Combined effect of fungicide, herbicide and plant elicitor used in apple orchards on non-target epiphytic moss Hypnum cupressiforme

Apple production is a dynamic agricultural system in which pesticides are applied recurrently to control pests and diseases in the orchards. Understanding the impact of such agents on non-target organisms is crucial to minimise unintended consequences while maintaining their use in crop protection. The aim was to test how fungicide, herbicide, elicitor, and their combinations affect the physiology of the epiphytic moss Hypnum cupressiforme that naturally occurs in orchards. Our results showed that both dodine and diflufenican applied separately had a strong negative effect on moss physiology reflected in significantly decreased photosynthetic pigment contents, maximum quantum yield of PSII photochemistry, cell membrane integrity and dehydrogenase activity, and increased membrane lipid peroxidation, which indicates a high physiological stress. Furthermore, the combined use of herbicide and fungicide resulted in further deterioration of the physiological condition compared to the effects of both agents used separately. In many cases, the application of chitosan together with a diflufenican or dodine resulted in a reduction of the negative effects triggered by these agents. The compensatory effect was particularly pronounced in maintaining a low level of cell membrane permeability. Consequently, it can be concluded that chitosan could have a protective function against cell membrane damage in non-target mosses.

Length-dependent toxic effects of microplastic fibers on Chlorella pyrenoidosa

Microplastics (MPs), a pervasive pollutant in aquatic environments, are increasingly recognized for their detrimental effects on aquatic organisms. However, the present understanding of their impact on phytoplankton, particularly freshwater microalgae, remains limited. Furthermore, previous studies have predominantly focused on MP particles, largely overlooking the most prevalent form of MPs in aquatic settings-fibers. In this study, we scrutinized the toxicological implications of microplastic fibers (MFs) spanning four distinct lengths (50 μm, 100 μm, 150 μm, and 200 μm) on the protein-nucleated algae Chlorella pyrenoidosa over a six-day period. The study unequivocally demonstrated that MFs markedly impeded C. pyrenoidosa growth, diminished photosynthetic pigment content, and induced oxidative stress, with all observed effects exhibiting a length-dependent correlation. Electron microscopy further revealed notable damage to algal cell membranes. Cell membrane shrinkage, cytoplasm outflow, and abnormalities in cell division were observed in the 150 μm and 200 μm groups. Furthermore, C. pyrenoidosa clustered around the 200 μm MF were notably denser compared to other groups. The present study demonstrated that MFs had length-dependent toxic effects on C. pyrenoidosa. These findings offer novel insights into the deleterious impact of MFs on aquatic organisms, underscoring the pivotal role of length in influencing their toxicity.

Nanoplastics increase the adverse impacts of lead on the growth, morphological structure and photosynthesis of marine microalga Platymonashelgolandica

Nanoplastics and heavy metals are common pollutants in coastal environments with high concerns, but their joint ecological risk to marine primary productivity remains unclear. In this study, the effects of 7, 70, 700 μg/L lead (Pb) single exposure and in combination with 200 μg/L polystyrene nanoplastics (NPs, 70 nm) on marine microalga Platymonas helgolandica were investigated. Pb single exposure induced a dose-dependent inhibition on the growth of P. helgolandica, which was associated with the reduced photosynthetic efficiency and nutrient accumulation. Compared to Pb single exposure, the addition of NPs significantly reduced the photosynthetic efficiency and aggravated the damage to cell structure. Reduced esterase activity and increased membrane permeability also indicated that NPs exacerbated the adverse effects of Pb on P. helgolandica. Thus, co-exposure to NPs and Pb induced more severe impacts on marine microalgae, suggesting that the joint ecological risk of NPs and heavy metals to marine primary productivity merits more attention.

Changes in the behavior of Staphylococcus aureus strains in the presence of oxacillin under the effect of gamma radiation

Staphylococcus aureus (S. aureus) as a major pathogen is implicated in a wide range of foodborne and hospital-acquired infections, its methicillin resistant variants contribute to the spread of β-lactam antibiotic resistance. It is essentially important to destroy these pathogens, their resistance genes and the antibiotics in wastewaters. For this purpose reactions of reactive radicals (advanced oxidation processes), first of all hydroxyl radicals (•OH), are suggested. Here the radiolysis of water supplied these radicals. In the experiments B.01755 oxacillin sensitive and B.02174 resistant S. aureus strains were used to study their behaviorr in suspensions under the effect of irradiation in presence and absence of oxacillin. Oxacillin inactivation depended on concentration of the antibiotic used (0.042 and 1 g dm-3), higher concentration required a higher dose. When 106-109 CFU cm-3 S. aureus suspensions were irradiated with γ-radiation the bacteria were inactivated at low absorbed doses: 4 orders of magnitude decrease ocurred in the number of culturable cells at ∼0.6 kGy dose. Both cell membrane and DNA suffered considerable damages during irradiation. Due to the membrane damage the cells could not be stained, and the DNA content of cells in several days period was released into the solution. In DNA damage the oxacillin resistance mecA gene was also modified, it did not multiply in PCR test. These findings are important from the point of view of applying irradiation technology to stop the spread of antibiotic resistance.

