Molecular genetics of autochthonous lactic acid bacteria

Autohtoni sojevi bakterija mlečne kiseline (BMK) su izolovane iz fermentisanih mlečnih proizvoda rađenih u domaćoj radinosti. Fermentisani mlečni proizvodi su sakupljani sa specifičnih ekoloških lokaliteta kao što su visoke planine (iznad 1200 m nadmorske visine), planinske visoravni, rečne doline, ostrva, obala Jadranskog mora, itd. Analiza kolekcije prirodnih izolata BMK je pokazala da izolati proizvode proteinaze, bakteriocine i egzopolisaharide. Pokazano je, takođe, da neki izolati laktokoka i laktobacila proizvode istovremeno dva različita bakteriocina. Pored toga određeni broj izolata proizvodi i proteinaze i bakteriocine. Nađeno je da prirodni izolati sintetišu specifične proteinaze. Analiza organizacije prt gena u prirodnim izolatima BMK je pokazala da četiri laktobacila poseduju organizaciju prt gena koja se razlikuje od do sada opisanih. Izučavanje regulacije gena koji kodiraju proteinaze, bakteriocine ili egzopolisaharide može olakšati konstrukciju specifičnih starter kultura za proizvodnju autohtonih fermentisanih mlečnih proizvoda, tj. fermentisanih proizvoda sa geografskim poreklom.Autochthonous strains of lactic acid bacteria (LAB) were isolated from homemade fermented milk products. These products were collected from specific ecological localities such as high mountains (above 1200 m above sea level) mountain plateaus, river valleys, islands, Adriatic coast, etc. Analysis of LAB from the collection of natural isolates revealed that they produce proteinases, bacteriocins and exopolysaccharides. It was also shown that some isolates of lactococci and lactobacilli produce two bacteriocins simultaneously. According to their antimicrobial and biochemical properties most of the analyzed bacteriocins in natural isolates of lactococci were class 11 bacteriocins. In addition some isolates produced both proteinase and bacteriocin. Biosynthesis of specific proteinases was detected in natural isolates. Analysis of the prt gene organization among natural isolates of LAB showed that four isolates of lactobacilli exhibited prt genes organization different from those described so far. Elucidation of the regulation of the genes encoding proteinases, bacteriocins and exopolysaccharides could facilitate the construction of specific starter cultures for production of autochthonous fermented milk products, i.e. fermented products with a geographical origin

