Cd-Induced Apoptosis through the Mitochondrial Pathway in the Hepatopancreas of the Freshwater Crab Sinopotamon henanense

Cd is one of the most common pollutants in the environment that also induces the apoptosis. To explore the mechanism of apoptosis in the hepatopancreas, freshwater crab S. henanense were treated with 0, 3.56, 7.12, 14.25, 28.49 and 56.98 mg/L Cd for 72 h. Apoptosis was noticeable in every treatment group and necrosis was observed clearly in the high concentration Cd groups. Classical apoptotic bodies were found by transmission electronic microscopy, which revealed chromatin condensation under nuclear membrane and mitochondrial membrane rupture. An increasing number of autolysosomes, damaged rough endoplamic reticulum and Golgi complex were observed as the Cd concentration increase. Brown colored apoptotic cells were detected by the TUNEL test in all Cd-treatment groups. The apoptosis index increased following the elevation of Cd concentration and got 32.9% in the highest Cd group. Caspase-9 and caspase-3 activities increased in the lower Cd treatment groups but no changes in the higher Cd concentration groups (comparing to the control group). The activity of caspase-8 did not change significantly. No significant change in the content of mitochondrial cytochrome c (cyt c) in Cd exposed groups except the decrease in the 56.98 mg/L group. In crabs treated with 3.56, 7.12 and 14.25 mg/L Cd, hyperpolarization of mitochondrial membrane potential (Δψ_m) significantly increased. These results implied that apoptosis in the hepatopancreas induced by Cd occurrs through the mitochondrial caspase-dependent pathway. However, whether there are other apoptotic pathways needs to be studied further.     

Cadmium Induces Apoptosis in Freshwater Crab Sinopotamon henanense through Activating Calcium Signal Transduction Pathway

Calcium ion (Ca²⁺) is one of the key intracellular signals, which is implicated in the regulation of cell functions such as impregnation, cell proliferation, differentiation and death. Cadmium (Cd) is a toxic environmental pollutant that can disturb cell functions and even lead to cell death. Recently, we have found that Cd induced apoptosis in gill cells of the freshwater crab Sinopotamon henanense via caspase activation. In the present study, we further investigated the role of calcium signaling in the Cd-induced apoptosis in the animals. Our data showed that Cd triggered gill cell apoptosis which is evidenced by apoptotic DNA fragmentation, activations of caspases-3, -8 and -9 and the presence of apoptotic morphological features. Moreover, Cd elevated the intracellular concentration of Ca²⁺, the protein concentration of calmodulin (CaM) and the activity of Ca²⁺-ATPase in the gill cells of the crabs. Pretreatment of the animals with ethylene glycol-bis-(b-aminoethyl ether)-N,N,N’,N’-tetraacetic acid (EGTA), Ca²⁺ chelator, inhibited Cd-induced activation of caspases-3, -8 and -9 as well as blocked the Cd-triggered apoptotic DNA fragmentation. The apoptotic morphological features were no longer observed in gill cells pretreated with the Ca²⁺ signaling inhibitors before Cd treatment. Our results indicate that Cd evokes gill cell apoptosis through activating Ca²⁺-CaM signaling transduction pathway.     

Cytoplasmic Bacteria and the Autophagic Pathway

Cytoplasmic bacteria may assist in our study of the autophagic pathway. This review highlights the use of Listeria monocytogenes for examining the assembly of autophagic vacuoles in mammalian cells. Inhibiting protein synthesis of cytoplasmic L. monocytogenes results in their being sequestered into the autophagic pathway. Autophagic vacuoles form around the easily identified bacterial particles making the assembly process easy to study using morphological and biochemical methods. L. monocytogenes, which appears to be ideally adapted to life in the cell cytoplasm, does not normally become a target of autophagy. In model systems the bacteria thrive within host cell cytoplasm, indicating the importance of de novo protein synthesis in avoiding the autophagic pathway. This observation indicates an interesting opportunity for identifying the bacterial mechanisms that are mobilized to avoid the autophagic pathway.     

