Degradation of extracellular genomic,plasmid DNA and specific antibiotic resistance genes by chlorination

Extracellular DNA structure damaged by chlorination was characterized. Integrity of extracellular ARG genetic information after chlorination was determined. Typical chlorine doses will likely effectively diminish extracellular DNA and ARGs. Plasmid DNA/ARGs were less readily broken down than genomic DNA. The Bioanalyzer methodology effectively documented damage incurred to DNA. There is a need to improve understanding of the effect of chlorine disinfection on antibiotic resistance genes (ARGs) in order to advance relevant drinking water, wastewater, and reuse treatments. However, few studies have explicitly assessed the physical effects on the DNA. Here we examined the effects of free chlorine (1–20 mg Cl₂/L) on extracellular genomic, plasmid DNA and select ARGs. Chlorination was found to decrease the fluorometric signal of extracellular genomic and plasmid DNA (ranging from 0.005 to 0.05 mg/mL) by 70%, relative to a no-chlorine control. Resulting DNA was further subject to a fragment analysis using a Bioanalyzer, indicating that chlorination resulted in fragmentation. Moreover, chlorine also effectively deactivated both chromosomal- and plasmid-borne ARGs, mecA and tetA, respectively. For concentrations >2 mg Cl₂//L × 30 min, chlorine efficiently reduced the qPCR signal when the initial concentration of ARGs was 10⁵ copies/mL or less. Notably, genomic DNA and mecA gene signals were more readily reduced by chlorine than the plasmid-borne tetA gene (by ~2 fold). Based on the results of qPCR with short (~200 bps) and long amplicons (~1200 bps), chlorination could destroy the integrity of ARGs, which likely reduces the possibility of natural transformation. Overall, our findings strongly illustrate that chlorination could be an effective method for inactivating extracellular chromosomal- and plasmid-borne DNA and ARGs.     

Diversity of antibiotic resistance genes and encoding ribosomal protection proteins gene in livestock waste polluted environment

The rapid development and increase of antibiotic resistance are global phenomena resulting from the extensive use of antibiotics in human clinics and animal feeding operations. Antibiotics can promote the occurrence of antibiotic resistance genes (ARGs), which can be transferred horizontally to humans and animals through water and the food chain. In this study, the presence and abundance of ARGs in livestock waste was monitored by quantitative PCR. A diverse set of bacteria and tetracycline resistance genes encoding ribosomal protection proteins (RPPs) from three livestock farms and a river were analyzed through denaturing gradient gel electrophoresis (DGGE). The abundance of sul(I) was 10³ to 10⁵ orders of magnitude higher than that of sul(II). Among 11 tet-ARGs, the most abundant was tet(O). The results regarding bacterial diversity indicated that the presence of antibiotics might have an evident impact on bacterial diversity at every site, particularly at the investigated swine producer. The effect of livestock waste on the bacterial diversity of soil was stronger than that of water. Furthermore, a sequencing analysis showed that tet(M) exhibited two genotypes, while the other RPPs-encoding genes exhibited at least three genotypes. This study showed that various ARGs and RPPs-encoding genes are particularly widespread among livestock.     

不同喷雾方式下低阻文丘里振弦栅除尘配置优化实验研究

为了对比径向外喷和轴向喷雾下的低阻文丘里振弦栅耦合除尘效果，以除尘效率和系统阻力为参照，选定喉管气速、振弦栅数、纤维丝间隙和喉管液气比进行单因素实验。结果表明2种喷雾方式的除尘效率和系统阻力的变化趋势相同。利用SPSS软件进行4因素3水平正交实验设计，在特定参数条件下，2种喷雾方式的因素影响排序相同，除尘效率为纤维栅数＞纤维丝间隙＞喉管气速＞喷雾量；系统阻力为喉管气速＞纤维栅数＞纤维丝间隙＞喷雾量；径向外喷最佳配置为喉管气速24 m/s、喷雾量2.3 L/min、2块间隙为0.8 mm纤维栅板；轴向喷雾为喉管气速28 m/s、喷雾量2.4 L/min、2块间隙为0.8 mm纤维栅板；在最优配置下的除尘性能为径向外喷＞轴向喷雾。     

通风机站风流间相互影响阻力特性研究*

为研究双风机并联机站进口、出口风流相互影响的机站局部阻力特性，构建机站通风局部阻力计算的数学模型，同时运用相似原理建立双风机并联通风机站实验模型，并佐以数值模拟对比验证，分析计算不同风机间距的无量纲数A、不同扩散器结构参数条件下的综合影响系数Kc。结果表明:A与Kc具有二次函数关系，且存在较优的A，使得Kc值最小；Kc值随着L/Df增加而线性减小。研究结果有利于Kc的选取，为高效率通风机站结构设计提供技术及数据支撑。     

基于SVM的矿井通风阻力系数影响因素分析与预测

矿井通风阻力系数是通风安全最重要的基础参数之一，为了实现矿井通风阻力系数简单准确地预测，提出了利用支持向量机（SVM）来预测矿井通风阻力系数的方法。通过分析影响因子与矿井通风阻力系数的相关性关系，并利用MATLAB逐步建立单影响因素与矿井通风阻力系数、多影响因素与矿井通风阻力系数之间的SVM预测模型，对比分析各预测模型的相对误差，确定最佳矿井通风阻力系数预测模型，即当输入模型影响因素为巷道断面积、周长和支护方式时，预测相对误差小于10%的样本数占测试样本的76%，相对误差小于20%的样本数占测试样本的90%。结果表明:该预测方法在矿井通风阻力系数预测中是可行的，并具较高的准确性。     

