细胞寒害的热力学熵理论(Ⅱ)──超熵产生作为寒害稳定性判据的理论研究

本文从物质和能量交换的角度,运用非平衡态热力学超熵产生理论,分析了寒害定态的稳定性,并建立了超熵产生判据．理论分析所得的结论与实验结果基本相符．     

蚂蚁筑巢对西双版纳热带森林土壤微生物生物量碳及熵的影响

蚂蚁筑巢能够改变热带森林土壤理化环境,从而对土壤微生物生物量碳及熵的时空动态产生重要影响.本研究以西双版纳高檐蒲桃热带森林群落为对象,采用氯仿熏蒸法对蚂蚁巢地和非巢地土壤微生物生物量碳及熵时空动态进行测定.结果表明: 1)蚁巢地平均微生物生物量碳及熵(1.95 g·kg^-1,6.8%)显著高于非巢穴(1.76 g·kg^-1,5.1%);蚁巢地和非蚁巢地土壤微生物生物量碳呈单峰型时间变化趋势,而土壤微生物熵呈“V”型变化格局.2)蚁巢地和非巢地土壤微生物生物量碳及熵均具有明显的垂直变化:微生物生物量碳随土层加深显著降低,微生物熵则沿土层加深显著升高,但蚁巢微生物生物量碳及熵的垂直变化较非巢穴显著. 3)蚂蚁筑巢引起了巢内水分和温度的显著改变,进而影响土壤微生物生物量碳及熵的时空动态.土壤水分分别解释微生物生物量碳及熵的66%～83%和54%～69%,而土壤温度分别解释土壤微生物生物量碳及熵的71%～86%和67%～76%. 4)蚂蚁筑巢引起土壤理化性质变化对土壤微生物生物量碳和熵产生重要影响.蚁巢土壤微生物生物量碳与土壤有机碳、温度、全氮、含水率呈极显著正相关,与容重、硝态氮,水解氮呈显著正相关,与土壤pH呈极显著负相关;除土壤微生物熵与pH呈显著正相关外,与其他土壤理化指标均呈显著负相关.土壤总有机碳、全氮和温度对微生物生物量碳的贡献最大,而土壤总有机碳和全氮对微生物熵的负作用最小.因此,蚂蚁筑巢能够显著改变微生境(如土壤水分与温度)及土壤理化性质(如总有机碳及全氮),进而调控热带森林土壤微生物生物量碳及熵的时空动态.     

玉米幼苗根际土壤微生物活性对芘污染的响应

用根际袋法土培试验研究了玉米幼苗根际与非根际土壤微生物量碳、微生物熵、代谢熵和土壤酶活性对不同芘污染水平(50、200、800mg·kg-1,记为T1、T2、T3)的响应差异。结果表明,较低浓度芘可适当的刺激玉米幼苗的生长,而较高浓度芘则抑制幼苗生长,其抑制作用随芘处理浓度的提高而增强;芘对玉米根系的影响要大于对茎叶的影响。玉米幼苗能够明显促进土壤中芘的去除。根际和非根际土壤中芘的去除率分别为56.67%-76.18%和32.64%-70.44%,根际土壤中芘的平均去除率比非根际土壤高16.06%。同处理中根际土壤芘含量显著低于非根际土壤,随着芘处理浓度的提高其差异更加显著。根际土壤微生物量碳、微生物熵、多酚氧化酶活性、脱氢酶活性和磷酸酶活性均高于非根际土壤,代谢熵低于非根际土壤,且其差异随芘处理浓度的提高而增大。在不同芘污染水平下,微生物量碳、微生物熵和脱氢酶活性根际和非根际土壤为T1T2T3,代谢熵为T3T2T1;多酚氧化酶活性根际土壤为T2T1T3,非根际土壤为T1T2T3;磷酸酶活性根际土壤为T3T1T2,非根际土壤为T1T2T3。土壤中残余芘含量与土壤微生物量碳、微生物熵、多酚氧化酶、脱氢酶和磷酸酶活性呈显著负相关,与代谢熵呈显著正相关。     

微生物与新型农业

论述了微生物新型农业的理论基础：营养结构原理、增加食物链原理、生态位原理和熵定律等。简述了微生物在新型农业中的广泛应用,如发展微生物饲料、微生物肥料、微生物农药、微生物食品、微生物能源和微生物环保制剂等。分析了微生物新型农业的发展前景。     

熵理论在生态系统稳定性研究中的应用

本文从李亚普诺夫（Lyapounov）的稳定性原理出发,运用最小熵和超熵理论分析了线性非平衡态和远离平衡态生态系统的稳定性,并给出了相应的稳定性判据。以完善和促进生态系统稳定性研究的理论水平。     