Antibody Constant Region Peptides Can Display Immunomodulatory Activity through Activation of the Dectin-1 Signalling Pathway

We previously reported that a synthetic peptide with sequence identical to a CDR of a mouse monoclonal antibody specific for difucosyl human blood group A exerted an immunomodulatory activity on murine macrophages. It was therapeutic against systemic candidiasis without possessing direct candidacidal properties. Here we demonstrate that a selected peptide, N10K, putatively deriving from the enzymatic cleavage of the constant region (Fc) of human IgG(1), is able to induce IL-6 secretion and pIkB-α activation. More importantly, it causes an up-regulation of Dectin-1 expression. This leads to an increased activation of β-glucan-induced pSyk, CARD9 and pIkB-α, and an increase in the production of pro-inflammatory cytokines such as IL-6, IL-12, IL-1β and TNF-α. The increased activation of this pathway coincides with an augmented phagocytosis of non opsonized Candida albicans cells by monocytes. The findings suggest that some Fc-peptides, potentially deriving from the proteolysis of immunoglobulins, may cause an unexpected immunoregulation in a way reminiscent of innate immunity molecules.     

Bacteria Associated with the Gills of Salmonid Fishes in Freshwater

The bacteria on the gills of 7 species of freshwater salmonid fishes were examined qualitatively and quantitatively. Both wild and hatchery cultured salmonids were examined. The former were obtained from 12 different locations in British Columbia. Species of Pseudomonas and Cytophaga predominated on both groups of fish. The microflora of the wild fish also contained Aeromonas and members of the Brevibacterium –coryneform– Erysipelothrix group. The microflora of cultured fish was less varied. As many as 10⁶ viable organisms/g wet weight of gill tissue were recovered.     

Involvement of a Broccoli COQ5 Methyltransferase in the Production of Volatile Selenium Compounds

