抗生素的胁迫与抗生素抗性基因产生与传播关系的研究

抗生素的环境残留和抗生素抗性基因(antibiotic resistance genes,ARGs)污染日益增加,对全球公共卫生构成重大威胁。目前,关于环境中抗生素与ARGs产生与传播的关系的研究较多,但结果却不尽相同。为了确定抗生素的胁迫与ARGs产生与传播的关系,用磺胺类抗生素(SAs)对大肠杆菌(Escherichia coli,E.coli)毒性作用表征SAs的胁迫作用,用突变和接合转移表征ARGs的产生与传播,测定了SAs对大肠杆菌的毒性、突变频率和结合转移频率的影响,根据剂量-效应曲线,计算了毒性参数(无观察效应浓度(NOEC)、抑制率为50%的化合物浓度(EC_(50))、抑制率为80%的化合物浓度(EC_(80))),突变效应参数(促进率为1%时最低可观测突变促进效应浓度(MC_(0-1))、促进率为50%时突变促进效应浓度(MC_(50))、促进率最大时突变促进效应浓度(MC_(max)))和接合转移效应参数(促进率为1%时最低可观测接合转移促进效应浓度(RC_(0-1))、促进率最大时接合转移促进效应浓度(RC_(max))和促进率为1%时最高可观测接合转移促进效应浓度(RC_(0-2))),利用线性回归分析的方法探究SAs的胁迫与大肠杆菌突变频率和结合转移频率之间的关系,并分析其可能的机制。结果表明,磺胺的高胁迫作用导致核苷酸碱基的大量减少,在DNA复制与转录时,碱基对错配的概率大大增加,从而开始促进突变频率。SAs的低胁迫作用可能引起大肠杆菌的SOS反应,SOS反应可以上调质粒编码的基因以及控制细胞膜的通透性基因,从而提高其接合转移频率。此外,真实环境中存在许多其他的因素也会影响ARGs的产生和传播,据此,本文建议在探索真实环境中ARGs的产生和传播时,应考虑真实环境中其他影响因素和抗生素胁迫的综合作用。上述研究为探索抗生素胁迫对ARGs产生与传播的影响提供了新的思路。     

莱州湾近岸海域中典型抗生素与抗性细菌分布特征及其内在相关性

为了揭示海陆衔接区环境中抗生素与抗性细菌分布特征及其内在相关性,以莱州湾及其主要入海河流为研究区域,利用HPLC-MS/MS分析样品中15种磺胺类抗生素(SAs)和6种喹诺酮类抗生素(QNs)的浓度,并通过改良的Method 1604(US EPA)评估海水与沉积物中2种典型水传病原微生物大肠杆菌(E.coli)与金黄色葡萄球菌(S.aureus)的抗生素抗性水平,进而探讨该区域水体中抗性菌株的分布特点以及微生物抗性率与相应抗生素浓度的相关性。结果显示,莱州湾水体与沉积物中普遍存在磺胺与喹诺酮类抗生素残留及抗性污染问题。两大类抗生素在水体中平均残留浓度分别为3.89 ng·L~(-1)(SAs)和234.68ng·L~(-1)(QNs),在沉积物中分别为0.91 ng·g~(-1)(SAs)和49.37 ng·g~(-1)(QNs),且分布特征基本呈现自河流向海洋逐渐递减的趋势,说明河流输入是莱州湾抗生素污染的主要来源。在水体中,具有磺胺类抗性的E.coli和S.aureus平均检出量分别达到2 018和4 683 CFU·L~(-1),抗性率范围分别在0%~37.3%和10.6%~45.8%之间;而2种喹诺酮类抗性病原微生物的平均检出量则相对较低,分别为1 315 CFU·L~(-1)(E.coli)和1 461 CFU·L~(-1)(S.aureus),抗性率分别为0%~50.0%和0%~20.8%;此外,相比于E.coli,S.aureus为沉积物中的主要抗性病原微生物,磺胺与喹诺酮类抗性S.aureus检出率均高于80%,平均检出量分别为24CFU·g~(-1)和18 CFU·g~(-1)。相关性分析表明,莱州湾近岸海域水体中磺胺类抗生素浓度与磺胺类抗性微生物总量之间具有良好的线性关系,然而其与微生物抗性率之间并未表现出相似的规律,说明近岸海洋环境中抗生素的残留量不是影响抗性菌株丰度的唯一因素。     