喀斯特峰丛洼地植被恢复过程中土壤微生物特性

以喀斯特峰丛洼地草丛、灌丛、次生林和原生林生态系统为对象,研究了植被恢复过程中土壤微生物生物量、土壤微生物碳熵、土壤呼吸及其呼吸熵等微生物特性。结果表明:土壤微生物生物量与土壤微生物碳熵随着植被恢复呈增加趋势(P0.05),土壤呼吸熵变化规律与之相反,土壤呼吸变化不显著,说明随着植被的恢复土壤质量不断提高,顺序为乔木(原生林、次生林)灌丛草丛;同一生态系统中土壤微生物生物量氮、土壤呼吸及其呼吸熵均表现为冬季夏季(P0.05),土壤微生物碳熵为冬季夏季(草丛例外)(P0.05),而土壤微生物生物量碳却未呈现显著性季节变化;土壤微生物生物量氮与微生物碳熵不仅对地上植被及季节变化响应敏感,且与土壤有机质及其他微生物指标相关性较好(P0.05),可以灵敏表征喀斯特峰丛洼地不同植被恢复土壤质量变化。     

长期施肥对双季稻田土壤微生物学特性的影响

为探明不同施肥处理对早稻和晚稻各个生育时期稻田土壤微生物生物量碳、氮和微生物熵的影响,以湖南宁乡长期定位试验为平台,应用氯仿熏蒸-K_2SO_4提取法和化学分析法系统分析了定位长达29年5种施肥处理之间(化肥、秸秆还田+化肥、30%有机肥+70%化肥、60%有机肥+40%化肥和无肥)双季稻田土壤微生物生物量碳、氮和微生物熵的差异。结果表明,早稻和晚稻各主要生育时期,长期施肥均能提高土壤微生物生物量碳、氮含量和微生物熵,各施肥处理土壤微生物生物量碳、氮含量和微生物熵均随水稻生育期推进呈先增加后降低的变化趋势,均于齐穗期达到最大值,成熟期达到最低值;其中,以60%有机肥和30%有机肥处理双季稻田土壤微生物生物量碳、氮含量和微生物熵均为最高,均显著高于其他处理,其大小顺序表现为60%有机肥30%有机肥秸秆还田化肥无肥。长期有机无机配施可以提高土壤微生物生物量碳、氮和微生物熵,有机肥与化肥配施对提高土壤肥力效果最好。土壤微生物生物量碳、氮及微生物熵可以反映土壤质量的变化,可作为评价土壤肥力的生物学指标。     

荒漠草地土壤微生物生物量和微生物熵对沙漠化的响应

采用空间序列代替时间演替的方法,分析宁夏中北部盐池县荒漠草地不同沙漠化阶段(荒漠草地、固定沙地、半固定沙地和流动沙地)土壤微生物生物量(SMB)和微生物熵(qMB)的变化特征及其影响因子.结果表明:从荒漠草地到流动沙地,土壤微生物生物量碳、氮、磷分别降低46.1%、80.8%和30.0%.随着荒漠草地沙漠化程度的加剧,土壤微生物熵碳(qMBC)、土壤微生物熵氮(qMBN)、土壤微生物熵磷(qMBP)均表现为荒漠草地>固定沙地>半固定沙地>流动沙地,而土壤-微生物化学计量不平衡性(C∶Nimb、C∶Pimb、N∶Pimb)基本呈增加趋势.土壤微生物生物量氮与C∶Nimb呈显著正相关,与N∶Pimb呈显著负相关;土壤微生物生物量磷与C∶Pimb呈显著正相关.冗余分析(RDA)显示,土壤生态化学计量(C∶N、C∶P)对微生物熵碳的负效应最明显.荒漠草地沙漠化显著影响土壤微生物生物量和微生物熵.     

洞庭湖典型湿地植被群落土壤微生物特征

以洞庭湖湿地3种典型植被(虉草、苔草、芦苇)为对象,研究了不同植被下土壤微生物生物量和微生物呼吸等特征,并对其主要影响因子进行了分析.结果表明:微生物生物量碳、氮和微生物呼吸以虉草群落最高,苔草群落次之,芦苇群落最低,微生物碳熵变化趋势为虉草群落＞苔草群落＞芦苇群落,微生物呼吸熵具有与微生物碳熵相反的变化趋势.相关分析表明:土壤含水量、容重和有机质是影响土壤微生物特征变化的重要因子,同时,土壤pH和土壤总氮与土壤微生物生物量碳、微生物生物量氮、微生物呼吸等也有较强的关联性.     

微生物肥料作用机理的研究新进展

综述了近几年国内外有关微生物肥料研究与应用的文献,系统阐述了微生物肥料的作用及其研究进展.涉及微生物肥料的作用主要有产生和协助植物对营养元素的吸收、产生多种生理活性物质刺激调节植物生长、产生抑病作用间接促进植物生长、提高植物抗逆能力、改善农作物产品的品质等以综合作用来降低化肥用量的效应等.指出微生物肥料的功效和发展趋势,为进一步开发和应用微生物肥料提供依据.     

