浙江天台山不同林型土壤环境的微生物区系和细菌生理群的多样性

研究了天台山8种土壤环境的微生物区系,细菌生理群分布、组成和多样性。结果表明：黄山松林、竹林和云锦杜鹃林土壤中细菌、真菌和放线菌数量较多,而柳杉林土壤中较少。微生物数量与土壤有机质、全氮、全磷含量以及土壤凋落物的关系较大。每种土壤环境的细菌、真菌和放线菌占微生物总量的比例为：细菌数量最多,放线菌居中,真菌较少。土壤细菌生理群在天台山8种土壤环境中的分布有较大的差异。好气纤维素分解菌、好气固氮菌、氨化细菌、有机磷分解菌、无机磷分解菌在8种土壤环境中均占有较大的比例,是每种土壤环境的优势菌群,而反硝化细菌和反硫化细菌在每种土壤环境中占有的数量比例均相对较小,处于次要地位。七子花林、竹林、云锦杜鹃林和日本花柏林土壤细菌生理群的Simpson指数和Shannon-Wiener指数均较小,柳杉林、茶园、金钱松林、黄山松林土壤细菌生理群的Simpson指数和Shannon-Wiener指数相对较大。     

细菌在实体肿瘤治疗中的应用

150多年前就发现某些细菌能够选择性地在实体肿瘤部位生长聚集,而在正常组织器官则否。尽管对产生这一现象的原因尚不明了,但人们已经利用细菌的这一特性,就试图将其作为治疗实体肿瘤的一种非常有前景的方法进行了研究。随着基因工程技术的日益完善,以及新的具有肿瘤靶向性细菌的发现,细菌作为肿瘤靶向性载体用于治疗肿瘤已日益受到青睐。这些细菌被用来传递抗肿瘤生长或杀伤肿瘤的物质,如毒素、前药转化酶、血管生长抑制剂、细胞因子等。     

Distribution of urea-decomposing bacteria in waters of lake suwa

The present study deals with the distribution of free and attached urea-decomposing bacteria in waters of Lake Suwa, one of the typical eutrophic lakes in Japan.Urea-decomposing bacteria are proved to be not an exceptional population among the populations of the heterotrophic bacteria studied. The percentage of attached urea-decomposing bacteria versus attached heterotrophic bacteria seems to be higher than that of free urea-decomposing bacteria versus free heterotrophic bacteria. Based on the assumption that most bacterial ureases are inducible ones, it is inferred that their ureases may not be induced under a such degree of urea concentration as is generally encountered in natural waters.     

细菌的信息交流

细菌与细菌之间的信息交流是通过相互交换一种自动诱导物(autoinducer)的信号分子来实现的。这种信息交换的过程被称为群体感应(quorumsystem)。细菌根据这种特定信号分子浓度的变化来监测环境中其它细菌数量的变化。细菌的群体感应系统分为种内和种间信息交流两大类。细菌间的信息交流涉及到细菌的多种生理功能,如细菌的致病能力等。因此研究细菌间的信息交流有可能找到一条新的防治细菌感染途径。     

百合组织中细胞内生菌的分布与传播

在百合鳞茎、根、地上茎、叶和花蕾组织细胞中观察到细菌的分布。但各组织器官之间、细胞内所含细菌的数量差异很大。鳞茎组织细胞内含菌量最多。同一鳞茎,外围鳞片细胞内含菌量高于内侧。生长锥顶端分生组织细胞内未观察到细菌的分布。在生长锥中部有少量细菌出现,而基部则含有较多的细菌。百合鳞茎最外一层鳞片的外表皮中,细胞内有许多呈树丛状分布的类似侵染线的管状结构,它们与细胞壁发生联系,推测这些细菌可能是外源的。细菌随着植株的生长发育,由已成熟的含菌细胞向幼嫩的不含菌细胞中传播。细菌在细胞之间的传播可能是通过细胞壁上纹孔间的胞间连丝孔道。     

细菌的信息交流

细菌与细菌之间的信息交流是通过相互交换一种自动诱导物(autoinducer)的信号分子来实现的.这种信息交换的过程被称为群体感应(quorum system).细菌根据这种特定信号分子浓度的变化来监测环境中其它细菌数量的变化.细菌的群体感应系统分为种内和种间信息交流两大类.细菌间的信息交流涉及到细菌的多种生理功能,如细菌的致病能力等.因此研究细菌间的信息交流有可能找到一条新的防治细菌感染途径.     

