Structure of genes narL and narX of the nar (nitrate reductase) locus in Escherichia coli K-12

narL and narX mediate nitrate induction of nitrate reductase synthesis and nitrate repression of fumarate reductase synthesis. We report here the nucleotide sequences of narL and narX. The deduced protein sequences aid in defining distinct subclasses of regulators and sensors in the family of two-component regulatory proteins.     

人微小病毒3个主要蛋白基因真核表达载体的构建

目的:分别克隆人细小病毒B19三个主要蛋白VP1、VP2、NS1全长基因,构建真核表达载体。方法:利用PCR和分子克隆技术,分别将B19病毒vp1、vp2、ns1基因全长片段扩增后,构建带荧光标签的真核表达载体;在人体细胞中表达并通过荧光、RT-PCR和Western Blot、测序等方法鉴定。结果:成功构建了包含B19病毒vp1、vp2、ns1全长基因,并在人体细胞中表达了VP1、VP2、NS1蛋白。结论:人微小病毒B19三个主要蛋白基因得到克隆和表达,为进行相关的研究奠定了基础。     

Toluene-degrading bacteria are chemotactic towards the environmental pollutants benzene, toluene, and trichloroethylene

The bioremediation of polluted groundwater and toxic waste sites requires that bacteria come into close physical contact with pollutants. This can be accomplished by chemotaxis. Five motile strains of bacteria that use five different pathways to degrade toluene were tested for their ability to detect and swim towards this pollutant. Three of the five strains (Pseudomonas putida F1, Ralstonia pickettii PKO1, and Burkholderia cepacia G4) were attracted to toluene. In each case, the response was dependent on induction by growth with toluene. Pseudomonas mendocina KR1 and P. putida PaW15 did not show a convincing response. The chemotactic responses of P. putida F1 to a variety of toxic aromatic hydrocarbons and chlorinated aliphatic compounds were examined. Compounds that are growth substrates for P. putida F1, including benzene and ethylbenzene, were chemoattractants. P. putida F1 was also attracted to trichloroethylene (TCE), which is not a growth substrate but is dechlorinated and detoxified by P. putida F1. Mutant strains of P. putida F1 that do not oxidize toluene were attracted to toluene, indicating that toluene itself and not a metabolite was the compound detected. The two-component response regulator pair TodS and TodT, which control expression of the toluene degradation genes in P. putida F1, were required for the response. This demonstration that soil bacteria can sense and swim towards the toxic compounds toluene, benzene, TCE, and related chemicals suggests that the introduction of chemotactic bacteria into selected polluted sites may accelerate bioremediation processes.     

Fish community changes after minimum flow increase: testing quantitative predictions in the Rhône River at Pierre-Bénite, France

1. Many aspects of the flow regime influence the structure of stream communities, among which the minimum discharge left in rivers has received particular attention. However, instream habitat models predicting the ecological impacts of discharge management often lack biological validation and spatial generality, particularly for large rivers with many fish species. 2. The minimum flow at Pierre‐Bénite, a reach of the Rhône river bypassed by artificial channels, was increased from 10 to 100 m³ s^?1 in August 2000 (natural mean discharge 1030 m³ s^?1), resulting in a fivefold increase in average velocity at minimum flow. Fish were electrofished in several habitat units on 12 surveys between 1995 and 2004. 3. Principal components analysis revealed a significant change in the relative abundance of fish species. The relative abundance of species preferring fast‐flowing and/or deep microhabitats increased from two‐ to fourfold after minimum flow increase. A change in community structure confirmed independent quantitative predictions of an instream habitat model. This change was significantly linked to minimum flow increase, but not to any other environmental variables describing high flows or temperature at key periods of fish life cycle. The rapidity of the fish response compared with the lifespan of individual species can be explained by a differential response of specific size classes. 4. The fish community at Pierre‐Bénite is in a transitional stage and only continued monitoring will indicate if the observed shift in community structure is perennial. We expect that our case study will be compared with other predictive tests of the impacts of flow restoration in large rivers, in the Rhône catchment and elsewhere.     

