奇异变形杆菌周期性群集运动的研究

目的研究奇异变形杆菌(proteus mirabilis,PM)迁徙生长过程中形态、数量、呼吸酶活性等指标周期性变化.方法在培养基中加入2,3,5-三苯基四唑氯化物(2,3,5-tetraphenyltetrazolium chloride,TTC)作为呼吸酶活性的指示剂观察细菌呼吸酶活性的变化.采用透射电子显微镜对细菌形态、鞭毛进行对比观察.比浊法计数PM在时间、空间上的数量的变化.结果PM在固体培养基迁徙生长过程中出现菌体数量逐渐减少、形态由短小到细长、鞭毛由少变多、呼吸酶从有活性向无活性转变的周期性变化.结论PM在培养基迁徙生长过程中,微观上出现菌体长度、鞭毛数量、细菌密度等周期性变化,宏观上出现水波样的环状运动,这是环境、鞭毛、细胞间信号传递和细菌密度等多因素联合作用的结果.     

The melatonin-sensitive circadian clock of the enteric bacterium Enterobacter aerogenes

Circadian clocks are fundamental properties of all eukaryotic organisms and at least some prokaryotic organisms. Recent studies in our laboratory have shown that the gastrointestinal system contains a circadian clock that controls many, if not all, aspects of gastrointestinal function. We now report that at least one species of intestinal bacteria, Enterobacter aerogenes, responds to the pineal and gastrointestinal hormone melatonin by an increase in swarming activity. This swarming behavior is expressed rhythmically, with a period of approximately 24 hrs. Transformation of E. aerogenes to express luciferase with a MotA promoter reveals circadian patterns of bioluminescence that are synchronized by melatonin and whose periods are temperature compensated from 26°C to 40°C. Bioinformatics suggest similarities between the E. aerogenes and cyanobacterial clocks, suggesting the circadian clock may have evolved very early in the evolution of life. They also point to a coordination of host circadian clocks with those residing in the microbiota themselves.     

Self-organization of bacterial biofilms is facilitated by extracellular DNA

Twitching motility-mediated biofilm expansion is a complex, multicellular behavior that enables the active colonization of surfaces by many species of bacteria. In this study we have explored the emergence of intricate network patterns of interconnected trails that form in actively expanding biofilms of Pseudomonas aeruginosa. We have used high-resolution, phase-contrast time-lapse microscopy and developed sophisticated computer vision algorithms to track and analyze individual cell movements during expansion of P. aeruginosa biofilms. We have also used atomic force microscopy to examine the topography of the substrate underneath the expanding biofilm. Our analyses reveal that at the leading edge of the biofilm, highly coherent groups of bacteria migrate across the surface of the semisolid media and in doing so create furrows along which following cells preferentially migrate. This leads to the emergence of a network of trails that guide mass transit toward the leading edges of the biofilm. We have also determined that extracellular DNA (eDNA) facilitates efficient traffic flow throughout the furrow network by maintaining coherent cell alignments, thereby avoiding traffic jams and ensuring an efficient supply of cells to the migrating front. Our analyses reveal that eDNA also coordinates the movements of cells in the leading edge vanguard rafts and is required for the assembly of cells into the “bulldozer” aggregates that forge the interconnecting furrows. Our observations have revealed that large-scale self-organization of cells in actively expanding biofilms of P. aeruginosa occurs through construction of an intricate network of furrows that is facilitated by eDNA.     

弗氏枸橼酸杆菌脂多糖突变株发生鞭毛合成异常

目的探讨弗氏枸橼酸杆菌群集运动的分子机制。方法用M in i-Tn5 Km转座子诱导获得弗氏枸橼酸杆菌群集运动突变株;通过反向PCR扩增突变基因并测序,从而确定发生突变的基因;观察突变株的运动和形态等特征。结果研究表明有7株突变株涉及3个与脂多糖合成有关的基因突变,分别为wzxB、waaW、waaL,导致弗氏枸橼酸杆菌群集运动能力显著下降。同时,这些突变株的鞭毛合成也出现异常,即培养的细菌中仅有小部分呈现正常的鞭毛合成,而大多数菌体聚集在一起,且鞭毛合成呈抑制状态,电镜观察发现多数聚集的菌体没有鞭毛或只有很少的鞭毛。与之相对应的是,野生株没有这个现象。结论脂多糖结构的缺失影响弗氏枸橼酸杆菌鞭毛的生成,进而影响其群集运动能力。     

Plasmid gene AZOBR_p60126 impacts biosynthesis of lipopolysaccharide II and swarming motility in Azospirillum brasilense Sp245

