Responsiveness to Exogenous Camp of a Saccharomyces Cerevisiae Strain Conferred by Naturally Occurring Alleles of Pde1 and Pde2

The Saccharomyces cerevisiae strain P-28-24C, from which cAMP requiring mutants derived, responded to exogenously added cAMP. Upon the addition of cAMP, this strain showed phenotypes shared by mutants with elevated activity of the cAMP pathway. Genetic analysis involving serial crosses of this strain to a strain with another genetic background revealed that the responsiveness to cAMP results from naturally occurring loss-of-function alleles of PDE1 and PDE2, which encode low and high affinity cAMP phosphodiesterases, respectively. In addition, P-28-24C was found to carry a mutation conferring slow growth that lies in CYR1, which encodes adenylate cyclase, and the slow growth phenotype caused by the cyr1 mutation was suppressed by the pde2 mutation. Therefore P-28-24C is fortuitously a pde1 pde2 cyr1 triple mutant. Responsiveness to cAMP conferred by pde mutations suggests that S. cerevisiae cells are permeable to cAMP to some extent and that the apparent absence of effect of exogenously added cAMP on wild-type cells is due to immediate degradation by cAMP phosphodiesterases.     

Repression of Hybrid Dysgenesis in Drosophila Melanogaster by Individual Naturally Occurring P Elements

Individual P elements that were genetically isolated from wild-type strains were tested for their abilities to repress two aspects of hybrid dysgenesis: gonadal dysgenesis and mutability of a double-P element-insertion allele of the singed locus (sn(w)). These elements were also characterized by Southern blotting, polymerase chain reaction amplification and DNA sequencing. Three of the elements were 1.1-kb KP elements, one was a 1.2-kb element called D50, and one was a 0.5-kb element called SP. These three types of elements could encode polypeptides of 207, 204, and 14 amino acids, respectively. Gonadal dysgenesis was repressed by two of the KP elements (denoted KP(1) and KP(6)) and by SP, but not by the third KP element (KP(D)), nor by D50. Repression of gonadal dysgenesis was mediated by a maternal effect, or by a combination of zygotic and maternal effects generated by the P elements themselves. The mutability of sn(w) was repressed by the KP(1) and KP(6) elements, by D50 and by SP, but not by KP(D); however, the SP element repressed sn(w) mutability only when the transposase came from complete P elements and the D50 element repressed it only when the transposase came from the modified P element known as Δ2-3. In all cases, repression of sn(w) mutability appeared to be mediated by a zygotic effect of the isolated P element. Each of the isolated elements was also tested for its ability to suppress the phenotype of a P-insertion mutation of the vestigial locus (vg(21-3)). D50 was a moderate suppressor whereas SP and the three KP elements had little or no effect. These results indicate that each isolated P element had its own profile of repression and suppression abilities. It is suggested that these abilities may be mediated by P-encoded polypeptides or by antisense P RNAs initiated from external genomic promoters.     

Transfer in Marine Sediments of the Naturally Occurring Plasmid pRAS1 Encoding Multiple Antibiotic Resistance

The results of microcosm experiments performed with the fish-pathogenic bacterium Aeromonas salmonicida acting as a donor showed that promiscuous plasmid pRAS1, which encodes tetracycline resistance, is transferred at a high frequency in marine sediments even in the absence of a selective factor. The presence of oxytetracycline resulted in an increase in the transfer frequency compared with that of a microcosm to which no selective factor was added. Transfer frequencies of 3.4 × 10^-1 transconjugant per recipient and 3.6 transconjugants per donor cell were obtained in a microcosm to which oxytetracycline had been added. Hybridization with a DNA probe specific for plasmid pRAS1 revealed that 45.8% of the oxytetracycline-resistant isolates obtained from a microcosm with no selective pressure carried the plasmid, while 86.8% of the isolates obtained from a microcosm to which oxytetracycline had been added carried the plasmid. Phenotypic characterization of the transconjugants revealed that the plasmid had been transferred to a variety of different biotypes in both microcosms. The diversity among the transconjugants isolated from the microcosm to which oxytetracycline had been added was substantially lower than the diversity among the transconjugants isolated from the microcosm to which no selective agent had been added.     

