Purple acid phosphatase in the walls of tobacco cells

Purple acid phosphatase isolated from the walls of tobacco cells appears to be a 220 kDa homotetramer composed of 60 kDa subunits, which is purple in color and which contains iron as its only metal ion. Although the phosphatase did not require dithiothreitol for activity and was not inhibited by phenylarsine oxide, the enzyme showed a higher catalytic efficiency (k_cat/K_m) for phosphotyrosine-containing peptides than for other substrates including p-nitrophenyl-phosphate and ATP. The phosphatase formed as a 120 kDa dimer in the cytoplasm and as a 220 kDa tetramer in the walls, where Brefeldin A blocked its secretion during wall regeneration. According to our double-immunofluorescence labeling results, the enzyme might be translocated through the Golgi apparatus to the walls at the interphase and to the cell plate during cytokinesis.     

EPR, ENDOR, and Special TRIPLE measurements of P•+ in wild type and modified reaction centers from Rb. sphaeroides

The influence of the protein environment on the primary electron donor, P, a bacteriochlorophyll a dimer, of reaction centers from Rhodobacter sphaeroides, has been investigated using electron paramagnetic resonance and electron nuclear double resonance spectroscopy. These techniques were used to probe the effects on P that are due to alteration of three amino acid residues, His L168, Asn L170, and Asn M199. The introduction of Glu at L168, Asp at L170, or Asp at M199 changes the oxidation/reduction midpoint potential of P in a pH-dependent manner (Williams et al. (2001) Biochemistry 40, 15403-15407). For the double mutant His L168 to Glu and Asn at L170 to Asp, excitation results in electron transfer along the A-side branch of cofactors at pH 7.2, but at pH 9.5, a long-lived state involving B-side cofactors is produced (Haffa et al. (2004) J Phys Chem B 108, 4-7). Using electron paramagnetic resonance spectroscopy, the mutants with alterations of each of the three individual residues and a double mutant, with changes at L168 and L170, were found to have increased linewidths of 10.1-11.0 G compared to the linewidth of 9.6 G for wild type. The Special TRIPLE spectra were pH dependent, and at pH 8, the introduction of aspartate at L170 increased the spin density ratio, rho (L)/rho (M), to 6.1 while an aspartate at the symmetry related position, M199, decreased the ratio to 0.7 compared to the value of 2.1 for wild type. These results indicate that the energy of the two halves of P changes by about 100 meV due to the mutations and are consistent with the interpretation that electrostatic interactions involving these amino acid residues contribute to the switch in pathway of electron transfer.     

Purple acid phosphatase-like sequences in prokaryotic genomes and the characterization of an atypical purple alkaline phosphatase from Burkholderia cenocepacia J2315

Purple acid phosphatases (PAP) are a group of dimetallic phosphohydrolase first identified in eukaryotes. Bioinformatics analysis revealed 57 prokaryotic PAP-like sequences in the genomes of 43 bacteria and 4 cyanobacteria species. A putative PAP gene (BcPAP) from the bacteria Burkholderia cenocepacia J2315 was chosen for further studies. Synteny analysis showed that this gene is present as an independent gene in most of the members of the genus Burkholderia. The predicted 561 a.a. polypeptide of BcPAP was found to harbour all the conserved motifs of the eukaryotic PAPs and an N-terminal twin-arginine translocation signal. Expression and biochemical characterization of BcPAP in Escherichia coli revealed that this enzyme has a relatively narrow substrate spectrum, preferably towards phosphotyrosine, phosphoserine and phosphoenolpyruvate. Interestingly, this enzyme was found to have a pH optimum at 8.5, rather than an acidic optima exhibited by eukaryotic PAPs. BcPAP contains a dimetallic ion centre composed of Fe and Zn, and site-directed mutagenesis confirmed that BcPAP utilizes the invariant residues for metal-ligation and catalysis. The enzyme is secreted by the wild type bacteria and its expression is regulated by the availability of orthophosphate. Our findings suggest that not all members in the PAP family have acidic pH optimum and broad substrate specificity.     

Vancomycin-resistant Enterococcus spp. in marine environments from the West Coast of the USA

Aims:  The aim of the study was to determine if vancomycin-resistant Enterococcus spp. [VRE] carrying vanA and/or vanB genes were present in public marine beaches and a fishing pier [2001–2003, 2008] from Washington and California [2008].
Methods:  PCR assays for the vanA and/or vanB genes with verification by DNA–DNA hybridization of the PCR products were used. Positive isolates were speciated using the BD BBL Crystal™ Identification and/or by sequencing the 16S ribosomal region.
Results:  Eighteen (8%) of 227 isolates including Enterococcus faecalis , Enterococcus faecium , Enterococcus casseliflavus/gallinarum and a Staphylococcus epidermidis carrying vanA and/or vanB genes, from four of six Washington and one of two California sites, were identified. Selected VRE and the S. epidermidis were able to transfer their van genes to an E. faecalis recipient at frequencies ranging from 1·9 × 10⁻⁶ to 6·7 × 10⁻⁹.
Conclusions:  Vancomycin-resistant Enterococcus spp. was isolated from five of the seven sites suggesting that other North America public beaches could be the reservoirs for VRE and should be assessed.
Significance & Impact of the Study:  This is the first report of isolation and characterization of VRE strains (and a vanB Staphylococcus sp.) from North American environmental sources suggesting that public beaches may be a reservoir for possible transmission of VRE to beach visitors.     

