[Vertical Distribution Characteristics of Boundary Layer Volatile Organic Compounds in Autumn in the Mixed Industrial and Rural Areas over the Northern Suburb of Nanjing]

Based on the sounding data of VOCs in the lower troposphere (0-1000 m) in the northern suburb of Nanjing in the autumn of 2020, the vertical profile distribution, diurnal variation, and photochemical reactivity of VOCs in this area were analyzed. The results showed that the volume fraction of VOCs decreased with the increase in height (72.1×10^-9±28.1×10^-9-56.4×10^-9±24.8×10^-9). Alkanes at all heights accounted for the largest proportion (68%-75%), followed by aromatics (10%-12%), halohydrocarbons (10%-11%), alkenes (3%-7%), and acetylene (2%). The diurnal variation of the boundary layer had a great influence on the VOCs profile. The lower boundary layer in the morning and evening caused the volume fraction of VOCs to accumulate near the ground and lower in the upper layer. The vertical distribution of VOCs was more uniform in the afternoon. In the morning, the volume fraction proportion of alkenes (alkanes) with strong (weak) photochemical reactivity decreased (increased) with the increase in height, indicating that the photochemical aging of VOCs in the upper layer was significant. In the afternoon, the vertical distribution of VOCs volume fraction and OFP in the lower troposphere were more uniform. Affected by the surrounding air masses with different sources, the volume fraction and component proportion of VOCs at each height were significantly different. The alkanes in rural air masses were vertically evenly distributed, and the proportion increased gradually with the height. The vertical negative gradient of VOCs volume fraction in the urban air mass was the largest, the volume fraction of VOCs near the ground was high, and it was rich in aromatics. The proportion of aromatics increased with the increase in VOCs volume fraction between 200-400 m height of industrial air mass. The near-surface VOCs volume fraction of the highway traffic air mass was high, and alkanes accounted for the largest proportion.

[Concentration and Reactivity of Carbonyl Compounds in the Atmosphere of North China]

To reveal the characteristics of photochemical pollution in North China, adsorbing columns with 2, 4-dinitrophenylhydrazine(DNPH) were used to sample carbonyl compounds in Shijiazhuang and Xinglong between May 2018 and April 2019. The samples were analyzed by high-performance liquid chromatography to understand the composition, volume fraction, source, ·OH loss rate, and ozone formation potential of the carbonyl compounds. A total of 13 carbonyl compounds containing carbonyl groups were determined, of which acetone, formaldehyde, and acetaldehyde were highest at(6.46±5.25)×10^-9, (3.76±2.29×10^-9), and(2.65±1.74)×10^-9 in Shijiazhuang compared to(1.85±1.27)×10^-9, (1.29±1.02)×10^-9, and(0.72±0.48)×10^-9 in Xinglong, respectively. The estimated maximum ozone formation potential(OFP) of formaldehyde was much higher than that of acetaldehyde; the C1/C2 and C2/C3 ozone formation potential(OFP) of formaldehyde was much higher than that of acetaldehyde; and the C1/C2 and C2/C3 values showed that vehicle exhaust and fossil fuel combustion were the main sources in Shijiazhuang in association with the higher level of industrialization. In Xinglong, the carbonyl compounds mainly originated from natural sources. Acetaldehyde(1.77 s^-1), formaldehyde(1.57 s^-1), and butyraldehyde(0.42 s^-1) contributed most to L_·OH in Shijiazhuang, and formaldehyde(0.53 s^-1), acetaldehyde(0.47 s^-1), and butyraldehyde(0.12 s^-1) were the three main contributors to L_·OH in Xinglong. The carbonyl compounds contributing most to O₃ production were formaldehyde and acetaldehyde at(34.61×10^-9 O₃) and (16.73×10^-9 O₃) in Shijiazhuang, compared to (11.77×10^-9 O₃) and (4.47×10^-9 O₃) in Xinglong, respectively.