Chromosomal Location by Use of Trisomics and New Alleles of an Endopeptidase in ZEA MAYS

An association was found earlier between the Ep₁ gene locus coding for an endopeptidase and the endosperm color gene Y₁ on chromosome 6 of Zea mays. By employing primary trisomics we have unequivocally placed the Ep₁ gene on chromosome 6, closely linked to the Y₁ locus. Additionally we describe new alleles at the Ep₁ locus, and present evidence for the existence of a second endopeptidase system in maize.     

Ethanol Production from Glucose by Torulopsis glabrata Occurring Naturally in the Stomachs of Newborn Animals

S ummary : The elucidation of the mechanism of ethanol production in the stomachs of newborn animals is described. The condition was reproduced in lambs and piglets by feeding glucose in fat-free milk, and shown to arise from fermentation by the naturally occurring yeast Torulopsis glabrata , which can reach population densities of 10⁶ viable cells/ml of stomach contents. These yeasts ferment glucose, producing up to 500 mg of ethanol/100 ml of contents in the stomach, but do not ferment sucrose or lactose. High levels of ethanol in plasma of lambs are accompanied by obvious symptoms of intoxication. The characteristics of a constantly occurring coliform type bacterium, found at densities up to 10⁸ viable cells/ml in association with the Torulopsis yeasts were examined. Its precise role is not clear.     

The Role of Light in the Germination of Naturally Occurring Populations of Buried Weed Seeds

Large populations of viable buried arable weed seeds have beenfound in soil which has been continuously used as pasture forthe last six years. Small numbers of dicotyledonous seedlingswere found to germinate within the grass sward, but did notappear to become established. A disturbance of this soil, ascaused by cultivation, resulted in a large flush of germinationduring the subsequent 4 weeks. Under laboratory conditions only10 per cent of these seedlings emerged in the absence of illumination.Under field conditions there was no germination at all in thedark. A short ‘light-break’ of only 90 sec was sufficientto cause the germination of a large proportion of seeds. Onthe basis of these results it is concluded that the appearanceof all weed seedlings from buried seeds, following cultivation,is dependent upon the exposure of these seeds to light.     

喀斯特峰丛洼地不同植被恢复阶段优势种根系构型特征

以喀斯特峰丛洼地不同植被恢复阶段灌丛、次生林、原生林为研究对象,采用全挖法分析了各阶段4个优势种的根系构型参数,探讨该特殊生境条件下植物根系构型的差异性、相似性以及资源合理高效的利用方式。结果表明:(1)各个植被恢复阶段优势种拓扑指数TI均趋向于0.5,呈叉状分支结构,并表现为次生林(0.57)原生林(0.49)灌丛(0.46),有利于根系在贫瘠且浅薄的土壤环境中拓展生存空间。(2)3种植被恢复阶段优势种的根系平均连接长度在34.29cm以上,平均为37.01cm,增加连接长度对植物在养分贫瘠的喀斯特土壤环境的生存有利。(3)次生林根系分支率低于灌丛和原生林,这是不同植被恢复阶段优势种对环境所采取的不同适应策略。(4)3种植被恢复阶段优势种根系的横截面积比均符合Leonardo da Vinci法则,且不随直径的变化而变化。(5)3种植被恢复阶段优势种在土壤养分、水分获取及土壤空间拓展方面没有显著差异性。研究认为,在喀斯特峰丛洼地异质性很强的生境下,3种植被恢复阶段优势种的根系均为叉状分支结构,且均以较长的连接长度和较低的分支率策略适应其特殊的生态环境。     

The Isolation and Evaluation of Two Naturally Occurring Mild Strains of Vanilla Necrosis Potyvirus for Control by Cross-Protection