Selenium (Se) is an essential micronutrient for animals and humans but becomes toxic at high dosage. Biologically based Se volatilization, which converts Se into volatile compounds, provides an important means for cleanup of Se-polluted environments. To identify novel genes whose products are involved in Se volatilization from plants, a broccoli (Brassica oleracea var italica) cDNA encoding COQ5 methyltransferase (BoCOQ5-2) in the ubiquinone biosynthetic pathway was isolated. Its function was authenticated by complementing a yeast coq5 mutant and by detecting increased cellular ubiquinone levels in the BoCOQ5-2-transformed bacteria. BoCOQ5-2 was found to promote Se volatilization in both bacteria and transgenic Arabidopsis (Arabidopsis thaliana) plants. Bacteria expressing BoCOQ5-2 produced an over 160-fold increase in volatile Se compounds when they were exposed to selenate. Consequently, the BoCOQ5-2-transformed bacteria had dramatically enhanced tolerance to selenate and a reduced level of Se accumulation. Transgenic Arabidopsis expressing BoCOQ5-2 volatilized three times more Se than the vector-only control plants when treated with selenite and exhibited an increased tolerance to Se. In addition, the BoCOQ5-2 transgenic plants suppressed the generation of reactive oxygen species induced by selenite. BoCOQ5-2 represents, to our knowledge, the first plant enzyme that is not known to be directly involved in sulfur/Se metabolism yet was found to mediate Se volatilization. This discovery opens up new prospects regarding our understanding of the complete metabolism of Se and may lead to ways to modify Se-accumulator plants with increased efficiency for phytoremediation of Se-contaminated environments.Selenium (Se) has been studied extensively because of its essentiality for animals and humans and because of its toxicity at high dosage. Like a double-edged sword, Se is essential for the function of selenoenzymes but becomes toxic due to the nonspecific replacement of sulfur in sulfur-containing proteins (Stadtman, 1974; Brown and Shrift, 1982). The difference between beneficial and toxic levels of Se is quite narrow, making both Se deficiency and Se pollution common problems in different regions (Terry et al., 2000).Plants appear to be a promising solution for both sides of the Se problem (Pilon-Smits and LeDuc, 2009). Some crops have the ability to accumulate Se in health-beneficial chemical forms (Whanger, 2002; Dumont et al., 2006). Wheat (Triticum aestivum) grain grown in seleniferous soils accumulates selenomethionine (SeMet) and is one of the main dietary sources for Se (Lyons et al., 2005). Broccoli (Brassica oleracea var italica) has the ability to accumulate high level of Se-methylselenocysteine (SeMCys) and SeMet when grown on seleniferous soil (Cai et al., 1995). These selenoamino acids have been shown to be potent chemoprotective agents against cancer (Ip et al., 2000; Whanger, 2002). Other plant foods, such as garlic (Allium sativum) and Brazil nut (Bertholletia excelsa), have been enriched with Se and marketed as dietary Se supplements (Dumont et al., 2006). On the other hand, Se-hyperaccumulating plant species such as Astragalus bisulcatus and secondary accumulators such as Indian mustard (Brassica juncea) have attracted great interest for their ability to accumulate and volatilize Se for phytoremediation of Se-contaminated soils (Banuelos et al., 2007). Se volatilization converts highly toxic selenate and selenite into volatile dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe), which are 500 to 700 times less toxic (Wilber, 1980). This process provides a low-cost, environmentally friendly, and highly efficient approach for cleanup of Se-contaminated environments (Banuelos et al., 2002; Pilon-Smits, 2005).The conversion of inorganic forms of Se into volatile Se in plants is believed to occur via the sulfur metabolic pathway, as outlined in Figure 1 (Terry et al., 2000; Sors et al., 2005). Se is present in soils predominantly as selenate (SeO₄²⁻) and selenite (SeO₃²⁻). While selenate is actively taken up into plants through sulfur transporters, selenite enters plant cells passively. The reduction of these oxidized forms of Se results in the production of selenoamino acids, such as selenocysteine (SeCys) and SeMet (Fig. 1). In Se-nonaccumulator plants, SeCys and SeMet are readily incorporated into proteins nonspecifically. In Se-accumulating plants, they are metabolized primarily into various nonproteinogenic selenoamino acids. These selenoamino acids can be further metabolized into the volatile Se compounds DMSe and DMDSe. While Se nonaccumulators mainly volatilize DMSe, accumulators primarily emit DMDSe (Terry et al., 2000; Ellis and Salt, 2003). Although Se volatilization is an important step in the Se cycle and provides a protective mechanism for plants and microorganisms to avoid toxicity in seleniferous environments, this metabolic process is not well understood.Open in a separate windowFigure 1.Outline of Se metabolism in plants. The open arrows indicate that both selenate (SeO₄²⁻) and selenite (SeO₃²⁻) in soil are taken up into plants. Se metabolism from selenate involves a series of reduction steps to form selenide (Se²⁻), which is assimilated into the selenoamino acids SeCys and SeMet. These selenoamino acids can be methylated and further metabolized into the volatile Se compounds DMDSe and DMSe. Abbreviations not defined in the text: SeMMet, Se-methylmethionine; SeMCysMT, Se-methylselenocysteine methyltransferase; SMetMT, S-adenosyl-l-Met:l-Met S-methyltransferase.Several sulfur metabolic pathway enzymes have been evaluated for their roles in stimulating Se volatilization (Pilon-Smits and LeDuc, 2009). Cystathionine-γ-synthase is believed to be involved in the formation of SeMet. Overexpression of this enzyme resulted in a 2- to 3-fold increased rate of Se volatilization in transgenic Indian mustard (Van Huysen et al., 2003). S-Adenosyl-l-Met:l-Met S-methyltransferase is responsible for the methylation of SeMet to Se-methylselenomethionine. Overexpression of this enzyme in Escherichia coli produced a 10-fold increase in the rate of Se volatilization when the bacteria were supplied with SeMet (Tagmount et al., 2002). Similarly, expression of a Se-methylselenocysteine methyltransferase to methylate SeCys to SeMCys was shown to stimulate a 2- to 3-fold increase of Se volatilization in transgenic Indian mustard (LeDuc et al., 2004). Although increasing the activities of these known sulfur metabolism enzymes causes increased Se volatilization, additional proteins may be involved in this process (Van Hoewyk et al., 2008).Microorganisms adapted to high-Se-contaminated environments develop mechanisms to convert inorganic Se compounds into volatile forms. Several methyltransferases from these bacteria were reported to stimulate the emission of DMSe and DMDSe by unknown mechanisms (Ranjard et al., 2002, 2004; Swearingen et al., 2006). To identify novel plant genes whose products promote the production of volatile Se and to gain a better understanding of the metabolic processes associated with Se volatilization, we used a genomics-based approach to isolate genes from broccoli, a plant species known to have high capacity to volatilize Se (Duckart and Waldron, 1992; Terry et al., 1992). Using this approach, a broccoli COQ5 methyltransferase gene designated BoCOQ5-2 was isolated. Functional complementation of a yeast coq5 mutant by BoCOQ5-2 confirmed its identity. BoCOQ5-2 was found to promote Se volatilization when it was expressed in both bacteria and transgenic Arabidopsis (Arabidopsis thaliana).COQ5 genes encode C-methyltransferases involved in the biosynthesis of ubiquinone or coenzyme Q (Dibrov et al., 1997; Lee et al., 1997). Ubiquinone is an important lipid-soluble compound found in membranes of almost all living species. Ubiquinone is well known for its function as the electron carrier in the mitochondrial respiratory chain for energy production. Moreover, it is widely accepted that ubiquinone also participates in other cellular processes, such as control of cellular redox status and detoxification of harmful reactive oxygen species (ROS; Kawamukai, 2002; Turunen et al., 2004). Indeed, plants with high ubiquinone levels have been demonstrated to be able to suppress ROS generation (Ohara et al., 2004). Increased ubiquinone biosynthesis was found to be associated with increases in tolerance to a variety of stresses in both plants and other organisms (Ohara et al., 2004; Zhang et al., 2007). Se has been shown to induce the production of ROS in Arabidopsis (Tamaoki et al., 2008). Ubiquinone functioning as an antioxidant may protect cells against the oxidative stress to facilitate Se metabolism.BoCOQ5 methyltransferase represents, to our knowledge, the first plant enzyme that is not known to be involved in sulfur/Se metabolism yet mediates Se volatilization. The cloning and characterization of the methyltransferase from the economically important vegetable crop broccoli extends our understanding of factors affecting Se metabolism. Such information may lead to ways to generate modified Se-accumulator plants with increased efficiency in the phytoremediation of Se-contaminated soils.     