Interplay Between Ferroelectricity and Surface Chemistry in BaTiO3

Els materials ferroelèctrics tenen una polarització elèctrica permanent que pot reorientar-se entre els estats d'equilibri si s'aplica un camp elèctric extern amb l'orientació i magnitud adequada. Degut a que els materials ferroelèctrics tenen una mida finita, aquesta polarització presenta una discontinuïtat a la interfície entre el ferroelèctric i el medi que l'envolta, donant-hi lloc a l'acumulació de càrregues i el conseqüent camp de despolarització. En alguns casos, si aquest camp no es compensa prou, pot arribar a ser suficientment gran com per desestabilitzar el material ferroelèctric. Aquesta compensació necessària pot produir-se internament per portadors de càrrega lliure, externament amb elèctrodes metàl·lics, o en el cas de mostres sense elèctrodes, amb diferents adsorbats com per exemple, l'aigua present a l'ambient i els seus productes de dissociació. Per tant, segons la compensació del camp de despolarització, ambdós mecanismes interns i externs juguen un rol important a l'hora de definir la química de superfície en els ferroelèctrics. En aquest sentit, els materials ferroelèctrics són capaços de crear estats químics específics a la superfície segons la polarització (p. ex. estequiometria, configuració electrònica i estructural); els quals a més, governen l'adsorció, desorció i les barreres per a les reaccions químiques de molècules d'adsorbats en superfícies polaritzades de ferroelèctrics. A més a més, la relació entre la química de superfície i la ferroelectricitat és bidireccional: qualsevol canvi en la composició química de la superfície comporta un canvi en les condicions de contorn d'aquesta i en els camps de despolarització, que en conjunt, pot tenir profundes conseqüències en les interaccions dipolars i sobre les propietats ferroelèctriques en capes primes (on la proporció superfície/volum és gran). Al mateix temps, això obre nous camins cap al control químic de la ferroelectricitat, on mitjançant l'ajust de la química de superfície es podrien assolir les propietats ferroelèctriques desitjades o, vici versa, la modificació de la polarització amb camps externs es podria utilitzar en processos (ferro)catalítics. Malgrat això, aquestes tasques en realitat són un repte, ja que existeixen fortes limitacions en el coneixement experimental de les interaccions químiques a la superfície de capes primes ferroelèctriques. Aquestes limitacions inclouen tant les espècies químiques involucrades, com la dinàmica dels processos electroquímics de compensació - els quals, al seu torn, afecten la mida dels dominis (que serien els "bits" en memòries ferroelèctriques), al voltatge coercitiu, i a la velocitat màxima a la qual la informació pot ser enregistrada en capes primes ferroelèctriques, sent d'interès pràctic en aplicacions d'emmagatzematge d'informació. Aquesta tesi doctoral investiga tots aquests aspectes. Començant amb la preparació de capes primes epitaxials d'alta qualitat de BaTiO3 ferroelèctric, utilitzat com el material principal en aquesta tesi, el treball presentat englobarà l'estudi de la interacció entre ferroelectricitat i química de superfície des de diferents perspectives. La química superficial de les capes primes de BaTiO3, dependent de la polarització i l'exposició ambiental, i la seva evolució durant la modulació dinàmica de la polarització a traves de la temperatura de transició de Curie en condicions de vapor d'aigua, s'estudia per espectroscòpia fotoelectrònica de rajos X convencional i a pressió ambiental (AP-XPS). L'efecte de l'aigua adsorbida serà també examinat en el marc d'experiments de litografia ferroelèctrica i estudis de microscòpia de força per piezoresposta (PFM) en condicions controlades d'humitat, mitjançant la investigació de l'efecte de la humitat relativa en la velocitat màxima de gravat de dominis, la seva mida i la dinàmica de la commutació. Finalment, la influència de molècules diferents a la de l'aigua serà estudiada mitjançant la funcionalització química amb molècules d'àcid para-aminobenzòic (pABA).Los materiales ferroeléctricos tienen una polarización eléctrica permanente que puede reorientarse entre los estados de equilibrio si se aplica un campo eléctrico externo con la orientación y magnitud adecuada. Debido a que los materiales ferroeléctricos tienen un tamaño finito, esta polarización presenta una discontinuidad en la interfaz entre el ferroeléctrico y el medio que lo rodea, dando lugar a la acumulación de cargas y el consecuente campo de despolarización. En algunos casos, si este campo no se compensa suficientemente, puede llegar a ser bastante grande como para desestabilizar el material ferroeléctrico. Esta compensación necesaria puede producirse internamente por portadores de carga libre, externamente con electrodos metálicos, o en el caso de muestras sin electrodos, con diferentes adsorbatos como por ejemplo, el agua presente en el ambiente y sus productos de disociación. Por lo tanto, según la compensación del campo de despolarización, ambos mecanismos internos y externos juegan un rol importante a la hora de definir la química de superficie en los ferroeléctricos. En este sentido, los materiales ferroeléctricos son capaces de crear estados químicos específicos en la superficie según la polarización (p. ej. estequiometria, configuración electrónica y estructural), los cuales también gobiernan la adsorción, desorción y las barreras para las reacciones químicas de moléculas de adsorbatos en superficies polarizadas de ferroeléctricos. Además, la relación entre la química de superficie y la ferroelectricidad es bidireccional: cualquier cambio en la composición química de la superficie comporta un cambio en las condiciones de contorno de esta y en los campos de despolarización, que, en conjunto, puede tener profundas consecuencias en las interacciones dipolares y sobre las propiedades ferroeléctricas en capas delgadas (donde la proporción superficie/volumen es elevada). Al mismo tiempo, esto