In an attempt to find mild virus strains that would cross-protect sgainst vanilla necrosis potyvirus (VNPV), Vanilla fragrans plants in Tonga were surveyed for the presence of mild or symptomless potyvirus infections. Potyviruses were detected by indirect ELISA using a commercially available portyvirus group monoclonal anibody. From 28 plants with mild or symptomless infections two portyvirus isolates, designated V1 and V3, included systemic infections in Nicotiana benthamiana following mechanical inoculation. V1, which causes a mild mottle in N. benthamiana, is serologically related to VNPV, while V3 which causes mild vein banding is serologically unrelated to VNPV. Prior inoculation with V1 protected N. benthamiana against the severe mosaic symptoms of VNPV when challenge inoculated after 14 and 21 days, but not after 7 days. When V3 was used as the protecting strain, cross-protection was observed in some, but not all plants, when chalenged with VNPV after 14 and 21 days.     

Suppression by Citrus Exocortis Viroid Infection of the Naturally Occurring Inhibitor of the Conversion of 1-aminocyclopropane-1-carboxylic Acid to Ethylene by Tomato Microsomes

Citrus exocortis viroid (CEVd) infection of tomato cell cultures suppresses the constitutive inhibitor which blocks the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by tomato microsomes. The inhibitor is associated to microsomal membranes and is also found in the water soluble fraction co-isolated from the cells. The inhibitory effect is concentration dependent, heat stable and could be removed from solution by dialysis. Its possible relationship with regulation of the viroid-induced ethylene production is discussed.     

The Gut Microbial Community of Midas Cichlid Fish in Repeatedly Evolved Limnetic-Benthic Species Pairs

Gut bacterial communities are now known to influence a range of fitness related aspects of organisms. But how different the microbial community is in closely related species, and if these differences can be interpreted as adaptive is still unclear. In this study we compared microbial communities in two sets of closely related sympatric crater lake cichlid fish species pairs that show similar adaptations along the limnetic-benthic axis. The gut microbial community composition differs in the species pair inhabiting the older of two crater lakes. One major difference, relative to other fish, is that in these cichlids that live in hypersaline crater lakes, the microbial community is largely made up of Oceanospirillales (52.28%) which are halotolerant or halophilic bacteria. This analysis opens up further avenues to identify candidate symbiotic or co-evolved bacteria playing a role in adaptation to similar diets and life-styles or even have a role in speciation. Future functional and phylosymbiotic analyses might help to address these issues.     

The K1 Toxin of Saccharomyces cerevisiae Kills Spheroplasts of Many Yeast Species

The Saccharomyces cerevisiae K1 toxin killed spheroplasts from the genera Candida, Kluyveromyces, and Schwanniomyces. Cells of these organisms were toxin insensitive. The toxin bound poorly to Kluyveromyces lactis cells. In contrast, Candida albicans bound the toxin to an extent similar to that seen with S. cerevisiae. Thus, wall receptors can define toxin specificity and are necessary but not sufficient for toxin action on intact cells.     

Chromosomal Assignment of Mutations by Specific Chromosome Loss in the Yeast Saccharomyces Cerevisiae

Yeast 2-microns plasmids were integrated near the centromere of a different chromosome in each of 16 cir0 mapping strains of Saccharomyces cerevisiae. The specific chromosomes containing the integrated 2-microns plasmid DNA were lost at a high frequency after crossing the cir0 strains to cir+ strains. A recessive mutation in a cir+ strain can then be easily assigned to its chromosome using this set of mapping strains, since the phenotype of the recessive mutation will be manifested only in diploids having the integrated 2-microns plasmid and the unmapped mutation on homologous chromosomes.     

广州市屋顶自然生长的植物

本文报道了广州市屋顶自然生长的植物种类调查结果,共记录维管植物49科109属128种.通过调查及分析,推荐16种有较好屋顶绿化潜力的物种.     