p53-p21通路抑制组蛋白甲基转移酶NSD2的表达

NSD2(nuclear receptor-binding SET domain 2)是一种在黑色素瘤等多种肿瘤细胞中高表达的组蛋白甲基转移酶,其在Wolf-Hirschhorn综合症(wolf-Hirschhorn syndrome,WHS)和多发性骨髓瘤(multiple myeloma,MM)疾病中表达异常的原因已经得到了较好的阐明。而NSD2在其它肿瘤中的表达为何失调还未阐明。本研究选用p53野生型的恶性黑色素瘤细胞系92-1作为细胞模型,采用DNA损伤试剂依托泊苷处理和RNA干扰技术,通过定量PCR和蛋白质免疫印迹的方法首次证实了p53-p21通路对NSD2具有抑制作用。     

A Guide to the Natural History of Freshwater Lake Bacteria

Summary: Freshwater bacteria are at the hub of biogeochemical cycles and control water quality in lakes. Despite this, little is known about the identity and ecology of functionally significant lake bacteria. Molecular studies have identified many abundant lake bacteria, but there is a large variation in the taxonomic or phylogenetic breadths among the methods used for this exploration. Because of this, an inconsistent and overlapping naming structure has developed for freshwater bacteria, creating a significant obstacle to identifying coherent ecological traits among these groups. A discourse that unites the field is sorely needed. Here we present a new freshwater lake phylogeny constructed from all published 16S rRNA gene sequences from lake epilimnia and propose a unifying vocabulary to discuss freshwater taxa. With this new vocabulary in place, we review the current information on the ecology, ecophysiology, and distribution of lake bacteria and highlight newly identified phylotypes. In the second part of our review, we conduct meta-analyses on the compiled data, identifying distribution patterns for bacterial phylotypes among biomes and across environmental gradients in lakes. We conclude by emphasizing the role that this review can play in providing a coherent framework for future studies.     