微生物在矿物表面吸附的研究进展

微生物在矿物表面的吸附是微生物与矿物表面深度作用的前提, 也是生物药剂在选矿中的应用的基础研究。本文综述了影响微生物在矿物表面吸附的环境因素, 微生物细胞与矿物表面之间的相互作用, 微生物细胞表面基团、表面成分及其胞外聚合物对吸附过程的影响, 并提出了今后的研究方向。     

Comparison of the relative concentration of motile and non-motile bacteria in small pores

The effect of small pores (similar in size to the stomata of plants) on the diffusion constants and relative concentrations of non-motile, randomly motile and chemotactic bacteria is considered. It is shown that although the Brownian diffusion constant of non-motile bacteria is a couple of orders of magnitude lower than the diffusion constant of motile bacteria, non-motile bacteria will still be present in both short (100 microns) and long (0.5 cm) pores in similar numbers to motile bacteria. It is postulated that this is due, at least in part, to the smaller amount of excluded volume for non-flagellated bacteria.     

The Interaction of Protozoa with their Potential Prey Bacteria in the Rhizosphere

Extensive colonization of the rhizosphere by beneficial bacteria is desirable but it is not yet clear whether the feeding patterns of protozoa exert any ecological impact on the competence of bacteria in the rhizosphere. To determine whether the successful colonization of the rhizosphere by bacteria can be explained by inherent abilities of the bacteria to resist predation, six bacteria categorized as poor, mediocre or good rhizosphere colonists were tested. The populations of protozoa in the rhizosphere consistently increased to a maximum density in two days but then declined to a stable level. Grazing by protozoa increased the doubling time of all of the test bacteria but did not significantly affect the final densities of bacteria in the rhizosphere. The differences in the colonization ability of the six bacteria tested were not attributable to inherent differences in their susceptibility to predation by protozoa.     

池塘氮循环中各种细菌与理化因子的相关性研究

对精养鱼池的水体及淤泥进行多次采样,用统计学分析处理,结果表明：硝化类细菌总体上与各主要理化因子的相关性较强（R＞0．60）,其中氨化菌主要与溶氧相关程度较高;反硝化菌主要与有效磷相关程度较高;亚硝化菌主要与氨氮负相关程度较高;硝化菌主要与亚硝酸盐相关程度较高。硝化类细菌与异养菌之间的相关性则更强,如反硝化菌与厌养菌（R＝0．944,P＝0．001）、拓硝化菌和好氧异养菌（R＝0．832,P＝0．003）皆显正相关,亚硝化菌和厌氧异养菌（R＝－0．76,P＝0．009）显负相关;而在硝化类细菌之间的相关程度却较弱（R＜0．60）,表明池塘硝化类细菌对水质具有一定的调控作用,但相互之间的依赖性不强,各自相对独立地发挥作用。     

Method allowing biological and biochemical studies of vacuum-exposed bacteria

A method is described which allows quantitative biological and biochemical studies of the vacuum effect on bacteria. Quantitative studies can only be performed if vacuum-exposed bacteria can be removed completely from their support. This is achieved by exposing bacteria to vacuum on a polyvinylalcohol film. After vacuum exposure this film is dissolved in buffer, leading to a quantitative release of bacteria into the buffer. This suspension of vacuum-exposed bacteria can then be used for quantitative biological and biochemical studies of the vaccum effect on bacteria.     

Two-Dimensional Patterns in Bacterial Veils Arise from Self-generated,Three-Dimensional Fluid Flows

The behavior of collections of oceanic bacteria is controlled by metabolic (chemotaxis) and physical (fluid motion) processes. Some sulfur-oxidizing bacteria, such as Thiovulum majus, unite these two processes via a material interface produced by the bacteria and upon which the bacteria are transiently attached. This interface, termed a bacterial veil, is formed by exo-polymeric substances (EPS) produced by the bacteria. By adhering to the veil while continuing to rotate their flagella, the bacteria are able to exert force on the fluid surroundings. This behavior induces a fluid flow that, in turn, causes the bacteria to aggregate leading to the formation of a physical pattern in the veil. These striking patterns are very similar in flavor to the classic convection instability observed when a shallow fluid is heated from below. However, the physics are very different since the flow around the veil is mediated by the bacteria and affects the bacterial densities.     

