Effect of sublethal concentrations of four chemicals on susceptibility of juvenile rainbow trout (Oncorhynchus mykiss) to saprolegniosis.

The effects of sublethal concentrations of a variety of chemicals on the susceptibility of rainbow trout (Oncorhynchus mykiss) juveniles to Saprolegnia parasitica infection was examined. Sublethal concentrations of un-ionized ammonia (0.05 mg/liter) and nitrite (0.12 mg/liter) increased fish susceptibility after 10 days of exposure to the toxin, this increase being higher for ammonia (75% and 20% morbidity) than for nitrite (20% and 0% morbidity, respectively) with inoculum doses of 1.4 x 10(6) and 9.5 x 10(5) zoospores per liter, respectively. Sublethal concentrations of copper (0.05 mg/liter) or cyanide (0.05 mg/liter) did not show enhancement of infection by S. parasitica, even though the toxin exposure was for 21 days and the inoculum doses were higher than those for the experiments with the nitrogen compounds (4 x 10(6) and 3.2 x 10(6) zoospores per liter. However, infections began to appear in control animals.     

Effects of Waterborne Copper, Cyanide, Ammonia, and Nitrite on Stress Parameters and Changes in Susceptibility to Saprolegniosis in Rainbow Trout (Oncorhynchus mykiss)

The effects of toxic exposures on the susceptibility of rainbow trout (Oncorhynchus mykiss) to saprolegniosis were evaluated. Fish were exposed to sublethal concentrations of copper (0.25 mg/liter), cyanide (0.07 mg/liter), ammonia (0.5 mg/liter), and nitrite (0.24 mg/liter) for 24 h. After exposure, the fish were challenged by Saprolegnia parasitica (3.6 x 10(sup6) zoospores per liter) for 10 min. Cortisol and cholesterol were used to indicate stress response. Similar increases of cortisol were found for the four tested chemicals. All fish with cortisol levels higher than 370 ng/ml developed the disease, while only 24% of the fish with cortisol levels lower than 370 ng/ml were infected. Cholesterol levels remained unchanged after toxic exposure. Increased susceptibilities to the pathogen were observed for ammonia (71%), copper (57%), nitrite (50%), and cyanide (33%). The increases in susceptibility as a result of cyanide and nitrite exposure could be explained by the stress response. For copper and ammonia, the combination of two different effects, the stress response and specific impairments of the defense mechanism of trout against saprolegniosis, should be considered.     

Effects of disinfectants on Campylobacter jejuni

Because of the increasing recognition that Campylobacter jejuni is an important enteric pathogen of humans, we studied the effects of widely used disinfectants on the viability of this organism. At an inoculum size of 10(3) to 10(4) CFU/ml, 1.25 mg of hypochlorite per liter killed three strains within 1 min. At an inoculum size of 10(6) to 10(7) CFU/ml, 5 mg of hypochlorite per liter killed three strains within 15 min. Killing of similar concentrations of C. jejuni and Escherichia coli by hypochlorite was approximately the same. At the high inoculum, 0.15% phenolic compound, 10 mg of iodophor per liter, 1:50,000 quaternary ammonium compound, 70% ethyl alcohol, and 0.125% glutaraldehyde killed all three strains within 1 min. These studies demonstrate that, under the conditions we tested (pH 7.0; 24 to 26 degrees C), the recommended standard concentrations of disinfecting agents are adequate to destroy C. jejuni.     

Effects of disinfectants on Campylobacter jejuni.

Because of the increasing recognition that Campylobacter jejuni is an important enteric pathogen of humans, we studied the effects of widely used disinfectants on the viability of this organism. At an inoculum size of 10(3) to 10(4) CFU/ml, 1.25 mg of hypochlorite per liter killed three strains within 1 min. At an inoculum size of 10(6) to 10(7) CFU/ml, 5 mg of hypochlorite per liter killed three strains within 15 min. Killing of similar concentrations of C. jejuni and Escherichia coli by hypochlorite was approximately the same. At the high inoculum, 0.15% phenolic compound, 10 mg of iodophor per liter, 1:50,000 quaternary ammonium compound, 70% ethyl alcohol, and 0.125% glutaraldehyde killed all three strains within 1 min. These studies demonstrate that, under the conditions we tested (pH 7.0; 24 to 26 degrees C), the recommended standard concentrations of disinfecting agents are adequate to destroy C. jejuni.     

