Evaluating the efficacy of an attenuated Streptococcus equi ssp. zooepidemicus vaccine produced by multi-gene deletion in pathogenicity island SeseCisland_4

Streptococcus equi ssp. zooepidemicus(SEZ) is a pathogen associated with a wild range of animal species. Frequent outbreaks have occurred in recent years in pigs, horses, goats and dogs which is liable to infect humans. There is a lack of efficient vaccines against this disease and the occurrence of antibiotic resistance may render drug therapies ineffective. In this study, gene deletion mutant(ΔSEZ) in pathogenicity islands SeseCisland_4 was constructed. The mutant ΔSEZ had a 52-fold decrease in 50% lethal dose(LD_(50)) and had less capacity to adhere epithelial cells. Importantly, immunization of mice with attenuated vaccine ΔSEZ at the dose of 10~2 colony-forming units(CFU) mL~(–1) elicited a significant humoral antibody response, with an antibody titer of 1:12 800. Therefore, 10~2 CFU mL~(–1) might be used as the appropriate immune dose for the attenuated vaccine ΔSEZ, which provided mice with efficient protection against virulent SEZ. In addition, the hyperimmune sera against 10~2 CFU m L–1 attenuated vaccine ΔSEZ could confer significant protection against virulent SEZ infection in the passive immunization experiment and exhibited efficient bactericidal activity in the whole blood assay. Meanwhile, no viable bacteria was detected in blood when mice were immunized with ΔSEZ at the dose of 10~2 CFU mL~(–1) via hypodermic injection. Thereafter, the mutant ΔSEZ at the dose of 10~2 CFU mL~(–1) could confer significant protection in mice and had less negative effects on host, which could be an effective attenuated vaccine candidate for the prevention of SEZ.     

天一阁藏书及社会贡献史考略

从两个不同的方向记述了天一阁藏书楼四百多年来的藏书发展史．旨在从不同的角度了解天一阁藏书楼的历史，明白其在中国藏书文化史上的地位与影响。     

Ammonia toxicity and its effect on the growth of the South African abalone Haliotis midae Linnaeus

The current study investigated acute toxicity to ammonia of the South African abalone, Haliotis midae, from three size classes relevant to mariculture operations, and the chronic impact of sub-lethal ammonia levels on growth of juvenile abalone.Results showed that tolerance to ammonia (at pH 7.8 and T_a = 15 °C) increases with body size (i.e. age) as indicated by 36 h LC₅₀ values: juvenile abalone (1-2.5 cm shell length) had the lowest LC₅₀ of 9.8 μg l^− 1 FAN, whereas LC₅₀ was 12.9 μg l^− 1 FAN in “cocktail”-size abalone (5-8 cm shell length). The highest LC₅₀ of 16.4 μg l^− 1 FAN was observed in “brood stock”-size animals (10-15 cm). When “cocktail”-size abalone were allowed to acclimatize to sub-lethal ammonia levels for 48 h, their ammonia tolerance increased compared with non-acclimatized abalone of the same size: LC₅₀ was 2.0 μg l^− 1 FAN higher at 14.8 μg l^− 1 FAN.Growth of juvenile abalone (1-2.5 cm shell length) during chronic exposure to sub-lethal FAN levels is inhibited: specific growth rate (SGR) is significantly reduced by 58.7% to 0.10 ± 0.03% d^− 1 (weight) compared with 0.24 ± 0.06% d^− 1 of abalone of a control group (no ammonia).The results demonstrate the negative effects of ammonia not only on survival but also on growth of farmed abalone, both impair profitability of the farming operation. The information from the present study will be helpful in determining water quality requirements in South African abalone farms.     

Effect of settled sludge on dissolved ammonia concentration in tanks used to grow abalone (Haliotis midae L.) fed a formulated diet

The relative contribution that solid waste or 'sludge', which accumulates at the bottom of abalone ( Haliotis midae L.) tanks, makes to dissolved ammonia has not been established. Sludge was allowed to accumulate in 10 fully stocked abalone tanks, fed a formulated feed (Abfeed^®; Marifeed, South Africa), for 24 days. Sludge was subsequently siphoned from five of these tanks. Total ammonia nitrogen (TAN) production and toxic, free ammonia nitrogen (FAN) were recorded in the tanks from which sludge was removed and compared with those from which sludge was not removed over the subsequent 50 h. Tanks with neither abalone nor sludge present were used as a control. The mean production of TAN (±standard deviation) was an average of 44% higher in tanks from which sludge was not removed compared with those from which it was, indicating that the sludge was a significant contributor to dissolved ammonia in the tanks. The toxic FAN concentrations were correspondingly higher in tanks with sludge present (2.3±0.3 μL⁻¹) compared with cleaned tanks (1.9±0.1 μL⁻¹). Our results indicate that regular removal of sludge from abalone tanks should significantly reduce the dissolved ammonia levels, thereby improving water quality in the culture environment.     

南方设施菜地填闲苋菜筛选及其氮磷淋失阻控效果研究

筛选经济效益高、易推广,且对夏季休闲期氮磷淋失阻控效果好的填闲作物,对减轻我国珠三角地区设施菜地土壤氮磷流失、保护水体环境具有重要意义。通过淋溶管法研究了夏季休闲期(7月至8月)种植4种苋菜(圆红苋菜、心红苋菜、青苋与南星苋)对设施菜地土壤淋溶液p H、无机氮磷浓度及收获后土壤速效养分等的影响。结果表明:苋菜作为填闲作物种植可产生2.04～2.83万元/hm~2的经济效益,同时降低设施菜地土壤淋溶液NO_3~–-N、NH_4~+-N与总磷浓度,对三者淋溶损失的阻控效率依次达到31.2%～49.5%、35.5%～37.5%和30.1%～43.6%。与休闲对照处理相比,苋菜种植收获后土壤碱解氮与有效磷养分并没有表现出耗竭,其中有效磷含量提升31.9%～67.8%。综合本研究结果,4种苋菜均为可优选的填闲叶菜,皆具较高的减控设施蔬菜休闲期土壤氮磷淋溶损失效率与经济效益,且不影响后茬蔬菜生产的地力基础,其中,心红苋菜在环境效益和经济效益(2.83万元/hm~2)方面表现较为突出。