高位虾池水体细菌和弧菌的数量变化及影响因素

研究了位于广东湛江东海岛北寮村和庵里村的4个凡纳滨对虾(Penaeus vannamei)高位池养殖过程水体中的可培养异养细菌和弧菌的数量变化及其影响因素.结果表明:1)北寮村虾池BL1和BL2的可培养异养细菌数量变化均呈现中间高两头低、后期多于初期的单峰变化趋势;BL1的弧菌数量变化趋势和可培养异养细菌的变化趋势相似,而BL2则是前期稍微升高而后下降,后期又呈升高态势,峰值出现在养殖末期;水源地BL3的可培养异养细菌数量变化为初期平缓,后期明显多于初期,大体呈上升态势;而BL3弧菌数量变化趋势则比较平缓.2)庵里村发病的虾池AL1的可培养异养细菌和弧菌数量呈现出单峰变化趋势,在养殖中途爆发病害时,可培养异养细菌数量高出未发病的正常池2个数量级;庵里村虾池AL2的可培养异养细菌数量变化趋势也是中间高两头低,而弧菌的数量变化则是无规律的波动;水源地AL3的可培养异养细菌数量变化大体呈下降趋势,弧菌数量放养初期最高.3)高位虾池的可培养异养细菌和弧菌数量虽多于水源地,但差异不显著,同一个位点,细菌和弧菌数量呈现同步增多或减少.虾场水体的可培养异养细菌和弧菌数量与多数环境因子之间相关性不显著,这与虾池养殖生态系统受人为因素影响较大有关,同时反映了高位虾池生态系统受多种因子作用的复杂性.     

高位虾池水体细菌和弧菌的密度变化及影响因素

研究了位于广东湛江东海岛北寮村和庵里村的4个凡纳滨对虾(Penaeus vannamei)高位池养殖过程水体中的可培养异养细菌和弧菌的密度变化及其影响因素.结果表明:1)北寮村虾池BL1和BL2的可培养异养细菌密度变化均呈现中间高两头低、后期多于初期的单峰变化趋势;BL1的弧菌密度变化趋势和可培养异养细菌的变化趋势相似,而BL2则是前期稍微升高而后下降,后期又呈升高态势,峰值出现在养殖末期;水源地BL3的可培养异养细菌密度变化为初期平缓,后期明显多于初期,大体呈上升态势,而BL3弧菌密度变化趋势则比较平缓.2)庵里村发病的虾池AL1的可培养异养细菌和弧菌密度呈现出单峰变化趋势,在养殖中途爆发病害时,可培养异养细菌密度高出未发病的正常池2个数量级;庵里村虾池AL2的可培养异养细菌密度变化趋势也是中间高两头低,而弧菌的密度变化则是无规律的波动;水源地AL3的可培养异养细菌密度变化大体呈下降趋势,弧菌密度放养初期最高.3)高位虾池的可培养异养细菌和弧菌密度虽多于水源地,但差异不显著,同一个位点,细菌和弧菌密度呈现同步增多或减少.虾场水体的可培养异养细菌和弧菌密度与多数环境因子之间相关性不显著,这与虾池养殖生态系统受人为因素影响较大有关,同时反映了高位虾池生态系统受多种因子作用的复杂性.     

南美白对虾苗种淡化期间异养细菌和弧菌的数量动态

采集南美白对虾苗种淡化期间各阶段的水样和虾苗,用平板计数法对水体和虾体的异养细菌和弧菌进行计数,采样时间从淡化开始到淡化结束.结果表明:南美白对虾虾苗经逐步淡化,随着盐度从14.36降至1.000,水体异养细菌从3.21×107CFU/ml降至(5.05～6.27)×105CFU/mL,弧菌数从1.57×106CFU/mL降至(2.63～16.8)×104CFU/mL;虾体中的异养细菌从3.24×104CFU/mL降至(1.19～1.66)×103CFU/mL,弧菌数从2.30×104CFU/mL降至(4.30～6.90)×102CFU/mL.通过苗种淡化,水体和虾体的异养细菌和弧菌数量都明显下降,虾体内的弧菌数量占总菌数比例由淡化开始时的71.6%下降到39.6%.实验结果表明南美白对虾淡化养殖可减少弧菌的数量,减少弧菌病的发生.     