Cellular absorption of polystyrene nanoplastics with different surface functionalization and the toxicity to RAW264.7 macrophage cells

Nanoplastics (NPs) are a matter of widespread concern, as they are easily absorbed by a wide variety of organisms and accumulate in biological tissues. While there is evidence that nanoplastics are toxic to various organisms, few studies have investigated the mechanisms underlying the toxicities of NPs with different surface functionalizations to macrophage cells. In this study, mouse mononuclear macrophage (RAW264.7) cells were exposed to polystyrene nanoplastics (PS-NPs) with three different surface functionalizations, namely pristine polystyrene (PS), carboxyl-functionalized polystyrene (PS-COOH), and amino-functionalized polystyrene (PS-NH₂), to evaluate the cellular endocytosis, lactate dehydrogenase (LDH) release, cell viability, reactive oxygen species (ROS), mitochondrial membrane potential, apoptosis, and related gene expression. Results showed that all three PS-NPs were endocytosed into cells. However, in the concentration range of 0-100 μg/mL, PS had no effect on cell viability or apoptosis, but it slightly increased cellular ROS and decreased mitochondrial membrane potential. PS-NH₂ exhibited the highest cytotoxicity. PS-COOH and PS-NH₂ induced ROS production, altered the mitochondrial membrane potential, and caused cell apoptosis regulated by the mitochondrial apoptosis pathway. Results also showed that cell membrane damage induced by PS-NH₂ is one of the primary mechanisms of its cytotoxicity to RAW264.7 cells. The results of this study clarify the toxicities of PS-NPs with different surface functionalizations to macrophages, thereby improving the identification of immune system risks related to nanoplastics.

Interaction effect of fungicide and chitosan on non-target lichenized fungi

Excessive use of plant growth stimulants and pesticides is currently a considerable problem, especially in agriculture, horticulture, and arboriculture. Understanding the impacts of these compounds and their combinations on non-target organisms is crucial to minimize unintended consequences, while maintaining their use in plant protection. The aim of this study was to test how long-term spraying with different solutions of natural biostimulator chitosan, synthetic fungicide Switch 62.5 WG, and their combinations affects the physiology of epiphytic lichen Xanthoria parietina naturally occurring in fruit orchards and farmlands. We showed that fungicides composed of fludioxionil and cypronidil, as well as the combined use of such fungicides together with chitosan, can cause the considerable impairment of lichen physiology, and these disturbances relate to both algal and fungal partners of the symbiotic association. This negative effect was especially visible in the loss of cell membrane integrity, the high level of membrane lipid peroxidation, and changes in chlorophyll fluorescence parameters on the last day of the experiment. The combined use of these agents also leads to clear disturbances in the functioning of the mitochondrial respiratory chain, which was manifested by increased NADH dehydrogenase activity, while the use of these compounds separately led to a decrease in the activity of this enzyme. We concluded that the regular use of these agents in fruit tree cultivation may cause serious ecological consequences for epiphytic lichen communities as a result of the death of lichen thalli. This study suggests that the impact of some plant protection agents, both individually and in combinations, merits further attention in terms of their impact on non-target fungi.

Mechanistic insight into the inhibitory effect of artemisinin sustained-release inhibitors with different particle sizes on Microcystis aeruginosa

Environment-friendly algaecides based on allelopathy have been widely used to control harmful algal blooms. In this research, micro and nano scale artemisinin sustained-release algal inhibitor was prepared, the optimal preparation conditions were explored, and the inhibitory mechanism of artemisinin algaecides was turned perfect. The results showed that when the particle size of artemisinin sustained-release microspheres (ASMs) was 2/10,000 of artemisinin sustained-release granules (ASGs), the inhibitory effect was more remarkable. The optimal concentration of ASMs was 0.2 g L^-1, and the inhibitory effect reached 99% on the 10th day. The algal density and chlorophyll a both showed a downward trend, indicating that ASGs and ASMs could promote the degradation of chlorophyll a. The inhibition rate of ASGs was faster than that of ASMs on the 4th day, and the inhibitory effect of ASMs was more significant after the 5th day. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased rapidly at first and then decreased, which indicated that ASGs and ASMs caused oxidative damage to Microcystis aeruginosa and inhibited the activity of antioxidant enzymes. Furthermore, the content of the oxygen free radical (O^2-) and malondialdehyde (MDA) continued to rise after the 5th day, and the protein, nucleic acid, and conductivity in the culture medium increased. These results showed that lipid peroxidation occurred in the algal cell membrane, and the permeability of the membrane increased. In summary, the ASMs had a significant sustained inhibitory effect while the ASGs had a better short-term effect. The main inhibitory mechanism of artemisinin algaecides is the irreversible damage of cell membrane.

