Effect of different operational conditions on biofilm development, nitrification, and nitrifying microbial population in moving-bed biofilm reactors

In this study, the effect of different operational conditions on biofilm development and nitrification in three moving-bed biofilm reactors (MBBRs) was investigated: two reactors were operated in a continuously fed regime and one in sequencing-batch mode. The presence of organic carbon reduced the time required to form stable nitrifying biofilms. Subsequent stepwise reduction of influent COD caused a decrease in total polysaccharide and protein content, which was accompanied by a fragmentation of the biofilm, as shown by scanning electron microscopy, and by an enrichment of the biofilm for nitrifiers, as observed by fluorescent in situ hybridization (FISH) analysis. Polysaccharide and protein concentrations proved to be good indicators of biomass development and detachment in MBBR systems. Ammonium- and nitrite-oxidizing bacteria activities were affected when a pulse feeding of 4 g of NH(4)-N/(m(2)·day) was applied. Free nitrous acid and free ammonia were likely the inhibitors for ammonium- and nitrite-oxidizing bacteria.     

Effects of chain length, chlorination degree, and structure on the octanol-water partition coefficients of polychlorinated n-alkanes

Log octanol-water partition coefficients (log Kow) of 40 synthesized polychlorinated n-alkanes (PCAs) with different chlorination degrees were determined using reversed-phase high performance liquid chromatography (RP-HPLC). In addition, log Kow values of a technical mixture namely Cereclor 63L as well as 15 individual in house synthesized C10, C11, and C12 chloroalkanes with known chlorine positions were estimated. Based on these results, the effects of chain length, chlorination degree, and structure were explored. The estimated log Kow values ranged from 4.10 (polychlorinated n-decanes with 50.2% chlorine content) to 11.34 (polychlorinated n-octacosanes with 54.8% chlorine content) for PCAs and from 3.82 (1,2,5,6,9,10-hexachlorodecane) to 7.75 (1,1,1,3,9,11,11,11-octachlorododecane) for the individual chloroalkanes studied. The results showed that log Kow value was influenced linearly at a given chlorine content by chain length, while a polynominal effect was observed in dependence on the chlorination degree of an alkane chain. Chlorine substitution pattern influenced markedly the log Kow value of chloroalkanes.     

Significant population structure in Australian Cryptolestes ferrugineus and interpreting the potential spread of phosphine resistance

An analysis of the population genetics of Cryptolestes ferrugineus, across all major regions in Australia where grain is grown and stored in bulk, provides an initial step in investigating the movement of these insects and implications for the spread of phosphine resistance. Microsatellite data revealed two levels of genetic structure. Across Australia, two clusters were detected, one in eastern Australia (Queensland, New South Wales, Victoria and Tasmania) and Western Australia (Cluster 1) and one in South Australia (Cluster 2). Intermediate between them, in eastern South Australia, are a couple of populations that are equally admixed for the two clusters. Populations in Western Australia and western SA belong to different clusters suggesting that the extensive and arid Nullarbor Plain restricts the natural dispersal of these beetles. Isolation-by-distance and the detection of clustering among local populations suggests there is considerable gene flow at a local scale in C. ferrugineus, and we infer this is by flight. Limited natural gene flow between eastern and western Australia might, in part, explain why extremely high resistance has not been detected in Western Australia.     

Comparison of population level and individual level endpoints to evaluate ecological risk of chemicals

Ecological risk assessments (ERA) of chemicals are often based on mortality and reproduction of individuals. To protect populations, fixed safety factors are applied to the data. However, the relationship between individuals and populations cannot easily be described by predefined numbers. The use of population models may reduce uncertainty and, hence, the risk for erroneous assessments. However, introducing models also introduces additional complexity. Therefore, it is desirable to keep the models as simple as possible. The objective of the present study was to determine whether simple risk equations or matrix models can improve ERA compared to traditional endpoints. To examine this, complex models that included environmental stochasticity and density dependence were used to simulate population level risk based on dose-response data for five chemicals. The risk, measured as probability for pseudo extinction and recovery time, was then compared to risk estimates based on individual level data (acute and chronic), risk equations, and simple matrix models. The results showed that the simple matrix models reduced uncertainty by more than 88% and 76% compared to acute and chronic data, respectively. Also the simple risk equation reduced uncertainty considerably (80% and 61% compared to acute and chronic data, respectively).     

