Comparative Genomics Within the Bacillus Genus Reveal the Singularities of Two Robust Bacillus amyloliquefaciens Biocontrol Strains.

Bacillus amyloliquefaciens CECT 8237 and CECT 8238, formerly known as Bacillus subtilis UMAF6639 and UMAF6614, respectively, contribute to plant health by facing microbial pathogens or inducing the plant's defense mechanisms. We sequenced their genomes and developed a set of ad hoc scripts that allowed us to search for the features implicated in their beneficial interaction with plants. We define a core set of genes that should ideally be found in any beneficial Bacillus strain, including the production of secondary metabolites, volatile compounds, metabolic plasticity, cell-to-cell communication systems, and biofilm formation. We experimentally prove that some of these genetic elements are active, such as i) the production of known secondary metabolites or ii) acetoin and 2-3-butanediol, compounds that stimulate plant growth and host defense responses. A comparison with other Bacillus genomes permits us to find differences in the cell-to-cell communication system and biofilm formation and to hypothesize variations in their persistence and resistance ability in diverse environmental conditions. In addition, the major protection provided by CECT 8237 and CECT 8238, which is different from other Bacillus strains against bacterial and fungal melon diseases, permits us to propose a correlation with their singular genetic background and determine the need to search for additional blind biocontrol-related features.

Rotational diffusion of coumarin 153 in nanoscopic micellar environments of n-dodecyl-ß-D-maltoside and n-dodecyl-hexaethylene-glycol mixtures.

The microstructure of mixed micelles containing n-dodecyl-ß-D-maltoside and n-dodecyl-hexaethylene-glycol, two nonionic surfactants belonging to the alkyl polyglucoside and polyoxyethyelene alkyl ether families, respectively, has been investigated. With the aim of understanding how the micellar composition affects the microenvironmental properties of micelles, we have examined the photophysics and dynamics of the neutral probe coumarin 153 in the binary mixtures of the surfactants across the entire composition range. We present data on the steady-state absorption and emission spectra of the probe, as well as fluorescence lifetimes and both steady-state and time-resolved fluorescence anisotropies. These data indicate that the participation of the ethoxylated surfactant in the mixed micelle induces an increasing hydration in the palisade layer of the micelle, which forces the probe to migrate toward the inner micellar region, where it senses a slightly less polar environment. The time-resolved fluorescence anisotropy data were analyzed on the basis of the two-step and wobbling-in-cone model. The average reorientation time of the probe molecule was found to decrease with the presence of the ethoxylated surfactant, in good agreement with steady-state fluorescence anisotropy data, suggesting a reduction of the microviscosity in the solubilization site of the probe. The behavior of all diffusion reorientation parameters was analyzed on the basis of two factors: the micellar hydration and the headgroup flexibility of both surfactants. It was concluded that the increasing participation of the ethoxylated surfactant induces a greater hydration in the micellar palisade layer, producing the formation of a less compact microenvironment where the probe experiences a faster rotational reorientation.

On the urea action mechanism: a comparative study on the self-assembly of two sugar-based surfactants.

Studies on the effect of urea on micelle formation and structure of n-octyl-beta-D-thioglucoside (OTG) and N-decanoyl-N-methylglucamide (MEGA-10) were carried out by using the steady-state and time-resolved fluorescence techniques, together with combined static and dynamic light scattering measurements. A similar increase in the critical micelle concentration with the urea addition was observed for both surfactants. This behavior was attributed to a rise in the solubility of hydrocarbon tails and the increase of solvation of the headgroup of the surfactants in the presence of urea. Structural studies mainly based on the analysis of the hydrodynamic radius and aggregation number of micelles revealed that urea induces changes much more significant on micelles of OTG. Particularly, it was found that, whereas the surface area per headgroup of OTG increases with the urea concentration, it does decrease in the case of MEGA-10. This fact suggests that different action mechanisms operate for both surfactants. Accordingly, investigations on the micellar microstructure based on the study of microenvironmental properties such as micropolarity and microviscosity also indicated a more pronounced effect in the case of OTG. Although changes were not observed in the hydrophobic inner region of both micellar systems, a significant increase of polarity and viscosity in the micellar interface of OTG suggests a direct participation of urea in the micellar solvation layer. The differences between the observed behaviors for both micellar systems were interpreted on the basis of two features: the weaker hydration and greater rigidity of the OTG headgroup as compared with MEGA-10.

Self-assembly, hydration, and structures in N-decanoyl-N-methylglucamide aqueous solutions: effect of salt addition and temperature.