秋冬季凡纳滨对虾养殖池塘细菌的数量动态

2007年9月～2008年2月,研究了珠海市斗门区凡纳滨对虾4个低盐度池塘水体、沉积物中异养细菌、弧菌、芽孢杆菌数量动态,结果表明,水体中异养细菌、弧菌、芽孢杆菌在养殖前期不稳定,中后期趋于稳定,数量波动范围分别为1.8×103～1.2×105/mL、1.4×102～4.0×103/mL、1.6×102～1.7×103/mL,水体中异养细菌数量平均为1.95×104/mL;沉积物中异养细菌较稳定,弧菌呈先升后降趋势,芽孢杆菌呈上升趋势,三者的数量均高出水体2～3个数量级,数量波动范围分别为1.0×106～2.2×107/g、7.0×103～4.7×105/g、4.7×106～2.4×106/g,异养细菌数量平均为9.16×106/g     

蛭弧菌对草鱼池水质及细菌类群的影响

研究了蛭弧菌对草鱼池水质及细菌类群的影响,结果表明:蛭弧菌对养殖环境的主要水化指标具有明显的改善作用,实验组的平均COD、NH3-N、硫化物值显著低于对照组(P＜0.05),实验组的DO显著高于对照组(P＜0.05),而实验组与对照组的pH值差异不显著(P＞0.05);池水细菌总数及致病菌的数量也随着蛭弧菌浓度的增加而发生几何级数减少.     

喀斯特森林典型先锋植物香叶树凋落叶分解速率的室内模拟

本研究旨在对比不同植被类型下土壤提取液对相同植物物种凋落叶分解速率的影响。选取贵州茂兰国家级喀斯特自然保护区内典型先锋植物香叶树(Lindera communis)凋落叶,通过室内模拟控制温度、湿度的条件下对照分析几种分解的过程。室内模拟实验摸索性的研究表明:凋落叶分解初始阶段释放CO_2速率顺序为:非喀斯特森林样地喀斯特原生林样地喀斯特灌木林样地;分解速率上下波动大,先后出现分解速率较快和较慢两个阶段,最后分解阶段速率趋于一致;相关性分析结果表明,分解过程中喀斯特原生林与非喀斯特森林提取液分解香叶树凋落叶速率呈显著正相关关系(p0.05),两者呼吸速率显著正相关(p0.05);非喀斯特森林提取液与分解时间呈极显著正相关关系(p0.01)。检验结果表明,不同土壤微生物不同时间段分解凋落叶产生CO_2速率不显著(p0.05)。结论:喀斯特森林一旦退化,其功能退化明显;非喀斯特森林以及喀斯特原生林土壤微生物分解枯落物速率较快,土壤养分归还速率更快,而退化的喀斯特喀灌木林次之;喀斯特森林环境复杂多样,其生态功能随时间变化线性关系不明显。     