[Characteristics of Water-soluble Inorganic Ions in PM2.5 in Beijing During 2017-2018]

To explore the characteristics of water-soluble inorganic ions (WSIIs) in PM_2.5 during the process of continuous improvement of air quality in Beijing in recent years, a continuous collection of PM_2.5 sample campaign was conducted in Beijing from 2017 to 2018. The PM_2.5 mass concentration and WSIIs were then determined. The results showed that the average concentration of PM_2.5 in Beijing was (77.1±52.1) μg ·m^-3, with the highest and lowest values during spring [(102.9±69.1) μg ·m^-3]and summer [(54.7±19.9) μg ·m^-3], respectively. The average concentration of WSIIs was (31.7±30.1) μg ·m^-3, accounting for 41.1% of the PM_2.5 mass, and the seasonal contributions were: autumn (45.9%) > summer (41.9%) > spring (39.9%) ≥ winter (39.2%). SNA was an important component of the WSIIs that accounted for 86.0%, 89.5%, 74.6%, and 73.0% of the total WSIIs during spring, summer, autumn, and winter, respectively. With an increase in temperature, the concentration of NO₃^- increased initially and then decreased, while the concentration of SO₄^2- increased. When the relative humidity was less than 90%, the concentrations of both NO₃^- and SO₄^2- increased with an increase in relative humidity. With the aggravation of pollution, the overall contribution of WSIIs in PM_2.5 increased significantly, and the evolution characteristics of different ions were different. Among them, the concentration and contribution of NO₃^- continued to increase, while the contributions of SO₄^2- and the ions from dust (Mg²⁺, Ca²⁺, and Na⁺) decreased. During the observation period, the primary sources of WSIIs were secondary conversion, combustion source, and dust. The control of coal combustion and motor vehicles is critical to reduce the emission of WSIIs. The backward trajectory analysis showed that the air masses from the south and west of Beijing corresponded to the high PM_2.5 concentration and proportion of WSIIs, and the contribution of secondary ions was significant. However, the concentrations and proportions of the air masses from the northwest and north were relatively low, but the contribution of Ca²⁺ was high.

[Characteristics of Carbonaceous Species in PM2.5 in Southern Beijing]

To investigate the characteristics of carbonaceous species in PM_2.5 in Beijing after the implementation of the Action Plan for the Prevention and Control of Air Pollution, PM_2.5 was continuously sampled in the heavily polluted southern urban area of Beijing from December 2017 to December 2018. The characteristics of organic carbon (OC) and element carbon (EC) were then determined. The results showed that the annual concentrations of PM_2.5, OC, and EC in Beijing varied in wide ranges of 4.2-366.3, 0.9-74.5, and 0.0-5.5 μg ·m^-3, respectively, and the average mass concentration were (77.1±52.1), (11.2±7.8), and (1.2±0.8) μg ·m^-3. Overall, the carbonaceous species (OC and EC) accounted for 16.1% of the PM_2.5 mass. The seasonal characteristics of the OC mass concentrations were: winter [(13.8±8.7) μg ·m^-3] > spring [(12.7±9.6) μg ·m^-3] > autumn [(11.8±6.2) μg ·m^-3] > summer [(6.5±2.1) μg ·m^-3]. The concentration of the EC during the four seasons was low, ranging from 0.8 to 1.5 μg ·m^-3. The annual average mass concentration and contribution of secondary organic carbon (SOC) were (5.4±5.8) μg ·m^-3 and 48.2%, respectively, highlighting the significant contribution of the secondary process. With the aggravation of pollution, although the contribution proportion of OC and EC decreased, their mass concentrations during "heavily polluted" days were 6.3 and 3.2 times that of "excellent" days, respectively. Compare to non-heating period, the mass concentrations of PM_2.5, OC, and SOC increased by 14.4%, 47.9%, and 72.1% in heating period, respectively, which emphasized the importance of carbonaceous species during heating periods. Potential source contribution function (PSCF) analysis showed that the southwest areas of Beijing (such as Shanxi and Henan province) were the main potential source areas of PM_2.5 and OC. The high value area of the PSCF of EC was less and the main potential source area was in the south of Beijing (such as Shandong and Henan province).