Physiological and biochemical responses of hybrid maize (Zea mays L.) varieties grown under heat stress conditions

Maize (Zea mays L.) is the second most commonly produced and consumed crop after wheat globally and is adversely affected by high heat, which is a significant abiotic stress factor. This study was carried out to determine the physiological and biochemical responses of hybrid corn varieties under heat stress ('HS') compared to control ('C') conditions during the 2020 and 2021 growing seasons. The experiment was conducted under natural conditions in the Southeastern region of Turkey, where the most intense temperatures are experienced. This experiment used split plots in randomized blocks with three replications, with 'HS' and 'C' growing conditions applied to the main plots and the different hybrid corn varieties (FAO 650) planted on the sub plots. Mean values of days to 50% tasseling (DT, day), grain yield (GY, kg ha^-1), leaf water potential (LWP, %), chlorophyll-a (Chl-a, mg g^-1), cell membrane damage (CMD, %), and total phenol content (TPC, μg g^-1) were significantly different between years, growing conditions, and hybrid corn varieties. Changes in the climate played a significant role in the differences between the years and growing conditions (GC), while the genetic characteristics of the different corn varieties explained the differences in outcomes between them. The values of DT, GY, LWP, Chl-a, CMD, and TPC ranged from 49.06-53.15 days, 9,173.0-10,807.2 kg ha^-1, 78.62-83.57%, 6.47-8.62 mg g^-1, 9.61-13.54%, and 232.36-247.01 μg g^-1, respectively. Significant correlations were recorded between all the parameters. Positive correlations were observed between all the variables except for CMD. The increased damage to cell membranes under 'HS' caused a decrease in the other measured variables, especially GY. In contrast, the GY increased with decreased CMD. CMD was important in determining the stress and tolerance level of corn varieties under 'HS' conditions. The GY and other physiological parameters of ADA 17.4 and SYM-307 candidate corn varieties surpassed the control hybrid corn cultivars. The results revealed that the ADA 17.4 and SYM-307 cultivars might have 'HS'-tolerate genes.

A mini-review: mechanism of antimicrobial action and application of surfactin

Surfactin, an antibacterial lipopeptide produced by different strains of Bacillus subtilis, is a powerful biosurfactant. It also has multiple biological activities including antiviral, anti-mycoplasma and antiprotozoal activities, in addition to the broad-spectrum antimicrobial activities against Gram-positive bacteria, Gram-negative bacteria and fungi. Surfactin may be one of the promising alternatives to antibiotics. Surfactin's chemical structure and physicochemical properties are briefly discussed in this mini-review. Surfactin's antibacterial mechanism is mainly outlined as follows: (1) attacking pathogenic bacteria's cell membrane, causing cell membrane disintegration or osmotic pressure imbalance; (2) inhibiting pathogenic bacteria's protein synthesis, preventing cell reproduction; (3) inhibiting pathogenic bacteria's enzyme activity, affecting normal cell metabolism. This provides basis for the further research and application of surfactin. Finally, the application of surfactin in food and its prospect are summarized in brief.

Acid treatment enhances phosphorus release and recovery from waste activated sludge: Performances and related mechanisms

Waste activated sludge (WAS) has attracted considerable attention as an excellent material for P recovery from sewage. This study took concentrated phosphorus removal sludge as objective, and aimed at providing an effective route to promote the transformation of polyphosphate in sludge pellets to dissolved phosphate. After acid pH adjustment, total dissolved phosphate at pH 3.0 was 37.3-fold higher than that at natural pH. The P distribution results illustrated that acid pH accelerated the degradation of short chain polyphosphate into orthophosphate. Furthermore, cell staining results confirmed that the polyphosphate was sourced from the leakage of intracellular matters. Low field NMR and rheology properties analysis were adopted to illustrate that acid pH treatment further improved WAS dewatering performances. Accompanied with the reduction of heavy metals in WAS pellets, the acid pH treatment was also beneficial for WAS subsequent treatment or final disposal. Lastly, Fe³⁺ addition was proposed as favorable P recovery method, and spherical nanometric materials of FePO₄ crystal was obtained accordingly.