Distribution and abundance of meiofauna in intertidal sand substrata around Iceland

Iceland is situated in an important subarctic transition area where complex oceanographic dynamics occur. The intertidal, subtidal, and deep-sea faunal communities of Iceland are being intensively studied, as a critical resource for continued sustainability of fisheries and the preservation of northern littoral ecosystems. However, the meiofaunal communities and the environmental factors affecting them are still relatively poorly known. The meiobenthic metazoan community was studied with core sampling in 23 sandy beaches along the intertidal zone of the Iceland coast in a campaign developed in September 2003. Small-scale variation in meiofauna composition (major taxa) was explored and related to biotic and abiotic factors at different scales, such as beach exposure, granulometry, and organic matter content. Differences in meiofaunal community structure at a low taxonomic resolution appeared among beaches located within wide biogeographical zones of hydrobiological significance (NE and SW Shelf regions) and exposure degrees. Seventeen major taxa were recorded. In contrast with more local and taxon-focused studies, oligochaetes were the dominant group all around Iceland, followed by nematodes, turbellarians, gastrotrichs, and copepods (mainly harpacticoids). Acari, ascidians, bivalves, cnidarians, collembolans, gastropods, isopods, kinorhynchs, insects, nemerteans, ostracods, and polychaetes were relatively scarce groups, together being less than 1.6% of the meiofauna. There was a large variation in meiofaunal abundance between sites. Maximum abundances (>500 ind. cm^?2) were found in Sau?arkrökur, Hraunhafnartangi, and Skálaness, whereas minimum abundances (<40 ind. cm^?2) were recorded in Magnavík, Jokülsárlón (glacier beach site), Vikurnúpur, Breidalsvík, and Stokknes. We did not find a clear pattern in overall meiofaunal abundance regarding the degree of exposure of beaches. Oligochaetes, nematodes, and copepods were relatively more abundant in sheltered beaches, whereas turbellarians and gastrotrichs tended to be more abundant in exposed beaches. The best correlates of meiofaunal composition and abundance within beaches were the proportion of gravels and the content of utilizable organic matter in the sediment. We should consider factors operating at wider scales (importantly beach exposure and overall situation in the complex oceanographical context of Iceland) to find a pattern in the local structure of intertidal meiofaunal assemblages.     

表面活性剂CHAPS对紫膜脂双层微环境的作用

利用顺磁性自旋标记技术,探测在表面活性剂ＣＨＡＰＳ（３－〔（３－Ｃｈｏｌａｍｉｄｏｐｒｏｐｙｌ）ｄｉｍｅｔｈｙｌ－ａｍｍｏｎｉｏ〕ｐｒｏｐａｎｅｓｕｌｆｏｎｉｃ ａｃｉｄ）作用下,紫膜脂双层微环境的物理参数（序参数Ｓ和旋转相关不同。表层序参数Ｓ值随ＣＨＡＰＳ浓度的增加而逐渐减小;深层旋转相关时间τｃ值开始随ＣＨＡＰＳ浓度的增加而增大,在ＣＨＡＰＳ浓度为５ｍｍｏｌ／Ｌ时,τｃ值呈现最大值,随着ＣＨＡ     

紫色土人工林生态系统碳库与碳吸存变化

采用时空代换法,以福建省宁化县严重退化紫色土人工林生态系统为对象,按侵蚀强度由强到弱选取4种生态恢复措施Ⅰ、Ⅱ、Ⅲ、Ⅳ,对比研究了碳库与碳吸存能力．结果表明,随着恢复程度的提高,生态系统的碳吸存能力逐渐增加,即Ⅰ<Ⅱ<Ⅲ<Ⅳ,4种措施生态系统碳库分别为1．4、8．5、25．6和37．6t·hm^-2;CO2年同化量分别是712．87、1458．01、9718．10和11109．56k·hm^-2．可见,恢复过程中的生态系统是本地区重要的碳汇之一．水土保持工程措施与生物措施相结合应是退化生态系统生态恢复的重要手段,但是减少人为干扰才是目前较为合理的恢复策略,使森林生态系统成为大气中CO2的一个重要的碳汇．     