abre nuevos caminos hacia el control químico de la ferroelectricidad, donde mediante el ajuste de la química de superficie se podrían lograr las propiedades ferroeléctricas deseadas o, viceversa, la modificación de la polarización con campos externos se podría emplear en procesos (ferro)catalíticos. A pesar de esto, estas tareas en realidad son un reto, puesto que existen grandes limitaciones en el conocimiento experimental de las interacciones químicas en la superficie de capas delgadas ferroeléctricas. Estas limitaciones incluyen tanto a las especies químicas involucradas, como la dinámica de los procesos electroquímicos de compensación - los cuales, a su vez, afectan el tamaño de los dominios (que serían los "bits" en memorias ferroeléctricas), al voltaje coercitivo, y a la velocidad máxima en la cual la información puede ser grabada en capas delgadas ferroeléctricas, siendo de interés práctico en aplicaciones de almacenamiento de información. Esta tesis doctoral investiga todos estos aspectos. Empezando con la preparación de capas delgadas epitaxiales de alta calidad de BaTiO3 ferroeléctrico, utilizado como el material principal en esta tesis, el trabajo presentado englobará el estudio de la interacción entre ferroelectricidad y química de superficie desde diferentes perspectivas. La química superficial de las capas delgadas de BaTiO3, dependiente de la polarización y la exposición ambiental, y su evolución durante la modulación dinámica de la polarización a través de la temperatura de transición de Curie en condiciones de vapor de agua, se estudia por espectroscopia fotoelectrónica de rayos X convencional y a presión ambiental (AP-XPS). El efecto del agua adsorbida será también examinado en el marco de experimentos de litografía ferroeléctrica y estudios de microscopia de fuerza por piezorespuesta (PFM) en condiciones controladas de humedad, mediante la investigación del efecto de la humedad relativa en la velocidad máxima de grabado de dominios, su tamaño y la dinámica de la conmutación. Finalmente, la influencia de moléculas diferentes a la del agua será estudiada mediante la funcionalización química con moléculas de ácido para-aminobenzóico (pABA).Ferroelectric materials possess permanent electric polarization, which can be reoriented between possible equilibrium states by the application of external electric field of proper orientation and magnitude. Due to the finite size of ferroelectric materials, a discontinuity of polarization arises at the interface between ferroelectric and surrounding medium, giving rise to the bound charge and a depolarizing field. In some cases, this field might be sufficiently high to jeopardize ferroelectric stability if not properly screened. Necessary screening charges can be supplied internally, in the form of free charge carriers, externally by metallic electrodes or, alternatively in the case of bare (electrode-free samples), by different adsorbate species such as atmospheric water and its dissociation products. Driven by the depolarization field screening, both internal and external mechanisms play important roles in defining surface chemistry of ferroelectrics. In this sense, ferroelectric materials are able to develop polarization-specific surface chemical states (e.g. stoichiometry, electronic and structural configurations), which further govern adsorption, desorption and barriers for chemical reactions of adsorbate molecules on polarized ferroelectric surfaces. Moreover, the relation between surface chemistry and ferroelectricity is bidirectional: any change in the surface-chemical composition leads to a change in surface boundary conditions and depolarizing fields, that altogether may have profound effect on the dipolar interactions and ferroelectric properties of thin films, where surface-to-volume ratios are high. In turn, this opens new pathways towards chemically controlled ferroelectricity, where by the tuning of surface chemistry desired ferroelectric properties could be achieved or, vice versa, the modification of polarization by external fields can be exploited in (ferro)catalytic processes. However, in reality these are challenging tasks due to severe limitations in our experimental knowledge of the chemical interactions at the surfaces of ferroelectric thin films. These limitations include both the actual chemical species involved, and the dynamics of the electrochemical screening process - which, in turn, affect domain size (which would be the 'bits' in ferroelectric memories), coercive voltage, and maximum speed at which information can be encoded in ferroelectric thin films, being of practical interest for information storage applications. This doctoral thesis sets out to explore these aspects. Starting from the preparation of high quality epitaxial and ferroelectric BaTiO3 thin films, used as the main material in this thesis, the presented work will encompass study of interplay between ferroelectricity and surface chemistry from different perspectives. The polarization- and environmental exposure- dependent surface chemistry of BaTiO3 thin films, and furthermore its evolution during dynamic polarization modulation across the Curie transition temperature in water vapor conditions, relevant in the frame of catalytic processes on ferroelectric materials, is studied by conventional and ambient pressure X-Ray photoelectron spectroscopy (AP-XPS). The effect of adsorbed water will be further assessed in the frame of ferroelectric lithography experiments and Piezoresponse Force Microscopy (PFM) studies in controlled humidity conditions, by investigating effect of relative humidity on the maximum speed of domain writing, domain size and domain switching dynamics. Lastly, influence of molecules different from water, achieved by deliberate chemical functionalization with aromatic para-aminobenzoic acid (pABA) molecules, will be studied with respect to ferroelectric polarization stability.Universitat Autònoma de Barcelona. Programa de Doctorat en Ciència de Material