凡纳对虾淡化养殖健康虾池水体生态研究

对20个凡纳对虾Litopenaeus vannamai淡化养殖健康虾池水体理化及生物因子进行调查,调查结果健康虾池大小(0.48±0.19)hm2,水深(145±13)cm,最适放苗密度(148±30)万尾/hm2,盐度(2±2)‰,水温(30.6±3.3)℃,溶解氧(5.5±1.5)mg/L,pH值8.5±0.7,透明度(19±5)cm,氨氮(0.65±0.76)mg/L,亚硝基氮(0.15±0.17)mg/L,化学耗氧量(21.52±5.45)mg/L.虾池藻类种类数为43±8种,密度(1.51±0.76)×10 8个/L,多样性指数2.15±0.49,藻类优势种12种,蓝藻6种,硅藻2种,绿藻3种,隐藻1种,健康虾池优势种以螺旋藻Spirulina sp.为主,种群丰富度高而稳定.虾池原生动物种类数为14±3种,密度(2.71±1.79)×10 5 个/L,多样性指数2.01±0.47,优势种9种,圆筒状拟铃壳虫Tintinnopsis cylindrata、毛板壳虫Coleps hirtus和海洋帆口虫Pleuronema marinuum为常见优势种,优势种主要是食细菌-碎屑类.健康虾池水体异养菌群数量(2.37±1.83)×10 7 cfu/L,弧菌数量(11.77±13.86)×10 5 cfu/L,底泥异养细菌总数(7.90±29.08)×10 8 cfu/L,弧菌总数(1.18±3.27)×107cfu/L.     

凡纳滨对虾育苗水环境的细菌学初探

通过对凡纳滨对虾育苗过程中细菌的数量、组成以及部分水质因子进行全程跟踪检测,分析了甲醛和抗生素对育苗水体细菌的影响,研究了蛭弧菌微生态制剂的水质调节效果.结果表明,使用甲醛和抗生素不能有效控制育苗水体的细菌总数,但能改变水体的优势菌群和组成,保持水体蛭弧菌的优势地位对控制细菌总数有较为明显的效果.     

光合细菌在养虾池中的应用

一、前言 虾池投放光合细菌效益显著,光合细菌在水产养殖中的应用具有现实意义。养虾池中投放光合细菌的对比试验表明,光合细菌能净化养虾池水质,促进对虾的生长发育,从而提高对虾产量,增加养虾的效益。 1996年,潮阳市科技局和市水产局合作,在河溪镇六十一斗海滩的3口虾池(面积共4.5公顷)进行了投放光合细菌的试验。分别于4月24日和5月     

贝类生态综合养殖系统中细菌丰度的变化

2011年4—10月在福建云霄,对以贝类为主的生态综合养殖系统内的藻类池（A池）和贝类池（B池）逐月采样检测,并分析两池水体及B池沉积物中细菌丰度的时空变化规律.结果发现:水体中细菌丰度,B池为1.01×106～4.35×106 cell/mL;A池为1.09×106～6.61×106 cell/mL.A池和B池水体中细菌丰度没有明显的月变化规律,但昼夜变化明显.B池水体中细菌丰度与叶绿素a、总氮、总磷、温度和盐度的关系4—7月呈明显的正相关(r=0.984,n=4);8月细菌丰度急剧下降,因采样期间有连续降雨,细菌丰度变化和降雨可能有一定的关系.A池水体中细菌丰度与叶绿素a呈显著负相关（r=-0.821,n=7）,与温度呈显著负相关（r=-0.830,n=7）,温度不是影响A池细菌增殖的主要因子.B池底泥样品中细菌丰度比水体中的低,主要可能是水交换和养殖贝类活动共同作用的结果.采样期间发现,在阴雨天气时池塘水面会有泡沫漂浮,细菌丰度高于其所在水体达2.25×107 cell/mL,其作用机制有待于进一步研究     

细菌Hfq蛋白的结构、功能及作用机制

非编码小RNA(small RNA, sRNA)是细菌基因转录后调控的一个重要层次,也是近十年来原核生物研究领域的焦点之一。大多数sRNA的作用与Hfq蛋白密切相关,即Hfq可以促进sRNA与其靶标mRNA的互补配对,进而影响翻译的进行或者mRNA的稳定性。笔者对Hfq的结构、Hfq参与sRNA调节作用的机制、Hfq在多种细菌中的功能表型进行了综述。Hfq是一个保守的蛋白质,在很多细菌中广泛存在,并与真核生物中参与mRNA剪切与降解活动的Sm蛋白同源。在结构上,Hfq具有两个非等同的RNA结合面,可以结合并介导多个RNA分子的相互作用,其结构体现了和功能的高度统一性。目前,对Hfq的研究主要集中于革兰氏阴性细菌中,在革兰氏阳性细菌中,Hfq的功能尚不明晰; 此外,在许多重要的细菌中,Hfq影响功能表型的具体机制也不清楚。因此,今后有必要进一步精细研究Hfq的分子结构特征和功能特点,深入分析Hfq对细菌表型多样化的影响机制,探究Hfq影响靶标分子和功能表型的详尽机制。     