利用AFLP遗传连锁图定位大麦苗期对叶锈病的部分抗性基因

借助大麦染色体ＡＦＬＰ标记遗传连锁图和ＭａｐＱＴＬＶ３．０作图软件,对大麦叶病的数量抗性基因进行了定位分析,明确了大麦部分抗性品种Ｖａｄａ对叶锈病的潜育期由分别位于染色体１、２、６、７上离短臂末端７９ｃＭ、１８６ｃＭ、５８ｃＭ和１１７ｃＭ处的４个数量抗性基因所控制。     

Micropropagation by tissue culture triggers differential expression of infectious endogenous Banana streak virus sequences (eBSV) present in the B genome of natural and synthetic interspecific banana plantains

The genome of Musa balbisiana spp. contains several infectious endogenous sequences of Banana streak virus (eBSV). We have shown previously that in vitro micropropagation triggers the activation of infectious eBSOLV (endogenous sequences of Banana streak Obino l'Ewai virus ) in the synthetic tetraploid interspecific hybrid FHIA21 (AAAB). In this work, we show that another synthetic tetraploid (AAAB) hybrid and two natural triploid (AAB) plantains are equally prone to the activation of infectious eBSOLV during tissue culture. These results are a strong indication that such activation is a general phenomenon in interspecific Musa cultivars, whether synthetic or natural. We also report the first in-depth study of the correlation between the duration of tissue culture and the level of activation of infectious eBSOLV, and show that specific and common activation patterns exist in these banana plants. We hypothesize that these patterns result from the concomitant activation of infectious eBSOLV and a decrease in the virus titre in neoformed plantlets, resulting from cell multiplication outcompeting virus replication. We provide experimental data supporting this hypothesis. No activation of infectious eBSGFV (endogenous sequences of Banana streak Goldfinger virus) by tissue culture was observed in the two natural AAB plantain cultivars studied here, whereas such activation occurred in the AAAB synthetic hybrid studied. We demonstrate that this differential activation does not result from differences in the structure of eBSGFV, as all banana genomes harbour eaBSGFV-7.     

Carbon accumulation in agricultural soils after afforestation: a meta-analysis

Deforestation usually results in significant losses of soil organic carbon (SOC). The rate and factors determining the recovery of this C pool with afforestation are still poorly understood. This paper provides a review of the influence of afforestation on SOC stocks based on a meta-analysis of 33 recent publications (totaling 120 sites and 189 observations), with the aim of determining the factors responsible for the restoration of SOC following afforestation. Based on a mixed linear model, the meta-analysis indicates that the main factors that contribute to restoring SOC stocks after afforestation are: previous land use, tree species planted, soil clay content, preplanting disturbance and, to a lesser extent, climatic zone. Specifically, this meta-analysis (1) indicates that the positive impact of afforestation on SOC stocks is more pronounced in cropland soils than in pastures or natural grasslands; (2) suggests that broadleaf tree species have a greater capacity to accumulate SOC than coniferous species; (3) underscores that afforestation using pine species does not result in a net loss of the whole soil-profile carbon stocks compared with initial values (agricultural soil) when the surface organic layer is included in the accounting; (4) demonstrates that clay-rich soils (> 33%) have a greater capacity to accumulate SOC than soils with a lower clay content (< 33%); (5) indicates that minimizing preplanting disturbances may increase the rate at which SOC stocks are replenished; and (6) suggests that afforestation carried out in the boreal climate zone results in small SOC losses compared with other climate zones, probably because trees grow more slowly under these conditions, although this does not rule out gains over time after the conversion. This study also highlights the importance of the methodological approach used when developing the sampling design, especially the inclusion of the organic layer in the accounting.     

Aspartate 205 in the catalytic domain of naphthalene dioxygenase is essential for activity

The naphthalene dioxygenase enzyme system carries out the first step in the aerobic degradation of naphthalene by Pseudomonas sp. strain NCIB 9816-4. The crystal structure of naphthalene dioxygenase (B. Kauppi, K. Lee, E. Carredano, R. E. Parales, D. T. Gibson, H. Eklund, and S. Ramaswamy, Structure 6:571-586, 1998) indicates that aspartate 205 may provide the most direct route of electron transfer between the Rieske [2Fe-2S] center of one alpha subunit and mononuclear iron in the adjacent alpha subunit. In this study, we constructed four site-directed mutations that changed aspartate 205 to alanine, glutamate, asparagine, or glutamine to test whether this residue is essential for naphthalene dioxygenase activity. The mutant proteins were very inefficient in oxidizing naphthalene to cis-naphthalene dihydrodiol, and oxygen uptake in the presence of naphthalene was below detectable levels. The purified mutant protein with glutamine in place of aspartate 205 had identical spectral properties to wild-type naphthalene dioxygenase and was reduced by NADH in the presence of catalytic amounts of ferredoxinNAP and reductaseNAP. Benzene, an effective uncoupler of oxygen consumption in purified naphthalene dioxygenase, did not elicit oxygen uptake by the mutant protein. These results indicate that electron transfer from NADH to the Rieske center in the mutant oxygenase is intact, a finding consistent with the proposal that aspartate 205 is a necessary residue in the major pathway of electron transfer to mononuclear iron at the active site.