[Regulation of m^(6)A RNA Methylation and Its Effect on Myogenic Differentiation in Murine Myoblasts]

N^(6)-methyladenosine (m^(6)A) has been identified as a conserved epitranscriptomic modification of eukaryotic mRNAs, and plays important biological roles in the regulation of cellular metabolic processes. However, its role in myogenic differentiation is unclear. Here, we altered the m^(6)A RNA methylation level by overexpression of METTL3, and explored the effect of m^(6)A RNA methylation on myogenic differentiation of murine myoblasts in vitro. The m6A RNA methylation level is regulated by exogenous methylation inhibitor cycloleucine (Cyc) and methyl donor betaine (Bet). Therefore, chemical reagents of Cyc and Bet were used to test the regulatory effect of m^(6)A RNA methylation on myogenic differentiation. Results showed that METTL3 and Bet positively regulated the m^(6)A RNA methylation levels, and Cyc negatively regulated m^(6)A RNA methylation levels. In addition, m^(6)A methylation positively regulated myogenic differentiation in murine myoblasts. These findings provide insight in the mechanisms underlying the effect of m^(6)A RNA methylation on myogenesis.

[MiR-222-3р Regulates the Proliferation and Differentiation of C2C12 Myoblasts by Targeting BTG2]

MiR-222-3р has been implicated in tumor cell proliferation and has an important role in the differentiation and maturation of myogenic cells. However, its role in skeletal myoblast proliferation is still unclear. In this study, we found that miR-222-3р expression increases initially and then decreases during C2C12 myoblast proliferation. Using synthetic miRNA mimics and inhibitors in gain- or loss-of-function experiments, we snowed that miR-222-3р overexpression in C2C12 cells promotes myoblast proliferation and represses myofiber formation, while miR-222-3р downregulation has the opposite effect. Using a prediction program, BTG2 was identified as a possible target gene of miR-222-3р. During myogenesis, miR-222-3р mimics repress BTG2 expression, while miR-222-3р inhibitors promote BTG2 expression. Using dual-luciferase reporter assay, we further demonstrated that miR-222-3р specifically targets BTG2. Additionally, we show that siRNA-mediated downregulation of BTG2 expression in C2C12 myoblasts promotes the proliferation and suppresses differentiation. In conclusion, we provide a novel insight into the mechanism by which miR-222-3р regulates the proliferation and differentiation of C2C12 myoblasts by targeting BTG2. This information contributes to our understanding of the role of miRNAs in skeletal muscle development.

[Variation Characteristics and Sources Analysis of Atmospheric Volatile Organic Compounds in Changbai Mountain Station]

Volatile organic compounds (VOCs) play very important roles in the formation of ozone and secondary organic aerosols. The concentrations, compositions, and seasonal variation of VOCs were measured in 2012 at Changbai Mountain Forest Ecosystem Research Station, a remote station in Northeast China. Weekly samples were collected in the Changbai Mountain area and analyzed via gas chromatography-mass spectrometry. The results showed that the annual mean concentration of total VOCs (TVOCs) was 10.7×10^-9±6.2×10^-9. Halohydrocarbon was the most abundant component, accounting for 37% of the total VOCs, followed by alkanes and aromatics, accounting for 33% and 15% respectively, and alkenes accounted for 15%. The seasonal variation of TVOCs in this area was obvious, and the order was spring >autumn >summer >winter. TVOCs concentration in spring was very significantly higher than those in any other season (P<0.05). The principal component analysis (PCA) was used to identify the sources of the VOCs. Five sources were resolved by the PCA, including traffic sources, LPG,biogenic sources, combustion sources, industrial sources and regional transportation. The HYSPLIT-4.0 model was used to analyze the effect of pollutant transport, and the results indicated that the transport of pollutants from southwest had a significant effect on the increase of VOCs concentration.