Naturally Occurring Mutations in the PA Gene Are Key Contributors to Increased Virulence of Pandemic H1N1/09 Influenza Virus in Mice

We examined the molecular basis of virulence of pandemic H1N1/09 influenza viruses by reverse genetics based on two H1N1/09 virus isolates (A/California/04/2009 [CA04] and A/swine/Shandong/731/2009 [SD731]) with contrasting pathogenicities in mice. We found that four amino acid mutations (P224S in the PA protein [PA-P224S], PB2-T588I, NA-V106I, and NS1-I123V) contributed to the lethal phenotype of SD731. In particular, the PA-P224S mutation when combined with PA-A70V in CA04 drastically reduced the virus''s 50% mouse lethal dose (LD₅₀), by almost 1,000-fold.     

Persistence of Free Plasmid DNA in Soil Monitored by Various Methods, Including a Transformation Assay

The persistence and stability of free plasmid pUC8-ISP DNA introduced into 10-g samples of various soils and kept at 23°C were monitored over a period of 60 days. The soils were sampled at a plant science farm and included a loamy sand soil (no. 1), a clay soil (no. 2), and a silty clay soil (no. 3). Four different methods allowed monitoring of (i) the production of acid-soluble radioactive material from [³H]thymidine-labeled plasmid DNA, (ii) the decrease of hybridizing nucleotide sequences in slot blot analysis, (iii) the loss of plasmid integrity measured by Southern hybridization, and (iv) the decay of the biological activity as determined by transformation of Ca²⁺-treated Escherichia coli cells with the DNA extracted from soil. Acid-soluble material was not produced within the first 24 h but then increased to 45% (soil no. 1), 27% (soil no. 2), and 77% (soil no. 3) until the end of incubation. A quite parallel loss of material giving a slot blot hybridization signal was observed. Southern hybridization indicated that after 1 h in the soils, plasmid DNA was mostly in the form of circular and full-length linear molecules but that, depending on the soil type, after 2 to 5 days full-length plasmid molecules were hardly detectable. The transforming activity of plasmid DNA reextracted from the soils followed inactivation curves over 2 to 4 orders of magnitude and dropped below the detection limit after 10 days. The inactivation was slower in soil no. 2 (28.2-h half-life time of the transforming activity of a plasmid molecule) than in soils no. 3 (15.1 h) and no. 1 (9.1 h). The studies provide data on the persistence of free DNA molecules in natural bacterial soil habitats. The data suggest that plasmid DNA may persist long enough to be available for uptake by competent recipient cells in situ.     

栅藻对水环境中镍的累积效应与机理分析

对不同 Scenedesmus 品种的藻细胞从含镍水溶液(10mg/L)中累积金属镍的能力进行了分析,结果表明:藻细胞对镍的生物累积量表现出明显的品种差异性. Scenedesmus quadricauda FACHB 44 和 Scenedesmus quadricauda FACHB 506 表现出很强的累积能力(累积量达到5～6 mg Ni /g干重),而 Scenedesmus sp. FACHB 416 和 Scenedesmus sp. FACHB 489在相同条件对金属镍累积量要少得多(1～1.5 mg Ni /g干重).这种差异可能与不同品种藻细胞间的形态结构和生理特性是相关的.对 S. quadricauda FACHB 44 重金属抗性和累积能力进一步的分析表明, S. quadricauda FACHB 44用于含镍重金属废水处理是非常有效的,在高浓度(100 mg/L)的镍溶液中,藻细胞的最大累积量能达到(26.7 mg Ni/g 干重).对该藻细胞镍累积动力学分析发现:藻细胞对镍的生物累积包括一个快速的被动吸附过程(5 min, 结合70%的镍)和一个缓慢的耗能累积过程(2～3 h时间内的累积量占总量的20%～30%).与其他藻类相比, S. quadricauda FACHB 44对水溶液中镍的耗能累积量明显高于其他藻类.透射电子显微镜(TEM)和X射线能谱(EDX)分析结果均表明,藻细胞耗能累积的镍主要集中在原生质体中,尤以淀粉粒和染色质中为多.