Locomotion and phenotypic transformation of the amoeboflagellate Naegleria gruberi at the water-air interface

The protozoon Naegleria gruberi is able to carry out amoeboid locomotion at the water-air interface in a manner indistinguishable from that exhibited on solid substrata with the production of focal contacts and associated filopodia. The speed of locomotion at this interface can be modulated by changes in electrolyte concentrations; these speed changes are identical to those observed at a water-glass interface. The nature of the water-air interface is discussed leading to the hypothesis that surface tension alone could provide suitable properties for the adhesion and translocation of amoebae at this interface without necessitating specific, absorbed molecules. The temporary swimming flagellate stage of Naegleria is able to dock at the interface, make stable adhesions to it, and revert to the amoeboid phenotype. Conversely, amoebae resident at the water-air interface can transform to swimming flagellates and escape into the bulk liquid phase. We report the presence of Naegleria amoebae in the surface microlayers of natural ponds; thus, in freshwater bodies there may be active shuttling of Naegleria amoebae from the benthos to the surface microlayers by means of the non-feeding, swimming flagellate phenotype. The public health implication of this behaviour in the case of the pathogenic relative, Naegleria fowleri, is discussed.     

气候变暖与富营养化交互作用对浅水湖泊水-气界面N2O通量的影响

研究通过构建中尺度控温围隔模拟系统,模拟21世纪末气候变化与富营养化趋势,探讨未来气候变暖与富营养化趋势下浅水湖泊水-气界面N₂O交换过程的响应特征及机制。结果表明:(1)恒定与波动升温引起的代谢过程及生物间相互作用的改变显著促进了水-气界面间N₂O的排放及年累积释放量,而磷的添加可能因为影响了水体中反硝化代谢的效率而削弱了水-气界面N₂O排放及年累积释放量;(2)实验期间随季节转换,控制系统内优势的初级生产者由水生植物转变为浮游植物,水体中有机质含量亦不断积累,研究结果表明季节变化及初级生产者转换均对水-气界面N₂O排放量的增加起到了显著促进作用。在气候变化与富营养化趋势下浅水湖泊水-气界面的N₂O交换过程主要受到水体中氮磷含量及其比例的变化、水生植物与浮游植物的转换及有机质的积累过程的影响。因此,气候变暖(恒定和波动升温)能够促进湖泊N₂O排放量的上升,而变暖和营养盐的交互作用会使水-气界面N₂O交换更加复杂。     

How a fungus escapes the water to grow into the air

Fungi are well known to the casual observer for producing water-repelling aerial moulds and elaborate fruiting bodies such as mushrooms and polypores. Filamentous fungi colonize moist substrates (such as wood) and have to breach the water-air interface to grow into the air. Animals and plants breach this interface by mechanical force. Here, we show that a filamentous fungus such as Schizophyllum commune first has to reduce the water surface tension before its hyphae can escape the aqueous phase to form aerial structures such as aerial hyphae or fruiting bodies. The large drop in surface tension (from 72 to 24 mJ m-2) results from self-assembly of a secreted hydrophobin (SC3) into a stable amphipathic protein film at the water-air interface. Other, but not all, surface-active molecules (that is, other class I hydrophobins and streptofactin from Streptomyces tendae) can substitute for SC3 in the medium. This demonstrates that hydrophobins not only have a function at the hyphal surface but also at the medium-air interface, which explains why fungi secrete large amounts of hydrophobin into their aqueous surroundings.     

Distribution of protozoa in subsurface sediments of a pristine groundwater study site in oklahoma