Effects of muscle fiber type on glycolytic potential and meat quality traits in different Tibetan pig muscles and their association with glycolysis-related gene expression

The myosin heavy chain (MyHC) composition, glycolytic potential, mitochondrial content, and gene expression related to energy metabolism were analyzed in eight muscles from Tibetan pigs, to study how meat quality develops in different muscle tissues. The muscles were classified into three clusters, based on MyHC composition: masseter, trapezius, and latissimus dorsi as 'slow-oxidative-type'; psoas major and semimembranosus as 'intermediate-type'; and longissimus dorsi, obliquus externus abdominis, and semitendinosus as 'fast-glycolytic-type'. The 'slow-oxidative-type' muscles had the highest MyHC I and MyHC IIA content (P < 0.01); 'intermediate-type' muscles, the highest MyHC IIx content (P < 0.01); and 'fast-glycolytic-type' muscles, the highest MyHC IIb content (P < 0.01). The pH values measured in 'slow-oxidative-type' muscles were higher than those in the other clusters were; however, the color of 'fast-glycolytic-type' muscles was palest (P < 0.01). Mitochondrial content increased in the order: fast-glycolytic-type < intermediate-type < slow-oxidative-type. In the 'slow-oxidative-type' muscles, the expression levels of genes related to ATP synthesis were higher, but were lower for those related to glycogen synthesis and glycolysis. Mitochondrial content was significantly positively correlated with MyHC I content, but negatively correlated with MyHC IIb content. MyHC I and mitochondrial content were both negatively correlated with glycolytic potential. Overall, muscles used frequently in exercise had a higher proportion of type I fibers. 'Slow-oxidative-type' muscles, rich in type I fibers with higher mitochondrial and lower glycogen and glucose contents, had a higher ATP synthesis efficiency and lower glycolytic capacity, which contributed to their superior meat quality.

Carcass and meat quality traits of four commercial pig crossbreeds in China

We evaluated carcass and meat quality traits of two Chinese native crossbreeds Landrace x Meishan (LM) and Duroc x (Landrace x Meishan) (DLM) and two foreign crossbreeds Duroc x (Landrace x Yorkshire) (DLY) and PIC (an imported five-way crossbreed). One hundred and twenty weaned pigs (half castrated males and half females) were reared and slaughtered at a predestinated slaughter age. The general carcass and meat quality traits were measured and analyzed. The DLY and PIC crosses had significantly heavier live weights (93.39 and 96.33 kg, P < 0.01), significantly higher dressing percentages (80.65 and 79.39%, P < 0.05), significantly bigger loin areas (42.69 and 43.91 cm(2), P < 0.001), and significantly more lean carcasses (65.78 and 66.40%, P < 0.001) than LM and DLM. On the other hand, LM had a significantly lower live weight (70.29 kg, P < 0.01), significantly thicker back fat (3.54 cm, P < 0.001), significantly less lean carcasses (46.82%, P < 0.001), and significantly less ham and breech (26.53%, P < 0.05) than the other crossbreeds. Among meat quality parameters, LM had the highest intramuscular fat content (5.02%, P < 0.001) and the smallest fiber area (3126.45 μm(2), P < 0.01). However, PIC showed the lowest pH(1) (5.82, P < 0.01) and pH(2) (5.63, P < 0.01), the highest drip loss (2.89%, P < 0.01), and the lowest intramuscular fat (1.35%, P < 0.001). We concluded that LM and DLM had good meat quality traits but poorer carcass traits than DLY and PIC; DLY had good carcass and meat quality traits; PIC had good carcass traits, but it had less intramuscular fat, lower pH and higher drip loss.