Radiogrammetric analysis of upper limb long bones

Radiogrammetry is radiological method of bone mineral density quantification. Besides giving an insight in diagnostics and evolution of metabolic bone disorders (osteoporosis, osteomalacia, osteitis deformans- Paget's disease), it can also explain some specific biomechanical characteristics of bone structures. The aim of this study is to evaluate the significance and perspectives of radiogrammetry as a scientific model for further inquiry of skeletal system. The work demonstrates mathematical parameters (Ca-Cortical area, CI- Cortical index, GI- Garn's index, ESI- Exton Smith's index) of upper limb long bones (humerus, radius, ulna). Two standard radiological projections of bones were taken: antero-posterior (AP) and latero-lateral (LL). Correlation with metacarpal and lower limb bones was also performed. The value of the cortical area of humerus is significantly higher comparing with the two other examined bones (Xmean 2,2443 cm2, p < 0.01). Radial bone has the highest values of the relational mathematical parameters, which implicates its higher strength by volumetric unit concerning humerus and ulna. Despite the development of contemporary osteometric procedures (ultrasound densitometry, dual X-ray absorptiometry, digital X-ray radiogrammetry), the classical radiogrammetry sustains its important role in diagnostics of metabolic bone disorders and it can be successfully used for biomechanical inquiry of skeletal system

High concentration of hematite nanoparticles in a silica matrix: Structural and magnetic properties

The alpha-Fe(2)O(3)/SiO(2) nanocomposite containing 45 wt% of hematite was prepared by the sol-gel method followed by heating in air at 200 degrees C. The so-obtained composite of iron(III) nanoparticles dissolved in glassy silica matrix was investigated by X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. XRPD confirms the formation of a single-phase hematite sample, whereas TEM reveals spherical particles in a silica matrix with an average diameter of 10 nm. DC magnetization shows bifurcation of the zero-field-cooled (ZFC) and field-cooled (FC) branches up to the room temperature with a blocking temperature TB 65 K. Isothermal M( H) dependence displays significant hysteretic behaviour below TB, whereas the room temperature data were successfully fitted to a weighted Langevin function. The average particle size obtained from this fit is in agreement with the TEM findings. The small shift of the TB value with the magnetic field strength, narrowing of the hysteresis loop at low applied field, and the frequency dependence of the AC susceptibility data point to the presence of inter-particle interactions. The analysis of the results suggests that the system consists of single-domain nanoparticles with intermediate strength interactions. (c) 2008 Elsevier B.V. All rights reserved

Unusual magnetic properties of NiO nanoparticles embedded in a silica matrix

We have observed unusual magnetic properties of NiO (nickel oxide) nanoparticles embedded in a silica matrix. The sample was synthesized by a method based on the contribution of sol-gel and combustion processes. X-ray powder diffraction (XRPD) of the sample shows the formation of the nanocrystalline NiO phase whereas transmission electron microscope (TEM) reveals spherical-shaped nanoparticles of about 4 nm diameter. Moreover, HRTEM images show lattice fringes of the nanoparticles and defects in the crystal structure. The temperature and field dependence of the magnetization are also measured. The zero-field-cooled (ZFC) measurements show two maximums, one sharp and narrow at low temperatures similar to 6.5K and an other broad one at higher temperature similar to 64 K. The FC magnetization shows a continuous increase upon lowering the temperature. The M(H) measurements reveal that NiO nanoparticles display anomalous hysteretic behaviors at low temperatures (below the low temperature maximum in the ZFC curve, 2K and 5K) showing that the magnetization initial curve lies below the hysteresis loop for a certain field range. Moreover, jump of the magnetization at low temperatures (2K and 5K) are also observed. These features represent novel magnetic properties for nanosized NiO which may be attributed to the surface spins. Moreover, these results indicate that the NiO nanoparticle consists of magnetically disorder shell and antiferromagnetically order core with an uncompensated magnetic moment. (C) 2011 Elsevier B. V. All rights reserved

Enhancing Analytical Performance of (Mg,Fe)3O4/Glassy Carbon Electrodes by Tailoring Chemical Composition of (Mg,Fe)3O4 Nanoparticles