Sediment core samples were obtained at a groundwater study site in Oklahoma in January and June 1985. Most-probable-number estimates showed that protozoan numbers declined steeply with depth in subsoil. Flagellates and amoebae dominated the protozoan population, which declined to a most probable number of 28 . g (dry weight) in a clay loam layer at the bottom of the unsaturated zone. Samples from a texturally variable interface zone between 3 and 4 m down also were variable in their content of protozoa. Four contiguous clay loam samples in a single core from this zone contained variable numbers of amoebae ranging from 0.2 to 44 . g (dry weight). However, a sandy clay loam layer at the bottom of the core contained a mixture of flagellates and amoebae with a combined population density of 67 . g (dry weight). A slow-growing filose amoeba was isolated from interface zone samples and was tentatively classified in a new family in the order Aconchulinida. Protozoa were not detected in the saturated zone except in a very permeable gravelly, loamy sand layer at a depth of approximately 7.5 m. Low numbers (4 to 6 . g [dry weight]) of surface-type flagellates and amoebae, as well as the filose amoeba seen in the interface zone, were observed in this layer. Acid-treated and untreated samples contained equivalent numbers of protozoa, showing that the majority of protozoa in the layer at 7.5 m and the interface zone samples were encysted. Increased numbers of bacteria also were found in the layer at 7.5 m, indicating that it was biologically more active than other saturated-zone layers. Cyanobacteria grew in illuminated samples from this layer, suggesting that it may be connected hydrologically to a nearby river.     

鄱阳湖秋季水-气界面CH4排放通量的区域差异及影响因素

有限的观测点以及空间的异质性已经成为准确估算湖泊水-气界面CH4通量的挑战。鄱阳湖是我国最大的淡水湖,为了解秋季湖区水-气界面的CH4排放通量,2010年10月利用密闭静态箱-气象色谱法对星子、都昌、南矶山和吴城4个湖区水-气界面CH4排放通量及气象、底泥、水体等因素进行了测定。研究表明,都昌湖区CH4排放通量平均值为0.26mg·m-2·h-1,显著高于星子(0.15mg·m-2·h-1)、吴城(0.13mg·m-2·h-1)和南矶山(0.10mg·m-2·h-1)湖区。鄱阳湖水-气界面秋季CH4排放通量平均为0.17mg·m-2·h-1,变异系数为58.6%。相关分析表明,风速显著影响CH4排放通量(P<0.01)。在排除风速>5m·s-1的数据后,底泥有机碳以及水体铵态氮含量与CH4排放通量显著相关,而水体DOC含量与CH4排放通量呈显著负相关(P<0.05)。对鄱阳湖CH4排放量的精确估算,依赖于较广区域和较长时间的观测。     

Surface-plasmon microscopic observation of site-selective recognition reactions

We demonstrate that surface-plasmon microscopy allows one to monitor the specific binding of streptavidin to biotinylated lipid molecules selectively enriched in one of the two coexisting phase domains of a phospholipid monolayer transferred in its phase transition region from the water-air interface to a solid support.     

不同许氏平鮋与栉孔扇贝养殖系统水-气界面CO2通量及其主要影响因子

本试验建立了4组中型实验生态系统,即空白对照系统、许氏平鮋单养系统、栉孔扇贝单养系统和许氏平鮋-栉孔扇贝混养系统,利用静态箱-气相色谱法对各养殖系统水-气界面CO2通量进行观测,并测定养殖水体物理、化学和生物指标.结果表明:试验期间,空白对照系统表现为稳定的对大气CO2的源,平均通量为12.42 mg·m^-2·h^-1.扇贝单养系统在试验前期和中期为CO2的源,后期为CO2的汇,试验期间整体为CO2的源,平均通量为10.95 mg·m^-2·h^-1.许氏平鮋单养系统和许氏平鮋-栉孔扇贝混养系统在试验前期表现为CO2源,实验中后期为CO2的汇,试验期间平均通量分别为-3.53和-10.49 mg·m^-2·h^-1,整体上均为对大气CO2的汇.回归分析结果显示,水体pH是水-气界面CO2通量较好的预测因子,pH=8.25是系统水-气界面碳源/汇功能发生转变的临界值.线性混合模型分析结果显示,水体净初级生产力是影响各系统水-气界面CO2通量的主要因子,表明浮游植物是调控系统水-气界面CO2通量的主要生物内动力.在本试验混养密度条件下的栉孔扇贝能一定程度上促进浮游植物生物量和水体初级生产力,从而增强系统水-气界面CO2的碳汇功能.     