北黄海近岸海域磺胺类抗生素及其抗性Escherichia coli分布

致病菌耐药性的增加和扩散目前已成为全球公共安全问题,为提供解决该问题的重要理论数据,在我国北黄海近岸海域采集排污口、海水养殖区和海滨浴场等水样和沉积物样品,利用HPLC-MS/MS分析水体样品中14种磺胺类(SAs)抗生素浓度含量,同时根据EPA方法(Method 1604)对水和沉积物中Escherichia coli(E.coli)和磺胺抗性E.coli(Re-E.coli)总量进行测定,计算出E.coli磺胺抗性水平,进而探讨该区域水体中E.coli磺胺抗性率与磺胺类抗生素浓度含量的相关性以及E.coli磺胺抗性菌株的分布特点及来源.结果显示,北黄海近岸海域水体中抗生素检出浓度差异性较大,磺胺浓度含量范围为ND-584.32 ng/L;E.coli和Re-E.coli每100 mL总量范围在27×104-5.5×104和8×104-1.6×104株,在每克沉积物中分别为0-1 363和0-320株;E.coli磺胺抗性率范围为18.18%-66.91%.研究表明,E.coli磺胺抗性率与磺胺类抗生素浓度含量存在显著相关性(P=0.846),说明环境残留抗生素可诱导抗性微生物;E.coli和Re-E.coli分布和抗性水平显示,抗性基因之间存在水平转移,且其主要来源是渔业养殖.     

磺胺氯哒嗪对大肠杆菌的生长、突变及接合转移效应的影响

抗生素的大量使用导致细菌的耐药性,直接威胁了人类的生命健康,加剧了抗生素的环境生态风险.为了研究抗生素抗性基因(antibiotic resistance genes,ARGs)的扩散与抗生素浓度之间的关系,本文以磺胺氯哒嗪(sulfachloropyridazine,SCP)为研究对象,测定了SCP对只有磺胺敏感大肠杆菌的单一菌液的生长和突变效应的影响,SCP对含有耐磺胺大肠杆菌和磺胺敏感大肠杆菌的混合菌液的生长、突变及RP4质粒和R388质粒的接合转移效应的影响.研究结果显示,单一菌液的突变促进效应浓度区间(RCS)和突变促进无效应浓度RC0-1皆小于混合菌液;4.0×10~(-5)—8.7×10~(-5)mol·L~(-1)浓度范围内SCP作用下,单一菌液的突变效应受抑制而混合菌液的突变效应相较于空白组显著促进(P0.05);1.9×10~(-5)—6.3×10~(-5)mol·L~(-1)浓度范围的SCP能够促进混合菌液的突变,对ARGs的筛选风险较大,且SCP在6.3×10~(-5)—1.5×10~(-4)mol·L~(-1)范围对RP4和R388质粒的接合转移效应有明显的抑制作用,说明在本实验浓度范围内SCP对接合子的促进风险较小.综上,单一菌液的效应不足以说明环境中磺胺类抗生素的突变风险,研究磺胺类抗生素对耐药基因传播的影响时应混合耐磺胺大肠杆菌和磺胺敏感大肠杆菌作为受试菌,实验证明环境中低浓度的SCP对抗性基因的产生的促进风险较大.     