Biodiversity of Magnetotactic Bacteria in the Freshwater Lake Beloe Bordukovskoe,Russia

Microbiology - According to 16S rRNA gene- or genome-based phylogeny, magnetotactic bacteria (MTB) belong to diverse taxonomic groups. Here we analyzed the diversity of MTB in a sample taken from...     

Assessment of Salinity-Related Mortality of Freshwater Bacteria in the Saint Lawrence Estuary

The growth response of freshwater bacteria from the St. Lawrence River, exposed to brackish waters (salinity of 0 to 20(permil)) from the upper estuary, was assessed by a methodology requiring the combined use of dilution cultures and diffusion chambers. The longitudinal distribution of bacterial abundance in waters within this salinity range was also examined. Growth of the freshwater bacteria was reduced by 15 and 50% after exposure to salinities of 10 and 20(permil), respectively. At lower salinities, no growth reduction was observed, and at a salinity of 2(permil), growth was even stimulated. Longitudinal distribution data showed that bacterial abundance also peaked at this salinity. In contrast with an earlier hypothesis, this study shows that the decline of bacterial abundance in the low-salinity waters of the estuary is not caused by salinity-related mortality of freshwater bacteria, because the mixing time between fresh and marine (>20(permil)) waters is relatively long (days). However, results suggest that mortality of freshwater bacteria can be an important process in estuaries with shorter mixing times (hours). The combined use of diffusion chambers and dilution cultures proved to be a valuable methodology for assessing growth (or mortality) of bacteria exposed to environmental gradients.     

Carbon Monoxide Oxidation by Bacteria Associated with the Roots of Freshwater Macrophytes

The potential rates and control of aerobic root-associated carbon monoxide (CO) consumption were assessed by using excised plant roots from five common freshwater macrophytes. Kinetic analyses indicated that the maximum potential uptake velocities for CO consumption ranged from 0.4 to 2.7 μmol of CO g (dry weight)⁻¹ h⁻¹ for the five species. The observed rates were comparable to previously reported rates of root-associated methane uptake. The apparent half-saturation constants for CO consumption ranged from 50 to 370 nM CO; these values are considerably lower than the values obtained for methane uptake. The CO consumption rates reached maximum values at temperatures between 27 and 32°C, and there was a transition to CO production at ≥44°C, most likely as a result of thermochemical organic matter decomposition. Incubation of roots with organic substrates (e.g., 5 mM syringic acid, glucose, alanine, and acetate) dramatically reduced the rate of CO consumption, perhaps reflecting a shift in metabolism by facultative CO oxidizers. Based on responses to a suite of antibiotics, most of the CO consumption (about 90%) was due to eubacteria rather than fungi or other eucaryotes. Based on the results of acetylene inhibition experiments, methanotrophs and ammonia oxidizers were not active CO consumers.     

Freshwater bacteria can methylate selenium through the thiopurine methyltransferase pathway

Involvement of the bacterial thiopurine methyltransferase (bTPMT) in natural selenium methylation by freshwater was investigated. A freshwater environment that had no known selenium contamination but exhibited reproducible emission of dimethyl selenide (DMSe) or dimethyl diselenide (DMDSe) when it was supplemented with an organic form of selenium [(methyl)selenocysteine] or an inorganic form of selenium (sodium selenite) was used. The distribution of the bTPMT gene (tpm) in the microflora was studied. Freshwater bacteria growing on 10 micro M sodium selenite and 10 micro M sodium selenate were isolated, and 4.5 and 10% of the strains, respectively, were shown by colony blot hybridization to hybridize with a Pseudomonas syringae tpm DNA probe. Ribotyping showed that these strains are closely related. The complete rrs sequence of one of the strains, designated Hsa.28, was obtained and analyzed. Its closest phyletic neighbor was found to be the Pseudomonas anguilliseptica rrs sequence. The Hsa.28 strain grown with sodium selenite or (methyl)selenocysteine produced significant amounts of DMSe and DMDSe. The Hsa.28 tpm gene was isolated by genomic DNA library screening and sequencing. BLASTP comparisons of the deduced Hsa.28 bTPMT sequence with P. syringae, Pseudomonas aeruginosa, Vibrio cholerae, rat, and human thiopurine methyltransferase sequences revealed that the levels of similarity were 52 to 71%. PCR-generated Escherichia coli subclones containing the Hsa.28 tpm open reading frame were constructed. E. coli cells harboring the constructs and grown with sodium selenite or (methyl)selenocysteine produced significant levels of DMSe and DMDSe, confirming that the gene plays a role in selenium methylation. The effect of strain Hsa.28 population levels on freshwater DMSe and DMDSe emission was investigated. An increase in the size of the Hsa.28 population was found to enhance significantly the emission of methyl selenides by freshwater samples supplemented with sodium selenite or (methyl)selenocysteine. These data suggest that bTPMT can play a role in natural freshwater selenium methylation processes.     