Structural and functional role of the disulfide bridges in the hydrophobin SC3

Hydrophobins function in fungal development by self-assembly at hydrophobic-hydrophilic interfaces such as the interface between the fungal cell wall and the air or a hydrophobic solid. These proteins contain eight conserved cysteine residues that form four disulfide bonds. To study the effect of the disulfide bridges on the self-assembly, the disulfides of the SC3 hydrophobin were reduced with 1,4-dithiothreitol. The free thiols were then blocked with either iodoacetic acid (IAA) or iodoacetamide (IAM), introducing eight or zero negative charges, respectively. Circular dichroism and infrared spectroscopy showed that after opening of the disulfide bridges SC3 is initially unfolded. IAA-SC3 did not self-assemble at the air-water interface upon shaking an aqueous solution. Remarkably, after drying down IAA-SC3 or after exposing it to Teflon, it refolded into a structure similar to that observed for native SC3 at these interfaces. Iodoacetamide-SC3 on the other hand, which does not contain extra charges, spontaneously refolded in water in the amyloid-like beta-sheet conformation, characteristic for SC3 assembled at the water-air interface. From this we conclude that the disulfide bridges of SC3 are not directly involved in self-assembly but keep hydrophobin monomers soluble in the fungal cell or its aqueous environment, preventing premature self-assembly.     

Entrapment of Ciliates at the Water-Air Interface

The importance of water-air interfaces (WAI) on microorganism activities has been recognized by many researchers. In this paper, we report a novel phenomenon: the entrapment of ciliates Tetrahymena at the WAI. We first characterized the behavior of cells at the interface and showed that the cells'' swimming velocity was considerably reduced at the WAI. To verify the possible causes of the entrapment, we investigated the effects of positive chemotaxis for oxygen, negative geotaxis and surface properties. Even though the taxes were still effective, the entrapment phenomenon was not dependent on the physiological conditions, but was instead affected by the physical properties at the interface. This knowledge is useful for a better understanding of the physiology of microorganisms at interfaces in nature and in industry.     

Genome Sequence of “Candidatus Microthrix parvicella” Bio17-1, a Long-Chain-Fatty-Acid-Accumulating Filamentous Actinobacterium from a Biological Wastewater Treatment Plant

“Candidatus Microthrix” bacteria are deeply branching filamentous actinobacteria which occur at the water-air interface of biological wastewater treatment plants, where they are often responsible for foaming and bulking. Here, we report the first draft genome sequence of a strain from this genus: “Candidatus Microthrix parvicella” strain Bio17-1.     

Amoebic grazing of freshwater Synechococcus strains rich in phycocyanin

Fifteen strains of naked amoebae were presented with 19 strains of Synechococcus on an agar surface. After 14 days of incubation, each of the 285 combinations yielded one of three responses. 42.1% of combinations showed clearing (digestion) of the Synechococcus (C), 56.5% of combinations showed no clearing of the Synechococcus (N) while 1.4% of combinations showed partial clearing of the Synechococcus (P). In general, the Synechococcus strains showed variability in their susceptibility to digestion by the amoebae and the amoebae showed variability in their ability to digest the Synechococcus strains. There was no evidence for amoebae actively selecting profitable prey and equivalent-sized Synechococcus strains were ingested at the same rate, irrespective of their fate. There was some evidence of 'size-selective' grazing in that amoebae ingested the smaller Synechococcus strains at higher rates than the larger strains. However, there was no correlation between prey size and their ultimate fate. These data suggest that amoebae are not selective with regard to the ingestion of synechococci, but that 'selection' occurs at the digestion stage, i.e. whether the synechococci are digested or not.     

Concanavalin A-mediated agglutination and distribution of concanavalin A-binding sites in Acanthamoeba following treatment with colchicine and cytochalasin B

Incubation of Acanthamoeba castellanii (Neff strain) with FITC-ConA (15 micrograms/ml) resulted in the appearance of patches of fluorescence on the amoebae within 2 min of incubation. These patches disappeared following treatment of the amoebae with alpha-MeMan. Pretreatment of the amoebae with colchicine or cytochalasin B or with colchicine and cytochalasin B in combination did not significantly alter the distribution pattern of fluorescence in the amoebae. 2,4-Dinitrophenol and incubation at 4 degrees C on the other hand decreased the degree of patching of the amoebae. Pretreatment with 2,4-dinitrophenol and incubation at 4 degrees C also decreased the ConA-mediated agglutination of the amoebae. No effect on the ConA-mediated agglutination was, however, observed following pretreatment of the amoebae with colchicine and cytochalasin B neither alone nor in combination. Our results indicate that ConA-mediated agglutination and long-range ConA-receptor mobility in the Acanthamoeba are not under the control of structures sensitive to cytochalasin B or colchicine.     