基于群体感应抑制剂与磺胺对大肠杆菌联合毒性效应的QSAR模型建立

以大肠杆菌为模式生物,分别测定了7种磺胺(SAs,分别为磺胺二甲基嘧啶(SCP)、磺胺吡啶(SPY)、磺胺甲恶唑(SMX)、周效磺胺(SDX)、磺胺喹恶磷(SQ)、磺胺对甲氧嘧啶(SM)、磺胺甲氧哒嗪(SMP)),及3种群体感应抑制剂(QSIs,分别为3-甲基-2-(5H)-呋喃酮(MF)、N-乙烯基吡咯烷酮(VP)、(R)-3-吡咯烷醇(HPL))的单一毒性和联合毒性,并且采用分子对接技术建立了QSIs与SAs对大肠杆菌联合毒性的QSAR模型.结果表明其联合毒性效应表现为拮抗和相加作用;同时,基于SAs和QSIs分别与它们的目标靶蛋白二氢叶酸合成酶(DHP5)与大肠杆菌家族蛋白(Sdi A)之间相互作用的结合能(Ebinding)和混合物的辛醇-水分配系数Kow(mix)构建了SAs和QSIs对大肠杆菌的二元联合毒性的QSAR模型,具有较好的相关性(R2为0.901).该模型经过验证,具有良好的预测能力(预测值与实测值的R2为0.913),研究可为今后抗生素与群体感应抑制剂的环境联合生态风险评价以及毒性预测提供一定的理论依据和技术支持.     

二氧化氯对典型磺胺类抗生素的降解机制

磺胺类药物(sulfonamides,SAs)是十分常见且应用广泛的一类抗生素,由其引起的生态环境风险备受关注.本文研究了典型磺胺类药物磺胺醋酰(sulfacetamide,SFA)及磺胺噻唑(sulfathiazole,STZ)与二氧化氯(ClO_2)的反应机制及影响因素.结果表明,SFA及STZ与ClO_2的反应符合二级动力学模型,在pH 5.0和25℃条件下,反应二级速率常数分别为505.35 L·(mol·s)-1及1382.85 L·(mol·s)~(-1).温度、pH及水质条件等因素均对反应过程存在影响.SFA及STZ与ClO_2的反应机制受ClO_2投加量影响,在ClO_2过量时([ClO_2]∶[SAs]≥5),SAs得到一定程度的矿化,SFA及STZ与ClO_2的反应产物主要为乳酸、草酸及富马酸等有机酸;在ClO_2浓度较低时([ClO_2]∶[SAs]≤3),SAs与ClO_2发生亲电取代反应,生成毒性较强的氯代产物.     

磺胺类抗生素与群体感应抑制剂对发光菌的联合毒性及其机制初探

以Vibrio fischeri为模式生物,3类群体感应抑制剂(呋喃酮、吡咯酮和吡咯)与典型磺胺类抗生素为研究对象,测定了群体感应抑制剂与磺胺类抗生素联合急性毒性效应,通过群体感应抑制剂与信号分子竞争结合LuxR的实验和结合能Ebinding的测定,初步探讨了其联合毒性作用机制.结果显示,呋喃酮类化合物与磺胺类抗生素的二元等毒性比下的联合效应表现为协同与加和,吡咯酮类、吡咯类化合物与磺胺类抗生素的二元等毒性比下的联合效应分别表现为加和与拮抗;它们与LuxR的竞争结合力的差异,可能是它们与磺胺类抗生素等毒性比下的联合效应不同的原因.     

磺胺和四环素类抗生素对大肠杆菌联合突变效应的研究

抗生素的滥用造成的环境安全问题已不可忽视,关于抗生素联合毒性效应研究较多,但联合突变效应研究较少。因此,本文以大肠杆菌为受试生物,研究了2种磺胺类抗生素(磺胺氯哒嗪(SCP)、磺胺二甲嘧啶(SMZ))和3种四环素类抗生素(二甲胺四环素(MH)、盐酸四环素(TH)和盐酸强力霉素(DH))单一及联合暴露时对大肠杆菌的突变效应。结果表明:在单一暴露下,磺胺类抗生素会促进大肠杆菌的突变效应,四环素类抗生素没有明显的促进作用;联合暴露下,磺胺类抗生素对大肠杆菌突变效应为相加,磺胺和四环素类抗生素对大肠杆菌突变效应为拮抗。本研究初步探索了抗生素对大肠杆菌的联合致突变风险,为今后环境中抗生素混合暴露的生态风险评价和抗生素污染控制标准制定提供一种理论支撑。     