Exopolysaccharides Isolated from Hydrothermal Vent Bacteria Can Modulate the Complement System

The complement system is involved in the defence against bacterial infection, or in the elimination of tumour cells. However, disturbances in this system contributes to the pathogenesis of various inflammatory diseases. The efficiency of therapeutic anti-tumour antibodies is enhanced when the complement system is stimulated. In contrast, cancer cells are able to inhibit the complement system and thus proliferate. Some marine molecules are currently being developed as new drugs for use in humans. Among them, known exopolyssacharides (EPSs) generally originate from fungi, but few studies have been performed on bacterial EPSs and even fewer on EPSs extracted from deep-sea hydrothermal vent microbes. For use in humans, these high molecular weight EPSs must be depolymerised. Furthermore, the over-sulphation of EPSs can modify their biological activity. The aim of this study was to investigate the immunodulation of the complement system by either native or over-sulphated low molecular weight EPSs isolated from vent bacteria in order to find pro or anti-activators of complement.     

Mercury Methylation Independent of the Acetyl-Coenzyme A Pathway in Sulfate-Reducing Bacteria

Sulfate-reducing bacteria (SRB) in anoxic waters and sediments are the major producers of methylmercury in aquatic systems. Although a considerable amount of work has addressed the environmental factors that control methylmercury formation and the conditions that control bioavailability of inorganic mercury to SRB, little work has been undertaken analyzing the biochemical mechanism of methylmercury production. The acetyl-coenzyme A (CoA) pathway has been implicated as being key to mercury methylation in one SRB strain, Desulfovibrio desulfuricans LS, but this result has not been extended to other SRB species. To probe whether the acetyl-CoA pathway is the controlling biochemical process for methylmercury production in SRB, five incomplete-oxidizing SRB strains and two Desulfobacter strains that do not use the acetyl-CoA pathway for major carbon metabolism were assayed for methylmercury formation and acetyl-CoA pathway enzyme activities. Three of the SRB strains were also incubated with chloroform to inhibit the acetyl-CoA pathway. So far, all species that have been found to have acetyl-CoA activity are complete oxidizers that require the acetyl-CoA pathway for basic metabolism, as well as methylate mercury. Chloroform inhibits Hg methylation in these species either by blocking the methylating enzyme or by indirect effects on metabolism and growth. However, we have identified four incomplete-oxidizing strains that clearly do not utilize the acetyl-CoA pathway either for metabolism or mercury methylation (as confirmed by the absence of chloroform inhibition). Hg methylation is thus independent of the acetyl-CoA pathway and may not require vitamin B₁₂ in some and perhaps many incomplete-oxidizing SRB strains.     

Probiotic Potential of Autochthonous Bacteria Isolated from the Gastrointestinal Tract of Four Freshwater Teleosts

In this study, a total of 121 bacterial strains were isolated from the gastrointestinal tract of four teleostean species, namely striped snakehead (Channa striatus), striped dwarf catfish (Mystus vittatus), orangefin labeo (Labeo calbasu) and mrigal carp (Cirrhinus mrigala), among which 8 isolates showed promising antibacterial activity against four potential fish pathogens, Aeromonas hydrophila, Aeromonas salmonicida, Aeromonas sobria and Pseudomonas fluorescens and were non-hemolytic. The isolates were further screened in response to fish bile tolerance and extracellular digestive enzyme activity. Two bacterial strains MVF1 and MVH7 showed highest tolerance and extracellular enzymes activities, and selected for further studies. Antagonistic activity of these two isolates was further confirmed by in vitro growth inhibition assay against four selected fish pathogens in liquid medium. Finally, these two bacterial strains MVF1 and MVH7 were selected as potential probiotic candidates and thus identification by partial 16S rRNA gene sequence analysis. The bacterial isolates MVF1 and MVH7 were identified as two strains of Bacillus sp.     