The facultative plant endophyte Azospirillum brasilense Sp245 synthesizes two high-molecular-weight lipopolysaccharides, LPSI and LPSII, which comprise identical d -rhamnan O-polysaccharides and, presumably different core oligosaccharides. Previously, using random insertion mutagenesis, we constructed the LpsII⁻ mutant KM139 of strain Sp245 that possessed an Omegon-Km insertion in plasmid AZOBR_p6. Here, we found that in KM139, Omegon-Km disrupted the coding sequence AZOBR_p60126 for a putative glycosyltransferase related to mannosyltransferases and rhamnosyltransferases. To verify its function, we cloned the AZOBR_p60126 gene of strain Sp245 in the expression vector plasmid pRK415 and transferred the construct pRK415–p60126 into KM139. In the complemented mutant KM139 (pRK415–p60126), the wild-type LPSI⁺ LPSII⁺ profile was recovered. We also compared the swimming and swarming motilities of strains Sp245, Sp245 (pRK415), KM139, KM139 (pRK415), and KM139 (pRK415–p60126). All these strains had the same flagellar-dependent swimming speeds, but on soft media, the LpsI⁺ LpsII⁻ strains KM139 and KM139 (pRK415) swarmed significantly faster than the other LpsI⁺ LpsII⁺ strains. Such interstrain differences in swarming motility were more pronounced on 0.4% than on 0.5% soft agar plates. These data show that the AZOBR_p60126-encoded putative glycosyltransferase significantly affects the lipopolysaccharide profile and, as a consequence, the social motility of azospirilla.     

Sculpting crystals one Burgers vector at a time: Toward colloidal lattice robot swarms

Plastic deformation of crystalline materials with isotropic particle attractions proceeds by the creation and migration of dislocations under the influence of external forces. If dislocations are produced and migrated under the action of local forces, then material shape change can occur without the application of surface forces. We investigate how particles with variable diameters can be embedded in colloidal monolayers to produce dislocations on demand. We find in simulation that when embedded clusters of variable diameter particles are taken through multiple cycles of swelling and shrinking, large cumulative plastic slip is produced by the creation and biased motion of dislocation pairs in the solid for embedded clusters of particular geometries. In this way, dislocations emitted by these clusters (biased “dislocation emitters”) can be used to reshape colloidal matter. Our results are also applicable to larger-scale swarms of robotic particles that organize into dense ordered two-dimensional (2D) arrangements. We conclude with a discussion of how dislocations fulfill for colloids the role sought by “metamodules” in lattice robotics research and show how successive applications of shear as a unit operation can produce shape change through slicing and swirling.