The contribution of marine aggregate‐associated bacteria to the accumulation of pathogenic bacteria in oysters: an agent‐based model

Bivalves process large volumes of water, leading to their accumulation of bacteria, including potential human pathogens (e.g., vibrios). These bacteria are captured at low efficiencies when freely suspended in the water column, but they also attach to marine aggregates, which are captured with near 100% efficiency. For this reason, and because they are often enriched with heterotrophic bacteria, marine aggregates have been hypothesized to function as important transporters of bacteria into bivalves. The relative contribution of aggregates and unattached bacteria to the accumulation of these cells, however, is unknown. We developed an agent‐based model to simulate accumulation of vibrio‐type bacteria in oysters. Simulations were conducted over a realistic range of concentrations of bacteria and aggregates and incorporated the dependence of pseudofeces production on particulate matter. The model shows that the contribution of aggregate‐attached bacteria depends strongly on the unattached bacteria, which form the colonization pool for aggregates and are directly captured by the simulated oysters. The concentration of aggregates is also important, but its effect depends on the concentration of unattached bacteria. At high bacterial concentrations, aggregates contribute the majority of bacteria in the oysters. At low concentrations of unattached bacteria, aggregates have a neutral or even a slightly negative effect on bacterial accumulation. These results provide the first evidence suggesting that the concentration of aggregates could influence uptake of pathogenic bacteria in bivalves and show that the tendency of a bacterial species to remain attached to aggregates is a key factor for understanding species‐specific accumulation.     

丁酸菌与老年肠道功能的相关性

丁酸菌是一种专性厌氧芽胞杆菌,是以丁酸为主要代谢产物的益生菌,可定植于人体肠道,在某种程度上与乳酸菌有协同作用,可抑制人肠道内有害菌的生长、促进营养物质的吸收、改善肠道功能等。本研究主要对丁酸菌在临床中的应用研究进展进行综述,尤其是对丁酸菌与老年人肠道功能的相关性进行阐述,并展望丁酸菌对老年慢性疾病如糖尿病、心血管疾病、老年痴呆、风湿性疾病及骨质疏松症防治的研究未来。     

Quantification of bacteria in human feces using 16S rRNA-hybridization, DNA-staining and flow cytometry

Hybridization of bacteria with fluorescent probes targeting 16S rRNA and inspection of hybridized bacteria with fluorescence microscopy (microscopy-FISH, i.e. fluorescence in situ hybridization) have constituted an accessible method for the analysis of mixed bacterial samples such as feces. However, microscopy-FISH is a slow method and prone to errors. Flow cytometry (FCM) enables analysis of bacteria more rapidly, accurately and reliably than microscopy. In this study, a FCM method for the analysis of 16S rRNA-hybridized and DNA-stained fecal bacteria was developed. The results of FCM-FISH were comparable to those of microscopy-FISH, and the coefficients of variation of the FCM analyses were extraordinarily low. In previous FCM-FISH studies, the Eub 338 probe, which is supposed to hybridize all bacteria, has been used to detect all bacteria present in the sample. We found that Eub 338 did not bind to all bacteria, which could be detected by DNA-staining; while SYTOX Orange DNA-stain detected all bacterial species tested and produced high fluorescence intensities enabling clear separation of bacteria from non-bacterial material. Thus, DNA-staining is a method of choice for the detection of all bacteria in FCM-FISH. We conclude that FCM of 16S rRNA-hybridized and DNA-stained bacteria is a rapid and reliable method for the analysis of mixed bacterial samples including feces.     