Nitrification of swine waste

Complete oxidation of ammonia nitrogen (approximately 1000 mg/L) to nitrite was observed in stabilized swine waste after 49 days in incubation at 400 rpm and 29 degrees C, only if 10% (v/v) activated sludge from a wastewater treatment unit and 1.5% (w/v) CaCO3, were added. Stabilized swine waste contains less than 0.09 most probable number (MPN) per millilitre of nitrosobacteria and 2.3 MPN/mL of nitrobacteria. In activated sludge, the concentrations of these bacteria were 2.4 MPN/mL for nitrosobacteria and 4.2 x 10(5) MPN/mL for nitrobacteria. In the swine waste where ammonia was oxidized to nitrite, the nitrosobacteria growth increased to 5.5 x 10(5) MPN/mL, while the nitrobacteria growth decreased to 2.3 MPN/mL. Inoculation of a freshly stabilized swine waste with 10% (v/v) of the active nitrifying waste and addition of 1.5% (w/v) CaCO3, accelerated the oxidation of ammonia nitrogen to nitrite; the reaction was completed after only 5 days of incubation. Increasing the incubation period to 10 days resulted in the complete oxidation of the accumulated nitrite to nitrate. In the stabilized swine waste, complete nitrification without accumulation of nitrite was obtained in only 5 days of incubation when the waste was inoculated with both enriched nitrifying populations (10(6)-10(7) MPN/mL).     

Effect of monensin on the specific activity of ammonia production by ruminal bacteria and disappearance of amino nitrogen from the rumen.

When unadapted mixed ruminal bacteria (312 mg of protein per liter) were treated with monensin (5 mM) in vitro, the rates of ammonia production from enzymatic digests of casein, gelatin, and soy protein (0.5 g of N per liter) were decreased from 46 +/- 2 to 24 +/- 1, 20 +/- 1 to 7 +/- 1, and 40 +/- 2 to 18 +/- 2 nmol/mg of protein per min, respectively. Monensin also caused a decrease in ammonia production in vivo. Nonlactating dairy cows which were fed 0.56 kg of timothy hay 12 times per day had a steady-state ruminal ammonia concentration of 2.7 +/- 0.1 mM, and the ammonia concentration decreased to 1.2 +/- 0.2 mM when monensin (350 mg/day) was added to the diet. The decrease in ammonia production was associated with a 10-fold reduction (4.1 x 10(6) versus 4.2 x 10(5)/ml) in the most probable number of ammonia-producing ruminal bacteria that could use protein hydrolysate as an energy source. Monensin had little effect on the most probable number of carbohydrate-utilizing ruminal bacteria (6.5 versus 7.0 x 10(8)/ml). The addition of protein hydrolysates (560 g) to the rumen caused a rapid increase in the ammonia concentration, but this increase was at least 30% lower when the animals were fed monensin.(ABSTRACT TRUNCATED AT 250 WORDS)     

三种不同小球藻去除亚硝态氮和氨氮能力的研究

为了研究小球藻在不同质量浓度的氨氮和亚硝态氮环境下的去除能力与生长效果,从实验室挑选3株不同的小球藻CV315-1(Chlorella sp.)、CV315-2(Chlorella sorokiniana)和CV315-3(Chlorella pyrenoidosa)分别置于不同质量浓度的氨氮和亚硝态氮模拟污水中,在温...     

