Stimulation of n-alkane conversion to dicarboxylic acid by organic-solvent- and detergent-treated microbes

Summary A wild-type strain of Cryptococcus neoformans and Pseudomonas aeruginosa were used to convert n-pentadecane to the corresponding dioic acid, tridecane 1,13-dicarboxylic acid (DC-15). Altering the cell permeability by treating C. neoformans with 1% (v/v) toluene or 7% (v/v) Triton X-100 stimulated production of DC-15 by 1.5-fold and fourfold, respectively. Furthermore, DC-15 productivity was increased from 2.5 mg/l per hour to 18 or 30 mg/l per hour, respectively. If 10% (v/v) hexane was used to treat the yeast culture, stimulation of DC-15 production could reach 200% and more viable cells remained compared to the toluene-treated culture. Data from the organic solvent treatment experiment indicated that the solvent with a higher polarity showed a more adverse effect on DC-15 production. P. aeruginosa was vulnerable to most organic solvents; however, Tween 80 could greatly stimulate the conversion of n-pentadecane to DC-15. Although organic solvents and non-ionic detergents could enhance DC-15 formation by microbial conversion, it was inhibited by elevated levels of DC-15.Offprint requests to: E.-C. Chan     

Chaperonins GroEL and GroES: views from atomic force microscopy.

The Escherichia coli chaperonins, GroEL and GroES, as well as their complexes in the presence of a nonhydrolyzable nucleotide AMP-PNP, have been imaged with the atomic force microscope (AFM). We demonstrate that both GroEL and GroES that have been adsorbed to a mica surface can be resolved directly by the AFM in aqueous solution at room temperature. However, with glutaraldehyde fixation of already adsorbed molecules, the resolution of both GroEL and GroES was further improved, as all seven subunits were well resolved without any image processing. We also found that chemical fixation was necessary for the contact mode AFM to image GroEL/ES complexes, and in the AFM images. GroEL with GroES bound can be clearly distinguished from those without. The GroEL/ES complex was about 5 nm higher than GroEL alone, indicating a 2 nm upward movement of the apical domains of GroEL. Using a slightly larger probe force, unfixed GroEL could be dissected: the upper heptamer was removed to expose the contact surface of the two heptamers. These results clearly demonstrate the usefulness of cross-linking agents for the determination of molecular structures with the AFM. They also pave the way for using the AFM to study the structural basis for the function of GroE system and other molecular chaperones.     

Exchanging sequence domains between S-RNases from Nicotiana alata disrupts pollen recognition

In self-incompatible plants of the Solanaceae, the specificity of pollen rejection is controlled by a single multiallelic S-locus. Pollen tube growth is inhibited in the style when its single S-allele matches either S-allele present in the diploid pistil. Each S-allele encodes an S-RNase with a unique sequence. S-RNases are secreted into the extracellular matrix of the transmitting tract which guides pollen tubes toward the ovary. Although it is known that S-RNases are the determinants of S-allele specificity in the pistil, it is not known how allele-specific information is encoded in the sequence. Therefore, we exchanged domains between S-RNases with different recognition specificities and expressed the chimeric proteins in transgenic plants to determine their effects on pollination behavior. Nine chimeric constructs were prepared in which domains from Nicotiana alata S_A2- and S_C10-RNases were exchanged. Among these nine constructs, the entire S-RNase sequence was sampled by exchanging single variable domains as well as larger blocks of contiguous sequences. The chimeric S-RNases retained enzymatic activity and were expressed at levels comparable to control transformants expressing S_A2- and S_C10-RNase. However, none of the chimeric S-RNases caused rejection of either S_A2- or S_C10-pollen. We conclude that the recognition function of S-RNases can be disrupted by alterations in many parts of the sequence. It appears that the recognition function of S-RNase is not localized to a specific domain.     

高原人体左心室舒张功能和顺应性的改变

应用同步描记心电图、心音图、颈动脉搏动图和心尖搏动图以测定高原人体的左心室舒张功能和顺应性。在4个不同海拔高度进行实验,即76m(海平对照)、2161m、3270m和4179m,每一高度40名健康男性青年,高原3组世居、移居各20名。结果显示:随着海拔增高,主动舒张时间指数(TRTI)有减小趋势,RF波相对振幅(F/H)逐渐降低,A波相对振幅(A/D)则渐趋增大,3270m以上增大明显(p<0.05),舒张振幅时间指数(DATI)逐渐降低,3270m以上差异极显著(p<0.001)。高原世居与移居者相比,在海拔4179m出现明显差别,移居组TRTI、DATI、F/H较低而A/D较高(D<0.05)。测定射血前期与左室射血时间比值(PEP/LVET)、射血分数(EF)及左室周径纤维平均缩短速度(mVcf)3项指标作对照,显示在此高度左室收缩功能仍能保持。高原慢性心肌缺氧可能是导致左室舒张功能和顺应性轻度降低的原因。     

High-density Escherichia coli cultivation process for hyperexpression of recombinant porcine growth hormone.

Fermentation studies were performed on an Escherichia coli culture that carries a recombinant plasmid composed of an ampicillin-resistant gene, a temperature-regulated pL promoter, and a porcine pituitary cDNA sequence coding for growth hormone. The objective was to achieve high cell density while maintaining the specific expression level of recombinant porcine growth hormone (r-pGH) observed in shake flasks. At a specific expression level of 20% of total cell protein, the cell density of a glucose-limited fed-batch process reached 38 units of OD600 in 14 h, compared to flask cultivation, which resulted in only 1.4 units of OD600 in the same period. The observed critical fermentation conditions for maximal expression included (1) limiting glucose concentration below 1 g l-1 throughout the fed-batch growth and induction phases, (2) keeping postinduction temperature at 42 degrees C for 5-7 h, and (3) maintaining a postinduction growth rate around 0.17-0.21 h-1.     