Mechanisms underlying the antimicrobial actions of the antimicrobial peptides Asp-Tyr-Asp-Asp and Asp-Asp-Asp-Tyr

The peptides Asp-Tyr-Asp-Asp (DYDD) and Asp-Asp-Asp-Tyr (DDDY) extracted from Dendrobium aphyllum have antimicrobial effects on Escherichia coli, Pseudomonas aeruginosa, and Monilia albicans, but no effects on Bacillus subtilis and Staphylococcus aureus. The effects of a hydrophobic environment on the secondary structures of these molecules were determined using circular dichroism and atomic force microscopy. Although scanning electron microscopy revealed that DDDY was more destructive to membranes than DYDD, both peptides showed antimicrobial effects against three pathogens. The minimum inhibitory concentration (MIC) of DYDD (18.075 mg/mL) against E. coli was higher than that of DDDY (4.519 mg/mL), and the influence of DYDD on the cell surface potential energy of E. coli was also greater (a decrease of 6.4 ± 0.66 mV) than that of DDDY (a decrease of 4.37 ± 0.77 mV). Moreover, the cell membrane damage and content leakage of DYDD-treated E. coli cells were more severe than those observed in the DDDY-treated cells. However, DDDY showed stronger antibacterial activity against P. aeruginosa and M. albicans than DYDD. A molecular dynamic simulation revealed that the mechanisms underlying the interaction between these two peptides and lipid bilayers were remarkably different. Therefore, two separate models were proposed to describe their antimicrobial activities.

Ohmic heating as a method of obtaining paraprobiotics: Impacts on cell structure and viability by flow cytometry

This study aimed to evaluate the effects of ohmic heating (OH) on probiotic inactivation, cell viability and morphology of the probiotic strains Lactobacillus acidophilus LA 05 (LA), Lacticaseibacillus casei 01 (LC), and Bifidobacterium animalis Bb 12 (BA) to develop paraprobiotics. OH at different electric field magnitudes (4, 8, and 12 V/cm at 60 Hz) and conventional heat treatment (CONV) were performed to determine the most adequate condition for the obtainment of paraprobiotics. Analysis of culturability, flow cytometry (FC), and Scanning electron microscope (SEM) was carried out. The complete inactivation by CONV was achieved only in the following conditions: LA - 95 °C/5 min, LC and BA - 95 °C/7 min. The same temperature profile was used in OH treatments to study the OH electrical effects. The OH treatment (8 V/cm) caused lower damage to the cell membrane integrity compared to the CONV treatment (p < 0.05). The OH showed to be adequate technology for the efficient production of paraprobiotics.

Analysis of time varying response on uptake patterns of Cu and Zn ions under application of ethylene diamine disuccinic acid and gibberellic acid in Lolium perenne

The present study explores the effect of ethylene diamine disuccinic acid (EDDS) and gibberellic acid (GA) application on the phytoextraction of copper and zinc ions by Lolium perenne. When Cu was individually applied, accumulation diminished over time with little translocation from roots to shoots. In contrast, Zn accumulation and damage to roots rapidly increased over 3 days with increase in Zn translocation to shoots. Co-application of Zn to Cu amended treatments enhanced Cu concentration in shoots. For the Cu_EDDS application, EDDS significantly increased Cu accumulation and the damage to root increased over time, while gibberellic acid applied with Cu and Zn generally lowered metal uptake and decreased cell membrane damage. The application of EDDS and GA-EDDS, by themselves or with Cu and Zn, lowered transpiration and increased translocation, while GA increased transpiration but decreased translocation. EDDS application typically increased metal ion uptake by causing more cell damage, while GA typically lowered the damage and decreased metal uptake even though the transpiration increased over time and plant growth occurred. Furthermore, the behaviour of metal uptake changed over time and, for some treatments, the short-term and long-term response differed greatly. These results show that EDDS can be successfully used in phytoextraction of both Cu and Zn ions by Lolium perenne while GA can resist damage and protect against plant stress.

Mechanisms of Action of Luteolin Against Single- and Dual-Species of Escherichia coli and Enterobacter cloacae and Its Antibiofilm Activities

Escherichia coli and Enterobacter cloacae are major foodborne pathogens and can form challenging single/mixed biofilms. A recent study demonstrated that luteolin (LUT) exhibits antibacterial activities against some pathogens; however, the mechanisms underlying the effects of LUT on planktonic and biofilm bacteria have never been fully elucidated. This study aimed to determine the antibacterial activity and its mechanism of action against E. coli and E. cloacae. Here, the antimicrobial mode of LUT was explored by evaluating alterations in both cell membrane integrity and cell morphology, and the antibiofilm activity of LUT was investigated using quantitative and qualitative assays. The results showed that minimal inhibitory concentration and minimum bactericidal concentration values of LUT against E. coli were 64 and 128 μg/mL and 128 and 256 μg/mL for E. cloacae mono- and dual-species, respectively. LUT impaired cell membrane integrity, as demonstrated by the remarkable increase in the number of membrane-damaged cells and definite variations in cell morphology. Moreover, LUT presented robust inhibitory effects on biofilm formation and the capacity to kill mono- and dual-species biofilm cells. Overall, these data show the potential benefit of using a natural antimicrobial and/or preservative in the food industry, LUT, to control mono- and mixed-species or biofilm-associated infections.