磺胺类抗生素对斜生栅藻的协同和拮抗作用研究

环境中抗生素复合污染产生的毒性效应具有潜在风险。为系统考察磺胺类抗生素(SAs)混合物的联合毒性效应，以环境中常见的磺胺吡啶(SPY)、磺胺甲基嘧啶(SMR)、磺胺二甲嘧啶(SM2)、磺胺甲氧哒嗪(SMP)、磺胺甲恶唑(SMZ)和磺胺喹噁啉(SQ) 6种SAs及其二元混合物体系(共75条混合物射线)为研究对象，利用96孔微板测定6种SAs及其二元混合物对斜生栅藻(So)的生长抑制毒性，通过浓度加和(CA)、独立作用(IA)模型和模型偏移率(MDR)分析混合物的联合毒性及毒性相互作用。结果表明，6种SAs及其混合物射线对So在96 h呈现明显的毒性，但不同SAs的毒性大小不同，以半数效应浓度的负对数(pEC_(50))为毒性大小指标，6种SAs的毒性大小顺序为：SQ(pEC_(50)=5.311)>SPY(pEC_(50)=3.757)≈SMZ(pEC_(50)=3.749)>SMP(pEC_(50)=3.680)>SM2(pEC_(50)=3.090)>SMR(pEC_(50)=2.595);不同组分SAs混合物对So的联合毒性存在差异，大部分混合物毒性存在组分浓度依赖性，而有小部分混合物毒性则不存在组分浓度依赖性；15个SAs混合物体系以拮抗作用和协同作用为主。混合体系组分的浓度比不同会产生不同的相互作用类型。在10%效应下，含有组分SPY的混合体系大多呈现协同作用，且随组分SPY浓度比的增大，协同作用增强。含有组分SMR的混合体系均呈现拮抗作用，且随着组分SMR浓度比的增大，拮抗作用增强。研究成果为抗生素的生态风险评估提供重要的基础数据。     

快速评估近岸海洋水体与沉积物中E.coli与S.aureus抗生素抗性水平的新方法

随着抗生素抗性污染日益严重,快速评估环境中典型病原菌与条件性致病菌的抗生素抗性水平,对掌握区域环境抗生素抗性污染状况、揭示抗性污染传播规律至关重要。通过以最低抑菌浓度浸入抗生素改进MI、VJ培养基,并结合滤膜法,建立了针对近岸海洋环境中指示性病原微生物大肠杆菌(Escherichia coli,E.coli)与金黄色葡萄球菌(Staphylococcus aureus,S.aureus)的抗生素抗性监测方法。水体和沉积物样品抗生素抗性水平评估实验结果显示,该方法具有较好重现性(水体和沉积物中E.coli和S.aureus抗生素抗性水平的相对标准偏差分别为11%、8%)与准确度(水体和沉积物中E.coli和S.aureus的平均回收率分别为83.5%、68.4%;相对于CLSI药敏试验的偏离度为±0.1)。且与CLSI药敏实验相比,该方法过程简便、耗时短(36 h/84 h),能最大限度节约经济和人员成本提高抗性评价效率。应用该方法评估辽河口与莱州湾环境中2种病原微生物磺胺类抗生素抗性水平,结果显示辽河口水体中E.coli和S.aureus磺胺二甲嘧啶的平均抗性率分别为27.0%、28.4%,沉积物中分别为35.5%、34.6%;莱州湾水体中E.coli和S.aureus磺胺二甲嘧啶的平均抗性率分别为26.0%、14.5%,沉积物中分别为12.0%、32.9%。该方法适用于河口、近岸海洋及入海排污口水体与沉积物样品中E.coli与S.aureus的快速分析及抗生素抗性水平评估。     