介质阻挡放电对水龙带增强层黏结性能的影响

针对水龙带增强层高强涤纶管状织物与三元乙丙橡胶内衬黏结性能差的问题,采用介质阻挡放电(DBD)等离子体对高强涤纶管状织物表面进行处理,研究了处理时间对纤维表面形貌和化学组成、丝束断裂强力、织物芯吸高度及剥离强度的影响。结果表明:经DBD等离子体处理后,高强涤纶表面产生明显的刻蚀痕迹,纤维表面极性官能团增加,织物芯吸高度增加,丝束断裂强力随处理时间的延长而下降;处理时间为60 s时,强度损失率为3.9%;处理后高强涤纶管状织物与三元乙丙橡胶内衬的黏结性能得到显著改善,处理时间为60 s时,剥离强度提升35.1%。     

生物膜状态对食源性致病菌耐药与毒力的影响研究进展

生物膜是细菌抵御不利环境维持群体稳定性的一种常见的群落形态。生物膜状态增强了食源性致病菌的抗逆性和持久存活力,促进了细菌间的信息传导和物质交换。特别是生物膜状态显著增强了菌株对抗生素的耐受能力,提升了可移动元件在细菌间的转移效率,并且生物膜状态下的细菌具备更强的入侵和感染能力,成为食品安全和人类健康的重要危害。基于此,本文将从生物膜的结构特征与异质性、生物膜对基因突变和基因水平转移的影响、以及群体感应调控等多个角度,简述生物膜状态影响食源性致病菌耐药和毒力的研究进展,以期为深入研究生物膜的生物功能与危害防控提供新的思路。     

Effects of breed,farm intensiveness,and cow productivity level on cheese-making ability predicted using infrared spectral data at the population level

Fourier-transform infrared (FTIR) spectra collected during milk recording schemes at population level can be used for predicting novel traits of interest for farm management, cows' genetic improvement, and milk payment systems. The aims of this study were as follows. (1) To predict cheese yield traits using FTIR spectra from routine milk recordings exploiting previously developed calibration equations. (2) To compare the predicted cheese-making abilities of different dairy and dual-purpose breeds. (3) To analyze the effects of herds' level of intensiveness (HL) and of the cow's level of productivity (CL). (4) To compare the patterns of predicted cheese yields with the patterns of milk composition in different breeds to discern the drivers of cheese-making efficiency. The major sources of variation of FTIR predictions of cheese yield ability (fresh cheese or cheese solids produced per unit milk) of individual milk samples were studied on 115,819 cows of 4 breeds (2 specialized dairy breeds, Holstein and Brown Swiss, and 2 dual-purpose breeds, Simmental and Alpine Grey) from 6,430 herds and exploiting 1,759,706 FTIR test-day spectra collected over 7 yr of milk sampling. Calibration equations used were previously developed on 1,264 individual laboratory model cheese procedures (cross-validation R² 0.85 and 0.95 for fresh and solids cheese yields, respectively). The linear model used for statistical analysis included the effects of parity, lactation stage, year of calving, month of sampling, HL, CL, breed of cow, and the interactions breed × HL and breed × CL. The HL and CL stratifications (5 classes each) were based on average daily secretion of milk net energy per cow. All effects were highly significant. The major conclusions were as follows. (1) The FTIR-based prediction of cheese yield of milk goes beyond the knowledge of fat and protein content, partially explaining differences in cheese-making ability in different cows, breeds and herds. (2) Differences in cheese yields of different breeds are only partially explained by milk fat and protein composition, and less productive breeds are characterized by a higher milk nutrient content as well as a higher recovery of nutrients in the cheese. (3) High-intensive herds not only produce much more milk, but the milk has a higher nutrient content and a higher cheese yield, whereas within herds, compared with less productive cows, the more productive cows have a much greater milk yield, milk with a greater content of fat but not of protein, and a moderate improvement in cheese yield, differing little from expectations based on milk composition. Finally, (4) the effects of HL and CL on milk quality and cheese-making ability are similar but not identical in different breeds, the less productive ones having some advantage in terms of cheese-making ability. We can obtain FTIR-based prediction of cheese yield from individual milk samples retrospectively at population level, which seems to go beyond the simple knowledge of milk composition, incorporating information on nutrient retention ability in cheese, with possible advantages for management of farms, genetic improvement of dairy cows, and milk payment systems.     