Phytophthora Root Rot of Pepper Influence of Host Genotype and Pathogen Strain on the Inoculum Density-Disease Severity Relationships

The relationship between inoculum density and mortality or infection was studied for various pepper varieties (Capsicum annuum L.) inoculated with zoospores of two P. capsici isolates. The inoculum concentrations required for 50% mortality (LD 50) varied greatly between pepper varieties and P. capsici isolates: with one isolate, LD 50 was 40 zoospores/ml for a susceptible variety and reached 4,380 to 97,300 zoospores/ml for resistant varieties. For another isolate, LD 50 for the, same varieties ranged from 26 to 800 zoospores/ml. Comparisons between LD 50 and inoculum doses required for 50 % Infection (ID 50) also revealed differences between varieties but not between isolates. After multiple infection correction, regression slopes of infections/inoculum concentration were low for resistant varieties (0.28 to 0.50) but higher for susceptible varieties (0.72 to 0.94), indicating strong competition between spores for infection of resistant plants, but not for infection of susceptible plants. This analysis provided many criteria which can be used to differentiate susceptible from resistant varieties and to evaluate with precision the resistance level of the different resistance genitors used in our breeding program.     

Factors Influencing the Effectiveness of Swimming Pool Bactericides

Techniques for culturing, harvesting, and testing bacteria to evaluate bactericidal chemicals for swimming pools are described. Concentrations of 25, 50, and 100 mg of the chlorine stabilizer cyanuric acid per liter increased the time required for a 99% kill of Streptococcus faecalis by 0.5 mg of chlorine per liter at pH 7.4 and 20 C from less than 0.25 min without cyanuric acid to 4, 6, and 12 min, respectively. The effect of concentrations of ammonia nitrogen in the range found in swimming pools on the rate of kill of 0.5 mg of chlorine per liter and of chlorine plus cyanuric acid was tested. At concentrations of ammonia nitrogen greater than 0.05 mg per liter, faster rates of kill of S. faecalis were obtained with 100 mg of cyanuric acid per liter plus 0.5 mg of chlorine per liter than with 0.5 mg of chlorine per liter alone. When water samples from four swimming pools with low ammonia levels were used as test media, 0.5 mg of added chlorine per liter killed 99.9% of the added S. faecalis in less than 2 min, but water from a pool with a large number of children required 60 to 180 min of treatment.     

Cadmium removal by living cells of the marine microalga Tetraselmis suecica

Cadmium removal by living cells of the marine microalga Tetraselmis suecica was tested in cultures exposed to different cadmium concentrations (0.6, 3, 6, 15, 30 and 45 mg/l). The EC50 for growth was 7.9 mg Cd/l after six days of exposure. The cadmium removed was proportional to the concentration of this metal in the medium and it was dependent on the time of exposure; cultures with higher cadmium concentration removed a higher amount of this metal. In cultures exposed to 0.6 mg/l, T suecica cells removed 98.1% of added cadmium with 0.392 x 10(-6) microg Cd/cell, whereas in cultures with 45 mg/l only 7.7% was removed with 16.052 x 10(-6) microg Cd/cell. The highest amount of cadmium removed per liter of culture was observed in cultures exposed to 6 mg/l, with 3.577 mg/l of cadmium. After six days of incubation, the higher proportion of cadmium was bioaccumulated intracellularly in all cultures except in 45 mg/l cultures, the percentage of intracellular cadmium being always more than 50%. The highest percentage of bioadsorbed cadmium (60.1%) was found in cells of cultures with the highest cadmium concentration (45 mg/l). Furthermore, a relation between intracellular cadmium and the concentration of sulfhydryl groups was observed.     

Inhibitory effects of free ammonia on Anammox bacteria

Anammox bacteria can effectively treat high ammonia and nitrite concentrations under anoxic environments. However, the presence of high ammonia and nitrite concentrations may cause free ammonia and nitrous acid inhibition at high pH and temperature environments. In this study, the inhibitory effect of free ammonia on Anammox bacteria was investigated in a lab-scale upflow fixed-bed reactor with Kaldnes biofilm carriers. Results of continuous operation showed that inhibition was not observed in the Anammox reactor when the free ammonia concentration gradually increased up to 150?mg/L. However, Anammox activity suddenly dropped to 10 % when the free ammonia concentration reached to 190?mg/L. Nevertheless, high influent ammonia and nitrite concentrations up to 1,500 and 500?mg/L, respectively, did not noticeably inhibit the Anammox activity. Gradually decreasing Anammox activity was also supported by fluorescent in situ hybridization (FISH) analysis. FISH and 16S rRNA gene analysis results revealed that main Anammox organisms were phylogenetically related to Candidatus Kuenenia stuttgartiensis, Candidatus Jettenia asiatica and Candidatus Brocadia anammoxidans.     