[Application of passive sampler to monitor and study atmospheric trace gases in Beijing-Tianjin-Hebei area]

Applying of passive sampler which is a cheap and simple method, the concentrations of SO2, NO2, O3 and NH3 were monitored in ten stations as network in Beijing-Tianjin-Hebei area from Dec. 2007 to investigate the concentration level and change of contaminants as well as the compound pollution in this region. Passive sampler method was fully evaluated to check the applicability in the area and the concentration and spatial distribution of pollutants were studied in this paper. The evaluation results indicate that passive sampler method can be used for long-term sampling and the frequency was settled as one month. The coefficients of variation of parallel samplers of SO2, NO2, O3 and NH3 were 6.4%, 7.1%, 4.2% and 3.9% respectively which can represent the good stability of this method. The concentrations monitored by passive sampler had good consistency with the monthly average concentrations calculated from active monitoring. The correlation coefficients of SO2, NO2 and O3 were 0.91, 0.88 and 0.93, slopes of fitted curve were 1.25, 0.98 and 0.93 and average relative standard deviation were 23.3%, 14.9% and 8.5% respectively which indicated that passive sampler can basically meet the atmospheric sampling requirement. Short-term monitoring of NH3 also indicated that results of passive sampler and active monitoring were comparable. Passive sampler is proven to be a reliable atmospheric monitoring method and can be used in regional pollution investigation. In the summer of 2008, average concentrations which were monitored by passive sampler calculated from 10 observation stations of SO2, NO2, O3 and NH3 were (12.3 +/- 6. 3) x 10(-9), (13.2 +/- 7.0) x 10(-9), (40.5 +/- 9.5) x 10(-9) and (24.0 +/- 13.7) x 10(-9) respectively in Beijing-Tianjin-Hebei area. The concentrations of SO2 and NO2 were relatively higher in city sites and concentrations of NH3 were higher in agricultural sites. The pollution of SO2, NO, and NH3, are obviously influenced by local emission. The concentrations of O3 were about 40 x 10(-9) in most area around Beijing and Tianjin except background station Xinglong and showed regional pollution characteristic.

Antisense repression of sucrose synthase in carrot (Daucus carota L.) affects growth rather than sucrose partitioning

To unravel the roles of sucrose synthase in carrot, we reduced its activity in transgenic carrot plants by an antisense approach. For this purpose, the cDNA for the main form of carrot sucrose synthase was expressed in antisense orientation behind the 35S promoter of cauliflower mosaic virus. In independent antisense plant lines grown in soil, sucrose synthase activity was reduced in tap roots but not in leaves. In the sink organs, sucrose utilization was markedly decreased and higher levels of sucrose but lower levels of UDP-glucose, glucose, fructose, starch and cellulose were found. The phenotype of the antisense plants clearly differed from that of control plants. Both leaves and roots were markedly smaller, and the antisense line with the lowest sucrose synthase activity also developed the smallest plants. In most of the plant lines, the leaf-to-root dry weight ratios were not changed, suggesting that sucrose synthase in carrot is a major determinant of plant growth rather than of sucrose partitioning. In contrast to the acid invertases, which are critical for partitioning of assimilated carbon between source leaves and tap roots (Tang et al., Plant Cell 11: 177-189 (1999)), sucrose synthase appears to be the main sucrose-cleaving activity, feeding sucrose into metabolism.

The sucrose-cleaving enzymes of plants are crucial for development, growth and carbon partitioning

Sink organs of most plant species are supplied with carbon and energy in the form of sucrose. The channeling of sucrose into sink metabolism requires its cleavage by several isoforms of invertase and sucrose synthase, which are localized in different subcellular compartments. These activities regulate the entry of sucrose into distinct biochemical pathways, such as respiration or biosynthesis of cell wall polysaccharides and storage reserves. Other vital roles for the sucrose-cleaving enzymes include invertase activity at the site of phloem unloading and vacuolar invertase and sucrose synthase in sink organs, which drives the long-distance transport of sucrose. In addition, invertases have been implicated in the defense response and in turgor-driven cell expansion, and sucrose synthase expression is associated with low temperature and anaerobiosis responses. Finally, because sugars also regulate gene expression, the sucrose-cleaving enzymes play a fundamental role in controlling cell differentiation and development.