磺胺与群体感应抑制剂对费氏弧菌发光和生长联合毒性效应对比研究

抗生素类药物在广泛应用的同时,也带来了细菌耐药性问题。因此,越来越多的抗生素替代品如群体感应抑制剂(QSIs)被研究和应用,在未来二者可能共存于环境之中。为了对它们混合物联合毒性评价进行系统的研究,本文选择费氏弧菌(Vibrio fischeri,V.fischeri)为受试生物,测定了5种磺胺类抗生素(SAs)与6种QSIs对V.fischeri的发光强度(HV)和生长量(OD600)的联合毒性作用,初步探讨了SAs与QSIs对V.fischeri发光联合毒性和生长联合毒性差异的原因。结果表明:SAs与QSIs联合作用于V.fischeri时,对发光的联合毒性表现为拮抗,对生长的联合毒性表现为拮抗或加和,且TUHVTUOD。这可能是由于QSIs对V.fischeri的发光的抑制作用可以削弱SAs对发光的促进作用,而SAs与QSIs对V.fischeri的生长都表现出抑制作用,两者没有互相削弱作用。同时,基于分子对接和回归分析法的研究表明了靶蛋白上结合的化合物有效浓度不同也可能是造成SAs与QSIs联合作用于V.fischeri时TUHVTUOD的主要原因。该研究可以为抗生素与QSIs联合暴露的生态风险评价提供借鉴。     

基于形态修正的描述符构建可电离化合物对大型溞急性毒性的QSAR模型

在环境水体中,可电离有机化合物(IOCs)可解离为分子和离子形态。研究表明,IOCs离子形态的环境行为、毒性效应等都与其分子形态存在较大差异,因而在研究IOCs环境行为、毒性效应时不应忽略离子化的影响。在构建IOCs相关预测模型时如何表征离子化的影响是当前研究的重要内容之一。探讨了采用基于形态修正的描述符构建IOCs水生毒性预测模型的可行性。具体而言,采用逐步多元线性回归(MLR)方法,构建了可预测63种取代酚、取代苯甲酸和取代苯胺等IOCs对大型溞急性毒性的定量结构-活性关系(QSAR)模型。与仅采用分子形态描述符的模型相比,使用基于形态修正描述符的模型决定系数(R2)、去一法交叉验证系数(Q2LOO)、外部验证系数(Q2EXT)等参数从0.622～0.705提高到了0.840～0.875,表明基于形态修正描述符的模型具有更好的拟合优度、稳健性和预测能力。因此,在将来的研究中,可采用基于形态修正的描述符构建IOCs水生毒性效应预测模型。     

Chlorophyll fluorescence measures of seagrasses <Emphasis Type="Italic">Halophila ovalis</Emphasis> and <Emphasis Type="Italic">Zostera capricorni</Emphasis> reveal differences in response to experimental shading

In coastal waters and estuaries, seagrass meadows are often subject to light deprivation over short time scales (days to weeks) in response to increased turbidity from anthropogenic disturbances. Seagrasses may exhibit negative physiological responses to light deprivation and suffer stress, or tolerate such stresses through photo-adaptation of physiological processes allowing more efficient use of low light. Pulse Amplitude Modulated (PAM) fluorometery has been used to rapidly assess changes in photosynthetic responses along in situ gradients in light. In this study, however, light is experimentally manipulated in the field to examine the photosynthesis of Halophila ovalis and Zostera capricorni. We aimed to evaluate the tolerance of these seagrasses to short-term light reductions. The seagrasses were subject to four light treatments, 0, 5, 60, and 90% shading, for a period of 14 days. In both species, as shading increased the photosynthetic variables significantly (P < 0.05) decreased by up to 40% for maximum electron transport rates (ETR_max) and 70% for saturating irradiances (E_k). Photosynthetic efficiencies (α) and effective quantum yields (ΔF/Fm′) increased significantly (P < 0.05), in both species, for 90% shaded plants compared with 0% shaded plants. H. ovalis was more sensitive to 90% shading than Z. capricorni, showing greater reductions in ETR_max, indicative of a reduced photosynthetic capacity. An increase in E_k, Fm′ and ΔF/Fm′ for H. ovalis and Z. capricorni under 90% shading suggested an increase in photochemical efficiency and a more efficient use of low-photon flux, consistent with photo-acclimation to shading. Similar responses were found along a depth gradient from 0 to10 m, where depth related changes in ETR_max and E_k in H. ovalis implied a strong difference of irradiance history between depths of 0 and 5–10 m. The results suggest that H. ovalis is more vulnerable to light deprivation than Z. capricorni and that H. ovalis, at depths of 5–10 m, would be more vulnerable to light deprivation than intertidal populations. Both species showed a strong degree of photo-adaptation to light manipulation that may enable them to tolerate and adapt to short-term reductions in light. These consistent responses to changes in light suggest that photosynthetic variables can be used to rapidly assess the status of seagrasses when subjected to sudden and prolonged periods of reduced light.     