A series of MgxFe3-xO₄ (x ═ 0-1) nanoparticles was synthesized in order to prepare novel MgxFe3-xO₄/glassy carbon modified electrodes. Effects of magnesium content (x) on the analytical performance of the modified electrodes in the detection of gallic acid were evaluated. It was found that magnesium concentration and crystallite/particle size of the prepared nanoparticles play significant roles in the sensing properties of modified electrodes. The increase of magnesium concentration up to the value of x ═ 0.4 in MgxFe3-xO₄/glassy carbon paste was accompanied by an increase of the corresponding oxidation current of gallic acid. However, further growth of x value caused decline of the obtained oxidation current. An electroanalytical procedure was established, and the analytical performance of the proposed Mg0.4Fe2.6O₄/glassy carbon paste electrode was monitored using previously optimized experimental conditions. A working linear range from 1-39 µM gallic acid was obtained with detection limit of 0.29 µM. According to these results, the developed procedure can be applied for detection of low concentrations of gallic acid with satisfactory selectivity in the presence of some common naturally occurring compounds. Experimental results indicate that the developed procedure could be a novel approach in the detection of antioxidant, overcoming some known disadvantages such as passivation, and could be a promising replacement for sophisticated chromatographic methods

Anomalous behaviour of the magnetic hysteresis loop in the alpha-Fe2O3/SiO2 nanocomposite

The alpha-Fe2O3/SiO2 nanocomposite containing 45 wt.% of hematite was prepared by the sol-gel method and characterized by using X-ray diffractometer (XRD), transmission electron microscopy (TEM) and. superconducting quantum interference device (SQUID) magnetometer. TEM microscopy showed spherical particles with average size about 10 nm, whereas XRD diffraction confirmed the formation of the hematite phase. The magnetic measurements showed anomalous behavior of the hysteresis loops including decrease of high field isothermal magnetization and overlap of initial, remagnetization and magnetization curves. This anomalous behavior represents a novel effect for alpha-Fe2O3/SiO2 nanocomposites. We conjecture that a field-induced antiferromagnetic coupling between nanoparticles may produce this effect. (C) 2009 Elsevier B.V. All rights reserved

Lactobacillus extra cellular proteinases

U okviru veće kolekcije prirodnih izolata mezofilnih i termofilnih laktobacila, identifikovan je određen broj izolata koji sintetišu ekstracelularne proteinaze. Sve testirane proteinaze mezofilnih laktobacila pripadaju serinskoj klasi i hidrolizuju samo beta-kazein, sa izuzetkom proteinaze soja Lactobacillus divergens BG742 koja hidrolizuje sve tri kazeinske frakcije i koja, za razliku od ostalih, najefikasnije vrši hidrolizu supstrata na baznoj pH vrednosti. Totalna DNK sojeva Lactobacillus paracasei subsp. paracasei BGLi17 i BGLi18 hibridizuje sa laktokokalnim proteinaznim probama. Restrikcione mape proteinaznih regiona ovih sojeva pokazuju visoku homologiju sa laktokokalnim proteinaznim regionima. Razdvajanje genomske DNK ovih sojeva na PFGE i hibridizacija sa laktokokalnim proteinaznim probama pokazuje da su, za razliku od laktokoka, njihovi proteinazni geni locirani na hromozomu. Termofilni soj Lactobacillus delbruckli subsp. bulgaricus BGPF1 sintetiše proteinazu koja takođe hidrolizuje samo beta-kazein i koja, sudeći na osnovu rezultata PCR analize, pripada tipu koji je kod drugih sojeva ove vrste ranije okarakterisan. Soj Lactobacillus acidophilus BGRA43 sintetiše proteinazu koja hidrolizuje sve tri kazeinske frakcije, ali za koju se na osnovu hibridizacije i PCR analize može reći da ne pripada nijednom do sada opisanom tipu. .Within the large collection of natural isolates of mesophilic and thermophilic lactobacilli, some of the isollates were identified as extracelular proteinase producers. All tested proteinases from mesophilic lactobacilli belong to the serine class and hydrolize beta-casein only, except the proteinase from the strain Lactobacillus divergens BG742 which hydrolyze all three casein fractions, and which is, in contrast to the others, more efficient at basic pH values. Total DNA from strains Lactobacillus paracasei subsp. paracasei BGLi17 and BGLi18 hybridizes with the probes from lactococcal proteinase gene regions. On the basis of PFGE analysis of genomic DNA of these strains and hybridization with lactococcal proteinase probes, it could be suggested that their proteinase gene regions are chromosomaly located. Thermophilic strain Lactobacillus delbrueckii subsp. bulgaricus BGPF1 produces the proteinase which also hydrolyzes only beta-casein, and which is, according to the PCR analysis, of the same type already described in other strains of this species. Proteinase from strain Lactobacillus acidophilus BGRA43 hydrolyzes all three casein fractions, and on the basis of hydrodization and PCR analysis this enzyme is different from the proteinases described so far.