Ferric Iron Reduction by Bacteria Associated with the Roots of Freshwater and Marine Macrophytes

In vitro assays of washed, excised roots revealed maximum potential ferric iron reduction rates of >100 μmol g (dry weight)⁻¹ day⁻¹ for three freshwater macrophytes and rates between 15 and 83 μmol (dry weight)⁻¹ day⁻¹ for two marine species. The rates varied with root morphology but not consistently (fine root activity exceeded smooth root activity in some but not all cases). Sodium molybdate added at final concentrations of 0.2 to 20 mM did not inhibit iron reduction by roots of marine macrophytes (Spartina alterniflora and Zostera marina). Roots of a freshwater macrophyte, Sparganium eurycarpum, that were incubated with an analog of humic acid precursors, anthroquinone disulfate (AQDS), reduced freshly precipitated iron oxyhydroxide contained in dialysis bags that excluded solutes with molecular weights of >1,000; no reduction occurred in the absence of AQDS. Bacterial enrichment cultures and isolates from freshwater and marine roots used a variety of carbon and energy sources (e.g., acetate, ethanol, succinate, toluene, and yeast extract) and ferric oxyhydroxide, ferric citrate, uranate, and AQDS as terminal electron acceptors. The temperature optima for a freshwater isolate and a marine isolate were equivalent (approximately 32°C). However, iron reduction by the freshwater isolate decreased with increasing salinity, while reduction by the marine isolate displayed a relatively broad optimum salinity between 20 and 35 ppt. Our results suggest that by participating in an active iron cycle and perhaps by reducing humic acids, iron reducers in the rhizoplane of aquatic macrophytes limit organic availability to other heterotrophs (including methanogens) in the rhizosphere and bulk sediments.     

河蚌血细胞对细菌趋化移动的初步研究

采用改进的毛细管法 ,研究了圆背角无齿蚌 (Anodontawoodianapacifica)和三角帆蚌 (Hyriopsiscum ingii)两种淡水河蚌离体血细胞对两种水体中常见病原细菌的趋化移动作用 ,及血清对其的影响。结果显示 ,两种河蚌的离体血细胞对细菌都具有趋化移动作用 ,产生趋化移动的血细胞数量都显著高于无细菌的对照组 (P <0 0 5 )。在有血清时 ,血细胞对荧光极毛杆菌 (Pseudomonasfluorescens)的趋化移动活性略高于肠型点状气单孢菌 (Aeromonaspunctataf.intestinalis) ,圆背角无齿蚌离体血细胞的趋化移动能力显著高于三角帆蚌 (P <0 0 5 )。血清对河蚌离体血细胞的趋化移动作用有显著的促进作用 (P <0 0 5 )。     

Changing the Apoptosis Pathway through Evolutionary Protein Design

One obstacle in de novo protein design is the vast sequence space that needs to be searched through to obtain functional proteins. We developed a new method using structural profiles created from evolutionarily related proteins to constrain the simulation search process, with functions specified by atomic-level ligand–protein binding interactions. The approach was applied to redesigning the BIR3 domain of the X-linked inhibitor of apoptosis protein (XIAP), whose primary function is to suppress the cell death by inhibiting caspase-9 activity; however, the function of the wild-type XIAP can be eliminated by the binding of Smac peptides. Isothermal calorimetry and luminescence assay reveal that the designed XIAP domains can bind strongly with the Smac peptides but do not significantly inhibit the caspase-9 proteolytic activity in vitro compared with the wild-type XIAP protein. Detailed mutation assay experiments suggest that the binding specificity in the designs is essentially determined by the interplay of structural profile and physical interactions, which demonstrates the potential to modify apoptosis pathways through computational design.