Abundance and removal of antibiotic resistance genes (ARGs) in the rearing environments of intensive shrimp aquaculture in South China

Although research regarding antibiotic resistance genes (ARGs) in aquaculture environments has gained increasing scientific interest, further studies are required to understand the abundances and removal mechanisms of ARGs during the entire rearing period of shrimp aquaculture. Thus, in this study, abundances, distributions and removal rates of ARGs in different environmental compartments of intensive shrimp farms in South China were investigated during the entire rearing period. The results indicated that sul1 and cmlA were the predominant ARGs in the water and sediment samples. Additionally, the total abundance of ARGs was higher in shrimp pond water than in the source water and farm effluent. Moreover, sediment samples indicated significantly higher ARG abundances than water samples from the shrimp ponds (P?<?0.05). Environmental factors were found to significantly affect the distribution of ARGs in shrimp rearing environments. Furthermore, stable ponds aided the removal of ARGs from shrimp pond water. This study accounted for temporal variations in ARG abundances as well as removal of ARGs in different environmental compartments during the entire shrimp rearing period. However, additional research is required to optimize the water treatment process for removal of ARGs from the aquaculture.     

A method to estimate the impact of clear-cutting on nutrient concentrations in boreal headwater streams

Large-scale forestry operations, like clear-cutting, may impair surface water quality if not done with environmental considerations in mind. Catchment and country level estimates of nutrient loads from forestry are generally based on specific export values, i.e., changes in annual exports due to the implemented forestry operations expressed in kg ha⁻¹. We introduce here a specific concentration approach as a method to estimate the impact of clear-cutting on nutrient concentrations and export in headwater streams. This new method is potentially a more dynamic and flexible tool to estimate nutrient loads caused by forestry, because variation in annual runoff can be taken into account in load assessments. We combined water quality data from eight boreal headwater catchment pairs located in Finland and Sweden, where the effect of clear-cutting on stream water quality has been studied experimentally. Statistically significant specific concentration values could be produced for total nitrogen, nitrate, ammonium, and phosphate. The significant increases in the concentrations of these nutrients occurred between 2 and 6 years after clear-cutting. Significant specific concentration values could not be produced for total phosphorus and total organic carbon with the whole dataset, although in some single studies significant increases in their concentrations after clear-cutting were observed. The presented method enables taking into account variation in runoff, temporal dynamics of effects, and the proportional size of the treated area in load calculations. The number of existing studies considering large site-specific variation in responses to clear-cutting is small, and therefore further empirical studies are needed to improve predictive capabilities of the specific concentration values.     

阴角邻面火灾作用下L型钢管混凝土柱耐火极限研究

运用有限元软件ABAQUS计算L形带肋钢管混凝土柱阴角相邻两面受火全过程下的耐火极限,分析了阴角邻面受火方式下构件内部温度场和应力场的变化规律,在此基础上分析荷载比、宽厚比、计算长度、加劲肋纵向间距、荷载偏心率、荷载角等参数对耐火极限的影响规律。数据表明:荷载比、计算长度对构件耐火极限影响较大,随着荷载比和计算长度的增大,耐火极限基本呈线性下降;加劲肋间距对构件耐火性能影响较小;由于L形柱的特殊形式,偏心荷载对耐火极限的影响规律较复杂,荷载作用点偏向低温区可以提高耐火极限。     

双风机并联机站局阻特性研究

为探究双风机并联机站局部阻力特性、完善机站局部阻力及其系数的计算公式,以实际矿井通风机站为工程背景,在分析机站流场能量损失机理的基础上,采用物理模型实验和数值计算相结合的方法,分析了机站入口分流、出口汇流的断面速度不均匀程度与机站阻力损失的关系,同时对不同宽高比的矩形断面进行多工况模拟。结果表明:断面速度不均匀性越大,速度分布重组造成的阻力损失越大;确定了机站局阻计算所需参数的合理测定位置,得出机站局阻系数计算时的综合影响系数Kc随风机工况增大而增大、随断面宽高比A增大而减小,并呈现较好的线性关系。研究结果可为多级机站通风系统通风阻力特性分析以及工程优化设计提供参考。     

大豆种质资源对斜纹夜蛾(PRODENIA LITURA)抗性的鉴定

在网室人工均匀接虫条件下 ,以叶面积损失百分率为指标 ,分别于 1997年和 1998年鉴定了从 6 72 4份大豆资源中筛选的 46份抗感材料及 5份江淮与南方大豆推广良种共 5 1份对斜纹夜蛾的抗性差异表现 .结果表明 ,品种间、观测日期间、年份间抗虫性有极显著差异 ;品种与观测日期间互作显著 ;品种与年份之间互作极显著 ;年份之间抗虫性表现极显著相关 .从供试资源中筛选出一批年份间表现相对一致的高抗种质 ,其抗性优于国际常用的抗源PI2 2 76 87、PI17145 1、PI2 2 935 8.表 3参 10