GADD45γ, down-regulated in 65% Hepatocellular Carcinoma (HCC) from 23 Chinese patients,inhibits cell growth and induces cell cycle G2/M arrest for Hepatoma Hep-G2 cell lines

Growth-arrest and DNA-damage inducible (GADD) genes and Myeloid differentiation primary response (MyD) genes represent a family of genes that play a key role in negative control of cell growth. In the present study, following clone and location of human GADD45 (MyDL) gene, we have found that its mRNA expression level was down-regulated in 15/23 cases of clinic hepatocellular carcinoma (HCC) by comparing the northern hybridization results between the tumor tissues and adjacent normal tissues. Transient transfection of GADD45 cDNA with intact open reading frame sequence into the human hepatoma cells Hep-G2 resulted in dramatic growth suppression in colony formation assays. Furthermore, flow cytometry analysis indicated that GADD45 caused cell cycle arrest at G2/M transition when transfected into Hep-G2 cells. Therefore, the possible role of GADD45 in cell growth control was further confirmed in this paper.     

Shrub-encroachment induced alterations in input chemistry and soil microbial community affect topsoil organic carbon in an Inner Mongolian grassland

Shrub encroachment frequently occurs in arid and semi-arid grasslands worldwide and affects the regional carbon balance. Many previous studies have revealed the effects of shrub encroachment on bulk carbon content of grasslands, but molecular evidence is surprisingly lacking. In this study, we examined the chemical composition of plant tissues and soil organic carbon (SOC), and soil microbial communities to identify the effects of shrub (Caragana microphylla) encroachment on SOC storage in the top layer (0–10 cm) along a gradient of natural shrub cover in the grasslands of Inner Mongolia. We found that SOC in the shrub patches was derived mainly from leaves, whereas SOC in the grassy matrix was composed of a mixture of fresh root- and leaf-derived compounds. Compared with pure grassland, the SOC decreased by 29% in the shrub-encroached grasslands (SEGs), and this decrease was enhanced by increasing shrub cover. We also found that free lipids and lignin-derived phenols increased while the ratios of ω-C₁₈/∑C₁₈ and suberin/cutin decreased with increasing shrub cover. In addition, the ratios of fungal to bacterial phospholipid fatty acids (PLFAs) and gram-negative to gram-positive bacterial PLFAs decreased with increasing shrub cover. These results indicate that the encroachment of nitrogen-rich legume shrubs can lead to carbon loss by altering the chemical composition of plant inputs as well as the soil microbial community in grassland ecosystems.     

黄土丘陵区退耕地土壤可溶性氮组分季节变化与水热关系

为探究黄土丘陵区退耕地植被恢复土壤有效氮素养分累积的季节动态变化特征及水热驱动效应,以邻近坡耕地为对照,分析了植被恢复15 a的刺槐、柠条、荒草地土壤可溶性氮组分密度、分布比例在4—10月份内的动态变化状况及其与土壤温度和含水量间的关系。结果表明,整个采样期间,0—30 cm土层土壤硝态氮、可溶性有机氮和可溶性全氮动态变化显著,且各可溶性氮组分中仅硝态氮随土层变化差异显著。其中土壤硝态氮变化幅度整体为0.13—1.71 g/m~2,占可溶性全氮的5.1%—52.1%,其最大值出现在4月份,最小值出现在10月份;可溶性有机氮整体变化幅度为0.29—2.92 g/m~2,占可溶性全氮的30.9%—85.3%,在4月份和8月份分别达最小值和最大值;铵态氮动态变化不显著,4—10月份整体变化幅度为0.17—0.74 g/m~2,占6.4%—21.4%,其最小值出现在10月份,最大值出现在4月份;可溶性全氮整体变化幅度为1.25—3.52 g/m~2。可溶性氮组分中,各组分所占比例为可溶性有机氮硝态氮铵态氮,并且可溶性有机氮与硝态氮所占比例动态变化趋势相反。刺槐、柠条林和荒草地0—30 cm土壤硝态氮平均约为耕地的3.42倍、2.54倍和1.26倍,铵态氮平均为耕地的1.71倍、1.37倍和1.30倍,可溶性有机氮约为1.64倍、1.31倍和1.23倍。可溶性氮组分受土壤含水量的影响大于土壤温度,硝态氮对土壤含水量的变化最为敏感,而可溶性全氮则对土壤温度变化最为敏感。综上所述,人工林植被恢复有利于提高土壤可溶性氮组分,增加氮的有效性,同时除铵态氮外,土壤可溶性氮组分随季节变化显著。     

Effects of shrub encroachment on vertical changes in soil organic carbon in Mongolian grasslands: using a multi-biomarker approach

Background

This study started from typical replant disease symptoms limited to specific foci within three multi-generation orchards showing homogeneous growth.

Methods

A plant growth assay was conducted using soil from symptomatic and asymptomatic tree root zones along planted rows and from strip-rows. Root colonizing fungal communities were investigated, then the study turned to pathogenicity of Cylindrocarpon-like fungi (Dactylonectria and Ilyonectria spp) and their extracellular exudates.

Results

Growth of apple rootstock plantlets in soil from symptomatic trees was significantly lower than in those observed in soil from asymptomatic trees and from strip-rows. Among the main group of endophytic filamentous fungi isolated from roots, Cylindrocapon-like fungi (Dactylonectria torresensis and, to a lesser extent, Ilyonectria robusta), along with binucleate Rhizoctonia spp., prevailed mostly in plantlets grown in soil collected from planted rows. On the other hand, Fusarium spp. prevailed in plantlets grown in soil from the strip-rows. Cylindrocarpon-like fungi was found to be the most negatively correlated with plant growth. As findings of artificial inoculation with main root colonizing fungal species were not in line with what was observed in native soils, a further investigation was performed on secondary metabolites through which Dactylonectria torresensis exerts pathogenicity; this analysis revealed that both phytotoxins (tentoxin, HC toxin and zearalenone) and cytotoxic compounds (rabelomycin and nidulin) may be involved.