Antisense repression of vacuolar and cell wall invertase in transgenic carrot alters early plant development and sucrose partitioning

To unravel the functions of cell wall and vacuolar invertases in carrot, we used an antisense technique to generate transgenic carrot plants with reduced enzyme activity. Phenotypic alterations appeared at very early stages of development; indeed, the morphology of cotyledon-stage embryos was markedly changed. At the stage at which control plantlets had two to three leaves and one primary root, shoots of transgenic plantlets did not separate into individual leaves but consisted of stunted, interconnected green structures. When transgenic plantlets were grown on media containing a mixture of sucrose, glucose, and fructose rather than sucrose alone, the malformation was alleviated, and plantlets looked normal. Plantlets from hexose-containing media produced mature plants when transferred to soil. Plants expressing antisense mRNA for cell wall invertase had a bushy appearance due to the development of extra leaves, which accumulated elevated levels of sucrose and starch. Simultaneously, tap root development was markedly reduced, and the resulting smaller organs contained lower levels of carbohydrates. Compared with control plants, the dry weight leaf-to-root ratio of cell wall invertase antisense plants was shifted from 1:3 to 17:1. Plants expressing antisense mRNA for vacuolar invertase also had more leaves than did control plants, but tap roots developed normally, although they were smaller, and the leaf-to-root ratio was 1.5:1. Again, the carbohydrate content of leaves was elevated, and that of roots was reduced. Our data suggest that acid invertases play an important role in early plant development, most likely via control of sugar composition and metabolic fluxes. Later in plant development, both isoenzymes seem to have important functions in sucrose partitioning.

In vitro increases in plasmid DNA supercoiling by hydrostatic pressure

By conducting topoisomerase I-mediating supercoiling assays, effects of elevated pressure on DNA supercoiling were investigated for the first time. It was found that pressure elevations induced a progressive increase in plasmid DNA linking numbers, winding the DNA duplex by a magnitude of 1.1-1.6x10(-3) angular degree/base/MPa. Implications for the findings were discussed in terms of disturbance of the tertiary structure of DNA by elevated pressure.

Evidence for genetic linkage between the ure and trh genes in Vibrio parahaemolyticus

Although V. parahaemolyticus does not generally produce urease, several studies have reported urease-positive V. parahaemolyticus isolates from clinical sources. Recently, studies have shown a complete coincidence between the urease-producing phenotype of V. parahaemolyticus strains and the possession of the thermostable direct haemolysin (TDH)-related haemolysin (TRH) gene (trh). TRH, like TDH, is considered to be an important virulence factor in the pathogenesis of V. parahaemolyticus gastroenteritis. The present study attempted to identify the gene ure encoding urease in V. parahaemolyticus to clarify the relationship between urease production and possession of trh. The polymerase chain reaction with mixed oligonucleotide primers targeted for conserved sequences of reported ure genes from other species was used to prepare a DNA probe to detect the V. parahaemolyticus ure gene. Colony hybridisation with this ure probe demonstrated that all the ure-positive strains produced urease. Considering the coincidence between production of urease and possession of trh in V. parahaemolyticus, it was concluded that the presence or absence of the ure gene is completely coincident with that of the trh gene in V. parahaemolyticus strains. Furthermore, the relative location of ure and trh on V. parahaemolyticus chromosomal DNA was analysed by pulsed-field gel electrophoresis. The results showed that, in all the strains examined, ure and trh were detected on the same NotI fragment, showing that the two genes localise within a relatively small portion of the chromosome DNA. These results suggest that the ure and trh genes are genetically linked in V. parahaemolyticus strains.