RNase 1, 2, 5 & 8 role in innate immunity: Strain specific antimicrobial activity

The increase in microbial resistance to conventional antimicrobial agents is driving research for the discovery of new antibiotics and antifungal agents. The greatest challenge in this endeavor is to find antimicrobial agents with broad antimicrobial activity and low toxicity. Antimicrobial peptides, for example, RNases, are one of the promising areas. The production of RNases increases during infection, but their role is still being explored. Whereas the enzymatic activity of RNases is well documented, their physiological function is still being investigated. This study aimed to evaluate the antimicrobial activity of RNase 1, 2, 5, and 8 against E. coli strains, S. aureus, Streptococcus thermophilus, P. aeruginosa, Candida albicans, and Candida glabrata. The results demonstrated that RNases have a strain-specific antimicrobial activity. RNase 1 had the highest antimicrobial activity compared to other RNases. All the microorganisms screened had varying levels of susceptibility to RNases, except P. aeruginosa and E. coli DR115. RNase 1 showed dose-dependent activity against C. albicans. The RNase killed Candida albicans by lowering the mitochondrial membrane potential but did not damage the cell membrane. We concluded that strain-specific antimicrobial activity is one of the physiological roles of RNases.

Cell membrane damage induced by continuous stress of artemisinin sustained-release microspheres (ASMs) on Microcystis aeruginosa at different physiological stages

Artemisinin sustained-release microspheres (ASMs) with long-term inhibition effects (> 40 days) on harmful freshwater bloom-forming cyanobacteria have been found in previous studies, but the inhibition mechanism is not completely clear. In the present study, we examined the growth effect of ASMs on Microcystis aeruginosa (M. aeruginosa) cells at different physiological stages. Growth experiments indicated that M. aeruginosa of different initial densities could be inhibited immediately and chlorophyll-a content both showed significant decreases following exposure of cyanobacteria to optimal dosage of ASMs for 20 days. The algicidal mechanism of ASMs was tested through a suite of physiological parameters (membrane permeability, antioxidant enzymes activity, and lipid peroxidation). The rise of cell membrane permeability indices (intracellular protein, nucleic acid contents, and conductivity) showed that the cellular membrane structure of M. aeruginosa was attacked by ASMs directly causing the leakage of cytoplasm. Antioxidant enzyme activity was a sensitive indicator of the impacts of ASMs which showed a significant downtrend after a few days. ASMs caused a great increase in •O₂^- and malondialdehyde (MDA) level of the algal cells which indicated the increase in lipid peroxidation of M. aeruginosa. Irreversible membrane damage induced by ASMs via the oxidation of ROS may be an important factor responsible for the algicidal mechanism of ASMs on M. aeruginosa cells. The application of ASMs might provide a new direction to control M. aeruginosa, especially before the exponential phase according to the optimal economy and inhibition effect. Graphical abstract.

Antimicrobial activity of eugenol against carbapenem-resistant Klebsiella pneumoniae and its effect on biofilms

A preliminary study found that eugenol expressed an antibacterial activity against Klebsiella pneumoniae. However, the mechanism of action of eugenol against K. pneumoniae still remains unexplored. The aim of this study was to gain further insight into the antibacterial effect of eugenol against carbapenem-resistant Klebsiella pneumoniae (CRKP) and possible mode of action. Here, minimum inhibitory concentration (MIC) of eugenol against CRKP strains was determined using the agar dilution method. Moreover, variations in intracellular ATP concentration, intracellular pH (pH_in), membrane potential and membrane integrity were measured to evaluate the effect of eugenol on cell membrane. Besides, changes in cell structure and biofilm formation of CRKP as well as biofilm-associated cell damage were determined using field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) and confocal laser scanning microscopy (CLSM). Finally, gene expression of biofilm-related biosynthesis was investigated. The results showed that MICs of eugenol against four tested CRKP were 0.2 mg/mL. Eugenol damaged the cell membrane of CRKP, as evidenced by decreased intracellular ATP concentration, reduced pH_in and cell membrane hyperpolarization, coupled with enhanced membrane permeability. Furthermore, eugenol compromised cell structure and induced loss of intracellular components of CRKP. Additionally, eugenol inhibited biofilm formation and inactivated biofilm CRKP cells. Finally, eugenol presented strong inhibitory effects on biofilm formation and biofilm-associated gene expression, and inactivated CRKP cells growing in biofilms. These findings suggest that eugenol exhibits antimicrobial effect against CRKP strains and could be potentially used to control CRKP-related infections.