以亚硝氮为唯一氮源生长的海洋紫色硫细菌去除无机三态氮

【目的】揭示以亚硝氮为唯一氮源生长的海洋紫色硫细菌去除水体中无机三态氮的特征和规律。【方法】在光照厌氧环境下,以乙酸盐为唯一有机物,在分别以氨氮、亚硝态氮、硝态氮为唯一氮源和三氮共存的模拟水体中,采用Nessler’s试剂分光光度法、N-(1-萘基)-乙二胺分光光度法和紫外分光光度法分别测定水体中氨氮、亚硝态氮和硝态氮的含量,比浊法测定菌体生物量。【结果】随着时间的延长,海洋紫色硫细菌Marichromatium gracile YL28分别在氨氮、亚硝态氮和硝态氮为唯一氮源的水体中对三氮的去除量增加,生物量增大,水体pH升高,并逐渐趋于平衡;YL28对氨氮的最大去除量和最大耐受浓度分别为9.64 mmol/L和36.64 mmol/L,当氨氮浓度低于3.21 mmol/L时,去除率可达97.61%以上;与氨氮相比,以亚硝态氮和硝态氮为唯一氮源,菌体的生长速率、生物量和水体最终pH较低,但对亚硝态氮和硝态氮的去除速率和去除量仍然很高,当亚硝态氮和硝态氮浓度分别达13.50 mmol/L和22.90 mmol/L时,YL28仍能够完全去除。在三氮共存的水体中,YL28也能良好的去除无机三态氮,对亚硝态氮和硝态氮去除能力更强。【结论】在模拟水体中,海洋紫色硫细菌YL28能够分别以氨氮、亚硝态氮和硝态氮为唯一氮源生长,具有良好的耐受和去除无机三态氮的能力,尤其对亚硝态氮具有良好的去除能力。本研究为进一步开发高效脱氮,尤其是去除亚硝态氮的不产氧光合细菌水质调节剂奠定了基础,也为微生物制剂的合理应用提供参考。     

耕作方式对紫色水稻土轻组有机碳的影响

以位于西南大学实验农场的长期免耕试验田为研究对象,通过0—60cm分层采集土壤样品的方法,探讨了不同耕作方式———冬水田平作(DP)、水旱轮作(SH)、垄作免耕(LM)及垄作翻耕(LF)对土壤轻组有机碳的影响。结果表明,重组有机碳是土壤总有机碳的主体,约占土壤总有机碳的69.56%—95.66%,在土壤剖面上随土壤深度的增加其分配比例逐渐升高;其次是自由轻组有机碳,约占土壤总有机碳的5.03%—26.43%,从土壤表层向下,其分配比例迅速下降;闭合轻组有机碳最低,仅占土壤总有机碳的1.37%—4.93%,其分配比例随土壤深度的变化不明显。在0—60 cm土壤深度内,不同耕作方式下自由轻组有机碳的平均含量为LM(4.36 g/kg)>DP(2.11 g/kg)>LF(1.74 g/kg)>SH(1.46 g/kg),相应的有机碳分配比例分别为17.1%、14.0%、12.2%和11.3%;闭合轻组有机碳的平均含量为LM(0.82 g/kg)>DP(0.51 g/kg)>LF(0.36 g/kg)>SH(0.34g/kg),相应的有机碳分配比例分别为3.36%、3.45%、2.71%和3.00%。因此,在西南地区紫色水稻土上实行垄作免耕能提高轻组有机碳的含量及其分配比例,从而改善土壤有机碳质量。另外,与土壤总有机碳、重组有机碳及闭合轻组有机碳相比,自由轻组有机碳对耕作方式的变化最敏感,是指示土壤有机碳变化的良好指标。     

华西雨屏区植被恢复对紫色土酸化的影响

退耕还林是控制水土流失、恢复森林植被和改善生态环境的重要举措。植被恢复进程中会发生土壤酸化,进而影响植物生长,厘清不同还林树种对土壤酸化的影响程度及作用机制有助于更好地评估退耕还林工程的整体生态效益。以华西雨屏区紫色土坡耕地(玉米)为对照,分析了退耕20a后柳杉纯林、柳杉-光皮桦混交林、慈竹林和茶园土壤pH的变化及其垂直分异。结果表明：玉米地、慈竹林、茶园、混交林和柳杉纯林0—50 cm土壤pH平均值分别为5.66、5.55、5.12、5.03和5.00,相较于玉米地,柳杉纯林、混交林和茶园土壤pH值显著下降(P<0.01),土壤酸化严重。相较于玉米地土壤pH值的均匀分布,植被恢复不同类型人工林pH值随土壤深度的增加而增加,10—50 cm土壤pH值(4.89—5.90)显著高于0—10 cm土壤pH值(4.72—5.21)(P<0.01),表层土壤酸化最明显。土壤pH值与土壤有机质含量呈极显著负相关,而与风化指数Na/K比值呈显著正相关,有机质含量和Na/K比值共同解释了土壤pH值变化的53.9%,表明植被恢复引起的土壤有机质积累与长石类矿物风化是驱动紫色土酸化的重要过程...