The influence of NaCl addition and temperature on the self-assembly, hydration, and structures of N-decanoyl-N-methylglucamide (MEGA-10) in dilute solution has been investigated by using several experimental techniques, including tensiometry, steady-state fluorescence, density, viscosity, and static and dynamic light scattering. Tensiometry and fluorescence probe studies, by using pyrene as a probe, were used to obtain the critical micelle concentration (cmc) upon the electrolyte addition. The mean micellar aggregation numbers (N(agg)) as a function of the salt addition were obtained by both static light scattering and static quenching methods. The N(agg) values estimated by both methods were found to be in good agreement. It was found that the increase in the micelle size, produced by the addition of NaCl, is due to the increase in the aggregation number and in the amount of water non-specifically associated to the micelle. On the other hand, we have observed that the aggregation number remains invariant in the temperature range studied, whereas the hydrodynamic radius slightly decreases. The effect of electrolyte addition and temperature on the properties of MEGA-10 micelles is much less pronounced than those observed in the traditionally used POE-based surfactants.

Inclusion of silver nanoparticles for improving regenerated cellulose membrane performance and reduction of biofouling.

The preparation of silver nanoparticles (AgNPs) and their incorporation into the structure of a regenerated cellulose membrane by dip coating is presented. Morphological characterization of the AgNPs (average diameter of 20±2nm) was carried out by SEM/TEM, while elastic, electrical and antimicrobial properties of the hybrid membrane were also analyzed. The presence of silver nanoparticles in the membrane seems to increases its rigidity and its chemical stability against oxidation, but it only induces small changes in the transport parameters. As expected, AgNPs provide antimicrobial properties to the membrane and consequently the reduction of biofouling without affecting significantly other characteristic parameters, opening the application of the modified membrane to wastewaters treatment.

Effect of NaCl on the self-aggregation of n-octyl beta-D-thioglucopyranoside in aqueous medium.

This report investigates the effect of sodium chloride (NaCl) on the micellization, surface activity, and the evolution in the shape and size of n-octyl beta-D-thioglucopyranoside (OTG) aggregates. By using surface tension measurements, information was obtained on both changes in the critical micelle concentration and adsorption behavior in the air-liquid interface with the electrolyte concentration. These data were used to obtain the thermodynamic properties of micellization along with the corresponding adsorption parameters in the air-liquid interface. From extended static and dynamic light scattering measurements, the micelle molecular weight, the mean aggregation number, and the second virial coefficient, the apparent diffusion coefficient and the mean hydrodynamic radius of micelles in a range of NaCl concentrations were obtained. The light scattering data have shown that when the surfactant concentration is lower to 4.5 g/L, only spherical micelles are formed. However, an increase in the surfactant concentration induces an increase in micellar size, suggesting a rodlike growth of the micelles. This deviation of micelle geometry from spherical to rodlike is supported both by the ratio between the hydrodynamic radius and the radius of gyration and by the angular dependence of light scattering. On the other hand, the studies performed in the presence of high NaCl concentration (0.2 and 0.5 M) provide strong support for the view that the micelles may overlap together to form an entangled network above certain crossover concentration.

Interactions in binary mixed systems involving a sugar-based surfactant and different n-alkyltrimethylammonium bromides.

In this paper, mixtures of sugar-based decanoyl-N-methylglucamide with three different n-alkyltrimethylammonium bromides (n=12 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied using conductance and fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by both the conductance and the pyrene 1:3 ratio methods. The experimental results were interpreted using thermodynamic mixing approaches based on the pseudophase separation model. These analyses allowed us to determine the interaction parameters and the composition of the mixed micelles through the whole composition range. Since all the ionic surfactants used in this study have the same headgroup, the differences observed between the three mixed systems were attributed to the lengths of their hydrocarbon chains. It was established that, besides interactions of electrostatic character, additional short-range interactions must be considered. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In the cases of the mixed systems with DTAB and TTAB it was observed that the aggregation number is initially reduced with the participation of the ionic component, remaining almost constant and close to the aggregation number of the pure ionic micelle. However, in the systems involving CTAB it is observed that the size of micelles initially increases and then decreases slightly for mixtures with a high content of the ionic component. The hydrophobic index pyrene 1:3 ratio was used to examine possible changes in the micellar micropolarity; however, no definitive conclusions could be derived from these experiments. In order to study the evolution of the local viscosity of the mixed micelles upon addition of the ionic surfactant, fluorescence polarization measurements were carried out with two different probes, fluorescein and coumarin 6. It was found that the participation of the ionic component in the mixed micelle induces the formation of less ordered structure than that of pure nonionic micelles. An attempt was made to correlate these effects with the interaction parameters obtained from the theoretical mixing model and, consequently, with the alkyl chain length of the ionic components.

Exploring the affinity binding of alkylmaltoside surfactants to bovine serum albumin and their effect on the protein stability: A spectroscopic approach.