Integrity of lichen cell membranes as an indicator of heavy-metal pollution levels in soil

The epigeic lichens Cladonia rei and Diploschistes muscorum are effective heavy-metal-tolerant colonisers of highly polluted and disturbed sites. In this study we compare their bioaccumulation capacities, accumulation patterns, and responses to heavy-metal stress, as expressed in terms of cell membrane damage. We also aim at verifying the relationships between cell membrane damage and levels of soil pollution with heavy metals, and thereby to identify the bioindicative value of this physiological parameter. Total and intracellular concentrations of Zn, Pb, Cd, As, Cu, and Ni were measured in 140 samples of lichens and corresponding soil, collected from variously contaminated sites. Relative electrical conductivity (EC%) values were determined concurrently in the lichen samples. The studied lichens differ considerably in intracellular uptake susceptibility and the related reduction in membrane integrity. In C. rei thalli, more than half of Zn, Pb, Cd, and As loads are accumulated extracellularly, whereas D. muscorum exhibits a tendency towards intracellular accumulation of the same elements. This property is clearly reflected in cell membrane damage, which is considerably greater in the latter species irrespective of study site. This indicates that intracellular heavy-metal accumulation affects the level of cell membrane damage. Two soil pollution classes were distinguished for both lichens based on element contents in host-substrate samples. The losses of cell membrane integrity in lichen thalli are related to these classes. EC% values above 16 in C. rei and above 20 in D. muscorum suggest elevated levels of heavy metals in the soil. Consequently, this physiological parameter can serve as an early warning indicator for detection of elevated metal concentrations in soil. The biomonitoring method proposed here involves common and widespread lichen species and can be widely applied in post-industrial areas.

Exploring the membrane toxicity of decabromodiphenyl ethane (DBDPE): Based on cell membranes and lipid membranes model

Decabromodiphenyl ethane (DBDPE) is widely used in industry as an alternative to the decabromodiphenyl ether (BDEs). The large-scale use of DBDPE could lead to rapid growth of the human accumulation level of DBDPE. However, the biophysics of accumulation of DBDPE in cell membranes, as one of determinants of DBDPE metabolism is not clear. In the present study, detailed observations of cell lactate dehydrogenase (LDH) and reactive oxygen species (ROS) levels measurements proved that the DBDPE exposure to cell could result in significant cell membrane damage by concentration-dependent manners. The fluorescence anisotropy analysis supported the evidence that high concentration DBDPE bound decreased membrane fluidity significantly. Besides it, a detailed molecular dynamic (MD) simulation was approached to investigate the effects of DBDPE on the DPPC (dipalmitoyl phosphatidylcholine) phospholipid bilayer, which was constructed as the model of cell membrane. The molecular dynamic simulation revealed that DBDPE molecules can easily enter the membrane from the aqueous phase. Under the concentration of a threshold, the DBDPE molecules tended to aggregate inside the DPPC bilayer and caused pore formation. The bound of high concentration of DBDPE could result in significant variations in DPPC bilayer with a less dense, more disorder and rougher layer. The knowledge about DBDPEs interactions with lipid membranes is fundamentally essential to understand the in vivo process of DBDPE and the physical basis for the toxicity of DBDPE in cell membranes.

Inhibitory effect and mechanism of linoleic acid sustained-release microspheres on Microcystis aeruginosa at different growth phases

Environment-friendly algaecides based on allelopathy have been extensively studied to control harmful algal blooms (HABs). The inhibitory effects of linoleic acid (LA) sustained-release microspheres on different cell densities of Microcystis aeruginosa (M. aeruginosa) at different growth phases were studied. The results showed that the growth of M. aeruginosa could be inhibited within 4 days and the constant inhibitory rate with initial algal density of 8 × 10⁵ cells∙mL^-1 (exponential phase) was up to 96% compared with control. The chlorophyll-a content in the treatment group had the same change trend with the algal density and declined significantly at day 20th, which suggested that the microspheres could promote the degradation of chlorophyll-a. The activities of superoxide dismutase (SOD) and catalase (CAT) increased gradually within 5 days but then declined sharply, which indicated that LA microspheres could cause oxidative damage to M. aeruginosa during the process of inhibition and reduce the activities of antioxidant enzymes. In addition, the concentration of oxygen free radical (O₂^-) increased at day 10th and rose constantly, and the content of malodialdehyde (MDA) increased to 2.7 times as much as control at day 20th. Furthermore, the content of protein, nucleic acid and the conductivity in culture solution showed a significant rise. These results showed that algal cell membrane lipid peroxidation occurred and the membrane permeability increased, accompanied by the damage of cell membrane. To sum up, the destruction of algal cell membrane is the main mechanism of LA microspheres inhibiting algal growth.