With sufficient miniaturization it is possible to create materials that at the human length scale appear continuous but are in fact composed of discrete subunits that have been engineered. When the subunits are small and relatively simple, such materials are often referred to as “metamaterials.” As an example, the manipulation of optical material properties by engineering the response of so-called “metaatoms” has seen significant success (1, 2).When the complexity of the subunit is increased to the point where each “module” has some combination of independent sensing, actuation, self-propulsion, and communication ability, then the material is described as a modular robot (3). Many forms of reconfigurable modular robots have been proposed and prototyped. A subset of studies frames the aggregate collection of robotic modules as a new metamaterial type. Lattice robots (4–6), “programmable matter” (7), the “slimebot” (8), and the “particle robot” (9) are examples of this school of thought. While simulations of modular robots have advanced to the million-module scale (10–12), experimental realization of more than 100 robotic modules in the laboratory remains challenging [with the notable exception of Rubenstein et al. (13)]. The demanding requirements of robotic function necessitate considerable complexity and cost, restricting experimental studies to the macroscopic scale.Metamaterials and active matter, while conceptually linked, differ greatly in their subunit cost and in functionalities such as environment sensing, communication, or information processing capacity. In the last several decades, chemists have advanced techniques that permit submicrometer particles to perform work locally, increasing the functions available to very small subunits. For the first time, it is feasible to consider a continuum-scale material composed of devices (active particles) that locally perform work in a designed way. Swarms of self-propelled colloids can be controlled with a global field, such as light intensity (14), chemical signaling (15), or a rotating magnetic field (16–20). The behavior of such nonequilibrium colloidal swarms relies heavily on emergent phenomena to take the place of integrated communication and control often present in macroscale robotic swarms. Despite the stochasticity inherent in emergent interactions, certain actions are predictable, controllable, and repeatable.A fundamental function of a modular robot is to reconfigure its shape. Many applications of interest rely on shape change: moving cargo, crawling past obstacles, engulfing cargo, etc. When the number of subunits is small and subunit complexity is high, algorithmic planning can achieve near optimal reconfiguration characteristics. For colloidal-scale metamaterials composed of many thousands or millions of individual subunits, with no ability to locally communicate or algorithmically plan their actions, another approach is needed. Shape change on this scale might be better thought of as a controlled plastic deformation. In systems composed of isotropically attracting subunits (such as colloidal crystals of sticky hard spheres or atomic metals), plastic deformation is controlled by the production and migration of defects known as dislocations (21, 22). The creation and control of two-dimensional (2D) dislocations via optical fields have been reported in colloidal systems (23, 24).In this paper we explore how quasi-2D crystallites of colloids can be reshaped by the production and migration of dislocation defects. We present here a simplistic scheme of dislocation creation based on swelling the size of an anisotropically shaped subset of the crystallite’s particles. This approach to material reconfiguration relies upon consistent creation of dislocations (in our study, at the surface of the embedded swellable cluster) and a sink to absorb dislocations. The simplest such sink is a free surface of the material domain; however, other sinks include internal grain boundaries within extended crystalline domains or even other (complementary) dislocations. In this study we focus on the case of a finite-size crystallite domain as the material to be reconfigured and therefore use the material edges as the primary dislocation sink. Such finite-sized crystallites necessitate attractive interactions between the subunits. In a colloidal setting, such attraction might be supplied by depletion (25), electric fields (26, 27), magnetic fields (28), particle activity (14), DNA functionalization (29), or a variety of other tactics (30, 31). The important characteristic of the interparticle attraction here is isotropy. Strongly directional interactions will not permit the free motion of dislocations.We simulate a colloidal crystalline monolayer of finite size, such as might be prepared by sedimentation of sticky colloidal spheres on a flat surface. A cluster of colloids with variable diameter [achieved via, e.g., heating (32, 33), solvent swelling (34, 35), or other methods (36)] is embedded in this monolayer. We show that global control over a single degree of freedom (the diameter of the particles in the embedded cluster) is sufficient to effect significant reshaping of the crystallite’s boundary by the creation and emission of dislocations. Our results are also applicable to certain classes of “lattice robots,” which operate at larger length scales (4, 5).We begin with an overview of our concept to use dislocations to create colloidal shape shifters. Next, we show several examples of reshaping in finite-sized crystallites and bulk domains. We then present the necessary geometric features of the embedded clusters and the importance of anisotropy in dislocation emission. We conclude with a discussion of how this study relates to existing work on reconfiguration schemes for modular robots.     

鱼腥草素钠抑制铜绿假单胞菌致病相关运动能力的研究

鱼腥草素钠(sodium houttuyfonate,SH)是一种有效抑制致病菌感染的传统中药鱼腥草的活性成分的衍生物,但其抑菌机制尚没有被阐明.本研究通过铜绿假单胞菌运动能力试验发现,SH可在有效抑制与细菌致病性相关的浮泳运动、蹭行运动和集群运动能力.平板分析法实验结果表明24 h内SH对浮泳运动、蹭行运动和48 h内SH对集群运动的抑制趋势呈现显著的浓度依赖性特点;并且在1倍SH最小抑菌浓度(minimum inhibitory concentration,MIC) (512 mg·L-1)条件下,细菌的运动能力和阳性对照阿奇霉素(1倍MIC 16mg·L-1)一样基本丧失.进一步,基因表达分析发现SH显著抑制铜绿假单胞菌的鞭毛和菌毛结构基因flgB和pilG的表达,提示SH抑制细菌运动能力的可能机制是通过抑制细菌运动相关的特殊结构鞭毛和菌毛的合成而产生.因此,该研究结果首次证明SH可有效抑制细菌的运动能力,并探讨了抑制机制,为该药物在临床上治疗条件性致病菌铜绿假单胞菌提供理论依据.     

金坛市6楼居民家中白蚁分飞解析

本文以2013年金坛市某6楼居民家中白蚁分飞为例,对其发生原因做了较为详细的推理分析,得出该分飞白蚁为住户携带家具至高层所导致。并结合气象条件,从生态适应的角度讨论其分飞时间,认为生活在苛刻环境下的白蚁(如没有水分给养)有分飞提前的可能性。最后提出几点工作建议,为今后类似高层白蚁防治提供参考。     