Effects and molecular mechanism of sugar transporter ESA_RS15745 on desiccation resistance,motility, and biofilm formation of Cronobacter sakazakii

Cronobacter sakazakii, an important Gram-negative foodborne pathogen, can cause neonatal meningitis and sepsis with high rates of infection and death. Gene ESA_RS15745 encodes a sugar transporter protein, which is not only essential for osmotic pressure maintenance during bacterial growth and reproduction but also associated with their desiccation tolerance, motility, and biofilm formation. Here, a mutant strain of ESA_RS15745 (ΔESA_RS15745) and the complementation strain (cpESA_RS15745) were constructed using a suicide vector knockout and gene complementation. ΔESA_RS15745 was found to have a decrease in its ability to transport maltose and trehalose and resist desiccation, whereas an increase in the ability of motility and biofilm formation, implying that ESA_RS15745 may positively regulate sugar transport and desiccation tolerance and negatively regulate motility and biofilm formation. To further investigate the molecular mechanisms underlying the function of related genes, RNA-seq was performed to explore the differentially expressed genes in the mutants. RNA-seq results showed the upregulation of 114 genes (mainly including those regulating chemotaxis and flagellar motility) and the downregulation of 22 genes (mainly including those regulating sugar transport). qRT-PCR analysis supported the RNA-seq results and showed that ESA_RS15745 may influence the dehydration tolerance though decreasing the intracellular trehalose content and negatively regulate the motility though the chemotactic signaling pathway. In addition, the biofilm formation of C. sakazakii should also be speculated to negatively regulate by ESA_RS15745 by consuming the extracellular carbohydrates concentration and then downregulating the intracellular cyclic diguanosine monophosphate. This study offers a reference for comprehending the molecular mechanism of gene ESA_RS15745 in C. sakazakii.     

TG酶处理对羊毛染色织物耐洗性的影响

用TG酶处理普拉艳红B、普拉黄GN、普拉艳蓝RAWL 3种常用弱酸性染料染色的羊毛织物,通过生物和非生物洗涤液中的3种染料最大吸收波长处的吸光度测定及TG酶处理后羊毛染色织物强力的变化,分析TG酶处理对羊毛染色织物耐洗性的影响.结果表明:TG酶对羊毛染色织物的预处理,可以使染色织物在后续生物和非生物洗涤中掉色减少,耐洗性提高,TG酶对羊毛染色织物的生物和非生物洗涤具有护色效果;3种弱酸性染料染色的羊毛染色织物经TG酶处理后,强力有所提高.     

Influence of a nonfavorable environment, egg white, on resistance to heat and disinfectant, adhesion, and virulence of Salmonella enteritidis

Although liquid egg white may be subjected to limited heat treatment when it is used in the fabrication of various foodstuffs, pathogenic bacteria such Salmonella Enteritidis could persist in this environment. Liquid egg white is not a favorable medium for Salmonella growth because of its alkaline pH and iron deficiency and the presence of ovotransferrin. Microorganisms adapted to a nonfavorable environment are often more resistant to stresses than are their laboratory-cultured counterparts. The objective of this study was to determine whether Salmonella exposed to an environment mimicking egg white conditions exhibited modified behavior that could have an impact on food safety. A medium resembling egg white (filtrate of egg white with added ovotransferrin) was used as an adaptation treatment to mimic the stress imparted by the egg white environment. There were no changes in resistance to heat and disinfection, in stainless steel adhesion, or in the virulence of Salmonella Enteritidis cultivated in the egg white medium. Egg white conditions do not appear to make Salmonella more virulent or more difficult to inactivate.     