Conclusion

Findings suggest that extracellular compounds released by D. torresensis may have contributed to the severe growth reduction associated with replant disease-like symptoms.

     

Food web structure of a shallow eutrophic lake (Lake Taihu,China) assessed by stable isotope analysis

Lake Taihu is a large, shallow, and eutrophic lake in China. It has provided local communities with valuable fisheries for centuries, but little is known of the trophodynamics, or of its faunal communities. Carbon and nitrogen isotopic composition was used to assess its trophic pathways and the food web structure [food sources and trophic levels (TL)]. Basal food sources were distinguishable based on their δ¹³C values, ranging from −27.2 to −15.2‰. Consumers were also well separated in δ¹³C (−26.9 to −17.9‰ for invertebrates and −25.7 to −18.1‰ for fishes), which allowed for an effective discrimination of carbon sources between these fauna. An average trophic enrichment factor of 3.4‰ was used to calculate the TLs based on δ¹⁵N of zooplankton, with results indicating a food web having four TLs. Although δ¹⁵N values overlap and cover a large range within trophic compartments, the isotopic signatures of the species assessed revealed a general trend of ¹⁵N enrichment with increasing TL. Stable isotope signatures were also used to establish a general food web scheme in which five main trophic pathways were analyzed.     

巴西固氮螺菌ntrBC基因的克隆与核苷酸序列分析

以EMBL3为载体,构建了巴西固氮螺菌(Azospirillum brasilense)Yu62的基因文库.以巴西固氮螺菌Yu62中PCR扩增出的450bp DNA 片断作为探针,对该基因文库进行筛选,得到了10个阳性克隆(EA1—EA10),其中含有两种不同类型的克隆,分别以EA4和EA9为代表.对EA4的杂交分析发现目的基因位于2.9kb EcoRI片段上.DNA序列分析结果表明该片段含有完整的ntrC编码区,其编码产物由480个氨基酸组成.分子量为53469;ntrC上游是完整的ntrB编码区,其编码产物由400个氨基酸组成,分子量为43487.对相应的NtrC和NtrB氨基酸序列进行同源性分析,说明巴西固氮螺菌与根瘤菌的亲缘关系较与其它自生固氮菌的更为接近.     

黑曲霉产生的酶类及其应用

黑曲霉是应用和工业酶学领域使用最广泛的菌种之一,它能产生丰富的酶类。本文主要对黑曲霉所产的一部分酶及应用情况进行了综述。     

肺炎克氏杆菌nifA基因在巴西固氮螺菌固氮基因表达的铵调节中的作用

固氯螺菌(Azospirillum)是一类仅在限铵和微好氧条件下固氮的微生物,它可与许多禾本科作物联合共生⑴,具有较大的应用潜力。铵作为固氮作用的调节信号,在固氮螺菌的实际应用中是首要的限制因素。在固氯螺菌中,铵不但具有与肺炎克氏杆菌(Klebsiella pneumoniae)相似的阻遏固氮酶合成的作用,而且还对已合成的固氮酶进行活性调节⑵。研究表明,其固氮酶翻译后活性调节的机制类似于深红红螺菌(Rhodospirillum rubrum)⑶,即在有铵条件下其固氮酶铁蛋白的一个亚基被共价修饰而丧失活性,这一过程是可逆的。由于铵在固氮螺菌中双水平地调节固氮作用,使得在野生菌株中研究其固氮基因表达水平上的调节较为困难。Zhang等⑷利用区域定位诱变技术获得了巴西固氮螺菌Sp7（A．Brasilense Sp7)的draT-突变株,在该突变株中铵不再影响固氮酶的活性,这为其固氮基因表达调节的研究提供了一个良好的材料。本文将组成型表达的肺炎克氏杆菌nifA基围引入该突变株中,通过分析讨论铵对巴西固氮螺菌固氮基固表达的调节作用方式。     

Characterization of a new and thermostable esterase from a metagenomic library

A new gene encoding an esterase (designated as EstEP16) was identified from a metagenomic library prepared from a sediment sample collected from a deep-sea hydrothermal field in east Pacific. The open reading frame of this gene encoded 249 amino acid residues. It was cloned, overexpressed in Escherichia coli, and the recombinant protein was purified to homogeneity. The monomeric EstEP16 presented a molecular mass of 51.7 kDa. Enzyme assays using p-nitrophenyl esters with different acyl chain lengths as the substrates confirmed its esterase activity, yielding highest specific activity with p-nitrophenyl acetate. When p-nitrophenyl butyrate was used as a substrate, recombinant EstEP16 exhibited highest activity at pH 8.0 and 60 °C. The recombinant enzyme retained about 80% residual activity after incubation at 90 °C for 6 h, which indicated that EstEP16 was thermostable. Homology modeling of EstEP16 was developed with the monoacylglycerol lipase from Bacillus sp. H-257 as a template. The structure showed an α/β-hydrolase fold and indicated the presence of a typical catalytic triad. The activity of EstEP16 was inhibited by addition of phenylmethylsulfonyl fluoride, indicating that it contains serine residue, which plays a key role in the catalytic mechanism.