Fine structure and histochemistry of the gastric shield in the lamellibranch Donax trunculus L.

The histochemical observations performed by the authors on the stomach wall of Donax trunculus are not wholly in agreement with the results of workers on other bivalves. The ultrastructure of the gastric shield and underlying cells was therefore, studied. It was confirmed that the epithelial cells contain glycogen granules at the base. In addition two distanct P.A.S. positive inclusions were identified: lysosomal residual bodies and neutral mucopolysaccharidic inclusions. The gastric shield is composed largely of long narrow microvilli embedded in a chitinous glycocalyx but is nevertheless easily removable. Hence, there is no causal relationship between abundance of microvilli and the possibility of removing the shield.     

狭叶坡垒传粉生物学初探

狭叶坡垒(Hopea chinensis)为常绿乔木,是我国热带季雨林的代表树种之一。它树型优美,具一定的耐寒性,是我国珍稀濒危保护植物。为阐明其传粉生物学特征和迁地保护的繁殖潜力,该文在引种地桂林植物园对狭叶坡垒的开花物候、花尺寸和花气味进行了观察和测量,运用杂交指数(OCI)、花粉胚珠比(P/O)、花粉活力、柱头活性检测和人工自交等方法对其繁育系统进行了检测,观察了访花昆虫并检验了其传粉效率,通过人工异交检验了繁殖潜力和可能的传粉限制。结果表明:(1)桂林植物园内狭叶坡垒的花期为7月底到9月底,持续60 d左右,一个花序花期约12 d,单花期约3 d,花朵开放时间为17:00—18:45。(2)雌雄同熟,雌蕊空间位置高于雄蕊,高花粉活力和高柱头可授性出现时间基本一致。(3) OCI等于4,P/O为10 788±984。(4)无自动自花授粉能力且自交不亲和,自然条件下和异交授粉能坐果且坐果率无显著差异。(5)蕈蚊是狭叶坡垒唯一的传粉者。(6)主要花香成分为β-榄香烯、(E)-7,11-二甲基-3-亚甲基-1,6,10-十二碳三烯和1-石竹烯。综上所述,狭叶坡垒繁育系统为异交,在迁地保...     

Flow-Cytometric Cell Sorting and Subsequent Molecular Analyses for Culture-Independent Identification of Bacterioplankton Involved in Dimethylsulfoniopropionate Transformations

Marine bacterioplankton transform dimethylsulfoniopropionate (DMSP) into the biogeochemically important and climatically active gas dimethylsulfide. In order to identify specific bacterial taxa mediating DMSP processing in a natural marine ecosystem, we amended water samples from a southeastern U.S. salt marsh with 20 μM DMSP and tracked community shifts with flow cytometry (FCM) coupled to 16S rRNA gene analyses. In two out of four seasons studied, DMSP amendments induced the formation of distinct bacterioplankton populations with elevated nucleic acid (NA) content within 24 h, indicative of cells actively utilizing DMSP. The 16S rRNA genes of the cells with and without elevated NA content were analyzed following cell sorting and PCR amplification with sequencing and terminal restriction fragment length polymorphism approaches. Compared to cells in the control FCM populations, bacteria with elevated NA content in the presence of DMSP were relatively enriched in taxa related to Loktanella, Oceanicola, and Sulfitobacter (Roseobacter lineage, α-Proteobacteria); Caulobacter (α-Proteobacteria); and Brachymonas and Xenophilus (β-Proteobacteria) in the May-02 sample and to Ketogulonicigenium (Roseobacter lineage, α-Proteobacteria) and novel γ-Proteobacteria in the Sept-02 sample. Our study suggests that diverse bacterioplankton participate in the metabolism of DMSP in coastal marine systems and that their relative importance varies temporally.     

盐碱胁迫对染内生菌和不染菌苇状羊茅根系丛枝菌根真菌群落多样性和组成的影响

香柱菌属Epichloë内生真菌存在于宿主植物地上部组织,不仅能提高宿主植物对生物与非生物逆境的抗性,而且能对周围环境中的微生物产生影响。该研究以染内生菌(endophyte-infected,EI)和不染菌(endophyte-free,EF)苇状羊茅Festuca arundinacea为实验材料,探究内生真菌和不同水平盐碱胁迫处理对宿主根系丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)群落多样性和组成的影响。结果表明,内生真菌和盐碱胁迫处理对苇状羊茅根系AMF多样性影响存在交互作用。EF苇状羊茅根系AMF多样性随盐碱胁迫处理水平的增加而降低,内生真菌的存在缓解了这一效应,在200和400 mmol/L盐碱胁迫处理下,内生真菌感染增加了苇状羊茅根系AMF多样性;此外,内生真菌感染改变了苇状羊茅根系AMF群落组成,降低了优势属Funneliformis相对多度,增加了Claroideoglomus、Glomus和unclassified AMF相对多度。结构方程模型结果表明,内生真菌通过间接增加土壤总磷浓度对苇状羊茅根系AMF多样性产生影响。本研究为筛选盐碱污染区生态修复的植物-微生物共生体提供基础。