Structural mimicry in bacterial virulence

An important mechanism underlying the strategies used by microbial pathogens to manipulate cellular functions is that of functional mimicry of host activities. In some cases, mimicry is achieved through virulence factors that are direct homologues of host proteins. In others, convergent evolution has produced new effectors that, although having no obvious amino-acid sequence similarity to host factors, are revealed by structural studies to display mimicry at the molecular level.     

Three-dimensional structure of CheY, the response regulator of bacterial chemotaxis

Homologies among bacterial signal transduction proteins suggest that a common mechanism mediates processes such as chemotaxis, osmoregulation, sporulation, virulence, and responses to nitrogen, phosphorous and oxygen deprivation. A common kinase-mediated phosphotransfer reaction has recently been identified in chemotaxis, nitrogen regulation, and osmoregulation. In chemotaxis, the CheA kinase passes a phosphoryl group to the cytoplasmic protein CheY, which functions as a phosphorylation-activated switch that interacts with flagellar components to regulate motility. We report here the X-ray crystal structure of the Salmonella typhimurium CheY protein. The determination of the structure was facilitated by the use of site-specific mutagenesis to engineer heavy-atom binding sites. CheY is a single-domain protein composed of a doubly wound five-stranded parallel beta-sheet. The phosphoacceptor site in CheY is probably a cluster of aspartic-acid side chains near the C-terminal edge of the beta-sheet. The pattern of sequence similarity of CheY with components of other regulatory systems can be interpreted in the light of the CheY structure and supports the view that this family of proteins have a common structural motif and active site.     

Cooperation and conflict in quorum-sensing bacterial populations

It has been suggested that bacterial cells communicate by releasing and sensing small diffusible signal molecules in a process commonly known as quorum sensing (QS). It is generally assumed that QS is used to coordinate cooperative behaviours at the population level. However, evolutionary theory predicts that individuals who communicate and cooperate can be exploited. Here we examine the social evolution of QS experimentally in the opportunistic pathogen Pseudomonas aeruginosa, and show that although QS can provide a benefit at the group level, exploitative individuals can avoid the cost of producing the QS signal or of performing the cooperative behaviour that is coordinated by QS, and can therefore spread. We also show that a solution to the problem of exploitation is kin selection, if interacting bacterial cells tend to be close relatives. These results show that the problem of exploitation, which has been the focus of considerable attention in animal communication, also arises in bacteria.     

Functional interactions between receptors in bacterial chemotaxis

Bacterial chemotaxis is a model system for signal transduction, noted for its relative simplicity, high sensitivity, wide dynamic range and robustness. Changes in ligand concentrations are sensed by a protein assembly consisting of transmembrane receptors, a coupling protein (CheW) and a histidine kinase (CheA). In Escherichia coli, these components are organized at the cell poles in tight clusters that contain several thousand copies of each protein. Here we studied the effects of variation in the composition of clusters on the activity of the kinase and its sensitivity to attractant stimuli, monitoring responses in vivo using fluorescence resonance energy transfer. Our results indicate that assemblies of bacterial chemoreceptors work in a highly cooperative manner, mimicking the behaviour of allosteric proteins. Conditions that favour steep responses to attractants in mutants with homogeneous receptor populations also enhance the sensitivity of the response in wild-type cells. This is consistent with a number of models that assume long-range cooperative interactions between receptors as a general mechanism for signal integration and amplification.