Interpreting the effects of natural organic matter on antimicrobial activity of Ag2S nanoparticles with soft particle theory

Natural organic matter (NOM) ubiquitously exists in natural waters and would adsorb onto the particle surface. Previous studies showed that NOM would alleviate the toxicity of nanomaterials, while the mechanism is seldom quantitatively interpreted. Herein, the effects of humic substances [Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA)] and biomacromolecules [alginate and bovine serum albumin (BSA)] on the aggregation and antimicrobial effects of silver sulfide nanoparticles (Ag₂S-NPs) were investigated. The aggregation kinetics of Ag₂S-NPs in electrolyte solutions were in agreement with the results based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dynamic light scattering (DLS) results showed that the SRFA, SRHA, alginate and BSA molecules coated on the Ag₂S-NPs surfaces. The NOM coating layer prevented salt-induced coagulation of Ag₂S-NPs, and the effects of BSA and SRHA on Ag₂S-NPs stabilizing were more obvious than that of SRFA and alginate. Flow cytometry analysis results suggested that BSA and SRHA were more effective on alleviating the Ag₂S-NPs induced cell (Escherichia coli) membrane damage than SRFA and alginate. After interpreting the electrophoretic mobility (EPM) data of the NOM coated Ag₂S-NPs by Ohshima's soft particle theory, it was found that the thickness of the NOM coating layers followed the orders of BSA > SRHA > alginate > SRFA. The E.coli cell membrane damage level was negatively correlated with the thickness and softness of the coating layer. NOM coating may physically alleviate the contact between NPs and E. coli cells and thus attenuate the extent of cell membrane damage caused by the NP-cell interaction. This work provides a new perspective for quantitatively interpreting the influence of NOM on the environmental behaviors and risks of nanomaterials.

Enhanced toxicity to the cyanobacterium Microcystis aeruginosa by low-dosage repeated exposure to the allelochemical N-phenyl-1-naphthylamine

It has been puzzling whether and how a plant could exert a strong allelopathic inhibition to the target organisms by releasing low concentrations of allelochemicals. Plant allelochemicals have been proposed to be released continuously, however, direct evidence from specific allelochemicals is urgently required. In the present study, the toxicity of allelochemical N-phenyl-1-naphthylamine (NPN) towards the cyanobacterium Microcystis aeruginosa by two different exposure patterns was compared. One was low-dosage repeated exposure (LRE), in which 50  μg L^-1 NPN was repeatedly dosed to simulate the continual release of allelochemicals, and the other one was high-dosage single exposure (HSE) as per the routine toxicity assay. The results showed a significant growth inhibition to M. aeruginosa in the LRE group, where the inhibition rate reached above 90% from day 6 to day 9. The cell-membrane damage ratio increased from 64.05% on day 5 up to 96.60% on day 9. PSII photosynthesis activity expressed as Fv/Fm, Φ_PSII, NPQ and ETRmax was also thoroughly inhibited in this group. Whereas the growth and PSII photosynthesis activity of M. aeruginosa in the HSE group were inhibited initially, but recovered gradually from day 4 or 5, which was accompanied by a continuous reduction of NPN content in culture solutions. Although NPN content in the LRE group was relatively lower, it remained at a more stable level throughout the experiment. These results indicate that continual release of low-dosage allelochemicals by aquatic plants plays crucial roles in their potent inhibition against cyanobacteria. Low-dosage continual exposure pattern needs to be investigated further.

Comparison of cell membrane damage induced by the therapeutic ultrasound on human breast cancer MCF-7 and MCF-7/ADR cells

OBJECTIVES

The aim of this study was to compare the cell membrane damage induced by ultrasound at different intensities between MCF-7/ADR cells and MCF-7 cells.

METHODS

Tumor cells in the culture dishes (35 mm diameter) were exposed to planner ultrasound at intensities range from 0.25 W/cm(2) to 0.75 W/cm(2) for 60s. The viability of cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and Guava Viacount assay. The cell membrane integrity was estimated by flow cytometry using propidium iodide (PI) staining and cellular uptake of fluorescein isothiocyanate-dextran (FD500). The membrane lipid peroxidation and membrane fluidity were also specially compared between two cell lines in this paper using spectrophotometry. Ultrastructural alterations on membrane surface were observed by scanning electron microscopy.

RESULTS

The ultrasound produced cytotoxicity in both cell lines increased with the irradiation intensity increased from 0.25 W/cm(2) to 0.75 W/cm(2). Cell membrane permeability and the level of lipid peroxidation were remarkably enhanced after ultrasound application. In addition, relatively severe cell damage was observed under scanning electron microscopy after 0.75 W/cm(2) ultrasound treatment.

CONCLUSIONS

Ultrasound exposure decreased MCF-7 and MCF-7/ADR cell viability in an intensity-dependent manner and MCF-7/ADR cells were more sensitive to ultrasound exposure than MCF-7 cells at the same experimental conditions. The declined membrane fluidity in MCF-7/ADR cell may be one of the reasons for its increased membrane damage.