Flux analysis of recombinant Saccharomyces cerevisiae YPB-G utilizing starch for optimal ethanol production

Genetically modified Saccharomyces cerevisiae strain (YPB-G) which secretes a bifunctional fusion protein that contains both Bacillus subtilis -amylase and Aspergillus awamori glucoamylase activities was used for the direct conversion of starch into ethanol. Starch was either supplied initially to different nutrient media or added instantaneously to the reactor at various discrete time instants (pulse feeding). Stoichiometric modeling was used to investigate the effects of initial substrate concentration and growth rate of the recombinant yeast culture on ethanol production. Reaction stoichiometries describing both the anabolism and catabolism of the microorganism were used as an input to flux balance analysis (FBA), the preferred metabolic modeling approach since the constructed stoichiometric network was underdetermined. Experiments for batch and fed-batch systems at different substrate concentrations were analyzed theoretically in terms of flux distributions using ethanol production rate as the maximization criteria. Calculated ethanol rates were in agreement with experimental measurements, suggesting that this recombinant microorganism is sufficiently evolved to optimize its ethanol production. The function of the main pathways of yeast metabolism (PPP, EMP, TCA) are discussed together with the node analyses of glucose-6-P and pyruvate branch points. Theoretical node analysis revealed that if the split ratio in G6P branch point is changed by genetic manipulations, the ethanol yield would be affected considerably.     

Coarse-grained strategy for modeling protein stability in concentrated solutions

We present a coarse-grained approach for modeling the thermodynamic stability of single-domain globular proteins in concentrated aqueous solutions. Our treatment derives effective protein-protein interactions from basic structural and energetic characteristics of the native and denatured states. These characteristics, along with the intrinsic (i.e., infinite dilution) thermodynamics of folding, are calculated from elementary sequence information using a heteropolymer collapse theory. We integrate this information into Reactive Canonical Monte Carlo simulations to investigate the connections between protein sequence hydrophobicity, protein-protein interactions, protein concentration, and the thermodynamic stability of the native state. The model predicts that sequence hydrophobicity can affect how protein concentration impacts native-state stability in solution. In particular, low hydrophobicity proteins are primarily stabilized by increases in protein concentration, whereas high hydrophobicity proteins exhibit richer nonmonotonic behavior. These trends appear qualitatively consistent with the available experimental data. Although factors such as pH, salt concentration, and protein charge are also important for protein stability, our analysis suggests that some of the nontrivial experimental trends may be driven by a competition between destabilizing hydrophobic protein-protein attractions and entropic crowding effects.     

Modeling the role of disulfide bonds in protein folding: Entropic barriers and pathways

The role of disulfide bonds in directing protein folding is studied using lattice models. We find that the stability and the specificity of the disulfide bond interactions play quite different roles in the folding process: Under some conditions, the stability decreases the overall rate of folding; the specificity, however, by yielding a simpler connectivity of intermediates, always increases the rate of folding. This conclusion is intimately related to the selection mechanism entailed by entropic driving forces, such as the loop formation probability, and entropic barriers separating the native and the many native-like metastable states. The folding time is found to be a minimum for a certain range of the effective disulfide bond interaction. Examination of a model, which allows for the formation of disulfide bonded intermediates, suggests that folding proceeds via a threestage multiple pathways kinetics. We show that there are pathways to the native state involving only native-like intermediates, as well as those that are mediated by nonnative intermediates. These findings are interpreted in terms of the appropriate energy landscape describing the barriers connecting low energy conformations. The consistency of our conclusions with several experimental studies is also discussed. © 1995 Wiley-Liss, Inc.     

工业腐败微生物种属特性及抗药性分析

为科学治理工业领域中微生物对杀菌剂的抗药性,从工业产品、原料及水样中采集腐败微生物,细菌按照《常见细菌系统鉴定手册》、API鉴定系统及16SrDNA序列分析,真菌按《真菌鉴定手册》及18SrDNA序列分析分别进行鉴定;通过测定杀菌剂的最小抑制浓度(MIC)来评估微生物抗药性水平。结果显示,腐败微生物中革兰氏阴性细菌约占46.91%,主要包括假单胞菌属、肠杆菌属、气单胞菌属、克雷伯氏菌属等;革兰氏阳性菌约占32.71%,主要种属为芽孢杆菌属、微杆菌属、李斯特氏菌属及球菌等;真菌约占12%,主要包括青霉属、木霉属和曲霉属。MIC测试结果显示,主要抗药性微生物为假单胞菌属,约占33.78%,平均抗性水平达到36mg/L,且传代不稳定。结论认为,工业上微生物污染主要由细菌耐药性引起,细胞膜结构及细菌生物膜的形成在该类杀菌剂抗药性产生的过程中起重要作用。     

