DFT studies of the phenol adsorption on boron nitride sheets

We perform first principles total energy calculations to investigate the atomic structures of the adsorption of phenol (C₆H₅OH) on hexagonal boron nitride (BN) sheets. Calculations are done within the density functional theory as implemented in the DMOL code. Electron-ion interactions are modeled according to the local-spin-density-approximation (LSDA) method with the Perdew-Wang parametrization. Our studies take into account the hexagonal h-BN sheets and the modified by defects d-BN sheets. The d-BN sheets are composed of one hexagon, three pentagons and three heptagons. Five different atomic structures are investigated: parallel to the sheet, perpendicular to the sheet at the B site, perpendicular to the sheet at the N site, perpendicular to the central hexagon and perpendicular to the B-N bond (bridge site). To determine the structural stability we apply the criteria of minimum energy and vibration frequency. After the structural relaxation phenol molecules adsorb on both h-BN and d-BN sheets. Results of the binding energies indicate that phenol is chemisorbed. The polarity of the system increases as a consequence of the defects presence which induces transformation from an ionic to covalent bonding. The elastic properties on the BN structure present similar behavior to those reported in the literature for graphene.     

Hydrolysis of fish oil by hyperactivated rhizomucor miehei lipase immobilized by multipoint anion exchange

Rhizomucor miehei lipase (RML) is greatly hyperactivated (around 20‐ to 25‐fold toward small substrates) in the presence of sucrose laurate. Hyperactivation appears to be an intramolecular process because it is very similar for soluble enzymes and covalently immobilized derivatives. The hyperactivated enzyme was immobilized (in the presence of sucrose laurate) on cyanogen bromide‐activated Sepharose (very mild covalent immobilization through the amino terminal residue), on glyoxyl Sepharose (intense multipoint covalent immobilization through the region with the highest amount of Lys residues), and on different anion exchangers (by multipoint anionic exchange through the region with the highest density of negative charges). Covalent immobilization does not promote the fixation of the hyperactivated enzyme, but immobilization on Sepharose Q retains the hyperactivated enzyme even in the absence of a detergent. The hydrolysis of fish oils by these hyperactivated enzyme derivatives was sevenfold faster than by covalently immobilized derivatives and three and a half times faster than by the enzyme hyperactivated on octyl‐Sepharose. The open structure of the hyperactivated lipase is fairly exposed to the medium, and no steric hindrance should interfere with the hydrolysis of large substrates. These new hyperactivated derivatives seem to be more suitable for hydrolysis of oils by RML immobilized inside porous supports. In addition, the hyperactivated derivatives are fairly stable against heat and organic cosolvents. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011     

Getting a grip on the intertidal: flow microhabitat and substratum type determine the dislodgement of the crab Pachygrapsus crassipes (Randall) on rocky shores and in estuaries

Hydrodynamic forces can affect survival as well as limit the movement of motile benthic animals. An animal's danger of dislodgement depends on the hydrodynamic forces it experiences in its microhabitat relative to the force required to dislodge it (tenacity) from the substratum. We measured water flow and substratum characteristics in two different habitats of the shore crab Pachygrapsus crassipes: a wave-swept rocky shore and an intertidal mudflat. The maximum water velocities and accelerations in the microhabitats of the crabs at the wave-swept site were three times and two times greater, respectively, than at the mudflat site. In the laboratory, we measured the tenacity of crabs of various sizes on different substrata, and also measured their drag, lift and added-mass coefficients. Using these data, we calculated the flow conditions under which crabs would be overturned or sheared off the substratum in their two habitats. The net horizontal force (drag plus acceleration reaction) required to dislodge a crab on a rugose rock substratum was an order of magnitude greater than on smooth rock and two orders of magnitude greater than on mud. Our calculations indicate that, under non-storm conditions, crabs will not be dislodged from the substratum in either the mudflat or the wave-swept habitat when grasping the substratum with maximum tenacity. Moving crabs have lower tenacity and our calculations predict that hydrodynamic forces will restrict the mobility of large crabs more than that of small ones on smooth, but not on rugose rock.     

PHENOTYPIC PLASTICITY INDUCED IN TRANSPLANT EXPERIMENTS IN A MUTUALISTIC ASSOCIATION BETWEEN THE RED ALGA JANIA ADHAERENS (RHODOPHYTA,CORALLINALES) AND THE SPONGE HALICLONA CAERULEA (PORIFERA: HAPLOSCLERIDA): MORPHOLOGICAL RESPONSES OF THE ALGA1

The association between the red macroalga Jania adhaerens J. V. Lamour. and the sponge Haliclona caerulea is the most successful life‐form between 2 and 4 m depth in Mazatlán Bay (Mexican Pacific). J. adhaerens colonizes the rocky intertidal area and penetrates into deeper areas only when it lives in association with H. caerulea. The aposymbiotic form of the sponge has not been reported in the bay. To understand the ecological success of this association, we examined the capacity of J. adhaerens to acclimate in Mazatlán Bay using transplant experiments. The transplanted aposymbiotic J. adhaerens did not survive the first 2 weeks; however, J. adhaerens when living in association with H. caerulea, acclimated easily to depth, showing no sign of mortality during the 103 d of the experiment. We conclude that the ability of J. adhaerens to colonize in deeper areas in this hydrodynamic environment may in part rely on the protection provided by the sponge to the algal canopy. Both species contribute to the shape of the associated form. Nevertheless, the morphological variation in the association appears to be dominated by the variation in J. adhaerens canopy to regulate pigment self‐shading under light‐limited conditions and/or tissue resistance under high hydrodynamics. Consequently, our results are consistent with light as the abiotic controlling factor, which regulates the lower depth distribution of the association in Mazatlán Bay, through limiting the growth rate of J. adhaerens. Hydrodynamics may determine the upper limit of the association by imposing high mass losses.     

Temperature influences the expression of fimbriae and flagella in <Emphasis Type="Italic">Hafnia alvei</Emphasis> strains: an immunofluorescence study

Hafnia alvei, a Gram negative bacillus related to the Enterobacteriaceae family, is considered an opportunistic pathogen of several animal species and humans. In this communication, we describe fimbrial-like structures from different strains of H. alvei that cannot be easily ascribed to any of the previously reported fimbrial types in this species (type I or type III). Polymerase chain reaction (PCR) and immunofluorescence assays were carried out to study fimbriae and flagella in H. alvei strains isolated from different sources. No correlation between the results obtained by PCR and those obtained by phenotypic methods were found, and the antibodies used gave cross or different recognition patterns of the surface structures present in these strains. We report as well that strain and growth temperature influence fimbriation and expression of flagella in human and animal isolates of H. alvei. This study also indicates that the absence of fimbriae have a significant positive influence on the initial adhesion of H. alvei to human epithelial cells.     

Halobacterial megaplasmids are negatively supercoiled

Several covalently closed circular halobacterial megaplasmids (up to more than 500 kb) from different strains of Halolerax mediterranei, have been resolved by orthogonal-field alternating gel electro-phoresis (OFAGE). These molecules seem to be negatively supercoiled in vivo, as deduced from the effect of intercalating agents affecting their topology and, therefore, their electrophoretic mobility. It has also been demonstrated that the topolsomerase II Inhibitor novobiocin affects the native topological state of halobacterial megaplasmids impeding their migration in OFAGE under standard conditions for resolution of large supercoiled molecules.     

Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant

The effect of mixing on biogas production of a 1.5‐m³ pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.