Primary production as influenced by diel periodicity of phytoplankton photosynthesis

Diel periodicity in parameters of photosynthesis-irradiance (P-I) curves was incorporated into calculations of integral daily phytoplankton production for the Santa Barbara Channel off southern California (USA). Model equations of the relationship between photosynthesis and light were used in combination with observed slope () and asymptote (P _max) values presented in the preceding paper. Primary production was always 19 to 39% less than comparable estimates obtained with the assumption of constant maximum daily and P _max values. Regardless of which P-I formulation was used of 6 tested, observed production (using a temporal series of simulated in situ incubations) ranged from 13% less to 25% more than estimates from constant midday and P _max values. The amplitude and timing of diel oscillations differed somewhat among 3 field stations. Maximum to minimum ratios ranged from approximately 3 to 5 for , and 4 to 6 for P _max. The differences in amplitude and timing of oscillations in P-I curves both contributed to errors in calculating phytoplankton production. Thus, photosynthetic periodicity in the upwelling area of the Santa Barbara Channel influences phytoplankton production. There were oscillations in both and P _max, and the time-dependence of these parameters should be considered to improve the accuracy of predictive models of primary productivity.     

纳米银复合材料与抗生素的联合抗菌性能及相关机制研究

抗生素的滥用导致细菌耐药问题日益严重,人类迫切需要开发出新的抗菌药物以减少细菌耐药问题。基于纳米银制备而成的纳米银复合材料在兼顾纳米银抗菌性能的同时不仅能够克服单一纳米银释放速度快、不稳定等缺点,还能缓解细菌耐药的问题,因此被认为是一类具有广泛应用前景的新型抗菌剂。已有研究表明,单一纳米银与某些抗生素的联合使用可以达到协同抗菌效果,但目前尚缺乏对纳米银复合材料与抗生素的联合抗菌性能及机制的研究。本文首先制备出3种不同结构的纳米银复合材料,包括二氧化硅-聚多巴胺-纳米银复合材料(SiO_2-PD-AgNPs)、纳米银@二氧化硅复合材料(AgNPs@SiO_2)和纳米银@二氧化硅-聚多巴胺-纳米银复合材料(AgNPs@SiO_2-PD-AgNPs)。随后测定了纳米银复合材料对大肠杆菌(Escherichia coli, E. coli)和枯草芽孢杆菌(Bacillus subtilis, B. subtilis)的单一毒性效应。结果显示,AgNPs@SiO_2-PD-AgNPs复合材料对2种菌的单一毒性均大于其余2种纳米银复合材料。因此,笔者以AgNPs@SiO_2-PD-AgNPs作为代表,测定了纳米银复合材料与硫酸卡那霉素(kanamycin sulfate, KS)/盐酸土霉素(oxytetracycline hydrochloride, OH)的二元联合抗菌性能,发现AgNPs@SiO_2-PD-AgNPs与KS联合可以对E. coli产生协同效应。协同效应产生的主要原因可能是:AgNPs@SiO_2-PD-AgNPs释放出的纳米银会和KS发生键合反应生成KS-纳米银复合物,导致纳米银释放出大量的Ag+增加了细胞膜的通透性,从而使得进入细菌内的Ag~+和KS比单独作用时进入胞内的抗菌剂增多,产生更强的抗菌性能,从而表现出协同抗菌效应。本研究基于新型纳米银复合材料与抗生素的联合抗菌性能实验探究了纳米银复合材料与特定抗生素联合用药的最佳组合和相关机制,为今后开发新型抗菌材料提供了新思路并为相关联合用药提供参考。     

Scaling relationships,individual variation and the influence of temperature on maximum swimming speed in early settled stages of the turbot Scophthalmus maximus

