Effects of CO2 enrichment on the bloom-forming cyanobacterium Microcystis aeruginosa (Cyanophyceae): Physiological responses and relationships with the availability of dissolved inorganic carbon

Microcystis aeruginosa Kutz. 7820 was cultured at 350 and 700 muL.L-1 CO2 to assess the impacts of doubled atmospheric CO2 concentration on this bloom-forming cyanobacterium. Doubling Of CO2 concentration in the airflow enhanced its growth by 52%-77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO2. However, saturating irradiances for photosynthesis and light-saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO2 concentration in the airflow had less effect on DIC-saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO2 and HCO3- levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO2 dissolution into the liquid increased proportionally when CO2 in air was raised from 350 to 700 muL.L-1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO2 could enhance CO2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO3- concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO2 concentrating mechanism might decrease.

Establishment and characterization of dual-species biofilms formed between a 3,5-dinitrobenzoic-degrading strain and bacteria with high biofilm-forming capabilities

In this study, the possibility of establishing a dual-species biofilm from a bacterium with a high biofilm-forming capability and a 3,5-dinitrobenzoic acid (3,5-DNBA)-degrading bacterium, Comamonas testosteroni A3, was investigated. Our results showed that the combinations of strain A3 with each of five strains with a high biofilm-forming capability (Pseudomonas sp. M8, Pseudomonas putida M9, Bacillus cereus M19, Pseudomonas plecoglossicida M21 and Aeromonas hydrophila M22) presented different levels of enhancement regarding biofilm-forming capability. Among these culture combinations, the 24-h dual-species biofilms established by C. testosteroni A3 with P. putida M9 and A. hydrophila M22 showed the strongest resistance to 3,5-DNBA shock loading, as demonstrated by six successive replacements with DMM2 synthetic wastewater. The degradation rates of 3,5-DNBA by these two culture combinations reached 63.3-91.6% and 70.7-89.4%, respectively, within 6 h of every replacement. Using the gfp-tagged strain M22 and confocal laser scanning microscopy, the immobilization of A3 cells in the dual-species biofilm was confirmed. We thus demonstrated that, during wastewater treatment processes, it is possible to immobilize degrader bacteria with bacteria with a high biofilm-forming capability and to enable them to develop into the mixed microbial flora. This may be a simple and economical method that represents a novel strategy for effective bioaugmentation.

Sulfur forming an isoelectronic center in zinc telluride thin films

ZnTe1-xSx epitaxial layers grown on GaAs by molecular-beam epitaxy were studied by photoluminescence (PL) as a function of temperatures, excitation powers, and hydrostatic pressures. A sulfur-related emission peak, labeled as P-2, is identified as a deep-level emission by hydrostatic-pressure PL measurement. This indicates that sulfur atoms form isoelectronic centers in a ZnTe matrix. The results qualitatively agree with the theoretical prediction and show experimental evidence of isoelectronic S in ZnTe. A model is proposed to explain the emission mechanisms in the ZnTe1-xSx system with small x values.

Study of He-induced nano-cavities as sinks of oxygen for forming silicon-on-insulator

In the present work, a Cz-Silicon wafer is implanted with helium ions to produce a buried porous layer, and then thermally annealed in a dry oxygen atmosphere to make oxygen transport into the cavities. The formation of the buried oxide layer in the case of internal oxidation (ITOX) of the buried porous layer of cavities in the silicon sample is studied by positron beam annihilation (PBA). The cavities are formed by 15 keV He implantation at a fluence of 2 x 10(16) cm(-2) and followed by thermal annealing at 673 K for 30 min in vacuum. The internal oxidation is carried out at temperatures ranging from 1073 to 1473 K for 2 h in a dry oxygen atmosphere. The layered structures evolved in the silicon are detected by using the PBA and the thicknesses of their layers and nature are also investigated. It is found that rather high temperatures must be chosen to establish a sufficient flux of oxygen into the cavity layer. On the other hand high temperatures lead to coarsening the cavities and removing the cavity layer finally.

Rational Design, Synthesis, and Optical Properties of Film-Forming, Near-Infrared Absorbing, and Fluorescent Chiromophores with Multidonors and Large Heterocyclic Acceptors

A new series of film-forming, low-bandgap chromophores (1a,b and 2a,b) were rationally designed with aid of a computational study., and then synthesized and characterized. To realize absorption and emission above the 1000 nm wavelength, the molecular design focuses on lowering the LUMO level by fusing common heterocyclic units into a large conjugated core that acts an electron acceptor and increasing the charge transfer by attaching the multiple electron-donating groups at the appropriate positions of the acceptor core. The chromophores have bandgap levels of 1.27-0.71 eV, and accordingly absorb at 746-1003 nm and emit at 1035-1290 nm in solution. By design, the relatively high molecular weight (up to 2400 g mol(-1)) and non-coplanar structure allow these near-infrared (NIR) chromophores to be readily spin-coated as uniform thin films and doped with other organic semiconductors for potential device applications. Doping with [6,6]-phenyl-C-61 butyric acid methyl ester leads to a red shift in the absorption on]), for la and 2a. An interesting NIR electrochromism was found for 2a, with absorption being turned on at 1034 nm when electrochemically switched (at 1000 mV) from its neutral state to a radical cation state. Furthermore, a large Stokes shift (256-318 nm) is also unique for this multidonor-acceptor type of chromophore.

Electrochemical study of gramicidin D forming ion-permeable channels in the bilayer lipid membranes

Gramicidin within the lipid bilayer matrix is a well-known channel-forming polypeptide, but the mechanism of the ions across the membrane induced by gramicidin is not well understood. We found that at very low concentration of gramicidin in a bilayer lipid membrane, the channel behavior was controlled by the voltage applied across the membrane. When the voltage is higher than 75 mV, the channel is closing, while lower than 75 mV, the channel is opening. But when the concentration of the gramicidin in the BLMs is high, the channel behavior is changed into voltage-independent. (C) 1998 Elsevier Science Ltd. All rights reserved.