Phosphorylation of a 25 kDa protein is induced by thermostable direct hemolysin of Vibrio parahaemolyticus

Thermostable direct hemolysin (TDH) is a possible virulence factor produced by Vibrio parahaemolyticus. Although TDH has a variety of biological activities, including hemolytic activity, the biochemical mechanism of action remains uncertain. Here we analysed biochemical events, especially phosphorylation, caused by TDH in erythrocytes, and found that TDH caused significant phosphorylations of proteins on erythrocyte membrane. Phosphorylation of proteins was studies using [gamma-32P] ATP and SDS-PAGE. A number of protein kinase inhibitors were tested, to determine which types of kinases were involved in the phosphorylation events. TDH induced the phosphorylation of two proteins on membranes of human erythrocyte that are sensitive to TDH. The estimated molecular weight of these proteins was 25 and 22.5 kDa. Interestingly, the 22.5 kDa, but not the 25 kDa protein, was phosphorylated on the membrane of TDH-insensitive (resistant) horse erythrocytes. Moreover, a mutant TDH (R7), which retained binding ability but lost hemolytic activity, also phosphorylated only the 22.5 kDa protein on human erythrocyte membranes. Among the protein kinase inhibitors used the protein kinase C inhibitors, (staurosporine and calphostin C) showed marked inhibition of phosphorylation of 25kDa protein. In addition to phosphorylation, these protein kinase C inhibitors suppressed hemolysis by TDH. These results indicate that the phosphorylation of the 25 kDa protein seems to be essential for the hemolysis by TDH after it binds to erythrocyte membranes.

Ca(2+)-independent cytotoxicity of Vibrio parahaemolyticus thermostable direct hemolysin (TDH) on Intestine 407, a cell line derived from human embryonic intestine

The effects of Vibrio parahaemolyticus thermostable direct hemolysis on Intestine 407, a cell line derived from the intestine of human embryos, were investigated. The hemolysin was shown to be cytotoxic to Intestine 407. This cytotoxicity is accompanied by the damage of plasma membrane and lysosomes, as well as cellular degeneration in the form of large transparent blebs. Although an increase in cytosolic free Ca2+ due t the influx of extracellular Ca2+ was observed in cells treated with thermostable direct hemolysin, it was found to be irrelevant to any of the above effects. These results suggest that the effects of thermostable direct hemolysin observed in this study on Intestine 407 are not mediated by Ca(2+)-dependent pathways.

Isolation of mutant toxins of Vibrio parahaemolyticus hemolysin by in vitro mutagenesis

Thermostable direct hemolysin produced by Vibrio parahaemolyticus is a major virulence factor of the organism. The hemolysin has a variety of biological activities such as lethality to mice, cytotoxicity to cultured cells, cardiotoxicity, and fluid accumulating activity in rabbit ileal loop test. In this study, we attempted to isolate less hemolytic mutant toxins of the thermostable direct hemolysin to use them for analysis of mode of action of the hemolysin. Six mutant toxins were obtained by in vitro mutagenesis of the cloned gene for the hemolysin. Characterization of the mutant toxins demonstrated that single amino acid substitutions at Gly62, Trp65, Thr67, Gly86, Glu116 and Glu138 resulted in a loss or lowering of the hemolytic activity. Two of the mutant toxins inhibited hemolysis by wild-type toxin on rabbit blood agar plates, while their hemolytic activity was below the detectable level. These mutant toxins would be useful for identifying the as yet unknown receptor for the hemolysin on the target cell membrane.

A mutant toxin of Vibrio parahaemolyticus thermostable direct hemolysin which has lost hemolytic activity but retains ability to bind to erythrocytes

A mutant toxin, R7, of thermostable direct hemolysin (TDH) with a single amino acid substitution at glycine 62 was analyzed. The hemolytic activity of R7 decreased to less than 1/1,000 of that of wild-type TDH, and its mouse lethality was undetectable. This mutant toxin, however, showed a marked inhibitory effect on hemolysis by wild-type TDH. Enzyme immunoassay and flow cytometric analysis demonstrated that R7 retained approximately 50% of the ability to bind to erythrocytes compared with that of wild-type TDH, suggesting that its inhibition of hemolysis by wild-type TDH might be due to blocking the binding sites on the erythrocyte membrane. Wild-type TDH affected the erythrocyte membrane by causing an influx of calcium and propidium iodide, while R7 showed no detectable effects of these kinds. These results suggest that hemolysis by TDH consists of at least two steps, binding and postbinding, and that R7 is likely to be a postbinding activity-deficient mutant toxin of TDH.