Effect of disinfection of drinking water with ozone or chlorine dioxide on survival of Cryptosporidium parvum oocysts.

Demineralized water was seeded with controlled numbers of oocysts of Cryptosporidium parvum purified from fresh calf feces and subjected to different treatments with ozone or chlorine dioxide. The disinfectants were neutralized by sodium thiosulfate, and neonatal mice were inoculated intragastrically and sacrificed 7 days later for enumeration of oocyst production. Preliminary trials indicated that a minimum infection level of 1,000 oocysts (0.1-ml inoculum) per mouse was necessary to induce 100% infection. Treatment of water containing 10(4) oocysts per ml with 1.11 mg of ozone per liter (concentration at time zero [C0]) for 6 min totally eliminated the infectivity of the oocysts for neonatal mice. A level of 2.27 mg of ozone per liter (C0) was necessary to inactivate water containing 5 x 10(5) oocysts per ml within 8 min. Also, 0.4 mg of chlorine dioxide per liter (C0) significantly reduced infectivity within 15 min of contact, although some oocysts remained viable.     

Effect of disinfection of drinking water with ozone or chlorine dioxide on survival of Cryptosporidium parvum oocysts

Demineralized water was seeded with controlled numbers of oocysts of Cryptosporidium parvum purified from fresh calf feces and subjected to different treatments with ozone or chlorine dioxide. The disinfectants were neutralized by sodium thiosulfate, and neonatal mice were inoculated intragastrically and sacrificed 7 days later for enumeration of oocyst production. Preliminary trials indicated that a minimum infection level of 1,000 oocysts (0.1-ml inoculum) per mouse was necessary to induce 100% infection. Treatment of water containing 10(4) oocysts per ml with 1.11 mg of ozone per liter (concentration at time zero [C0]) for 6 min totally eliminated the infectivity of the oocysts for neonatal mice. A level of 2.27 mg of ozone per liter (C0) was necessary to inactivate water containing 5 x 10(5) oocysts per ml within 8 min. Also, 0.4 mg of chlorine dioxide per liter (C0) significantly reduced infectivity within 15 min of contact, although some oocysts remained viable.     

基于物种敏感性分布的微囊藻毒素与氮污染水体生态风险评估

应用物种敏感性分布(SSD)方法,可正向和反向评估物种的生态风险及确定保护物种的污染物浓度阈值,为水体生态风险管理提供依据.本文通过采集淡水生物毒性数据,构建SSD方程,在95%物种保护基础上评估微囊藻毒素、氨氮和亚硝态氮对淡水生物的生态风险浓度阈值(HC₅)和复合生态风险,以及不同暴露浓度下的潜在影响比例(PAF).结果表明: 微囊藻毒素对淡水生物的HC₅值为19.22 μg·L^-1,其水生态风险高于氨氮(HC₅ 6583.94 μg·L^-1)和亚硝态氮(HC₅ 334.33 μg·L^-1).不同类别生物对微囊藻毒素和氨氮、亚硝态氮的敏感性随暴露浓度不同存在差异.当微囊藻毒素与亚硝态氮的浓度低于临界浓度125.04、2989.40 μg·L^-1时,甲壳类对微囊藻毒素敏感性高于鱼类,对亚硝态氮敏感性则低于鱼类,而高于临界值其物种敏感性呈相反效应,但氨氮所引起的物种敏感性差异不显著.在代表性水体中,复合生态风险高于单一污染风险,微囊藻毒素、氨氮、亚硝态氮对全部物种的复合潜在影响比例msPAF为2.6%～5.6%,且太湖和红枫湖已超过HC₅生态风险阈值.     

