Utilization of Agro-industrial Residues for Poly(3-hydroxyalkanoate) Production by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> 42A2 (NCIMB 40045): Optimization of Culture Medium

In this study, central composite design and a response surface methodology are shown to be useful tools for medium optimization, in cultures of Pseudomonas aeruginosa 42A2 using an industrial oil byproduct, for polyhydroxyalkanoate (PHA) production. The optimum medium composition for PHA production includes: 80 g/L of the carbon source; 18.2 g/L of NaNO₃ and 3.3 g/L of K₂HPO₄/1.6 g/L KH₂PO₄ (R ² = 0.989). The models were validated experimentally by cultivating Pseudomonas aeruginosa 42A2 in optimum media that yielded similar biomass (18.73 g/L) and PHA (4.63 g/L) concentrations to the predicted values. The optimized media showed an increase in biomass productivity from 0.06 to 0.39 g biomass/L h, and an increase in PHA productivity from 0.03 to 0.1 g PHA/L h.     

Comparing simulation algorithms for multienvironment probabilistic P systems over a standard virtual ecosystem

Membrane Computing has recently proved to be a suitable framework for addressing the modelling of dynamical biological systems in general, and ecosystems in particular. Due to the inherent randomness and uncertainty in biological systems, when designing a model the relevant tasks to be addressed are the validation and virtual experimentation processes, rather than the formal verification. It is therefore crucial to rely on software implementations of efficient simulation algorithms. This paper presents a simple (but realistic enough) ecosystem where a carnivore and several herbivorous species interact. The model of this ecosystem has been used to compare experimentally the performance of two different simulation algorithms.     

A new strategy for controlling shrinkage of DGEBA resins cured by cationic copolymerization with hydroxyl‐terminated hyperbranched polymers and ytterbium triflate as an initiator

We report a novel strategy for preparing epoxy thermosetting systems with low shrinkage and improved flexibility and degradability. Diglycidyl ether of bisphenol A (DGEBA) resin was cured with different proportions of hydroxyl‐terminated hyperbranched polymer (HBP), using ytterbium triflate as a cationic initiator. The curing process was studied using differential scanning calorimetry and thermomechanical analysis. Characterization of the resulting materials was evaluated using DSC, thermogravimetric analysis, and dynamic mechanical thermal analysis, and the fracture surface was studied using scanning electron microscopy (SEM). When DGEBA is modified with HBP, it shows a homogeneous morphology and the HBP is incorporated chemically into the network, because hydroxyl groups can react with epoxides under cationic conditions. Higher proportions of HBP reduce the glass transition temperature (T_g) and thermal stability and increase the flexibility. When the proportion of HBP in the curing mixture is increased, the degree of shrinkage is reduced significantly and expansion can be observed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of new reworkable thermosetting coatings obtained by cationic and anionic curing of DGEBA and some Meldrum acid derivatives

Rare earth metal triflates, BF₃·MEA and N,N-dimethylaminopyridine (DMAP) were used as cationic and anionic initiators to cure mixtures of diglycidylether of bisphenol A (DGEBA) and Meldrum acid (2,2-dimethyl-4,6-dioxo-1,3-dioxane) derivatives in several proportions. The copolymerization process led to poly(ether-ester) three-dimensional networks. The linear ester groups in the final materials were evaluated by Fourier transform infrared in the attenuated-total-reflection mode (FTIR/ATR).     

Chemoenzymatic synthesis and antimicrobial and haemolytic activities of amphiphilic bis(phenylacetylarginine) derivatives

Novel bis(N(alpha)-phenylacetyl-L-arginine)-alpha,omega-alkanediamide dihydrochloride (bis(PhAcArg)) derivatives with antimicrobial activity were designed and synthesised by a chemoenzymatic strategy. The new structures consist of two N(alpha)-phenylacetyl-L-arginine moieties connected by an alkanediamine spacer chain of 6, 8, 10, 12, and 14 methylene units through amide bonds. The key step in the chemoenzymatic strategy is the double aminolysis of the N(alpha)-phenylacetyl-L-arginine methyl ester by the corresponding alpha,omega-alkanediamine catalyzed by papain in ethanolic media. The compounds synthesised were tested as antimicrobials against 15 bacterial and 8 fungal species. The antimicrobial activity and selectivity depend strongly on the spacer chain length. The bis(PhAcArg) derivative with the spacer chain of 12 methylene groups gave the lowest MIC values against Gram-positive bacteria, whereas that with 14 methylene units was the best against Gram-negative bacteria. Interestingly, these novel compounds showed enhanced antibacterial activity relative to the lead compound, bis(N(alpha)-caproyl-L-arginine)-1,3-propanediamide dihydrochloride (C(3)(CA)(2)), and moderate antifungal activity. Moreover, tests of haemolytic activity toward human erythrocytes revealed that haemolysis increases with spacer chain length. Importantly, the compounds were classified as not irritating to eyes, with the exception of the compound with the spacer chain of 14 methylene groups, which was a slight eye irritant.     