Hydrophobins, the fungal coat unravelled

Hydrophobins are among the most surface active molecules and self-assemble at any hydrophilic-hydrophobic interface into an amphipathic film. These small secreted proteins of about 100 amino acids can be used to make hydrophilic surfaces hydrophobic and hydrophobic surfaces hydrophilic. Although differences in the biophysical properties of hydrophobins have not yet been related to differences in primary structure it has been established that the N-terminal part, at least partly, determines wettability of the hydrophilic side of the assemblage, while the eight conserved cysteine residues that form four disulphide bridges prevent self-assembly of the hydrophobin in the absence of a hydrophilic-hydrophobic interface. Three conformations of class I hydrophobins have been identified: the monomeric state, which is soluble in water, the alpha-helical state, which is the result of self-assembly at a hydrophobic solid, and the beta-sheet state, which is formed during self-assembly at the water-air interface. Experimental evidence strongly indicates that the alpha-helical state is an intermediate and that the beta-sheet state is the end form of assembly. The latter state has a typical ultrastructure of a mosaic of 10 nm wide rodlets, which have been shown to resemble the amyloid fibrils.     

Evidence for a Second Chemotactic System in the Cellular Slime Mold, Dictyostelium discoideum

An unknown substance found in bacteria (Escherichia coli) is especially effective in attracting the vegetative amoebae of the cellular slime mold, Dictyostelium discoideum. However, the aggregating amoebae are not attracted to it at all. On the other hand, the vegetative amoebae show very little chemotactic response to cyclic adenosine monophosphate (cyclic AMP), whereas the aggregating amoebae are exceptionally responsive to it. It is suggested that the new factor may be used in food seeking, whereas cyclic AMP, the chemotactic substance responsible for aggregation, is the acrasin of this species. The important point is that the amoebae are differentially stage-specific in their responses to these two chemotactic agents.     

The survival of habitat desiccation by air breathing clariid catfishes

Synopsis African and Asian clariid catfishes have long been reputed to survive habitat desiccation by remaining dormant under dry mud or sand, in the manner of the lungfish Protopterus. A literature review of aestivation in Clarias species reveals that many of the early accounts are based on hearsay, native superstition or confusion with the lungfish. Recent evidence indicates that clariids may survive whilst buried in moist sand, or in burrows with water-air interface, but that survival is unlikely in dried mud or sand     

High numbers of naked amoebae in the planktonic waters of a mangrove stand in southern Florida, USA

This is the first study to examine the abundance of naked amoebae in the water column of a mangrove stand. A total of 37 different morphotypes was noted and at least 13 of these are probably new species. Over a one-year sampling interval, amoebae averaged 35,400 cells liter(-1) (range 2,000-104,000) by an indirect enrichment cultivation method. Densities in the upper end of this range are the highest ever reported for any planktonic habitat. Variation between samples was related to the quantity of suspended aggregates (flocs) in the water column emphasizing that amoebae are usually floc-associated. The study also showed that it is essential to disrupt floc material prior to withdrawing sample aliquots for the indirect counting method since several amoebae can occupy the interstices of aggregates. There is concern that indirect enumeration methods that require organisms to be cultured in the laboratory seriously underestimate the true count. A direct counting method using acridine orange staining and epifluorescence microscopy was attempted to assess the possible magnitude of the error associated with indirect counting. While this direct method had limitations, notably the difficulty of unambiguously differentiating between small amoebae and nanoflagellates, the results suggested that the indirect method gave estimates that were close to the true count (within a factor of two). Mangrove waters are rich in heterotrophic protozoa (approximately 3 x 10 liter(-1)) and while the heterotrophic flagellates are by far the dominant group, naked amoebae outnumber ciliates some 20-fold. The ecological consequences of high numbers of amoebae, particularly the common small forms less than 10 microm in length, need to be examined for these important coastal sites.     