Rapid mineralization of benzo[a]pyrene by a microbial consortium growing on diesel fuel

A microbial consortium which rapidly mineralized the environmentally persistent pollutant benzo[a]pyrene was recovered from soil. The consortium cometabolically converted [7-(14)C]benzo[a]pyrene to (14)CO(2) when it was grown on diesel fuel, and the extent of benzo[a]pyrene mineralization was dependent on both diesel fuel and benzo[a]pyrene concentrations. Addition of diesel fuel at concentrations ranging from 0.007 to 0.2% (wt/vol) stimulated the mineralization of 10 mg of benzo[a]pyrene per liter 33 to 65% during a 2-week incubation period. When the benzo[a]pyrene concentration was 10 to 100 mg liter(-1) and the diesel fuel concentration was 0.1% (wt/vol), an inoculum containing 1 mg of cell protein per liter (small inoculum) resulted in mineralization of up to 17.2 mg of benzo[a]pyrene per liter in 16 days. This corresponded to 35% of the added radiolabel when the concentration of benzo[a]pyrene was 50 mg liter(-1). A radiocarbon mass balance analysis recovered 25% of the added benzo[a]pyrene solubilized in the culture suspension prior to mineralization. Populations growing on diesel fuel most likely promoted emulsification of benzo[a]pyrene through the production of surface-active compounds. The consortium was also analyzed by PCR-denaturing gradient gel electrophoresis of 16S rRNA gene fragments, and 12 dominant bands, representing different sequence types, were detected during a 19-day incubation period. The onset of benzo[a]pyrene mineralization was compared to changes in the consortium community structure and was found to correlate with the emergence of at least four sequence types. DNA from 10 sequence types were successfully purified and sequenced, and that data revealed that eight of the consortium members were related to the class Proteobacteria but that the consortium also included members which were related to the genera Mycobacterium and Sphingobacterium.     

Toxicity of propylene oxide at low pressure against life stages of four species of stored product insects

The relative toxicity of propylene oxide (PPO) at a low pressure of 100 mm Hg to four species of stored product insect at 30 degrees C over a 4-h exposure period was investigated. PPO at 100 mm Hg was toxic to all four species tested: Tribolium castaneum (Herbst), Plodia interpunctella (Hübner), Ephestia cautella (Wlk.), and Oryzaephilus surinamensis (L.). There were differences in susceptibility between the life stages of the tested insect species. Mortality tests on all life stages of the insects resulted in LD99 values ranging from 4.7 to 26.1 mg/liter. The pupal stage of E. cautella, O. surinamensis, and T. castaneum was the most tolerant stage with LD99 values of 14.4, 26.1, and 25.7 mg/liter, respectively. For P. interpunctella, the egg stage was most tolerant, with a LD99 value of 15.3 mg/liter. Generally, PPO at 100 mm Hg was more toxic to P. interpunctella and E. cautella than to O. surinamensis and T. castaneum. A 99% mortality of all life stages of the tested species was achieved at a concentrations x time product of 104.4 mg h/liter. These findings indicate that a combination of PPO with low pressure can render the fumigant a potential alternative to methyl bromide for rapid disinfestation of commodities.     

Temporal effects of paraquat/maneb on microglial activation and dopamine neuronal loss in older rats

We investigated the effects of combined systemic exposure to the herbicide paraquat (PQ) and the fungicide maneb (MB) in 6-month-old rats, an animal model of Parkinson's disease resulting from environmental toxin exposure. Following two doses of PQ (10 mg/kg) and MB (30 mg/kg), 52% of animals developed fatal lung injury. Examination of the remaining animals showed degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta 6 weeks, but not 4 weeks, following PQ/MB. In contrast, microglial activation was observed at 4 weeks, but had abated by 6 weeks. Compared with our previous findings in younger rats, these results suggest increased susceptibility of older animals to lung and brain toxicity from PQ/MB exposure. Microglial activation preceded, and therefore likely contributed to, DA neurodegeneration. Further, electron microscopy revealed an abnormal appearance of the Golgi apparatus at 4 weeks that was confirmed using double immunostaining for tyrosine hydroxylase and Golgi. This suggests that PQ/MB causes protein processing dysfunction in nigral DA neurons that may be either a direct effect of PQ/MB or the result of microglial activation.     

