Stable integration of foreign DNA into the chromosome of the cyanobacterium Synechococcus R2

The blue-green alga, Synechococcus R2, is transformed to antibiotic resistance by chimeric DNA molecules consisting of Synechococcus R2 chromosomal DNA linked to antibiotic-resistance genes from Escherichia coli. Chimeric DNA integrates into the Synechococcus R2 chromosome by homologous recombination. The efficiency of transformation, as well as the stability of integrated foreign DNA, depends on the position of the foreign genes relative to Synechococcus R2 DNA in the chimeric molecule. When the Synechococcus R2 DNA fragment is interrupted by foreign DNA, integration occurs through replacement of chromosomal DNA by homologous chimeric DNA containing the foreign insert; transformation is efficient and the foreign gene is stable. Mutagenesis in some cases attends integration, depending on the site of insertion. Foreign DNA linked to the ends of Synechococcus R2 DNA in a circular molecule, however, integrates less efficiently. Integration results in duplicate copies of Synechococcus R2 DNA flanking the foreign gene and the foreign DNA is unstable. Transformation in Synechococcus R2 can be exploited to modify precisely and extensively the genome of this photosynthetic microorganism.     

Biotechnology applied to mining of metals

The present review describes the advances achieved during the last two years in the application of biotechnological principles in the extraction of metals from ores and minerals. Despite the fact that this branch of science is very young and many details are yet to be understood, the microbes are applied at commercial levels especially for the extraction of copper and uranium from low-grade ores. The technique is far from being developed to its full potential and it is generally recognized to be a technology of the future. The studies involved are complex and multidisciplinary in nature.     

Immunosuppressive properties of leukotriene D4 and E4 in vitro

Leukotrienes D₄ and E₄ whose physiological function has been associated with smooth muscle contraction, are demonstrated to be potent suppressors of immunocompetent cell function. In concentrations as low as 10^?12 M both leukotriene D₄ and E₄ can inhibit mitogen-induced lymphocyte transformation. Higher concentrations of leukotrienes E₄ and D₄ will inhibit appearance of antibody-forming cells in tissue culture. These data suggest another role for the leukotrienes in addition to their function as slow-reacting substances.     

2-Heptanone Production by Spores of Penicillium roquefortii in a Water-Organic Solvent Two-Phase System

The production of 2-heptanone from octanoic acid may be performed by free and entrapped spores of Penicillium roquefortii in a water-organic solvent two phase system.

An industrial, isoparafflnic solvent, i.e. Hydrosol IP 230 O.S., which may be considered as tetradecane, is well suited for the process. Activities nearly double those achieved with aqueous systems are observed using an initial fatty acid content in the organic layer close to 100 mM and a ratio of the volume of the organic phase to the total volume of the medium of 0.88. The presence of the solvent allows a better recovery of the metabolite by lowering its activity coefficient.

Fed-batch experiments performed in an aerated, stirred reactor show that the bioconversion may proceed in the two-phase system for at least 300 h. These conditions allow conversion of 750 mM (108 g · 1^-1) fatty acid, and production of 600 mM (68.5 g · 1^-1) 2-heptanone.     

不同胃疾患胃内微生态变化的研究

本文对75例不同胃疾患胃液内的菌群及影响胃内微生态环境的因素进行了研究,发现健康胃内基本无菌或只有少量口腔细菌,未发现厌氧菌。而不同胃疾患胃内均分离到细菌(log10~n/ml),慢性萎缩性胃炎:3.89±0.99,残胃炎:4.45±0.16,胃癌:4.23,十二指肠球部溃疡治疗前(2.8±0.62)与抗酸治疗后(4.35±0.61)差别显著,慢性浅表性胃炎:3.39±0.98,胃溃疡:3.42±0.29。所分离到的细菌既有来自于口腔的细菌,也有来自于肠道的细菌。影响胃内细菌增殖的主要因素是胃液的PH值,幽门功能失调及幽门切除亦可使胃内细菌过度生长。本研究提示对胃病的治疗亦应进行生态防治。     

Characterization of initial events in bacterial surface colonization by two Pseudomonas species using image analysis

The processes leading to bacterial colonization on solidwater interfaces are adsorption, desorption, growth, and erosion. These processes have been measured individually in situ in a flowing system in real time using image analysis. Four different substrata (copper, silicon, 316 stainless-steel and glass) and 2 different bacterial species (Pseudomonas aeruginosa and Pseudomonas fluorescens) were used in the experiments. The flow was laminar (Re = 1.4) and the shear stress was kept constant during all experiments at 0.75 N m(-2). The surface roughness varied among the substrata from 0.002 mum (for silicon) to 0.015 mum (for copper). Surface free energies varied from 25.1 dynes cm(-1) for silicon to 31.2 dynes cm(-1) for copper. Cell curface hydrophobicity, reported as hydrocarbon partitioning values, ranged from 0.67 for Ps. fluorescens to 0.97 for Ps. aeruginosa.The adsorption rate coefficient varried by as much as a factor of 10 among the combinations of bacterial strain and substratum material, and was positively correlated with surface free energy, the surface roughness of the substratum, and the hydrophobicity of the cells. The probability of desorption decreased with increasing surface free energy and surface roughness of the substratum. Cell growth was inhibited on copper, but replication of cells overlying an initial cell layer was observed with increased exposure time to the cell-containing bulk water. A mathematical model describing cell accumulation on a substratum is presented.     