From the Cover: Kin discrimination between sympatric Bacillus subtilis isolates

Kin discrimination, broadly defined as differential treatment of conspecifics according to their relatedness, could help biological systems direct cooperative behavior toward their relatives. Here we investigated the ability of the soil bacterium Bacillus subtilis to discriminate kin from nonkin in the context of swarming, a cooperative multicellular behavior. We tested a collection of sympatric conspecifics from soil in pairwise combinations and found that despite their history of coexistence, the vast majority formed distinct boundaries when the swarms met. Some swarms did merge, and most interestingly, this behavior was only seen in the most highly related strain pairs. Overall the swarm interaction phenotype strongly correlated with phylogenetic relatedness, indicative of kin discrimination. Using a subset of strains, we examined cocolonization patterns on plant roots. Pairs of kin strains were able to cocolonize roots and formed a mixed-strain biofilm. In contrast, inoculating roots with pairs of nonkin strains resulted in biofilms consisting primarily of one strain, suggestive of an antagonistic interaction among nonkin strains. This study firmly establishes kin discrimination in a bacterial multicellular setting and suggests its potential effect on ecological interactions.Living systems that exhibit cooperation such as insect colonies and multicellular organisms are theoretically open to exploitation by parasites or free-loaders that do not contribute, which can lead to collapse of the system. Kin discrimination is believed to stabilize cooperation by preferentially directing cooperative traits toward genetic relatives who likely share the genes for the traits (1–3). However, kin selection may not be the only mechanism driving evolution of kin discrimination. In fact, recent work indicates that bacterial kin discrimination can also evolve indirectly, possibly as a byproduct of other adaptations (4). The phenomenon of kin discrimination has been studied from many different angles and in different organisms including animals (5), plants (6), social insects (7), amoeba (8, 9), and bacteria (10). Microbes have a rich and varied social life, reflected in competition, cheating, altruism, and cooperation (11, 12). An example of bacterial cooperative behavior is surface swarming, a multicellular movement of flagellated bacteria over solid surfaces. It is dependent on secreted surfactants needed for efficient surface translocation (13). The ability to swarm is a potent survival strategy in low-nutrient, spatially structured environments such as soils and the rhizosphere, where plant exudates are a source of food for which microbes compete (14). Swarming is also important for biofilm assembly and colonization of plant roots (14, 15). Within swarms, kin discrimination may enhance cooperation among the kin swarmer cells by preventing the invasion of competing or antagonistic bacteria. However, in Proteus mirabilis, kin discrimination was associated with harmful behaviors, which occur only between nonkin (16).Discrimination of self and nonself between interacting swarms has been well studied in P. mirabilis. This Gram-negative urinary tract pathogen exhibits merging of genetically identical swarms, whereas swarms composed of different strains form a visible boundary and do not merge (16–20). Swarm merging has not been strictly correlated with relatedness in P. mirabilis, however, due to the lack of a diverse set of strains. The ability to discriminate between self and nonself during swarming was also studied in Myxobacteria, where incompatibility was always observed between unrelated strains (10). Incompatibility was even detected among some strains with 100% multilocus sequence tag identity (10) and was recently shown to evolve through modifications in many independent genetic loci (4).The soil bacterium Bacillus subtilis has been shown to exhibit several cooperative traits, yet its potential for kin discrimination during cooperative movement over surfaces has not been addressed before. We address this gap in knowledge by using a swarming assay and a collection of 39 highly related B. subtilis strains isolated from two 1-cm³ soil samples (21) that have been well-analyzed phylogenetically. The strains represent a sympatric population that coexisted at micrometer distances in soil and may have had a potential history of interactions in situ. These 39 strains are thus especially interesting candidates to study bacterial kin discrimination.We show that this group of sympatric B. subtilis isolates can discriminate kin from nonkin. This phenomenon was reflected in the appearance of a striking boundary line between nonkin swarm groups, which was always observed between swarms of distantly related strains within our collection. The frequency of boundary lines was higher among strains with lower phylogenetic relatedness, whereas the opposite was the case for merging strains, which tended to have very high phylogenetic relatedness. Finally, a subset of strain pairs were mixed and used to inoculate Arabidopsis thaliana roots. Therein, kin strains coexisted close to each other, whereas nonkin strains generally did not. These observations suggest that antagonistic interactions among nonkin may shape B. subtilis sociality in a setting other than meeting swarms.     

Collective motion and density fluctuations in bacterial colonies

Flocking birds, fish schools, and insect swarms are familiar examples of collective motion that plays a role in a range of problems, such as spreading of diseases. Models have provided a qualitative understanding of the collective motion, but progress has been hindered by the lack of detailed experimental data. Here we report simultaneous measurements of the positions, velocities, and orientations as a function of time for up to a thousand wild-type Bacillus subtilis bacteria in a colony. The bacteria spontaneously form closely packed dynamic clusters within which they move cooperatively. The number of bacteria in a cluster exhibits a power-law distribution truncated by an exponential tail. The probability of finding clusters with large numbers of bacteria grows markedly as the bacterial density increases. The number of bacteria per unit area exhibits fluctuations far larger than those for populations in thermal equilibrium. Such “giant number fluctuations” have been found in models and in experiments on inert systems but not observed previously in a biological system. Our results demonstrate that bacteria are an excellent system to study the general phenomenon of collective motion.