Inactivation of enteric adenovirus and feline calicivirus by chlorine dioxide

Chlorine dioxide (ClO2) inactivation experiments were conducted with adenovirus type 40 (AD40) and feline calicivirus (FCV). Experiments were carried out in buffered, disinfectant demand-free water under high- and low-pH and -temperature conditions. Ct values (the concentration of ClO2 multiplied by contact time with the virus) were calculated directly from bench-scale experiments and from application of the efficiency factor Hom (EFH) model. AD40 Ct ranges for 4-log inactivation (Ct99.99%) at 5 degrees C were >0.77 to <1.53 mg/liter x min and >0.80 to <1.59 mg/liter x min for pH 6 and 8, respectively. For 15 degrees C AD40 experiments, >0.49 to <0.74 mg/liter x min and <0.12 mg/liter x min Ct99.99% ranges were observed for pH 6 and 8, respectively. FCV Ct99.99% ranges for 5 degrees C experiments were >20.20 to <30.30 mg/liter x min and >0.68 mg/liter x min for pH 6 and 8, respectively. For 15 degrees C FCV experiments, Ct99.99% ranges were >4.20 to <6.72 and <0.18 mg/liter x min for pH 6 and 8, respectively. Viral inactivation was higher at pH 8 than at pH 6 and at 15 degrees C than at 5 degrees C. Comparison of Ct values and inactivation curves demonstrated that the EFH model described bench-scale experiment data very well. Observed bench-scale Ct99.99% ranges and EFH model Ct99.99% values demonstrated that FCV is more resistant to ClO2 than AD40 for the conditions studied. U.S. Environmental Protection Agency guidance manual Ct99.99% values are higher than Ct99.99% values calculated from bench-scale experiments and from EFH model application.     

The Effective Production of Shikonin by Cultures with an Increased Cell Population

We have studied the efficient production of shikonin derivatives by suspension cultures of Lithospermum erythrorhizon with an increased cell population. The yield of shikonin derivatives was highest (800 mg/liter) when 2.8 g dry wt/liter of the cells was inoculated into the M-2 medium which we had developed for the production, but the excess inoculum lowered the yield.

We investigated suitable conditions for production with the increased cell population. The optimum amount of inoculum rose to 4.9 g dry wt/liter when the concentrations of all the components contained in the M-8 medium, which we developed for increasing the productivity by modification of the M-2 medium, were increased in proportion to the amount of inoculum, and consequently we could increase the yield of the shikonin derivatives from 1400 mg/liter to 1900 mg/liter. Moreover, the increased rate of oxygen supply in addition to the enrichment of the medium made it possible to produce 2300 mg/liter of the shikonin derivatives from a culture for which 5.6 g dry wt/liter of the cells was inoculated.     

Simplified purification method for Clostridium botulinum type E toxin.

Clostridium botulinum type E toxin was purified in three chromatography steps. Toxin extracted from cells was concentrated by precipitation and dissolving in a small volume of citrate buffer. When the extract was chromatographed on DEAE-Sephadex without RNase or protamine treatment, the first protein peak had most of the toxin but little nucleic acid. When the toxic pool was applied to a carboxymethyl Sepharose column, toxin was recovered in the first protein peak in its bimolecular complex form. The final chromatography step at 4 degrees C on a DEAE-Sephacel column at a slightly alkaline pH purified the toxin (Mr, 145,000) by separating the nontoxic protein from the complex. At least 1.5 mg of pure toxin was obtained from each liter of culture, and the toxicity was 6 X 10(7) 50% lethal doses per mg of protein. These values are significantly higher than those previously reported.