Anti-MRSA activity of isoplagiochin-type macrocyclic bis(bibenzyl)s is mediated through cell membrane damage

We synthesized three geometrical isomers of a macrocyclic bis(bibenzyl) based on isoplagiochin, a natural product isolated from bryophytes, and evaluated their antibacterial activity towards methicillin-resistant Staphylococcus aureus (anti-MRSA activity). The isomer containing a 1,4-linked ring (5) showed only weak activity, whereas the isomers containing a 1,3-linked (6) or 1,2-linked (7) C ring showed potent anti-MRSA activity. Molecular dynamics calculations indicated that these differences are probably due to differences in the conformational flexibility of the macrocyclic ring; the active compounds 6 and 7 were more rigid than 5. In order to understand the action mechanism of anti-MRSA activity, we investigated the cellular flux of a fluorescent DNA-binder, ethidium bromide (EtBr), in the presence and absence of these macrocycles. The active compound 6 increased the levels of EtBr inflow and outflow in S. aureus cells, as did our potent anti-MRSA riccardin derivative (4), indicating that these compounds increased the permeability of the cytoplasmic membrane. Inactive 5 had no effect on EtBr inflow or outflow. Furthermore, compound 6 abrogated the normal intracellular concentration gradients of Na(+) and K(+) in S. aureus cells, increasing the intracellular Na(+) concentration and decreasing the K(+) concentration, while 5 had no such effect. These results indicate that anti-MRSA-active macrocyclic bis(bibenzyl) derivatives directly damage the gram-positive bacterial membrane, resulting in increased permeability.

Optimizing the design and in vitro evaluation of bioreactive glucose oxidase-microspheres for enhanced cytotoxicity against multidrug resistant breast cancer cells

Glucose oxidase (GOX) encapsulated in alginate-chitosan microspheres (GOX-MS) was shown in our previous work to produce reactive oxygen species (ROS) in situ and exhibit anticancer effects in vitro and in vivo. The purpose of present work was to optimize the design and thus enhance the efficacy of GOX-MS against multidrug resistant (MDR) cancer cells. GOX-MS with different mean diameters of 4, 20 or 140 μm were prepared using an emulsification-internal gelation-adsorption-chitosan coating method with varying compositions and conditions. The GOX loading efficiency, loading level, relative bioactivity of GOX-MS, and GOX leakage were determined and optimal chitosan concentrations in the coating solution were identified. The influence of particle size on cellular uptake, ROS generation, cytotoxicity and their underlying mechanisms was investigated. At the same GOX dose and incubation time, smaller sized GOX-MS produced larger amounts of H2O2 in cell culture medium and greater cytotoxicity toward murine breast cancer MDR (EMT6/AR1.0) and wild type (EMT6/WT) cells. Fluorescence and confocal laser scanning microscopy revealed significant uptake of small sized (4 μm) GOX-MS by both MDR and WT cells, but no cellular uptake of large (140 μm) GOX-MS. The GOX-MS were equally effective in killing both MDR cells and WT cells. The cytotoxicity of the GOX formulations was positively correlated with membrane damage and lipid peroxidation. GOX-MS induced greater membrane damage and lipid peroxidation in MDR cells than the WT cells. These results suggest that the optimized, small micron-sized GOX-MS are highly effective against MDR breast cancer cells.

Administering the Optimum Dose of l-Arginine in Regional Tumor Therapy

The purpose of this study is optimizing the l-arginine (l-Arg) doses on the basis of chemical structure in regional accessible tumor therapy to settle down a new protocol for the treatment of cancer. (3)H-thymidine-based cell proliferation assay was performed in vitro on tumor cell lines of fibrosarcoma (FS), lymphosarcoma-ascitic and on normal cell line of NIH 3T3 after treatment with different concentrations of l-Arg in phosphate buffered saline (PBS). The cultures were harvested after 22 h and the incorporated radioactivity was counted to identify their histologic grades as described in earlier studies. In vivo therapy of murine tumors was conducted where FS cells injected subcutaneously at ventro-lateral position of mice. Various drug delivery schedules were injected into the centre of tumor base, once a day for 4 days. Tumor diameter and survivals were monitored where the day of sacrifice was considered for monitoring the survival period. By identifying the histologic grades of the treated cultures in vitro and in vivo by different concentrations of l-Arg, the corresponding energy of such concentrations were determined. An efficient model with a good fit (R(2) = 0.98) was established to describe the energy yield by l-Arg dose. The equivalence between the tumor histologic grade and energy of the l-Arg dose delivered in saline (PBS) environment is the optimum condition for regional tumor therapy achieves higher survival rate. The selective cytotoxicity to tumor cells with minimal damage to normal cells by l-Arg due to its chemical structure suggests to be considered the most promising drug for regional therapy of the accessible tumors like breast cancers of early stage with no distant metastasis.