Influence of in situ biofilm coverage on the radionuclide adsorption capacity of subsurface granite

Any migration of radionuclides from nuclear waste repositories is expected to be mitigated by adsorption to the host rocks surrounding hydraulically conductive fractures. Fluid rock interfaces are considered to be important barriers for nuclear waste disposal schemes but their adsorptive capacity can be affected by the growth of microbial biofilms. This study indicates that biofilms growing on fracture surfaces decrease the rocks adsorption capacity for migrating radionuclides except for trivalent species. Potential suppression of adsorption by biofilms should, therefore, be accounted for in performance safety assessment models. In this study, the adsorptive capacity of in situ anaerobic biofilms grown 450 m underground on either glass or granite slides was compared to the capacity of the same surfaces without biofilms. Surfaces were exposed to the radiotracers 60Co(II), 147Pm(III), 241Am(III), 234Th(IV), and 237Np(V) for a period of 660 h in a pH neutral anaerobic synthetic groundwater. Adsorption was investigated at multiple time points over the 660 h using liquid scintillation and ICP-MS. Results indicate that these surfaces adsorb between 0 and 85% of the added tracers under the conditions of the specific experiments. After 660 h, the distribution coefficients, R (ratio between what is sorbed and what is left in the aqueous phase), approached 3 x 10(4) m for 60Co, 3 x 10(5) m for 147Pm and 241Am, 1 x 10(6)m for 234Th, and 1 x 10(3) m for 237Np. The highest rate of adsorption was during the first 200 h of the adsorption experiments and started to approach equilibrium after 500 h. Adsorption to colloids and precipitates contributed to decreases of up to 20% in the available 60Co, 147Pm, 241Am, and 237Np in the adsorption systems. In the 234Th system 95% of the aqueous 234Th was removed by adsorbing to colloids. Although the range of Rvalues for each surface tested generally overlapped, the biofilms consistently demonstrated lower R values except for the trivalant 147Pm and 241Am adsorption systems.     

Influence of nisin on the resistance of Bacillus anthracis sterne spores to heat and hydrostatic pressure

The influence of nisin on the heat and pressure resistance of Bacillus anthracis Sterne spores was examined. The decimal reduction times (D-value) of spores in milk (2% fat) at 80, 85, and 90 degrees C were determined. In the absence of nisin, the D-values were 30.09, 9.30, and 3.86 min, respectively. The D-values of spores heated in the presence of nisin (1 mg/ml) were not significantly different (P = 0.05). However, spores heated in the presence of nisin had a 1- to 2-log reduction in viability, after which the death kinetics became similar to those of spores in the absence of nisin. The z-values all were 11.2 degrees C regardless of the presence or absence of nisin. The pressure sensitivity of B. anthracis Sterne spores in the presence and absence of nisin also was determined. Spores treated with nisin were 10 times more pressure sensitive than were spores subjected to pressure in the absence of nisin under the conditions used in this study.     

三种耐高温纱线的结构与性能测试评价

玄武岩、芳纶、PTFE(聚四氟乙烯)等纱线广泛应用于高温过滤领域。对这三种纱线的结构形态、力学性能、热学性能进行测试评价。结果表明:三种纱线表面形态光滑,高温下纱线表面出现损伤;三种纱线常温下强度为2.8~5.8 c N/dtex,较常规化纤强度高;比较三种纱线的拉伸性能发现,PTFE纱线"小张力大变形",形态稳定性差,玄武岩纱线的弹性模量最大,刚度大,芳纶纱线的断裂强度最大,能耐较大外力;经140~260℃高温处理后,三种纱线的力学稳定性好,相比而言,芳纶纱线经高温处理后强度降低最快,PTFE纱线的强度稍有降低,玄武岩纱线的强度基本保持不变;三种纱线的勾结强度保持率差别较大,PTFE纱线的勾结强度明显高于其他两种纱线,耐弯曲性较好;三种纱线的起始分解温度均在500℃以上,热稳定性好;当温度超过500℃时,芳纶、PTFE纱线的热重损失迅速增大,但玄武岩纱线的热重损失较小。     

