186,311 research outputs found
Aggregation of Cesium Perfluorooctanoate on Poly(ethylene glycol) Oligomers in Water
No full textThe interaction of cesium perfluorooctanoate (CsPFO) with poly(ethylene glycol) (PEG) of different molecular
weight (300 e MW e 20000 Da) has been investigated at 298.15 K by isothermal titration calorimetry
(ITC), density, viscosity, and conductivity measurements. Calorimetric titrations exhibited peculiar trends
analogous to those already observed for sodium dodecyl sulfate (SDS). Micelles of the perfluorosurfactant,
as compared to those of SDS, yield complexes with the polymer of similar thermodynamic stability but are
able to interact with shorter PEG oligomers. The average number of surfactant molecules bonded per polymer
chain at the saturation is about twice that observed for SDS. ITC data at 308.15 K indicate a larger
thermodynamic stability of the aggregates but an almost constant stoichiometry. The peculiar thermal effects
and the viscosity trend observed during the titration of an aqueous PEG solution with the surfactant appear
consistent with a conformational change of the polymer. The PEG chain would evolve from a strained to an
expanded conformation, induced by the growing of the surfactant micellar clusters bonded to the polymer, as
suggested in a previous study of the PEG/SDS/H2O system
Vanillin production using metabolically engineered <it>Escherichia coli </it>under non-growing conditions
No full textAbstract Background Vanillin is one of the most important aromatic flavour compounds used in the food and cosmetic industries. Natural vanillin is extracted from vanilla beans and is relatively expensive. Moreover, the consumer demand for natural vanillin highly exceeds the amount of vanillin extracted by plant sources. This has led to the investigation of other routes to obtain this flavour such as the biotechnological production from ferulic acid. Studies concerning the use of engineered recombinant Escherichia coli cells as biocatalysts for vanillin production are described in the literature, but yield optimization and biotransformation conditions have not been investigated in details. Results Effect of plasmid copy number in metabolic engineering of E. coli for the synthesis of vanillin has been evaluated by the use of genes encoding feruloyl-CoA synthetase and feruloyl hydratase/aldolase from Pseudomonas fluorescens BF13. The higher vanillin production yield was obtained using resting cells of E. coli strain JM109 harbouring a low-copy number vector and a promoter exhibiting a low activity to drive the expression of the catabolic genes. Optimization of the bioconversion of ferulic acid to vanillin was accomplished by a response surface methodology. The experimental conditions that allowed us to obtain high values for response functions were 3.3 mM ferulic acid and 4.5 g/L of biomass, with a yield of 70.6% and specific productivity of 5.9 μmoles/g × min after 3 hours of incubation. The final concentration of vanillin in the medium was increased up to 3.5 mM after a 6-hour incubation by sequential spiking of 1.1 mM ferulic acid. The resting cells could be reused up to four times maintaining the production yield levels over 50%, thus increasing three times the vanillin obtained per gram of biomass. Conclusion Ferulic acid can be efficiently converted to vanillin, without accumulation of undesirable vanillin reduction/oxidation products, using E. coli JM109 cells expressing genes from the ferulic acid-degrader Pseudomonas fluorescens BF13. Optimization of culture conditions and bioconversion parameters, together with the reuse of the biomass, leaded to a final production of 2.52 g of vanillin per liter of culture, which is the highest found in the literature for recombinant strains and the highest achieved so far applying such strains under resting cells conditions.</p
Lutein production by coccomyxa sp. SCCA048 isolated from a heavy metal-polluted river in Sardinia (Italy)
No full text
Lutein production by coccomyxa sp. SCCA048 isolated from a heavy metal-polluted river in Sardinia (Italy)
No full textThe unicellular green alga, Coccomyxa sp. SCCA048 was previously isolated scraping the ferrous material deposited on the rocks along the heavy metals-contaminated river 'Rio Irvi' (Arburese mining district, Sardinia, Italy). The kinetics of autotrophic growth and pigment production of the strain in stressing (continuous light) and control cultures (12: 12 light-dark photoperiod) was described. Time course of both cultures reflected typical microbial growth curves. The maximum cell densities (3.1 × 107 and 1.1 × 107 cell/ml, for continuous light and control cultures, respectively) were found at the end of log phase (day 40). However, continuous light conditions accounted for ≅ 280% higher density than control cultures. The specific growth rate (μ) of the microalga during exponential phase in continuous light was 1.5 times higher than that recorded for the control. The pigment profile, characterised by HPLC, was particularly rich in carotenoids, especially lutein (up to 80% of total carotenoids). The algal strain, cultivated in continuous light, showed high intracellular contents of lutein (0.34 pg/cell) at the beginning of the exponential phase. In addition, lutein cell content, at maximum growth, was higher than those reported in literature for others carotenogenic strains of Coccomyxa. Pigment production by control cultures was always much lower. These data suggested that the microalga cultivated under conditions of stressing light might have potential for the large-scale production of antioxidant carotenoids
Calorimetric investigation of the Interaction between Lithium Perfluorononanoate and Poly(ethylene glycol) Oligomers in Water
No full textThe interaction of lithium perfluorononanoate (LiPFN) with poly(ethylene glycol) (PEG) molecules of different
molecular weights (300 < MW < 20000 Da) has been investigated in water at 298.15 and 308.15 K by isothermal
titration calorimetry (ITC). Density, viscosity, and conductivity measurements were also performed at 298.15 K. The
aggregation process of this surfactant on the PEG polymeric chain was found to be very similar to that exhibited by
cesium perfluorooctanoate (CsPFO) and appears to be consistent with the necklace model. ITC titrations indicated
that a fully formed LiPFN micellar cluster can be wrapped by a PEG chain having a molecular weight (MW) of 3200
Da, longer than that required by the shorter perfluorooctanoate (MW 2600 Da), and also suggested a stepwise
mechanism for the aggregation of successive micelles. Viscosity data indicate that the formation of polymer-surfactant
complexes between PEG and LiPFN involves a conformational change of the polymer. The aggregation of preformed
micelles of LiPFN or CsPFO or SDS on the PEG polymeric chain always gives rise to further stabilization
Study of bacterial diversity of a saltern crystallization pond ("Saline di Tarquinia, Italy) and its correlation with salinity variations
No full textBARGHINI P., PASQUALETTI M., GORRASI S., AND FENICE M. 2018. Study of bacterial diversity of a saltern crystallization pond (“Saline di Tarquinia", Italy) and its correlation with salinity variations. J environ prot ecol. 19(1): 139–145.
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Bioconversion of ferulate into vanillin by Escherichia coli strain JM109/pBB1 in an immobilized-cell reactor
No full textThe present work deals with a novel bioconversion of ferulate into vanillin using resting cells of Escherichia coli strain JM/109pBB1 as a biocatalyst. Biomass recycling from four successive bioconversion steps demonstrated the possibility of employing the proposed resting cell system for the continuos production of vanillin. Among the tested immobilization supports (polyurethane, synthetic sponge and porous glass)the synthetic sponge proved to be the best material in terms of both vanillin formation (Cv=0.080 g/l) and productivity (Qv=0.019 g/lh) at the end of entrapment tests. Thus, it was used in preliminary continuos tests using a fixed-bed column with immobilized E. coli JM/109pBB1 cells. The highest vanillin yield (YP/S=0.851 mol/mol) was obtained at a dilution rate of 0.022 1/h
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