Settlement of the diazotrophic,phytoeffective bacterial strain Pantoea agglomerans on and within winter wheat: An investigation using ELISA and transmission electron microscopy

The aim of this study was to investigate the ability of Pantoea agglomerans, a plant growth-promoting bacterium, to colonize various regions and tissues of the wheat plant (Triticum aestivum L.) by using different inoculation methods and inoculum concentrations. In addition, the enzyme-linked immunosorbent assay (ELISA) and transmission electron microscopy (TEM) were used to determine: (a) the ability of the bacterial cells to grow and survive both on the surface and within internal tissue of the plant and (b) the response of the plant to bacterial infection. After inoculation, cells of the diazotrophic bacterial strain P. agglomerans were found to be located in roots, stems and leaves. Colony development of bacterial cells was only detected within intercellular spaces of the root and on the root surface. However, single bacterial cells were observed in leaves and stems on the surface of the epidermis, in the vicinity to stomatal cells, within intercellular spaces of the mesophyll and within xylem vessels. Inoculated bacterial cells were found to be able to enter host tissues, to multiply in the plant and to maintain a delicate relationship between endophyte and host. The density of bacterial settlement in the plant in all experiments was about 10⁶ to 10⁷ cells per mL root or shoot sap. Establishment was confirmed by a low coefficient of variation of ELISA means at these concentrations.     

Testing of different antibiotics against Gram-positive and Gram-negative bacteria isolated from plant tissue culture

Different Gram-positive and Gram-negative bacteria (Staphylococcus xylosus, S. aureus, S. cohnii, Bacillus sp., Corynebacterium sp., Pseudomonas vesicularis) were isolated from homogenized shoot tips of Drosera rotundifolia, Spatiphyllum sp., Syngonium cv. White butterfly, Nephrolepis exaltata cv. Teddy Junior. Growth inhibition of selected bacterial strains was examined using 28 different single antibiotics and 7 antibiotic mixtures. It was found that with the two mixtures Imipenem/Ampicillin and Imipenem/Penicillin G at concentrations of 5 mg l^–1 each, bacterial growth inhibition was most effective. Because of the lack of toxic effects on in vitro plants of 7 species it was proposed that these antibiotic mixtures can be applied advantageously to inhibit bacterial growth in tissue culture.     

Measurement of bacterial random motility and chemotaxis coefficients: I. Stopped-flow diffusion chamber assay

Bacterial chemotaxis, the directed movement of a cell population in response to a chemical gradient, plays a critical role in the distribution and dynamic interaction of bacterial populations in nonmixed systems. Therefore, in order to make reliable predictions about the migratory behavior of bacteria within the environment, a quantitative characterization of the chemotactic response in terms of intrinsic cell properties is needed.The design of the stopped-flow diffusion chamber (SFDC) provides a well-characterized chemical gradient and reliable method for measuring bacterial migration behavior. During flow through the chamber, a step change in chemical concentration is imposed on a uniform suspension of bacteria. Once flow is stopped, diffusion causes a transient chemical gradient to develop, and bacteria respond by forming a band of high cell density which travels toward higher concentrations of the attractant. Changes in bacterial spatial distributions observed through light scattering are recorded on photomicrographs during a 10-min period. Computer-aided image analysis converts absorbance of the photographic negatives to a digital representation of bacterial density profiles. A mathematical model (part II) is used to quantitatively characterize these observations in terms of intrinsic cell parameters: a chemotactic sensitivity coefficient, mu(0), from the aggregate cell density accumulated in the band and a random motility coefficient, mu, from population dispersion in the absence of a chemical gradient.Using the SFDC assay and an individual-cell-based mathematical model, we successfully determined values for both of these population parameters for Escherichia coli K12 responding to fucose. The values obtained were mu = 1.1 +/- 0. 4 x 10(-5) cm(2)/s and chi(o) = 8 +/- 3 +/- 10(-5) cm(2)/s. We have demonstrated a method capable of determining these parameter values from the now validated mathematical model which will be useful for predicting bacterial migration in application systems.