Mechanisms and rates of bacterial colonization of sinking aggregates

Quantifying the rate at which bacteria colonize aggregates is a key to understanding microbial turnover of aggregates. We used encounter models based on random walk and advection-diffusion considerations to predict colonization rates from the bacteria's motility patterns (swimming speed, tumbling frequency, and turn angles) and the hydrodynamic environment (stationary versus sinking aggregates). We then experimentally tested the models with 10 strains of bacteria isolated from marine particles: two strains were nonmotile; the rest were swimming at 20 to 60 microm s(-1) with different tumbling frequency (0 to 2 s(-1)). The rates at which these bacteria colonized artificial aggregates (stationary and sinking) largely agreed with model predictions. We report several findings. (i) Motile bacteria rapidly colonize aggregates, whereas nonmotile bacteria do not. (ii) Flow enhances colonization rates. (iii) Tumbling strains colonize aggregates enriched with organic substrates faster than unenriched aggregates, while a nontumbling strain did not. (iv) Once on the aggregates, the bacteria may detach and typical residence time is about 3 h. Thus, there is a rapid exchange between attached and free bacteria. (v) With the motility patterns observed, freely swimming bacteria will encounter an aggregate in <1 day at typical upper-ocean aggregate concentrations. This is faster than even starving bacteria burn up their reserves, and bacteria may therefore rely solely on aggregates for food. (vi) The net result of colonization and detachment leads to a predicted equilibrium abundance of attached bacteria as a function of aggregate size, which is markedly different from field observations. This discrepancy suggests that inter- and intraspecific interactions among bacteria and between bacteria and their predators may be more important than colonization in governing the population dynamics of bacteria on natural aggregates.     

Quorum Sensing Circuits in the Communicating Mechanisms of Bacteria and Its Implication in the Biosynthesis of Bacteriocins by Lactic Acid Bacteria: a Review

It is well established that bacteria communicate between each other by using different mechanisms; among which, quorum sensing (QS) is the best known one. Indeed, intra- and intercellular communications of microorganisms, as well as the regulation of metabolism and reaction to the surrounding environmental conditions, are carried out by using different signaling molecules. N-Acyl homoserine lactones control the QS in Gram-negative bacteria, while Gram-positive bacteria use communicating peptides. These compounds, by diffusing through the bacterial membrane cell from the extracellular medium, directly or indirectly control the expression of specific genes that induce bacteria to react to their surrounding environment and stressing agents. In the case of lactic acid bacteria and bifidobacteria which are widely used in the dairy industry, QS is of extreme importance for their survival and the extent of their activity in the dairy matrix. Moreover, it is also via QS that these bacteria synthesize various antimicrobial agents such as bacteriocins. The aim of this review is to highlight the quorum sensing circuits involved in the communicating mechanisms of bacteria with emphasis on current applications of QS in lactic acid bacteria. More particularly, the implication of QS in the biosynthesis of bacteriocins by lactic acid bacteria will be detailed.

     

An instrument for the immediate quantification of bacteria in potable waters.

A new semiautomated instrument is described which quantifies the number of bacteria in potable waters within 3 min, providing a permanent colorimetric record of the results. The bacteria detection device can measure as few as 100 CFU/ml in potable waters. In brief, a 100- to 1,000-ml sample of tap water is drawn through a large surface, customized filter housed in the device, and bacteria, rust, and humic acid in the water are concentrated thereon. A reducing agent is used to remove the rust and humic acid from the filter. The filter is inverted and backflushed to elute the bacteria which are collected and reconcentrated onto a 7-mm-diameter filter surface. The reconcentrated bacteria are stained, and the filter fibers are preferentially decolorized without removing the dye from the bacteria. The color intensity of the filter surface is compared with a color guide to determine the amount of bacteria in the test water.     

Mutation rate and genome reduction in endosymbiotic and free-living bacteria

Genome reduction has been considered the hallmark of endosymbiotic bacteria, such as endocellular mutualists or obligatory pathogens until it was found exactly the same in several free-living bacteria. In endosymbiotic bacteria genome reduction is mainly attributed to degenerative processes due to small population size. These cannot affect the free-living bacteria with reduced genomes because they are known to have very large population sizes. It has been proposed that selection for simplification drove genome reduction in these free-living bacteria. For at least one of them (Prochlorococcus), genome reduction is associated with accelerated evolution and we suggest an alternative hypothesis based on increase in mutation rate as the primary cause of genome reduction in free-living bacteria.