Influence of exopolysaccharides on the structure,texture, stability and sensory properties of yoghurt and related products

The impact of microbial exopolysaccharides (EPS) from lactic acid bacteria (LAB) on dairy products such as yoghurt, cheese, or milk based desserts has been extensively described in recent years. It is well known that EPS influence viscosity, syneresis, firmness, as well as sensory properties. The rheological properties of milk products may depend on several factors, such as EPS location (capsular, free), EPS structure (molecular mass, side chains, stiffness, charge), EPS concentration, and the interaction of EPS with other product compounds (proteins, minerals, or bacteria). This review summarises literature concerning the structural and rheological characterisation, localisation and specific application of several EPS from LAB, and intends to critically evaluate different methods and conclusions reported in research. The main focus is on the behaviour and effect of EPS, either produced in situ or added as stabiliser, on acid milk gels.     

捏合淀粉颗粒形貌和结晶结构的研究

利用扫描电子显微、偏光显微、X-射线衍射等现代分析技术,研究了经捏合作用后淀粉颗粒形貌和结晶结构的变化。结果表明,与HylonV玉米淀粉相比,捏合后淀粉颗粒形貌和结晶结构都受到不同程度的破坏,尤其导致了结晶形态由B型向V型转变,由此引起淀粉的消化性能发生改变,为淀粉的改性提供了一种“绿色”深加工技术。     

氮素水平对烤烟根系形态、结构及其氮素积累的影响

  目的  探究不同氮素水平对烟株根系发育及地上部氮素积累与分配的影响。  方法  试验设置3个氮素水平: HNL(N 8 g/株)、MNL(N 6 g/株)、LNL(N 4 g/株), 分析不同时期烟株根系结构、生理指标、空间分布及其地上部干物质与氮素积累变化情况, 与氮素利用差异。  结果  与HNL相比, LNL显著提高了根系活力与活跃吸收面积, 不定根数量增加了15.2条, 一级侧根与不定根的平均长度提高了10 cm、6.6 cm, 不定根与一级侧根平均直径与干重降低。降低施氮水平, 根系20~50 cm土层的根长密度与根干重增加, 现蕾期LNL根干重占比较HNL提高了8.32 g。LNL抑制了烤烟地上部生长, HNL成熟期地上部干物质积累量与氮素积累量显著增加, 提高了29.30%、49.06%, 但与MNL差异不显著。  结论  烟株氮素少量缺乏, 烟株通过调节根系形态结构, 增加不定根数量, 提高了根系氮素吸收能力, 对烟株地上部发育影响不显著, 生产上可以通过改变施肥方式与施肥时间, 达到降低氮肥使用量的目的。      

烤烟种质资源遗传多样性和群体结构及亚群特异性研究

筛选多态性丰富的16对SRAP引物,对不同地理来源的276份烤烟资源的遗传变异进行分析,结果表明:16对SRAP引物共检测出611个等位位点,平均每对引物对38.19个,多态性较高;国外烤烟品种遗传多样性高于国内品种,贵州烤烟品种遗传多样性水平较低;NJ法聚类、PCA分析和STRUCTURE群体结构分析结果相互吻合,证明烤烟是与地理来源和亲缘关系密切相关的资源群,贵州烤烟资源形成了独立的组群,其遗传背景独特;各烤烟群体拥有独立的特有和特缺等位位点,群体间互补等位位点丰富,利用国外品种来拓宽国内烤烟品种的遗传基础最具潜力。