Escape-swimming speeds (U _max) were studied in settled turbot (Scophthalmus maximus L.) reared at 18°C. Metamorphosis was complete at 4.0 cm total length (TL). U _max scaled in proportion to TL^0.74 in fish of 0.88 5o 8.00 cm TL at 18C. The scaling relationship for U _max was similar for temperatures between 13 and 23°C and could be fitted by the model: . U _max temperature-dependent, with a Q₁₀ of 1.77 over the temperature range studied. Analysis of covariance showed that U _max for farmed turbot was 14% lower than for wild fish filmed within 2 wk of capture; 3 mo after capture the average differences in escape performance were no longer significant, which suggests that the lower escape speeds of farmed fish are due to acclimation effects and not genetic stock differences. In order to assess the individual variability of U _max, 18 wild juvenile turbot [TL=6.2±0.4 cm (Week 1) to 7.5±0.5 cm (Week 17); means±SD] were maintained in individual containers at 18°C. U _max was determined weekly for 6 wk, standardised for fish length using the scaling relationship U _max=1.46 TL ^0.74, and individuals were ranked in order of performance. Temperature was reduced after 6 wk to 13°C, resulting in a significant decline in U _max from 104.0±14.4 to 87.8±12.5 cm s^-1 (means±SD). After 3 wk at 13°C U _max had increased to a level not significantly different from that at 18°C. Kendall's coefficient of concordance showed that repeatability of ranking of the experimental U _max of individuals was maintained over a 13 wk period and through temperature change. The results demonstrate that escape-swimming speeds in juvenile turbot are repeatable, individually variable, and can be modified in response to temperature acclination.     

Residual veterinary antibiotics in pig excreta after oral administration of sulfonamides

Sulfonamides (SAs) are applied widely as feed additives in the farming of livestock and poultry. It can lead to the excretion of large amounts of SAs in manure and result in persistent environmental pollution. We evaluated the fate of four SAs, sulfamerazine (SM₁), sulfachloropyridazine (SCP), sulfadimoxine (SDM′) and sulfaquinoxaline (SQ), from oral administration to excretion in urine and feces in pigs. The four SAs were added to homemade feed to make them reach the required concentration gradient, which were 0, 50 and 100 mg/kg (low, normal and high concentrations, respectively). In different treatments, excretions of the four SAs were 35.68–86.88 %. With regard to total excretion, the order was SQ > SCP > SM₁ > SDM′ for all treatments. The concentration of SAs in the feed had significant effects on the amount of the four SAs excreted every day. The concentration of SAs in feces and in the urine for different treatments was 15.03–26.55 and 14.54–69.22 %, respectively. In each treatment, excretions of SCP, SDM′ and SQ in feces were lower than that in urine. The four SAs remained longer in urine than in feces. Excretions in urine and feces were lower if SAs were administered orally rather than by injection.     

Light response curve methodology and possible implications in the application of chlorophyll fluorescence to benthic diatoms

Chlorophyll a fluorescence has been increasingly applied to benthic microalgae, especially diatoms, for measurements of electron transport rate (ETR) and construction of rapid light response curves (RLCs) for the determination of photophysiological parameters [mainly the maximum relative ETR (rETR_max), the light saturation coefficient (E _k) and the maximum light use coefficient (α)]. Various problems with the estimation of ETR from the microphytobenthos have been identified, especially in situ. This study further examined the effects of light history of the cells and light dose accumulation during RLCs on the fluorescence measurements of ETR using the benthic diatom Navicula phyllepta. RLCs failed to saturate when using incremental increases in irradiance, however, curves with decreasing irradiance did saturate. Patterns indicating photoacclimation in response to light histories were observed, with higher rETR_max and E _k, and lower α, at high light compared to low light. However, these differences could be negated by increasing the RLC irradiance duration from 30 to 60 s. It is suggested that problems arose as a result of rapid fluorescence variations due to ubiquinone (Q_A) oxidation and non-photochemical chlorophyll fluorescence quenching (NPQ) which depended upon the light history of the cells and the RLCs accumulated light dose. Also, RLCs with irradiance duration of 10 s were shown to have a high level of error possibly specific to the fluorimeter programming. It is suggested that RLCs, using a Diving-PAM fluorimeter on benthic diatoms, should be run using decreasing irradiance steps of 30 s duration.