Hydration effects on the HET-s prion and amyloid-beta fibrillous aggregates, studied with three-dimensional molecular theory of solvation

We study the thermodynamic properties of the experimental fragments of the amyloid fibril made of the HET-s prion proteins (the infectious element of the filamentous fungus Podospora anserina) and of amyloid-β proteins (the major component of Alzheimer's disease-associated plaques) by using the three-dimensional molecular theory of solvation. The full quantitative picture of hydration effects, including the hydration thermodynamics and hydration structure around the fragments, is presented. For both the complexes, the hydration entropic effects dominate, which results in the entropic part offsetting the unfavorable energetic part of the free energy change upon the association. This is in accord with the fact that the hydrophobic cooperativity plays an essential role in the formation of amyloid fibrils. By calculating the partial molar volume of the proteins, we found that the volume change upon the association in both the systems is large and positive, with the implication that high pressure causes destabilization of the fibril. This observation is in good agreement with the recent experimental results. We also found that both the HET-s and amyloid-β pentamers have loose intermolecular packing with voids. The three-dimensional molecular theory of solvation predicts that water molecules can be locked in the interior cavities along the fibril axis for both the HET-s and amyloid-β proteins. We provide a detailed molecular picture of the structural water localized in the interior of the fibrils. Our results suggest that the interior hydration plays an important role in the structural stability of fibrils.     

产弹性蛋白酶细菌的发酵动力学研究

基于14L的发酵罐分批发酵实验数据,建立了发酵过程菌体生长、产物生成及基质消耗随时间变化的数学模型。Logistic方程、Luedeking—Piret方程能够很好地分别描述产弹性蛋白酶菌体生长;发酵产酶过程和基质消耗过程。并将3个动力学模型的预测值和实验值进行了比较,所建立的分批发酵动力学模型能较好地反映弹性蛋白酶分批发酵过程。     

Influence of 5-bromodeoxycytosine substitution on triplex DNA stability and conformation

Three triple-helical hairpin DNAs with substitution of 5-bromocytosine for cytosine in different strands have been investigated by molecular mechanics and Raman spectroscopy. The stability of the three substituted triplexes were compared with the corresponding unsubstituted triplex DNA by the molecular mechanics method. Base stacking interactions and strand--strand interactions of each triplex were analyzed in detail. Sugar conformations in these triplexes have been determined by both vibrational spectroscopy and molecular dynamics simulation. The hairpin triplexes with substitution occurring in strand I or both in strands I and III have the main sugar conformation of C3'-endo, while the triplex with substitution occurring in strand III is the combination of C3'-endo and C2'-endo sugar conformation. Theoretical results are basically in agreement with experiments.     

The effect of heme on the conformational stability of micro-myoglobin

Micro-myoglobin, the isolated heme-binding subdomain of myoglobin, is a valuable model system for the investigation of heme recognition and binding by proteins, and provides an example of protein folding induced by cofactor binding. Theoretical studies by molecular dynamics simulations on apo- and holo-micro-myoglobin show that, by contrast with the case of the full-length wild-type protein and in agreement with earlier experimental evidence, the apo-protein is not stably folded in a native-like conformation. With the cofactor bound, however, the protein fragment maintains its folded conformation over 1.5 ns in molecular dynamics simulations. Further inspection of the model structures reveals that the role of heme in stabilizing the folded state is not only a result of its direct interactions with binding residues (His93, Arg45 and Lys96), but also derives from its shielding effect on a long-range electrostatic interaction between Arg45 and Asp60, which, in the molecular dynamics simulations, apparently triggers the unfolding process of apo-micro-myoglobin.     

Stability of proteins in the presence of carbohydrates; experiments and modeling using scaled particle theory

The effects of sucrose and fructose on the free energy of unfolding, DeltaG(N-->D), and on the change in hydrodynamic radius, R(H), upon unfolding were measured for RNase A and alpha-lactalbumin. Recently we analyzed the results for RNase A and showed that the effects of the carbohydrates on the protein's thermal stability can be accurately accounted for by scaled particle theory (SPT), and are thus largely entropic in nature. In this paper we extend this analysis to alpha-lactalbumin and demonstrate the generality of this finding. We also investigate the relationship between SPT and the thermodynamic formalism of preferential interactions. The preferential binding parameters calculated using SPT are in excellent agreement with experimentally measured values available in the literature. This agreement is expected to hold as long as enthalpic interactions between the cosolute and the protein are not important, as appears to be the case here. Finally we use the experimental data and SPT to calculate the change in the number of sugar molecules excluded from the protein surface during unfolding from knowledge of the preferential binding parameter for the native and denatured state of the protein.