Steady-state and time-resolved fluorescence together with circular dichroism (CD) spectroscopic studies was performed to examine the interactions between bovine serum albumin (BSA) and two alkylmaltoside surfactants, i.e. n-decyl-ß-D-maltoside (ß-C10G2) and n-dodecyl-ß-D-maltoside (ß-C12G2), having identical structures but different tail lengths. Changes in the intrinsic fluorescence of BSA from static as well as dynamic measurements revealed a weak protein-surfactant interaction and gave the corresponding binding curves, suggesting that the binding mechanism of surfactants to protein is essentially cooperative in nature. The behavior of both surfactants is similar, so that the differences detected were attributed to the more hydrophobic nature of ß-C12G2, which favors the adsorption of micelle-like aggregates onto the protein surface. These observations were substantially demonstrated by data derived from synchronous, three-dimensional and anisotropy fluorescence experiments. Changes in the secondary structure of the protein induced by the interaction with surfactants were analyzed by CD to determine the contents of α-helix and ß-strand. It was noted that whereas the addition of ß-C10G2 appears to stabilize the secondary structure of the protein, ß-C12G2 causes a marginal denaturation of BSA for a protein:surfactant molar ratio as high as 1 to 100.

Membrane surface functionalization via theophylline derivative coating and streptavidin immobilization.

Poly(vinylidene fluoride) (PVDF) and regenerated cellulose (RC) membranes were surface-modified by the adsorption of one adenosine receptor antagonist: the theophylline-oligo(ethylene glycol)-alkene derivative, Theo1. Surface modification was carried out by immersion of the membrane in a dichloromethane solution of Theo1 (PVDF+Theo1 and RC+Theo1 samples). Membrane surfaces with partial coverage by theophylline and/or its inclusion in the membrane structures were studied by X-ray photoelectron spectroscopy (XPS), solid-state nuclear magnetic resonance (SNMR), impedance spectroscopy (IS) and contact angle (CA) measurements. The Theo1 orientation was inferred from the data. Streptavidin (SA) was immobilized onto the membrane/Theo1 hybrid material. The protein-theophylline Theo1 interaction was visualized with bright field microscopy (BFM).

Physicochemical Studies on the Interaction between N-Decanoyl-N-methylglucamide and Bovine Serum Albumin.

The protein-surfactant system constituted by bovine serum albumin (BSA) and N-decanoyl-N-methylglucamide (MEGA-10) has been studied by using surface tension, steady-state fluorescence, and dynamic light scattering measurements. It was found that the presence of protein delays the surfactant aggregation, which was interpreted as a sign of binding between surfactant and protein. Binding studies were carried out by two different methods. First, a treatment based on surface tension measurements was used to obtain information on the number of surfactant molecules bound per protein molecule under saturation conditions. Second, the binding curve for the BSA/MEGA-10 system was determined by examining the behavior of the intrinsic BSA fluorescence upon the surfactant addition. Both approaches indicate that the binding process is essentially cooperative in nature. The results of the aggregation numbers of MEGA-10 micelles, as well as those of resonance energy transfer from tryptophan residues to 8-anilinonaphthalene-1-sulfonate, corroborate the formation of micelle-like aggregates of surfactants, smaller than the free micelles, adsorbed on the protein surface. The dynamic light scattering results were not conclusive, in the sense that it was not possible to discriminate between protein-surfactant complexes and free micelles. However, the overall results suggest the formation of "pearl necklace" complexes in equilibrium with the free micelles of the surfactant.

Stability, interaction, size, and microenvironmental properties of mixed micelles of decanoyl-N-methylglucamide and sodium dodecyl sulfate.

The mixed micellization between the nonionic surfactant decanoyl-N-methylglucamide (MEGA-10) and the common sodium dodecyl sulfate (SDS) in aqueous solutions of 0.1 M NaCl was investigated by the fluorescence probe method. The critical micelle concentrations were determined by the pyrene 1:3 ratio method. The experimental data are discussed in light of two mixing thermodynamic models within the framework of the pseudophase separation model, including the conventional regular solution theory and a recent treatment proposed by Maeda (J. Phys. Chem. B 2004, 108, 6043). This last approach provides a more appropriate description of the mixed system, particularly in two aspects: the nature of the interactions responsible for the stability of the mixed micelle and the behavior of the excess free energy per monomer of the system. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles in the whole range of compositions were obtained. It was found that the micellar aggregation number initially increases with the content of the ionic component, then remains roughly constant, and, finally, decreases slightly for high content of this component. This behavior was analyzed taking into account the effects produced by the presence of the charged headgroups of sodium dodecyl sulfate, as this component increases its participation in the mixed micelle. The micropolarity of the mixed micelles was studied by the pyrene 1:3 ratio index. It was observed that the increasing participation of the ionic component induces the formation of micelles with a more dehydrated structure. Data of micellar microviscosity were obtained by using different methods, including fluorescence intensity measurements of Auramine O and steady-state fluorescence anisotropy of rhodamine B and diphenylbutadiene. The results obtained from these experiments are in good agreement and suggest the formation of mixed micelles with a less ordered structure as the content of SDS increases.