignant and non-malignant cells of the same cell type and same donor. Furthermore, clinical pilot studies and the assessment of systemic effects will be of tremendous importance towards bringing this innovative technology into clinical practice.

The State of Research on Antimicrobial Activity of Cold Plasma

Microbiological contamination is a big challenge to the food industry, medicine, agriculture, and environmental protection. For this reason, scientists are constantly looking for alternative methods of decontamination, which ensure the effective elimination of unwanted biological agents. Cold plasma is a new technology, which due to its unique physical and chemical properties becomes a point of interest to a growing group of researchers. The previously conducted experiments confirm its effective action, e.g. in the disinfection of skin wounds, air, and sewage treatment, as well as in food preservation and decontamination. The reactive compounds present in the plasma: high-energy electrons, ionized atoms and molecules, and UV photons are the key factors that cause an effective reduction in the number of microorganisms. The mechanism and effectiveness of the cold plasma are complex and depend on the process parameters, environmental factors and the type and properties of the microorganisms that are to be killed. This review describes the current state of knowledge regarding the effectiveness of the cold plasma and characterizes its interaction with various groups of microorganisms based on the available literature data.

The molecular chaperone Hsp33 is activated by atmospheric-pressure plasma protecting proteins from aggregation

Non-equilibrium atmospheric-pressure plasmas are an alternative means to sterilize and disinfect. Plasma-mediated protein aggregation has been identified as one of the mechanisms responsible for the antibacterial features of plasma. Heat shock protein 33 (Hsp33) is a chaperone with holdase function that is activated when oxidative stress and unfolding conditions coincide. In its active form, it binds unfolded proteins and prevents their aggregation. Here we analyse the influence of plasma on the structure and function of Hsp33 of Escherichia coli using a dielectric barrier discharge plasma. While most other proteins studied so far were rapidly inactivated by atmospheric-pressure plasma, exposure to plasma activated Hsp33. Both, oxidation of cysteine residues and partial unfolding of Hsp33 were observed after plasma treatment. Plasma-mediated activation of Hsp33 was reversible by reducing agents, indicating that cysteine residues critical for regulation of Hsp33 activity were not irreversibly oxidized. However, the reduction yielded a protein that did not regain its original fold. Nevertheless, a second round of plasma treatment resulted again in a fully active protein that was unfolded to an even higher degree. These conformational states were not previously observed after chemical activation with HOCl. Thus, although we could detect the formation of HOCl in the liquid phase during plasma treatment, we conclude that other species must be involved in plasma activation of Hsp33. E. coli cells over-expressing the Hsp33-encoding gene hslO from a plasmid showed increased survival rates when treated with plasma while an hslO deletion mutant was hypersensitive emphasizing the importance of protein aggregation as an inactivation mechanism of plasma.