Characteristics and Mechanisms of Cardiopulmonary Injury Caused by Mine Blasts in Shoals: A Randomized Controlled Study in a Rabbit Model

Background

Because the characteristics of blast waves in water are different from those in air and because kinetic energy is liberated by a pressure wave at the water-air interface, thoracic injuries from mine blasts in shoals may be serious. The aim of the present study was to investigate the characteristics and mechanisms of cardiopulmonary injury caused by mine blasts in shoals.

Methods

To study the characteristics of cardiopulmonary injury, 56 animals were divided randomly into three experimental groups (12 animals in the sham group, 22 animals in the land group and 22 animals in the shoal group). To examine the biomechanics of injury, 20 animals were divided randomly into the land group and the shoal group. In the experimental model, the water surface was at the level of the rabbit''s xiphoid process, and paper electric detonators (600 mg RDX) were used to simulate mines. Electrocardiography and echocardiography were conducted, and arterial blood gases, serum levels of cardiac troponin I and creatine kinase-MB and other physiologic parameters were measured over a 12-hour period after detonation. Pressures in the thorax and abdomen and the acceleration of the thorax were measured.

Conclusion

The results indicate that severe cardiopulmonary injury and dysfunction occur following exposure to mine blasts in shoals. Therefore, the mechanisms of cardiopulmonary injury may result from shear waves that produce strain at the water-air interface. Another mechanism of injury includes the propagation of the shock wave from the planta to the thorax, which causes a much higher peak overpressure in the abdomen than in the thorax; as a result, the abdominal organs and diaphragm are thrust into the thorax, damaging the lungs and heart.     

A Gene, ALCA, Affecting the Life Cycle Form Expressed in PHYSARUM POLYCEPHALUM

The usual sequence of forms in the Physarum polycephalum life cycle is plasmodium-spore-amoeba-plasmodium. So-called "amoebaless life cycle" or alc mutants of this Myxomycete undergo a simplified plasmodium-spore-plasmodium life cycle. We have analyzed three independently isolated alc mutants and found in each case that the failure of the spores to give rise to amoebae is due to a recessive Mendelian allele. The three mutations are tightly linked to one another and belong to a single complementation group, alcA. The mutations are pleiotropic, not only interfering with the establishment of the amoebal form at spore germination, but also affecting the phenotype of alc amoebae, which occasionally arise from alc spores. The alc amoebae (1) grow more slowly than wild type, particularly at elevated temperatures; (2) tend to transform directly into plasmodia, circumventing the sexual fusion of amoebae that usually accompanies plasmodium formation; and (3) form plasmodia by the sexual mechanism less efficiently than wild-type amoebae. The various effects of an alc mutation seem to derive from mutation of a single gene, since reversion for one effect is always accompanied by reversion for the other effects. Moreover, a mutation, aptA1, that blocks direct plasmodium formation by alcA amoebae, also increases their growth rate to near normal. The manner of plasmodium formation in alcA strains differs significantly from that in another class of mutants, the gad mutants. Unlike gad amoebae, alcA amoebae need not reach a critical density in order to differentiate directly into plasmodia and do not respond to the extracellular inducer of differentiation. In addition, alcA differentiation is not prevented by a mutation, npfA1, that blocks direct differentiation by most gad amoebae.     

Changes in the DNA content of amoebae of Dictyostelium discoideum during growth and development.

A fluorimetric assay has been used to determine the DNA content of amoebae of Dictyostelium discoideum during growth and development. Amoebae grown in axenic culture tended to be multinucleate and had a greater DNA content than amoebae grown with a bacterial substrate, which were mononucleate. During the first 10 h of development there was little change in the DNA content of amoebae grown with a bacterial substrate, but the average DNA content per cell in amoebae grown axenically decreased as the amoebae became virtually mononucleate. Amoebae at 10 h development that had been harvested during exponential axenic growth were divided into two populations by countercurrent distribution in a polymer two-phase system. DNA content indicated that one population was largely in the G2-phase of the cell cycle, whereas the other population was largely in the G1-phase. Similar results were obtained at 10 h development with amoebae harvested during the stationary phase of axenic growth, although these amoebae start development all in the G2-phase of the cell cycle. Spores had a low DNA content, indicating that they were in G1-phase. It is proposed that all amoebae in G2-phase after early development differentiate, after mitosis, into spores and that stalk cells are formed from amoebae that remain in G1-phase after 10 h development.