Fertilizer characterization: isotopic data (N, S, O, C, and Sr)

A detailed isotopic characterization (delta15N(Ntotal), delta15N(NO3), delta18O(NO3), delta34S(SO4), delta18O(SO4), (delta13C(Ctotal), and 87Sr/86Sr) of 27 commercial fertilizers used in Spain is presented in this paper. Results together with a compilation of fertilizer isotopic published data are used for two purposes: (i) to identify the origin of the primary constituents and raw materials used in fertilizer manufacture and relate these data with their heavy metals and rare earth elements (REE) contents; (ii) to compare the fertilizer isotopic signatures with natural values and other anthropogenic pollutants and evaluate the usefulness of multi-isotopic analyses to trace fertilizer contaminations in future study cases. Isotope data permit us to know, in most cases, the origin of the primary constituents of fertilizers, and the 87Sr/86Sr ratio distinguishes the origin of the phosphate content--phosphorites or carbonatites--which in turn implies a qualitatively defined and potentially contaminant presence of REE and heavy metals in fertilizers. Delta15N, delta34S, and 87Sr/86Sr have already been used to trace fertilizer contaminations. Their utility can be improved by the coupled use of delta15N(NO3)-delta18O(NO3) and delta34S(SO4)-delta18O(SO4) to evaluate the fractionation processes that can affect contaminants. Moreover, multi-isotopic analyses, using heavy isotopes, allow us to see beyond the fractionation effects to the fertilizer stable isotope signatures and a better distinction from other anthropogenic contaminants.     

New chemically reworkable epoxy coatings obtained by the addition of polyesters with star topologies to diglycidyl ether of bisphenol A resins

A new multiarm star with hyperbranched aromatic–aliphatic polyester core and poly(?-caprolactone) arms (HBPCL) was synthesized and characterized. Mixtures of diglycidyl ether of bisphenol A (DGEBA) resin and different proportions of this star type modifier were cured using a thermal cationic curing agent, Yb(OTf)₃. The HBPCL prepared has hydroxyl groups as chain ends, which are capable of chemically incorporating to the epoxy matrix by means of the monomer activated mechanism. This, together with the chemical structure of the modifier, allowed the preparation of new homogeneous thermosets for coating applications. The curing mixtures were investigated by differential scanning calorimetry (DSC) to study the curing process and evaluate the kinetic parameters of the formulations. These studies demonstrated that HBPCL decreased the curing rate and affected the gelation process. The thermosets obtained showed an improvement in impact strength with a discrete reduction of the T_g. The modified coatings showed an increased reworkability in alkaline solution with the maintenance of thermal stability.     

Utilization of response surface methodology to optimize the culture media for the production of rhamnolipids by Pseudomonas aeruginosa AT10

Pseudomonas aeruginosa AT10 produced a mixture of surface‐active rhamnolipids when cultivated on mineral medium with waste free fatty acids as carbon source. The development of the production process to an industrial scale included the design of the culture medium. A 2⁴ full factorial, central composite rotational design and response surface modelling method (RSM) was used to enhance rhamnolipid production by Pseudomonas aeruginosa AT10. The components that are critical for the process medium were the carbon source, the nitrogen source (NaNO₃), the phosphate content (K₂ HPO₄/KH₂PO₄ 2:1) and the iron content (FeSO₄·7H₂O). Two responses were measured, biomass and rhamnolipid production. The maximum biomass obtained was 12.06 g dm^?3 DCW, when the medium contained 50 g dm^?3 carbon source, 9 g dm^?3 NaNO₃, 7 g dm^?3 phosphate and 13.7 mg dm^?3 FeSO₄·7H₂O. The maximum concentration of rhamnolipid, 18.7 g dm^?3, was attained in medium that contained 50 g dm^?3 carbon source, 4.6 g dm^?3 NaNO₃, 1 g dm^?3 phosphate and 7.4 mg dm^?3 FeSO₄·7H₂O. © 2002 Society of Chemical Industry     

Identification of (e)-11-hydroxy-9-octadecenoic acid and (E)-9-hydroxy-10-octadecenoic acid by biotransformation of oleic acid by Pseudomonas sp. 32T3

Pseudomonas sp. 32T3, a newly identified strain originally isolated from a vegetable oil-contaminated soil, produces three monohydroxy acids—(E)-11-hydroxy-9-octadecenoic acid, (E)-10-hydroxy-8-octadecenoic acid, and (E)-9-hydroxy-10-octadecenoic acid—as bioconversion products of oleic acid. The bacterial cells were grown in a mineral medium containing oleic acid as the main carbon substrate. The compounds were identified as the corresponding methyl esters on the basis of their chromatographic and spectroscopic (¹H and ¹³C nuclear magnetic resonance and gas chromatography-mass spectrometry) features.     

Influence of volatile compounds on the development of off-flavours in pig back fat samples classified with boar taint by a test panel

Dynamic Head Space methodology was applied to evaluate the possible contribution of some volatile compounds to the development of boar taint in pig backfat samples with low concentrations of skatole and androstenone, but which had previously been classified as tainted by a trained test panel. Volatile compounds were collected in a trap of graphited charcoal and analysed by GC–MS in Scan mode. Aldehydes and short chain fatty acids, compounds that play a significant role in the development of undesirable aromas in food products, were the main classes of compounds identified in this study, although the possible contribution of other compounds that were detected in a minor proportion – such as alcohols and ketones – was evaluated. Styrene and 1,4-dichlorobenzene, compounds that may have come from an external contamination, showed a high concentration in the samples classified with boar taint, so these compounds could have been responsible for the development of some off-flavours in the fat samples studied in this work. In the same study, skatole and androstenone were also determined by normal phase HPLC and GCMS, respectively.